<?php
/**
 * @link http://www.yiiframework.com/
 * @copyright Copyright (c) 2008 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

namespace yii\helpers;

use Yii;
use yii\base\InvalidParamException;
use yii\db\ActiveRecordInterface;
use yii\validators\StringValidator;
use yii\web\Request;
use yii\base\Model;

/**
 * BaseHtml provides concrete implementation for [[Html]].
 *
 * Do not use BaseHtml. Use [[Html]] instead.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class BaseHtml
{
    /**
     * @var array list of void elements (element name => 1)
     * @see http://www.w3.org/TR/html-markup/syntax.html#void-element
     */
    public static $voidElements = [
        'area' => 1,
        'base' => 1,
        'br' => 1,
        'col' => 1,
        'command' => 1,
        'embed' => 1,
        'hr' => 1,
        'img' => 1,
        'input' => 1,
        'keygen' => 1,
        'link' => 1,
        'meta' => 1,
        'param' => 1,
        'source' => 1,
        'track' => 1,
        'wbr' => 1,
    ];
    /**
     * @var array the preferred order of attributes in a tag. This mainly affects the order of the attributes
     * that are rendered by [[renderTagAttributes()]].
     */
    public static $attributeOrder = [
        'type',
        'id',
        'class',
        'name',
        'value',

        'href',
        'src',
        'action',
        'method',

        'selected',
        'checked',
        'readonly',
        'disabled',
        'multiple',

        'size',
        'maxlength',
        'width',
        'height',
        'rows',
        'cols',

        'alt',
        'title',
        'rel',
        'media',
    ];
    /**
     * @var array list of tag attributes that should be specially handled when their values are of array type.
     * In particular, if the value of the `data` attribute is `['name' => 'xyz', 'age' => 13]`, two attributes
     * will be generated instead of one: `data-name="xyz" data-age="13"`.
     * @since 2.0.3
     */
    public static $dataAttributes = ['data', 'data-ng', 'ng'];


    /**
     * Encodes special characters into HTML entities.
     * The [[\yii\base\Application::charset|application charset]] will be used for encoding.
     * @param string $content the content to be encoded
     * @param boolean $doubleEncode whether to encode HTML entities in `$content`. If false,
     * HTML entities in `$content` will not be further encoded.
     * @return string the encoded content
     * @see decode()
     * @see http://www.php.net/manual/en/function.htmlspecialchars.php
     */
    public static function encode($content, $doubleEncode = true)
    {
        return htmlspecialchars($content, ENT_QUOTES | ENT_SUBSTITUTE, Yii::$app ? Yii::$app->charset : 'UTF-8', $doubleEncode);
    }

    /**
     * Decodes special HTML entities back to the corresponding characters.
     * This is the opposite of [[encode()]].
     * @param string $content the content to be decoded
     * @return string the decoded content
     * @see encode()
     * @see http://www.php.net/manual/en/function.htmlspecialchars-decode.php
     */
    public static function decode($content)
    {
        return htmlspecialchars_decode($content, ENT_QUOTES);
    }

    /**
     * Generates a complete HTML tag.
     * @param string $name the tag name
     * @param string $content the content to be enclosed between the start and end tags. It will not be HTML-encoded.
     * If this is coming from end users, you should consider [[encode()]] it to prevent XSS attacks.
     * @param array $options the HTML tag attributes (HTML options) in terms of name-value pairs.
     * These will be rendered as the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     *
     * For example when using `['class' => 'my-class', 'target' => '_blank', 'value' => null]` it will result in the
     * html attributes rendered like this: `class="my-class" target="_blank"`.
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated HTML tag
     * @see beginTag()
     * @see endTag()
     */
    public static function tag($name, $content = '', $options = [])
    {
        $html = "<$name" . static::renderTagAttributes($options) . '>';
        return isset(static::$voidElements[strtolower($name)]) ? $html : "$html$content</$name>";
    }

    /**
     * Generates a start tag.
     * @param string $name the tag name
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated start tag
     * @see endTag()
     * @see tag()
     */
    public static function beginTag($name, $options = [])
    {
        return "<$name" . static::renderTagAttributes($options) . '>';
    }

    /**
     * Generates an end tag.
     * @param string $name the tag name
     * @return string the generated end tag
     * @see beginTag()
     * @see tag()
     */
    public static function endTag($name)
    {
        return "</$name>";
    }

    /**
     * Generates a style tag.
     * @param string $content the style content
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated style tag
     */
    public static function style($content, $options = [])
    {
        return static::tag('style', $content, $options);
    }

    /**
     * Generates a script tag.
     * @param string $content the script content
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated script tag
     */
    public static function script($content, $options = [])
    {
        return static::tag('script', $content, $options);
    }

    /**
     * Generates a link tag that refers to an external CSS file.
     * @param array|string $url the URL of the external CSS file. This parameter will be processed by [[Url::to()]].
     * @param array $options the tag options in terms of name-value pairs. The following option is specially handled:
     *
     * - condition: specifies the conditional comments for IE, e.g., `lt IE 9`. When this is specified,
     *   the generated `link` tag will be enclosed within the conditional comments. This is mainly useful
     *   for supporting old versions of IE browsers.
     * - noscript: if set to true, `link` tag will be wrapped into `<noscript>` tags.
     *
     * The rest of the options will be rendered as the attributes of the resulting link tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated link tag
     * @see Url::to()
     */
    public static function cssFile($url, $options = [])
    {
        if (!isset($options['rel'])) {
            $options['rel'] = 'stylesheet';
        }
        $options['href'] = Url::to($url);

        if (isset($options['condition'])) {
            $condition = $options['condition'];
            unset($options['condition']);
            return self::wrapIntoCondition(static::tag('link', '', $options), $condition);
        } elseif (isset($options['noscript']) && $options['noscript'] === true) {
            unset($options['noscript']);
            return '<noscript>' . static::tag('link', '', $options) . '</noscript>';
        } else {
            return static::tag('link', '', $options);
        }
    }

    /**
     * Generates a script tag that refers to an external JavaScript file.
     * @param string $url the URL of the external JavaScript file. This parameter will be processed by [[Url::to()]].
     * @param array $options the tag options in terms of name-value pairs. The following option is specially handled:
     *
     * - condition: specifies the conditional comments for IE, e.g., `lt IE 9`. When this is specified,
     *   the generated `script` tag will be enclosed within the conditional comments. This is mainly useful
     *   for supporting old versions of IE browsers.
     *
     * The rest of the options will be rendered as the attributes of the resulting script tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated script tag
     * @see Url::to()
     */
    public static function jsFile($url, $options = [])
    {
        $options['src'] = Url::to($url);
        if (isset($options['condition'])) {
            $condition = $options['condition'];
            unset($options['condition']);
            return self::wrapIntoCondition(static::tag('script', '', $options), $condition);
        } else {
            return static::tag('script', '', $options);
        }
    }

    /**
     * Wraps given content into conditional comments for IE, e.g., `lt IE 9`.
     * @param string $content raw HTML content.
     * @param string $condition condition string.
     * @return string generated HTML.
     */
    private static function wrapIntoCondition($content, $condition)
    {
        if (strpos($condition, '!IE') !== false) {
            return "<!--[if $condition]><!-->\n" . $content . "\n<!--<![endif]-->";
        }
        return "<!--[if $condition]>\n" . $content . "\n<![endif]-->";
    }

    /**
     * Generates the meta tags containing CSRF token information.
     * @return string the generated meta tags
     * @see Request::enableCsrfValidation
     */
    public static function csrfMetaTags()
    {
        $request = Yii::$app->getRequest();
        if ($request instanceof Request && $request->enableCsrfValidation) {
            return static::tag('meta', '', ['name' => 'csrf-param', 'content' => $request->csrfParam]) . "\n    "
                . static::tag('meta', '', ['name' => 'csrf-token', 'content' => $request->getCsrfToken()]) . "\n";
        } else {
            return '';
        }
    }

    /**
     * Generates a form start tag.
     * @param array|string $action the form action URL. This parameter will be processed by [[Url::to()]].
     * @param string $method the form submission method, such as "post", "get", "put", "delete" (case-insensitive).
     * Since most browsers only support "post" and "get", if other methods are given, they will
     * be simulated using "post", and a hidden input will be added which contains the actual method type.
     * See [[\yii\web\Request::methodParam]] for more details.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * Special options:
     *  - `csrf`: whether to generate the CSRF hidden input. When is not defined, defaults to true.
     * @return string the generated form start tag.
     * @see endForm()
     */
    public static function beginForm($action = '', $method = 'post', $options = [])
    {
        $action = Url::to($action);

        $hiddenInputs = [];

