SpecialRedirect: Don't pass null to explode

[mediawiki.git] / includes / Html.php

<?php
/**
 * Collection of methods to generate HTML content
 *
 * Copyright © 2009 Aryeh Gregor
 * https://www.mediawiki.org/
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

use MediaWiki\MainConfigNames;
use MediaWiki\MediaWikiServices;

/**
 * This class is a collection of static functions that serve two purposes:
 *
 * 1) Implement any algorithms specified by HTML5, or other HTML
 * specifications, in a convenient and self-contained way.
 *
 * 2) Allow HTML elements to be conveniently and safely generated, like the
 * current Xml class but a) less confused (Xml supports HTML-specific things,
 * but only sometimes!) and b) not necessarily confined to XML-compatible
 * output.
 *
 * There are two important configuration options this class uses:
 *
 * $wgMimeType: If this is set to an xml MIME type then output should be
 *     valid XHTML5.
 *
 * This class is meant to be confined to utility functions that are called from
 * trusted code paths.  It does not do enforcement of policy like not allowing
 * <a> elements.
 *
 * @since 1.16
 */
class Html {
        /** @var bool[] List of void elements from HTML5, section 8.1.2 as of 2016-09-19 */
        private static $voidElements = [
                'area' => true,
                'base' => true,
                'br' => true,
                'col' => true,
                'embed' => true,
                'hr' => true,
                'img' => true,
                'input' => true,
                'keygen' => true,
                'link' => true,
                'meta' => true,
                'param' => true,
                'source' => true,
                'track' => true,
                'wbr' => true,
        ];

        /**
         * Boolean attributes, which may have the value omitted entirely.  Manually
         * collected from the HTML5 spec as of 2011-08-12.
         * @var bool[]
         */
        private static $boolAttribs = [
                'async' => true,
                'autofocus' => true,
                'autoplay' => true,
                'checked' => true,
                'controls' => true,
                'default' => true,
                'defer' => true,
                'disabled' => true,
                'formnovalidate' => true,
                'hidden' => true,
                'ismap' => true,
                'itemscope' => true,
                'loop' => true,
                'multiple' => true,
                'muted' => true,
                'novalidate' => true,
                'open' => true,
                'pubdate' => true,
                'readonly' => true,
                'required' => true,
                'reversed' => true,
                'scoped' => true,
                'seamless' => true,
                'selected' => true,
                'truespeed' => true,
                'typemustmatch' => true,
        ];

        /**
         * Modifies a set of attributes meant for button elements
         * and apply a set of default attributes when $wgUseMediaWikiUIEverywhere enabled.
         * @param array $attrs HTML attributes in an associative array
         * @param string[] $modifiers classes to add to the button
         * @see https://tools.wmflabs.org/styleguide/desktop/index.html for guidance on available modifiers
         * @return array Modified attributes array
         */
        public static function buttonAttributes( array $attrs, array $modifiers = [] ) {
                $useMediaWikiUIEverywhere = MediaWikiServices::getInstance()
                        ->getMainConfig()->get( MainConfigNames::UseMediaWikiUIEverywhere );
                if ( $useMediaWikiUIEverywhere ) {
                        if ( isset( $attrs['class'] ) ) {
                                if ( is_array( $attrs['class'] ) ) {
                                        $attrs['class'][] = 'mw-ui-button';
                                        $attrs['class'] = array_merge( $attrs['class'], $modifiers );
                                        // ensure compatibility with Xml
                                        $attrs['class'] = implode( ' ', $attrs['class'] );
                                } else {
                                        $attrs['class'] .= ' mw-ui-button ' . implode( ' ', $modifiers );
                                }
                        } else {
                                // ensure compatibility with Xml
                                $attrs['class'] = 'mw-ui-button ' . implode( ' ', $modifiers );
                        }
                }
                return $attrs;
        }

        /**
         * Modifies a set of attributes meant for text input elements
         * and apply a set of default attributes.
         * Removes size attribute when $wgUseMediaWikiUIEverywhere enabled.
         * @param array $attrs An attribute array.
         * @return array Modified attributes array
         */
        public static function getTextInputAttributes( array $attrs ) {
                $useMediaWikiUIEverywhere = MediaWikiServices::getInstance()
                        ->getMainConfig()->get( MainConfigNames::UseMediaWikiUIEverywhere );
                if ( $useMediaWikiUIEverywhere ) {
                        if ( isset( $attrs['class'] ) ) {
                                if ( is_array( $attrs['class'] ) ) {
                                        $attrs['class'][] = 'mw-ui-input';
                                } else {
                                        $attrs['class'] .= ' mw-ui-input';
                                }
                        } else {
                                $attrs['class'] = 'mw-ui-input';
                        }
                }
                return $attrs;
        }

        /**
         * Returns an HTML link element in a string styled as a button
         * (when $wgUseMediaWikiUIEverywhere is enabled).
         *
         * @param string $text The text of the element. Will be escaped (not raw HTML)
         * @param array $attrs Associative array of attributes, e.g., [
         *   'href' => 'https://www.mediawiki.org/' ]. See expandAttributes() for
         *   further documentation.
         * @param string[] $modifiers classes to add to the button
         * @see https://tools.wmflabs.org/styleguide/desktop/index.html for guidance on available modifiers
         * @return string Raw HTML
         */
        public static function