        $request = Yii::$app->getRequest();
        if ($request instanceof Request) {
            if (strcasecmp($method, 'get') && strcasecmp($method, 'post')) {
                // simulate PUT, DELETE, etc. via POST
                $hiddenInputs[] = static::hiddenInput($request->methodParam, $method);
                $method = 'post';
            }
            $csrf = ArrayHelper::remove($options, 'csrf', true);

            if ($csrf && $request->enableCsrfValidation && strcasecmp($method, 'post') === 0) {
                $hiddenInputs[] = static::hiddenInput($request->csrfParam, $request->getCsrfToken());
            }
        }

        if (!strcasecmp($method, 'get') && ($pos = strpos($action, '?')) !== false) {
            // query parameters in the action are ignored for GET method
            // we use hidden fields to add them back
            foreach (explode('&', substr($action, $pos + 1)) as $pair) {
                if (($pos1 = strpos($pair, '=')) !== false) {
                    $hiddenInputs[] = static::hiddenInput(
                        urldecode(substr($pair, 0, $pos1)),
                        urldecode(substr($pair, $pos1 + 1))
                    );
                } else {
                    $hiddenInputs[] = static::hiddenInput(urldecode($pair), '');
                }
            }
            $action = substr($action, 0, $pos);
        }

        $options['action'] = $action;
        $options['method'] = $method;
        $form = static::beginTag('form', $options);
        if (!empty($hiddenInputs)) {
            $form .= "\n" . implode("\n", $hiddenInputs);
        }

        return $form;
    }

    /**
     * Generates a form end tag.
     * @return string the generated tag
     * @see beginForm()
     */
    public static function endForm()
    {
        return '</form>';
    }

    /**
     * Generates a hyperlink tag.
     * @param string $text link body. It will NOT be HTML-encoded. Therefore you can pass in HTML code
     * such as an image tag. If this is coming from end users, you should consider [[encode()]]
     * it to prevent XSS attacks.
     * @param array|string|null $url the URL for the hyperlink tag. This parameter will be processed by [[Url::to()]]
     * and will be used for the "href" attribute of the tag. If this parameter is null, the "href" attribute
     * will not be generated.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated hyperlink
     * @see \yii\helpers\Url::to()
     */
    public static function a($text, $url = null, $options = [])
    {
        if ($url !== null) {
            $options['href'] = Url::to($url);
        }
        return static::tag('a', $text, $options);
    }

    /**
     * Generates a mailto hyperlink.
     * @param string $text link body. It will NOT be HTML-encoded. Therefore you can pass in HTML code
     * such as an image tag. If this is coming from end users, you should consider [[encode()]]
     * it to prevent XSS attacks.
     * @param string $email email address. If this is null, the first parameter (link body) will be treated
     * as the email address and used.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated mailto link
     */
    public static function mailto($text, $email = null, $options = [])
    {
        $options['href'] = 'mailto:' . ($email === null ? $text : $email);
        return static::tag('a', $text, $options);
    }

    /**
     * Generates an image tag.
     * @param array|string $src the image URL. This parameter will be processed by [[Url::to()]].
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated image tag
     */
    public static function img($src, $options = [])
    {
        $options['src'] = Url::to($src);
        if (!isset($options['alt'])) {
            $options['alt'] = '';
        }
        return static::tag('img', '', $options);
    }

    /**
     * Generates a label tag.
     * @param string $content label text. It will NOT be HTML-encoded. Therefore you can pass in HTML code
     * such as an image tag. If this is is coming from end users, you should [[encode()]]
     * it to prevent XSS attacks.
     * @param string $for the ID of the HTML element that this label is associated with.
     * If this is null, the "for" attribute will not be generated.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated label tag
     */
    public static function label($content, $for = null, $options = [])
    {
        $options['for'] = $for;
        return static::tag('label', $content, $options);
    }

    /**
     * Generates a button tag.
     * @param string $content the content enclosed within the button tag. It will NOT be HTML-encoded.
     * Therefore you can pass in HTML code such as an image tag. If this is is coming from end users,
     * you should consider [[encode()]] it to prevent XSS attacks.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated button tag
     */
    public static function button($content = 'Button', $options = [])
    {
        if (!isset($options['type'])) {
            $options['type'] = 'button';
        }
        return static::tag('button', $content, $options);
    }

    /**
     * Generates a submit button tag.
     *
     * Be careful when naming form elements such as submit buttons. According to the [jQuery documentation](https://api.jquery.com/submit/) there
     * are some reserved names that can cause conflicts, e.g. `submit`, `length`, or `method`.
     *
     * @param string $content the content enclosed within the button tag. It will NOT be HTML-encoded.
     * Therefore you can pass in HTML code such as an image tag. If this is is coming from end users,
     * you should consider [[encode()]] it to prevent XSS attacks.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated submit button tag
     */
    public static function submitButton($content = 'Submit', $options = [])
    {
        $options['type'] = 'submit';
        return static::button($content, $options);
    }

    /**
     * Generates a reset button tag.
     * @param string $content the content enclosed within the button tag. It will NOT be HTML-encoded.
     * Therefore you can pass in HTML code such as an image tag. If this is is coming from end users,
     * you should consider [[encode()]] it to prevent XSS attacks.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated reset button tag
     */
    public static function resetButton($content = 'Reset', $options = [])
    {
        $options['type'] = 'reset';
        return static::button($content, $options);
    }

    /**
     * Generates an input type of the given type.
     * @param string $type the type attribute.
     * @param string $name the name attribute. If it is null, the name attribute will not be generated.
     * @param string $value the value attribute. If it is null, the value attribute will not be generated.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated input tag
     */
    public static function input($type, $name = null, $value = null, $options = [])
    {
        if (!isset($options['type'])) {
            $options['type'] = $type;
        }
        $options['name'] = $name;
        $options['value'] = $value === null ? null : (string) $value;
        return static::tag('input', '', $options);
    }

    /**
     * Generates an input button.
     * @param string $label the value attribute. If it is null, the value attribute will not be generated.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated button tag
     */
    public static function buttonInput($label = 'Button', $options = [])
    {
        $options['type'] = 'button';
        $options['value'] = $label;
        return static::tag('input', '', $options);
    }

    /**
     * Generates a submit input button.
     *
     * Be careful when naming form elements such as submit buttons. According to the [jQuery documentation](https://api.jquery.com/submit/) there
     * are some reserved names that can cause conflicts, e.g. `submit`, `length`, or `method`.
     *
     * @param string $label the value attribute. If it is null, the value attribute will not be generated.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated button tag
     */
    public static function submitInput($label = 'Submit', $options = [])
    {
        $options['type'] = 'submit';
        $options['value'] = $label;
        return static::tag('input', '', $options);
    }

    /**
     * Generates a reset input button.
     * @param string $label the value attribute. If it is null, the value attribute will not be generated.
     * @param array $options the attributes of the button tag. The values will be HTML-encoded using [[encode()]].
     * Attributes whose value is null will be ignored and not put in the tag returned.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated button tag
     */
    public static function resetInput($label = 'Reset', $options = [])
    {
        $options['type'] = 'reset';
        $options['value'] = $label;
        return static::tag('input', '', $options);
    }

    /**
     * Generates a text input field.
     * @param string $name the name attribute.
     * @param string $value the value attribute. If it is null, the value attribute will not be generated.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated text input tag
     */
    public static function textInput($name, $value = null, $options = [])
    {
        return static::input('text', $name, $value, $options);
    }

    /**
     * Generates a hidden input field.
     * @param string $name the name attribute.
     * @param string $value the value attribute. If it is null, the value attribute will not be generated.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated hidden input tag
     */
    public static function hiddenInput($name, $value = null, $options = [])
    {
        return static::input('hidden', $name, $value, $options);
    }

    /**
     * Generates a password input field.
     * @param string $name the name attribute.
     * @param string $value the value attribute. If it is null, the value attribute will not be generated.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated password input tag
     */
    public static function passwordInput($name, $value = null, $options = [])
    {
        return static::input('password', $name, $value, $options);
    }

    /**
     * Generates a file input field.
     * To use a file input field, you should set the enclosing form's "enctype" attribute to
     * be "multipart/form-data". After the form is submitted, the uploaded file information
     * can be obtained via $_FILES[$name] (see PHP documentation).
     * @param string $name the name attribute.
     * @param string $value the value attribute. If it is null, the value attribute will not be generated.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated file input tag
     */
    public static function fileInput($name, $value = null, $options = [])
    {
        return static::input('file', $name, $value, $options);
    }

    /**
     * Generates a text area input.
     * @param string $name the input name
     * @param string $value the input value. Note that it will be encoded using [[encode()]].
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated text area tag
     */
    public static function textarea($name, $value = '', $options = [])
    {
        $options['name'] = $name;
        return static::tag('textarea', static::encode($value), $options);
    }

    /**
     * Generates a radio button input.
     * @param string $name the name attribute.
     * @param boolean $checked whether the radio button should be checked.
     * @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
     *
     * - uncheck: string, the value associated with the uncheck state of the radio button. When this attribute
     *   is present, a hidden input will be generated so that if the radio button is not checked and is submitted,
     *   the value of this attribute will still be submitted to the server via the hidden input.
     * - label: string, a label displayed next to the radio button.  It will NOT be HTML-encoded. Therefore you can pass
     *   in HTML code such as an image tag. If this is is coming from end users, you should [[encode()]] it to prevent XSS attacks.
     *   When this option is specified, the radio button will be enclosed by a label tag.
     * - labelOptions: array, the HTML attributes for the label tag. Do not set this option unless you set the "label" option.
     *
     * The rest of the options will be rendered as the attributes of the resulting radio button tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated radio button tag
     */
    public static function radio($name, $checked = false, $options = [])
    {
        $options['checked'] = (bool) $checked;
        $value = array_key_exists('value', $options) ? $options['value'] : '1';
        if (isset($options['uncheck'])) {
            // add a hidden field so that if the radio button is not selected, it still submits a value
            $hidden = static::hiddenInput($name, $options['uncheck']);
            unset($options['uncheck']);
        } else {
            $hidden = '';
        }
        if (isset($options['label'])) {
            $label = $options['label'];
            $labelOptions = isset($options['labelOptions']) ? $options['labelOptions'] : [];
            unset($options['label'], $options['labelOptions']);
            $content = static::label(static::input('radio', $name, $value, $options) . ' ' . $label, null, $labelOptions);
            return $hidden . $content;
        } else {
            return $hidden . static::input('radio', $name, $value, $options);
        }
    }

    /**
     * Generates a checkbox input.
     * @param string $name the name attribute.
     * @param boolean $checked whether the checkbox should be checked.
     * @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
     *
     * - uncheck: string, the value associated with the uncheck state of the checkbox. When this attribute
     *   is present, a hidden input will be generated so that if the checkbox is not checked and is submitted,
     *   the value of this attribute will still be submitted to the server via the hidden input.
     * - label: string, a label displayed next to the checkbox.  It will NOT be HTML-encoded. Therefore you can pass
     *   in HTML code such as an image tag. If this is is coming from end users, you should [[encode()]] it to prevent XSS attacks.
     *   When this option is specified, the checkbox will be enclosed by a label tag.
     * - labelOptions: array, the HTML attributes for the label tag. Do not set this option unless you set the "label" option.
     *
     * The rest of the options will be rendered as the attributes of the resulting checkbox tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated checkbox tag
     */
    public static function checkbox($name, $checked = false, $options = [])
    {
        $options['checked'] = (bool) $checked;
        $value = array_key_exists('value', $options) ? $options['value'] : '1';
        if (isset($options['uncheck'])) {
            // add a hidden field so that if the checkbox is not selected, it still submits a value
            $hidden = static::hiddenInput($name, $options['uncheck']);
            unset($options['uncheck']);
        } else {
            $hidden = '';
        }
        if (isset($options['label'])) {
            $label = $options['label'];
            $labelOptions = isset($options['labelOptions']) ? $options['labelOptions'] : [];
            unset($options['label'], $options['labelOptions']);
            $content = static::label(static::input('checkbox', $name, $value, $options) . ' ' . $label, null, $labelOptions);
            return $hidden . $content;
        } else {
            return $hidden . static::input('checkbox', $name, $value, $options);
        }
    }

    /**
     * Generates a drop-down list.
     * @param string $name the input name
     * @param string $selection the selected value
     * @param array $items the option data items. The array keys are option values, and the array values
     * are the corresponding option labels. The array can also be nested (i.e. some array values are arrays too).
     * For each sub-array, an option group will be generated whose label is the key associated with the sub-array.
     * If you have a list of data models, you may convert them into the format described above using
     * [[\yii\helpers\ArrayHelper::map()]].
     *
     * Note, the values and labels will be automatically HTML-encoded by this method, and the blank spaces in
     * the labels will also be HTML-encoded.
     * @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
     *
     * - prompt: string, a prompt text to be displayed as the first option;
     * - options: array, the attributes for the select option tags. The array keys must be valid option values,
     *   and the array values are the extra attributes for the corresponding option tags. For example,
     *
     *   ~~~
     *   [
     *       'value1' => ['disabled' => true],
     *       'value2' => ['label' => 'value 2'],
     *   ];
     *   ~~~
     *
     * - groups: array, the attributes for the optgroup tags. The structure of this is similar to that of 'options',
     *   except that the array keys represent the optgroup labels specified in $items.
     * - encodeSpaces: bool, whether to encode spaces in option prompt and option value with `&nbsp;` character.
     *   Defaults to false.
     * - encode: bool, whether to encode option prompt and option value characters.
     *   Defaults to `true`. This option is available since 2.0.3.
     *
     * The rest of the options will be rendered as the attributes of the resulting tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated drop-down list tag
     */
    public static function dropDownList($name, $selection = null, $items = [], $options = [])
    {
        if (!empty($options['multiple'])) {
            return static::listBox($name, $selection, $items, $options);
        }
        $options['name'] = $name;
        unset($options['unselect']);
        $selectOptions = static::renderSelectOptions($selection, $items, $options);
        return static::tag('select', "\n" . $selectOptions . "\n", $options);
    }

    /**
     * Generates a list box.
     * @param string $name the input name
     * @param string|array $selection the selected value(s)
     * @param array $items the option data items. The array keys are option values, and the array values
     * are the corresponding option labels. The array can also be nested (i.e. some array values are arrays too).
     * For each sub-array, an option group will be generated whose label is the key associated with the sub-array.
     * If you have a list of data models, you may convert them into the format described above using
     * [[\yii\helpers\ArrayHelper::map()]].
     *
     * Note, the values and labels will be automatically HTML-encoded by this method, and the blank spaces in
     * the labels will also be HTML-encoded.
     * @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
     *
     * - prompt: string, a prompt text to be displayed as the first option;
     * - options: array, the attributes for the select option tags. The array keys must be valid option values,
     *   and the array values are the extra attributes for the corresponding option tags. For example,
     *
     *   ~~~
     *   [
     *       'value1' => ['disabled' => true],
     *       'value2' => ['label' => 'value 2'],
     *   ];
     *   ~~~
     *
     * - groups: array, the attributes for the optgroup tags. The structure of this is similar to that of 'options',
     *   except that the array keys represent the optgroup labels specified in $items.
     * - unselect: string, the value that will be submitted when no option is selected.
     *   When this attribute is set, a hidden field will be generated so that if no option is selected in multiple
     *   mode, we can still obtain the posted unselect value.
     * - encodeSpaces: bool, whether to encode spaces in option prompt and option value with `&nbsp;` character.
     *   Defaults to false.
     * - encode: bool, whether to encode option prompt and option value characters.
     *   Defaults to `true`. This option is available since 2.0.3.
     *
     * The rest of the options will be rendered as the attributes of the resulting tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated list box tag
     */
    public static function listBox($name, $selection = null, $items = [], $options = [])
    {
        if (!array_key_exists('size', $options)) {
            $options['size'] = 4;
        }
        if (!empty($options['multiple']) && !empty($name) && substr_compare($name, '[]', -2, 2)) {
            $name .= '[]';
        }
        $options['name'] = $name;
        if (isset($options['unselect'])) {
            // add a hidden field so that if the list box has no option being selected, it still submits a value
            if (!empty($name) && substr_compare($name, '[]', -2, 2) === 0) {
                $name = substr($name, 0, -2);
            }
            $hidden = static::hiddenInput($name, $options['unselect']);
            unset($options['unselect']);
        } else {
            $hidden = '';
        }
        $selectOptions = static::renderSelectOptions($selection, $items, $options);
        return $hidden . static::tag('select', "\n" . $selectOptions . "\n", $options);
    }

    /**
     * Generates a list of checkboxes.
     * A checkbox list allows multiple selection, like [[listBox()]].
     * As a result, the corresponding submitted value is an array.
     * @param string $name the name attribute of each checkbox.
     * @param string|array $selection the selected value(s).
     * @param array $items the data item used to generate the checkboxes.
     * The array keys are the checkbox values, while the array values are the corresponding labels.
     * @param array $options options (name => config) for the checkbox list container tag.
     * The following options are specially handled:
     *
     * - tag: string, the tag name of the container element.
     * - unselect: string, the value that should be submitted when none of the checkboxes is selected.
     *   By setting this option, a hidden input will be generated.
     * - encode: boolean, whether to HTML-encode the checkbox labels. Defaults to true.
     *   This option is ignored if `item` option is set.
     * - separator: string, the HTML code that separates items.
     * - itemOptions: array, the options for generating the checkbox tag using [[checkbox()]].
     * - item: callable, a callback that can be used to customize the generation of the HTML code
     *   corresponding to a single item in $items. The signature of this callback must be:
     *
     *   ~~~
     *   function ($index, $label, $name, $checked, $value)
     *   ~~~
     *
     *   where $index is the zero-based index of the checkbox in the whole list; $label
     *   is the label for the checkbox; and $name, $value and $checked represent the name,
     *   value and the checked status of the checkbox input, respectively.
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated checkbox list
     */
    public static function checkboxList($name, $selection = null, $items = [], $options = [])
    {
        if (substr($name, -2) !== '[]') {
            $name .= '[]';
        }

        $formatter = isset($options['item']) ? $options['item'] : null;
        $itemOptions = isset($options['itemOptions']) ? $options['itemOptions'] : [];
        $encode = !isset($options['encode']) || $options['encode'];
        $lines = [];
        $index = 0;
        foreach ($items as $value => $label) {
            $checked = $selection !== null &&
                (!is_array($selection) && !strcmp($value, $selection)
                    || is_array($selection) && in_array($value, $selection));
            if ($formatter !== null) {
                $lines[] = call_user_func($formatter, $index, $label, $name, $checked, $value);
            } else {
                $lines[] = static::checkbox($name, $checked, array_merge($itemOptions, [
                    'value' => $value,
                    'label' => $encode ? static::encode($label) : $label,
                ]));
            }
            $index++;
        }

        if (isset($options['unselect'])) {
            // add a hidden field so that if the list box has no option being selected, it still submits a value
            $name2 = substr($name, -2) === '[]' ? substr($name, 0, -2) : $name;
            $hidden = static::hiddenInput($name2, $options['unselect']);
        } else {
            $hidden = '';
        }
        $separator = isset($options['separator']) ? $options['separator'] : "\n";

        $tag = isset($options['tag']) ? $options['tag'] : 'div';
        unset($options['tag'], $options['unselect'], $options['encode'], $options['separator'], $options['item'], $options['itemOptions']);

        return $hidden . static::tag($tag, implode($separator, $lines), $options);
    }

    /**
     * Generates a list of radio buttons.
     * A radio button list is like a checkbox list, except that it only allows single selection.
     * @param string $name the name attribute of each radio button.
     * @param string|array $selection the selected value(s).
     * @param array $items the data item used to generate the radio buttons.
     * The array keys are the radio button values, while the array values are the corresponding labels.
     * @param array $options options (name => config) for the radio button list container tag.
     * The following options are specially handled:
     *
     * - tag: string, the tag name of the container element.
     * - unselect: string, the value that should be submitted when none of the radio buttons is selected.
     *   By setting this option, a hidden input will be generated.
     * - encode: boolean, whether to HTML-encode the checkbox labels. Defaults to true.
     *   This option is ignored if `item` option is set.
     * - separator: string, the HTML code that separates items.
     * - itemOptions: array, the options for generating the radio button tag using [[radio()]].
     * - item: callable, a callback that can be used to customize the generation of the HTML code
     *   corresponding to a single item in $items. The signature of this callback must be:
     *
     *   ~~~
     *   function ($index, $label, $name, $checked, $value)
     *   ~~~
     *
     *   where $index is the zero-based index of the radio button in the whole list; $label
     *   is the label for the radio button; and $name, $value and $checked represent the name,
     *   value and the checked status of the radio button input, respectively.
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated radio button list
     */
    public static function radioList($name, $selection = null, $items = [], $options = [])
    {
        $encode = !isset($options['encode']) || $options['encode'];
        $formatter = isset($options['item']) ? $options['item'] : null;
        $itemOptions = isset($options['itemOptions']) ? $options['itemOptions'] : [];
        $lines = [];
        $index = 0;
        foreach ($items as $value => $label) {
            $checked = $selection !== null &&
                (!is_array($selection) && !strcmp($value, $selection)
                    || is_array($selection) && in_array($value, $selection));
            if ($formatter !== null) {
                $lines[] = call_user_func($formatter, $index, $label, $name, $checked, $value);
            } else {
                $lines[] = static::radio($name, $checked, array_merge($itemOptions, [
                    'value' => $value,
                    'label' => $encode ? static::encode($label) : $label,
                ]));
            }
            $index++;
        }

        $separator = isset($options['separator']) ? $options['separator'] : "\n";
        if (isset($options['unselect'])) {
            // add a hidden field so that if the list box has no option being selected, it still submits a value
            $hidden = static::hiddenInput($name, $options['unselect']);
        } else {
            $hidden = '';
        }

        $tag = isset($options['tag']) ? $options['tag'] : 'div';
        unset($options['tag'], $options['unselect'], $options['encode'], $options['separator'], $options['item'], $options['itemOptions']);

        return $hidden . static::tag($tag, implode($separator, $lines), $options);
    }

    /**
     * Generates an unordered list.
     * @param array|\Traversable $items the items for generating the list. Each item generates a single list item.
     * Note that items will be automatically HTML encoded if `$options['encode']` is not set or true.
     * @param array $options options (name => config) for the radio button list. The following options are supported:
     *
     * - encode: boolean, whether to HTML-encode the items. Defaults to true.
     *   This option is ignored if the `item` option is specified.
     * - itemOptions: array, the HTML attributes for the `li` tags. This option is ignored if the `item` option is specified.
     * - item: callable, a callback that is used to generate each individual list item.
     *   The signature of this callback must be:
     *
     *   ~~~
     *   function ($item, $index)
     *   ~~~
     *
     *   where $index is the array key corresponding to `$item` in `$items`. The callback should return
     *   the whole list item tag.
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated unordered list. An empty list tag will be returned if `$items` is empty.
     */
    public static function ul($items, $options = [])
    {
        $tag = isset($options['tag']) ? $options['tag'] : 'ul';
        $encode = !isset($options['encode']) || $options['encode'];
        $formatter = isset($options['item']) ? $options['item'] : null;
        $itemOptions = isset($options['itemOptions']) ? $options['itemOptions'] : [];
        unset($options['tag'], $options['encode'], $options['item'], $options['itemOptions']);

        if (empty($items)) {
            return static::tag($tag, '', $options);
        }

        $results = [];
        foreach ($items as $index => $item) {
            if ($formatter !== null) {
                $results[] = call_user_func($formatter, $item, $index);
            } else {
                $results[] = static::tag('li', $encode ? static::encode($item) : $item, $itemOptions);
            }
        }
        return static::tag($tag, "\n" . implode("\n", $results) . "\n", $options);
    }

    /**
     * Generates an ordered list.
     * @param array|\Traversable $items the items for generating the list. Each item generates a single list item.
     * Note that items will be automatically HTML encoded if `$options['encode']` is not set or true.
     * @param array $options options (name => config) for the radio button list. The following options are supported:
     *
     * - encode: boolean, whether to HTML-encode the items. Defaults to true.
     *   This option is ignored if the `item` option is specified.
     * - itemOptions: array, the HTML attributes for the `li` tags. This option is ignored if the `item` option is specified.
     * - item: callable, a callback that is used to generate each individual list item.
     *   The signature of this callback must be:
     *
     *   ~~~
     *   function ($item, $index)
     *   ~~~
     *
     *   where $index is the array key corresponding to `$item` in `$items`. The callback should return
     *   the whole list item tag.
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated ordered list. An empty string is returned if `$items` is empty.
     */
    public static function ol($items, $options = [])
    {
        $options['tag'] = 'ol';
        return static::ul($items, $options);
    }

    /**
     * Generates a label tag for the given model attribute.
     * The label text is the label associated with the attribute, obtained via [[Model::getAttributeLabel()]].
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * The following options are specially handled:
     *
     * - label: this specifies the label to be displayed. Note that this will NOT be [[encode()|encoded]].
     *   If this is not set, [[Model::getAttributeLabel()]] will be called to get the label for display
     *   (after encoding).
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated label tag
     */
    public static function activeLabel($model, $attribute, $options = [])
    {
        $for = array_key_exists('for', $options) ? $options['for'] : static::getInputId($model, $attribute);
        $attribute = static::getAttributeName($attribute);
        $label = isset($options['label']) ? $options['label'] : static::encode($model->getAttributeLabel($attribute));
        unset($options['label'], $options['for']);
        return static::label($label, $for, $options);
    }

    /**
     * Generates a hint tag for the given model attribute.
     * The hint text is the hint associated with the attribute, obtained via [[Model::getAttributeHint()]].
     * If no hint content can be obtained, method will return an empty string.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * If a value is null, the corresponding attribute will not be rendered.
     * The following options are specially handled:
     *
     * - hint: this specifies the hint to be displayed. Note that this will NOT be [[encode()|encoded]].
     *   If this is not set, [[Model::getAttributeHint()]] will be called to get the hint for display
     *   (without encoding).
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated hint tag
     * @since 2.0.4
     */
    public static function activeHint($model, $attribute, $options = [])
    {
        $attribute = static::getAttributeName($attribute);
        $hint = isset($options['hint']) ? $options['hint'] : $model->getAttributeHint($attribute);
        if (empty($hint)) {
            return '';
        }
        $tag = ArrayHelper::remove($options, 'tag', 'div');
        unset($options['hint']);
        return static::tag($tag, $hint, $options);
    }

    /**
     * Generates a summary of the validation errors.
     * If there is no validation error, an empty error summary markup will still be generated, but it will be hidden.
     * @param Model|Model[] $models the model(s) whose validation errors are to be displayed
     * @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
     *
     * - header: string, the header HTML for the error summary. If not set, a default prompt string will be used.
     * - footer: string, the footer HTML for the error summary.
     * - encode: boolean, if set to false then the error messages won't be encoded.
     *
     * The rest of the options will be rendered as the attributes of the container tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * @return string the generated error summary
     */
    public static function errorSummary($models, $options = [])
    {
        $header = isset($options['header']) ? $options['header'] : '<p>' . Yii::t('yii', 'Please fix the following errors:') . '</p>';
        $footer = isset($options['footer']) ? $options['footer'] : '';
        $encode = !isset($options['encode']) || $options['encode'] !== false;
        unset($options['header'], $options['footer'], $options['encode']);

        $lines = [];
        if (!is_array($models)) {
            $models = [$models];
        }
        foreach ($models as $model) {
            /* @var $model Model */
            foreach ($model->getFirstErrors() as $error) {
                $lines[] = $encode ? Html::encode($error) : $error;
            }
        }

        if (empty($lines)) {
            // still render the placeholder for client-side validation use
            $content = '<ul></ul>';
            $options['style'] = isset($options['style']) ? rtrim($options['style'], ';') . '; display:none' : 'display:none';
        } else {
            $content = '<ul><li>' . implode("</li>\n<li>", $lines) . '</li></ul>';
        }
        return Html::tag('div', $header . $content . $footer, $options);
    }

    /**
     * Generates a tag that contains the first validation error of the specified model attribute.
     * Note that even if there is no validation error, this method will still return an empty error tag.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. The values will be HTML-encoded
     * using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     *
     * The following options are specially handled:
     *
     * - tag: this specifies the tag name. If not set, "div" will be used.
     * - encode: boolean, if set to false then the error message won't be encoded.
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated label tag
     */
    public static function error($model, $attribute, $options = [])
    {
        $attribute = static::getAttributeName($attribute);
        $error = $model->getFirstError($attribute);
        $tag = isset($options['tag']) ? $options['tag'] : 'div';
        $encode = !isset($options['encode']) || $options['encode'] !== false;
        unset($options['tag'], $options['encode']);
        return Html::tag($tag, $encode ? Html::encode($error) : $error, $options);
    }

    /**
     * Generates an input tag for the given model attribute.
     * This method will generate the "name" and "value" tag attributes automatically for the model attribute
     * unless they are explicitly specified in `$options`.
     * @param string $type the input type (e.g. 'text', 'password')
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated input tag
     */
    public static function activeInput($type, $model, $attribute, $options = [])
    {
        $name = isset($options['name']) ? $options['name'] : static::getInputName($model, $attribute);
        $value = isset($options['value']) ? $options['value'] : static::getAttributeValue($model, $attribute);
        if (!array_key_exists('id', $options)) {
            $options['id'] = static::getInputId($model, $attribute);
        }
        return static::input($type, $name, $value, $options);
    }

    /**
     * If `maxlength` option is set true and the model attribute is validated by a string validator,
     * the `maxlength` option will take the value of [[\yii\validators\StringValidator::max]].
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression.
     * @param array $options the tag options in terms of name-value pairs.
     */
    private static function normalizeMaxLength($model, $attribute, &$options)
    {
        if (isset($options['maxlength']) && $options['maxlength'] === true) {
            unset($options['maxlength']);
            $attrName = static::getAttributeName($attribute);
            foreach ($model->getActiveValidators($attrName) as $validator) {
                if ($validator instanceof StringValidator && $validator->max !== null) {
                    $options['maxlength'] = $validator->max;
                    break;
                }
            }
        }
    }

    /**
     * Generates a text input tag for the given model attribute.
     * This method will generate the "name" and "value" tag attributes automatically for the model attribute
     * unless they are explicitly specified in `$options`.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * The following special options are recognized:
     *
     * - maxlength: integer|boolean, when `maxlength` is set true and the model attribute is validated
     *   by a string validator, the `maxlength` option will take the value of [[\yii\validators\StringValidator::max]].
     *   This is available since version 2.0.3.
     *
     * @return string the generated input tag
     */
    public static function activeTextInput($model, $attribute, $options = [])
    {
        self::normalizeMaxLength($model, $attribute, $options);
        return static::activeInput('text', $model, $attribute, $options);
    }

    /**
     * Generates a hidden input tag for the given model attribute.
     * This method will generate the "name" and "value" tag attributes automatically for the model attribute
     * unless they are explicitly specified in `$options`.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated input tag
     */
    public static function activeHiddenInput($model, $attribute, $options = [])
    {
        return static::activeInput('hidden', $model, $attribute, $options);
    }

    /**
     * Generates a password input tag for the given model attribute.
     * This method will generate the "name" and "value" tag attributes automatically for the model attribute
     * unless they are explicitly specified in `$options`.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * The following special options are recognized:
     *
     * - maxlength: integer|boolean, when `maxlength` is set true and the model attribute is validated
     *   by a string validator, the `maxlength` option will take the value of [[\yii\validators\StringValidator::max]].
     *   This option is available since version 2.0.6.
     *
     * @return string the generated input tag
     */
    public static function activePasswordInput($model, $attribute, $options = [])
    {
        self::normalizeMaxLength($model, $attribute, $options);
        return static::activeInput('password', $model, $attribute, $options);
    }

    /**
     * Generates a file input tag for the given model attribute.
     * This method will generate the "name" and "value" tag attributes automatically for the model attribute
     * unless they are explicitly specified in `$options`.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * @return string the generated input tag
     */
    public static function activeFileInput($model, $attribute, $options = [])
    {
        // add a hidden field so that if a model only has a file field, we can
        // still use isset($_POST[$modelClass]) to detect if the input is submitted
        $hiddenOptions = ['id' => null, 'value' => ''];
        if (isset($options['name'])) {
            $hiddenOptions['name'] = $options['name'];
        }
        return static::activeHiddenInput($model, $attribute, $hiddenOptions)
            . static::activeInput('file', $model, $attribute, $options);
    }

    /**
     * Generates a textarea tag for the given model attribute.
     * The model attribute value will be used as the content in the textarea.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. These will be rendered as
     * the attributes of the resulting tag. The values will be HTML-encoded using [[encode()]].
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     * The following special options are recognized:
     *
     * - maxlength: integer|boolean, when `maxlength` is set true and the model attribute is validated
     *   by a string validator, the `maxlength` option will take the value of [[\yii\validators\StringValidator::max]].
     *   This option is available since version 2.0.6.
     *
     * @return string the generated textarea tag
     */
    public static function activeTextarea($model, $attribute, $options = [])
    {
        $name = isset($options['name']) ? $options['name'] : static::getInputName($model, $attribute);
        if (isset($options['value'])) {
            $value = $options['value'];
            unset($options['value']);
        } else {
            $value = static::getAttributeValue($model, $attribute);
        }
        if (!array_key_exists('id', $options)) {
            $options['id'] = static::getInputId($model, $attribute);
        }
        self::normalizeMaxLength($model, $attribute, $options);
        return static::textarea($name, $value, $options);
    }

    /**
     * Generates a radio button tag together with a label for the given model attribute.
     * This method will generate the "checked" tag attribute according to the model attribute value.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
     *
     * - uncheck: string, the value associated with the uncheck state of the radio button. If not set,
     *   it will take the default value '0'. This method will render a hidden input so that if the radio button
     *   is not checked and is submitted, the value of this attribute will still be submitted to the server
     *   via the hidden input. If you do not want any hidden input, you should explicitly set this option as null.
     * - label: string, a label displayed next to the radio button.  It will NOT be HTML-encoded. Therefore you can pass
     *   in HTML code such as an image tag. If this is is coming from end users, you should [[encode()]] it to prevent XSS attacks.
     *   The radio button will be enclosed by the label tag. Note that if you do not specify this option, a default label
     *   will be used based on the attribute label declaration in the model. If you do not want any label, you should
     *   explicitly set this option as null.
     * - labelOptions: array, the HTML attributes for the label tag. This is only used when the "label" option is specified.
     *
     * The rest of the options will be rendered as the attributes of the resulting tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated radio button tag
     */
    public static function activeRadio($model, $attribute, $options = [])
    {
        $name = isset($options['name']) ? $options['name'] : static::getInputName($model, $attribute);
        $value = static::getAttributeValue($model, $attribute);

        if (!array_key_exists('value', $options)) {
            $options['value'] = '1';
        }
        if (!array_key_exists('uncheck', $options)) {
            $options['uncheck'] = '0';
        }
        if (!array_key_exists('label', $options)) {
            $options['label'] = static::encode($model->getAttributeLabel(static::getAttributeName($attribute)));
        }

        $checked = "$value" === "{$options['value']}";

        if (!array_key_exists('id', $options)) {
            $options['id'] = static::getInputId($model, $attribute);
        }

        return static::radio($name, $checked, $options);
    }

    /**
     * Generates a checkbox tag together with a label for the given model attribute.
     * This method will generate the "checked" tag attribute according to the model attribute value.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
     *
     * - uncheck: string, the value associated with the uncheck state of the radio button. If not set,
     *   it will take the default value '0'. This method will render a hidden input so that if the radio button
     *   is not checked and is submitted, the value of this attribute will still be submitted to the server
     *   via the hidden input. If you do not want any hidden input, you should explicitly set this option as null.
     * - label: string, a label displayed next to the checkbox.  It will NOT be HTML-encoded. Therefore you can pass
     *   in HTML code such as an image tag. If this is is coming from end users, you should [[encode()]] it to prevent XSS attacks.
     *   The checkbox will be enclosed by the label tag. Note that if you do not specify this option, a default label
     *   will be used based on the attribute label declaration in the model. If you do not want any label, you should
     *   explicitly set this option as null.
     * - labelOptions: array, the HTML attributes for the label tag. This is only used when the "label" option is specified.
     *
     * The rest of the options will be rendered as the attributes of the resulting tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated checkbox tag
     */
    public static function activeCheckbox($model, $attribute, $options = [])
    {
        $name = isset($options['name']) ? $options['name'] : static::getInputName($model, $attribute);
        $value = static::getAttributeValue($model, $attribute);

        if (!array_key_exists('value', $options)) {
            $options['value'] = '1';
        }
        if (!array_key_exists('uncheck', $options)) {
            $options['uncheck'] = '0';
        }
        if (!array_key_exists('label', $options)) {
            $options['label'] = static::encode($model->getAttributeLabel(static::getAttributeName($attribute)));
        }

        $checked = "$value" === "{$options['value']}";

        if (!array_key_exists('id', $options)) {
            $options['id'] = static::getInputId($model, $attribute);
        }

        return static::checkbox($name, $checked, $options);
    }

    /**
     * Generates a drop-down list for the given model attribute.
     * The selection of the drop-down list is taken from the value of the model attribute.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $items the option data items. The array keys are option values, and the array values
     * are the corresponding option labels. The array can also be nested (i.e. some array values are arrays too).
     * For each sub-array, an option group will be generated whose label is the key associated with the sub-array.
     * If you have a list of data models, you may convert them into the format described above using
     * [[\yii\helpers\ArrayHelper::map()]].
     *
     * Note, the values and labels will be automatically HTML-encoded by this method, and the blank spaces in
     * the labels will also be HTML-encoded.
     * @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
     *
     * - prompt: string, a prompt text to be displayed as the first option;
     * - options: array, the attributes for the select option tags. The array keys must be valid option values,
     *   and the array values are the extra attributes for the corresponding option tags. For example,
     *
     *   ~~~
     *   [
     *       'value1' => ['disabled' => true],
     *       'value2' => ['label' => 'value 2'],
     *   ];
     *   ~~~
     *
     * - groups: array, the attributes for the optgroup tags. The structure of this is similar to that of 'options',
     *   except that the array keys represent the optgroup labels specified in $items.
     * - encodeSpaces: bool, whether to encode spaces in option prompt and option value with `&nbsp;` character.
     *   Defaults to false.
     * - encode: bool, whether to encode option prompt and option value characters.
     *   Defaults to `true`. This option is available since 2.0.3.
     *
     * The rest of the options will be rendered as the attributes of the resulting tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated drop-down list tag
     */
    public static function activeDropDownList($model, $attribute, $items, $options = [])
    {
        if (empty($options['multiple'])) {
            return static::activeListInput('dropDownList', $model, $attribute, $items, $options);
        } else {
            return static::activeListBox($model, $attribute, $items, $options);
        }
    }

    /**
     * Generates a list box.
     * The selection of the list box is taken from the value of the model attribute.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $items the option data items. The array keys are option values, and the array values
     * are the corresponding option labels. The array can also be nested (i.e. some array values are arrays too).
     * For each sub-array, an option group will be generated whose label is the key associated with the sub-array.
     * If you have a list of data models, you may convert them into the format described above using
     * [[\yii\helpers\ArrayHelper::map()]].
     *
     * Note, the values and labels will be automatically HTML-encoded by this method, and the blank spaces in
     * the labels will also be HTML-encoded.
     * @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
     *
     * - prompt: string, a prompt text to be displayed as the first option;
     * - options: array, the attributes for the select option tags. The array keys must be valid option values,
     *   and the array values are the extra attributes for the corresponding option tags. For example,
     *
     *   ~~~
     *   [
     *       'value1' => ['disabled' => true],
     *       'value2' => ['label' => 'value 2'],
     *   ];
     *   ~~~
     *
     * - groups: array, the attributes for the optgroup tags. The structure of this is similar to that of 'options',
     *   except that the array keys represent the optgroup labels specified in $items.
     * - unselect: string, the value that will be submitted when no option is selected.
     *   When this attribute is set, a hidden field will be generated so that if no option is selected in multiple
     *   mode, we can still obtain the posted unselect value.
     * - encodeSpaces: bool, whether to encode spaces in option prompt and option value with `&nbsp;` character.
     *   Defaults to false.
     * - encode: bool, whether to encode option prompt and option value characters.
     *   Defaults to `true`. This option is available since 2.0.3.
     *
     * The rest of the options will be rendered as the attributes of the resulting tag. The values will
     * be HTML-encoded using [[encode()]]. If a value is null, the corresponding attribute will not be rendered.
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated list box tag
     */
    public static function activeListBox($model, $attribute, $items, $options = [])
    {
        return static::activeListInput('listBox', $model, $attribute, $items, $options);
    }

    /**
     * Generates a list of checkboxes.
     * A checkbox list allows multiple selection, like [[listBox()]].
     * As a result, the corresponding submitted value is an array.
     * The selection of the checkbox list is taken from the value of the model attribute.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $items the data item used to generate the checkboxes.
     * The array keys are the checkbox values, and the array values are the corresponding labels.
     * Note that the labels will NOT be HTML-encoded, while the values will.
     * @param array $options options (name => config) for the checkbox list container tag.
     * The following options are specially handled:
     *
     * - tag: string, the tag name of the container element.
     * - unselect: string, the value that should be submitted when none of the checkboxes is selected.
     *   You may set this option to be null to prevent default value submission.
     *   If this option is not set, an empty string will be submitted.
     * - encode: boolean, whether to HTML-encode the checkbox labels. Defaults to true.
     *   This option is ignored if `item` option is set.
     * - separator: string, the HTML code that separates items.
     * - itemOptions: array, the options for generating the checkbox tag using [[checkbox()]].
     * - item: callable, a callback that can be used to customize the generation of the HTML code
     *   corresponding to a single item in $items. The signature of this callback must be:
     *
     *   ~~~
     *   function ($index, $label, $name, $checked, $value)
     *   ~~~
     *
     *   where $index is the zero-based index of the checkbox in the whole list; $label
     *   is the label for the checkbox; and $name, $value and $checked represent the name,
     *   value and the checked status of the checkbox input.
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated checkbox list
     */
    public static function activeCheckboxList($model, $attribute, $items, $options = [])
    {
        return static::activeListInput('checkboxList', $model, $attribute, $items, $options);
    }

    /**
     * Generates a list of radio buttons.
     * A radio button list is like a checkbox list, except that it only allows single selection.
     * The selection of the radio buttons is taken from the value of the model attribute.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $items the data item used to generate the radio buttons.
     * The array keys are the radio values, and the array values are the corresponding labels.
     * Note that the labels will NOT be HTML-encoded, while the values will.
     * @param array $options options (name => config) for the radio button list container tag.
     * The following options are specially handled:
     *
     * - tag: string, the tag name of the container element.
     * - unselect: string, the value that should be submitted when none of the radio buttons is selected.
     *   You may set this option to be null to prevent default value submission.
     *   If this option is not set, an empty string will be submitted.
     * - encode: boolean, whether to HTML-encode the checkbox labels. Defaults to true.
     *   This option is ignored if `item` option is set.
     * - separator: string, the HTML code that separates items.
     * - itemOptions: array, the options for generating the radio button tag using [[radio()]].
     * - item: callable, a callback that can be used to customize the generation of the HTML code
     *   corresponding to a single item in $items. The signature of this callback must be:
     *
     *   ~~~
     *   function ($index, $label, $name, $checked, $value)
     *   ~~~
     *
     *   where $index is the zero-based index of the radio button in the whole list; $label
     *   is the label for the radio button; and $name, $value and $checked represent the name,
     *   value and the checked status of the radio button input.
     *
     * See [[renderTagAttributes()]] for details on how attributes are being rendered.
     *
     * @return string the generated radio button list
     */
    public static function activeRadioList($model, $attribute, $items, $options = [])
    {
        return static::activeListInput('radioList', $model, $attribute, $items, $options);
    }

    /**
     * Generates a list of input fields.
     * This method is mainly called by [[activeListBox()]], [[activeRadioList()]] and [[activeCheckBoxList()]].
     * @param string $type the input type. This can be 'listBox', 'radioList', or 'checkBoxList'.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for the format
     * about attribute expression.
     * @param array $items the data item used to generate the input fields.
     * The array keys are the input values, and the array values are the corresponding labels.
     * Note that the labels will NOT be HTML-encoded, while the values will.
     * @param array $options options (name => config) for the input list. The supported special options
     * depend on the input type specified by `$type`.
     * @return string the generated input list
     */
    protected static function activeListInput($type, $model, $attribute, $items, $options = [])
    {
        $name = isset($options['name']) ? $options['name'] : static::getInputName($model, $attribute);
        $selection = static::getAttributeValue($model, $attribute);
        if (!array_key_exists('unselect', $options)) {
            $options['unselect'] = '';
        }
        if (!array_key_exists('id', $options)) {
            $options['id'] = static::getInputId($model, $attribute);
        }
        return static::$type($name, $selection, $items, $options);
    }

    /**
     * Renders the option tags that can be used by [[dropDownList()]] and [[listBox()]].
     * @param string|array $selection the selected value(s). This can be either a string for single selection
     * or an array for multiple selections.
     * @param array $items the option data items. The array keys are option values, and the array values
     * are the corresponding option labels. The array can also be nested (i.e. some array values are arrays too).
     * For each sub-array, an option group will be generated whose label is the key associated with the sub-array.
     * If you have a list of data models, you may convert them into the format described above using
     * [[\yii\helpers\ArrayHelper::map()]].
     *
     * Note, the values and labels will be automatically HTML-encoded by this method, and the blank spaces in
     * the labels will also be HTML-encoded.
     * @param array $tagOptions the $options parameter that is passed to the [[dropDownList()]] or [[listBox()]] call.
     * This method will take out these elements, if any: "prompt", "options" and "groups". See more details
     * in [[dropDownList()]] for the explanation of these elements.
     *
     * @return string the generated list options
     */
    public static function renderSelectOptions($selection, $items, &$tagOptions = [])
    {
        $lines = [];
        $encodeSpaces = ArrayHelper::remove($tagOptions, 'encodeSpaces', false);
        $encode = ArrayHelper::remove($tagOptions, 'encode', true);
        if (isset($tagOptions['prompt'])) {
            $prompt = $encode ? static::encode($tagOptions['prompt']) : $tagOptions['prompt'];
            if ($encodeSpaces) {
                $prompt = str_replace(' ', '&nbsp;', $prompt);
            }
            $lines[] = static::tag('option', $prompt, ['value' => '']);
        }

        $options = isset($tagOptions['options']) ? $tagOptions['options'] : [];
        $groups = isset($tagOptions['groups']) ? $tagOptions['groups'] : [];
        unset($tagOptions['prompt'], $tagOptions['options'], $tagOptions['groups']);
        $options['encodeSpaces'] = ArrayHelper::getValue($options, 'encodeSpaces', $encodeSpaces);
        $options['encode'] = ArrayHelper::getValue($options, 'encode', $encode);

        foreach ($items as $key => $value) {
            if (is_array($value)) {
                $groupAttrs = isset($groups[$key]) ? $groups[$key] : [];
                if (!isset($groupAttrs['label'])) {
                    $groupAttrs['label'] = $key;
                }
                $attrs = ['options' => $options, 'groups' => $groups, 'encodeSpaces' => $encodeSpaces, 'encode' => $encode];
                $content = static::renderSelectOptions($selection, $value, $attrs);
                $lines[] = static::tag('optgroup', "\n" . $content . "\n", $groupAttrs);
            } else {
                $attrs = isset($options[$key]) ? $options[$key] : [];
                $attrs['value'] = (string) $key;
                $attrs['selected'] = $selection !== null &&
                        (!is_array($selection) && !strcmp($key, $selection)
                        || is_array($selection) && in_array($key, $selection));
                $text = $encode ? static::encode($value) : $value;
                if ($encodeSpaces) {
                    $text = str_replace(' ', '&nbsp;', $text);
                }
                $lines[] = static::tag('option', $text, $attrs);
            }
        }

        return implode("\n", $lines);
    }

    /**
     * Renders the HTML tag attributes.
     *
     * Attributes whose values are of boolean type will be treated as
     * [boolean attributes](http://www.w3.org/TR/html5/infrastructure.html#boolean-attributes).
     *
     * Attributes whose values are null will not be rendered.
     *
     * The values of attributes will be HTML-encoded using [[encode()]].
     *
     * The "data" attribute is specially handled when it is receiving an array value. In this case,
     * the array will be "expanded" and a list data attributes will be rendered. For example,
     * if `'data' => ['id' => 1, 'name' => 'yii']`, then this will be rendered:
     * `data-id="1" data-name="yii"`.
     * Additionally `'data' => ['params' => ['id' => 1, 'name' => 'yii'], 'status' => 'ok']` will be rendered as:
     * `data-params='{"id":1,"name":"yii"}' data-status="ok"`.
     *
     * @param array $attributes attributes to be rendered. The attribute values will be HTML-encoded using [[encode()]].
     * @return string the rendering result. If the attributes are not empty, they will be rendered
     * into a string with a leading white space (so that it can be directly appended to the tag name
     * in a tag. If there is no attribute, an empty string will be returned.
     */
    public static function renderTagAttributes($attributes)
    {
        if (count($attributes) > 1) {
            $sorted = [];
            foreach (static::$attributeOrder as $name) {
                if (isset($attributes[$name])) {
                    $sorted[$name] = $attributes[$name];
                }
            }
            $attributes = array_merge($sorted, $attributes);
        }

        $html = '';
        foreach ($attributes as $name => $value) {
            if (is_bool($value)) {
                if ($value) {
                    $html .= " $name";
                }
            } elseif (is_array($value)) {
                if (in_array($name, static::$dataAttributes)) {
                    foreach ($value as $n => $v) {
                        if (is_array($v)) {
                            $html .= " $name-$n='" . Json::htmlEncode($v) . "'";
                        } else {
                            $html .= " $name-$n=\"" . static::encode($v) . '"';
                        }
                    }
                } elseif ($name === 'class') {
                    if (empty($value)) {
                        continue;
                    }
                    $html .= " $name=\"" . static::encode(implode(' ', $value)) . '"';
                } elseif ($name === 'style') {
                    if (empty($value)) {
                        continue;
                    }
                    $html .= " $name=\"" . static::encode(static::cssStyleFromArray($value)) . '"';
                } else {
                    $html .= " $name='" . Json::htmlEncode($value) . "'";
                }
            } elseif ($value !== null) {
                $html .= " $name=\"" . static::encode($value) . '"';
            }
        }

        return $html;
    }

    /**
     * Adds a CSS class (or several classes) to the specified options.
     * If the CSS class is already in the options, it will not be added again.
     * If class specification at given options is an array, and some class placed there with the named (string) key,
     * overriding of such key will have no effect. For example:
     *
     * ~~~php
     * $options = ['class' => ['persistent' => 'initial']];
     * Html::addCssClass($options, ['persistent' => 'override']);
     * var_dump($options['class']); // outputs: array('persistent' => 'initial');
     * ~~~
     *
     * @param array $options the options to be modified.
     * @param string|array $class the CSS class(es) to be added
     */
    public static function addCssClass(&$options, $class)
    {
        if (isset($options['class'])) {
            if (is_array($options['class'])) {
                $options['class'] = self::mergeCssClasses($options['class'], (array) $class);
            } else {
                $classes = preg_split('/\s+/', $options['class'], -1, PREG_SPLIT_NO_EMPTY);
                $options['class'] = implode(' ', self::mergeCssClasses($classes, (array) $class));
            }
        } else {
            $options['class'] = $class;
        }
    }

    /**
     * Merges already existing CSS classes with new one.
     * This method provides the priority for named existing classes over additional.
     * @param array $existingClasses already existing CSS classes.
     * @param array $additionalClasses CSS classes to be added.
     * @return array merge result.
     */
    private static function mergeCssClasses(array $existingClasses, array $additionalClasses)
    {
        foreach ($additionalClasses as $key => $class) {
            if (is_int($key) && !in_array($class, $existingClasses)) {
                $existingClasses[] = $class;
            } elseif (!isset($existingClasses[$key])) {
                $existingClasses[$key] = $class;
            }
        }
        return array_unique($existingClasses);
    }

    /**
     * Removes a CSS class from the specified options.
     * @param array $options the options to be modified.
     * @param string|array $class the CSS class(es) to be removed
     */
    public static function removeCssClass(&$options, $class)
    {
        if (isset($options['class'])) {
            if (is_array($options['class'])) {
                $classes = array_diff($options['class'], (array) $class);
                if (empty($classes)) {
                    unset($options['class']);
                } else {
                    $options['class'] = $classes;
                }
            } else {
                $classes = preg_split('/\s+/', $options['class'], -1, PREG_SPLIT_NO_EMPTY);
                $classes = array_diff($classes, (array) $class);
                if (empty($classes)) {
                    unset($options['class']);
                } else {
                    $options['class'] = implode(' ', $classes);
                }
            }
        }
    }

    /**
     * Adds the specified CSS style to the HTML options.
     *
     * If the options already contain a `style` element, the new style will be merged
     * with the existing one. If a CSS property exists in both the new and the old styles,
     * the old one may be overwritten if `$overwrite` is true.
     *
     * For example,
     *
     * ```php
     * Html::addCssStyle($options, 'width: 100px; height: 200px');
     * ```
     *
     * @param array $options the HTML options to be modified.
     * @param string|array $style the new style string (e.g. `'width: 100px; height: 200px'`) or
     * array (e.g. `['width' => '100px', 'height' => '200px']`).
     * @param boolean $overwrite whether to overwrite existing CSS properties if the new style
     * contain them too.
     * @see removeCssStyle()
     * @see cssStyleFromArray()
     * @see cssStyleToArray()
     */
    public static function addCssStyle(&$options, $style, $overwrite = true)
    {
        if (!empty($options['style'])) {
            $oldStyle = is_array($options['style']) ? $options['style'] : static::cssStyleToArray($options['style']);
            $newStyle = is_array($style) ? $style : static::cssStyleToArray($style);
            if (!$overwrite) {
                foreach ($newStyle as $property => $value) {
                    if (isset($oldStyle[$property])) {
                        unset($newStyle[$property]);
                    }
                }
            }
            $style = array_merge($oldStyle, $newStyle);
        }
        $options['style'] = is_array($style) ? static::cssStyleFromArray($style) : $style;
    }

    /**
     * Removes the specified CSS style from the HTML options.
     *
     * For example,
     *
     * ```php
     * Html::removeCssStyle($options, ['width', 'height']);
     * ```
     *
     * @param array $options the HTML options to be modified.
     * @param string|array $properties the CSS properties to be removed. You may use a string
     * if you are removing a single property.
     * @see addCssStyle()
     */
    public static function removeCssStyle(&$options, $properties)
    {
        if (!empty($options['style'])) {
            $style = is_array($options['style']) ? $options['style'] : static::cssStyleToArray($options['style']);
            foreach ((array) $properties as $property) {
                unset($style[$property]);
            }
            $options['style'] = static::cssStyleFromArray($style);
        }
    }

    /**
     * Converts a CSS style array into a string representation.
     *
     * For example,
     *
     * ```php
     * print_r(Html::cssStyleFromArray(['width' => '100px', 'height' => '200px']));
     * // will display: 'width: 100px; height: 200px;'
     * ```
     *
     * @param array $style the CSS style array. The array keys are the CSS property names,
     * and the array values are the corresponding CSS property values.
     * @return string the CSS style string. If the CSS style is empty, a null will be returned.
     */
    public static function cssStyleFromArray(array $style)
    {
        $result = '';
        foreach ($style as $name => $value) {
            $result .= "$name: $value; ";
        }
        // return null if empty to avoid rendering the "style" attribute
        return $result === '' ? null : rtrim($result);
    }

    /**
     * Converts a CSS style string into an array representation.
     *
     * The array keys are the CSS property names, and the array values
     * are the corresponding CSS property values.
     *
     * For example,
     *
     * ```php
     * print_r(Html::cssStyleToArray('width: 100px; height: 200px;'));
     * // will display: ['width' => '100px', 'height' => '200px']
     * ```
     *
     * @param string $style the CSS style string
     * @return array the array representation of the CSS style
     */
    public static function cssStyleToArray($style)
    {
        $result = [];
        foreach (explode(';', $style) as $property) {
            $property = explode(':', $property);
            if (count($property) > 1) {
                $result[trim($property[0])] = trim($property[1]);
            }
        }
        return $result;
    }

    /**
     * Returns the real attribute name from the given attribute expression.
     *
     * An attribute expression is an attribute name prefixed and/or suffixed with array indexes.
     * It is mainly used in tabular data input and/or input of array type. Below are some examples:
     *
     * - `[0]content` is used in tabular data input to represent the "content" attribute
     *   for the first model in tabular input;
     * - `dates[0]` represents the first array element of the "dates" attribute;
     * - `[0]dates[0]` represents the first array element of the "dates" attribute
     *   for the first model in tabular input.
     *
     * If `$attribute` has neither prefix nor suffix, it will be returned back without change.
     * @param string $attribute the attribute name or expression
     * @return string the attribute name without prefix and suffix.
     * @throws InvalidParamException if the attribute name contains non-word characters.
     */
    public static function getAttributeName($attribute)
    {
        if (preg_match('/(^|.*\])([\w\.]+)(\[.*|$)/', $attribute, $matches)) {
            return $matches[2];
        } else {
            throw new InvalidParamException('Attribute name must contain word characters only.');
        }
    }

    /**
     * Returns the value of the specified attribute name or expression.
     *
     * For an attribute expression like `[0]dates[0]`, this method will return the value of `$model->dates[0]`.
     * See [[getAttributeName()]] for more details about attribute expression.
     *
     * If an attribute value is an instance of [[ActiveRecordInterface]] or an array of such instances,
     * the primary value(s) of the AR instance(s) will be returned instead.
     *
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression
     * @return string|array the corresponding attribute value
     * @throws InvalidParamException if the attribute name contains non-word characters.
     */
    public static function getAttributeValue($model, $attribute)
    {
        if (!preg_match('/(^|.*\])([\w\.]+)(\[.*|$)/', $attribute, $matches)) {
            throw new InvalidParamException('Attribute name must contain word characters only.');
        }
        $attribute = $matches[2];
        $value = $model->$attribute;
        if ($matches[3] !== '') {
            foreach (explode('][', trim($matches[3], '[]')) as $id) {
                if ((is_array($value) || $value instanceof \ArrayAccess) && isset($value[$id])) {
                    $value = $value[$id];
                } else {
                    return null;
                }
            }
        }

        // https://github.com/yiisoft/yii2/issues/1457
        if (is_array($value)) {
            foreach ($value as $i => $v) {
                if ($v instanceof ActiveRecordInterface) {
                    $v = $v->getPrimaryKey(false);
                    $value[$i] = is_array($v) ? json_encode($v) : $v;
                }
            }
        } elseif ($value instanceof ActiveRecordInterface) {
            $value = $value->getPrimaryKey(false);

            return is_array($value) ? json_encode($value) : $value;
        }

        return $value;
    }

    /**
     * Generates an appropriate input name for the specified attribute name or expression.
     *
     * This method generates a name that can be used as the input name to collect user input
     * for the specified attribute. The name is generated according to the [[Model::formName|form name]]
     * of the model and the given attribute name. For example, if the form name of the `Post` model
     * is `Post`, then the input name generated for the `content` attribute would be `Post[content]`.
     *
     * See [[getAttributeName()]] for explanation of attribute expression.
     *
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression
     * @return string the generated input name
     * @throws InvalidParamException if the attribute name contains non-word characters.
     */
    public static function getInputName($model, $attribute)
    {
        $formName = $model->formName();
        if (!preg_match('/(^|.*\])([\w\.]+)(\[.*|$)/', $attribute, $matches)) {
            throw new InvalidParamException('Attribute name must contain word characters only.');
        }
        $prefix = $matches[1];
        $attribute = $matches[2];
        $suffix = $matches[3];
        if ($formName === '' && $prefix === '') {
            return $attribute . $suffix;
        } elseif ($formName !== '') {
            return $formName . $prefix . "[$attribute]" . $suffix;
        } else {
            throw new InvalidParamException(get_class($model) . '::formName() cannot be empty for tabular inputs.');
        }
    }

    /**
     * Generates an appropriate input ID for the specified attribute name or expression.
     *
     * This method converts the result [[getInputName()]] into a valid input ID.
     * For example, if [[getInputName()]] returns `Post[content]`, this method will return `post-content`.
     * @param Model $model the model object
     * @param string $attribute the attribute name or expression. See [[getAttributeName()]] for explanation of attribute expression.
     * @return string the generated input ID
     * @throws InvalidParamException if the attribute name contains non-word characters.
     */
    public static function getInputId($model, $attribute)
    {
        $name = strtolower(static::getInputName($model, $attribute));
        return str_replace(['[]', '][', '[', ']', ' ', '.'], ['', '-', '-', '', '-', '-'], $name);
    }

    /**
     * Escapes regular expression to use in JavaScript
     * @param string $regexp the regular expression to be escaped.
     * @return string the escaped result.
     * @since 2.0.6
     */
    public static function escapeJsRegularExpression($regexp)
    {
        $pattern = preg_replace('/\\\\x\{?([0-9a-fA-F]+)\}?/', '\u$1', $regexp);
        $deliminator = substr($pattern, 0, 1);
        $pos = strrpos($pattern, $deliminator, 1);
        $flag = substr($pattern, $pos + 1);
        if ($deliminator !== '/') {
            $pattern = '/' . str_replace('/', '\\/', substr($pattern, 1, $pos - 1)) . '/';
        } else {
            $pattern = substr($pattern, 0, $pos + 1);
        }
        if (!empty($flag)) {
            $pattern .= preg_replace('/[^igm]/', '', $flag);
        }

        return $pattern;
    }
}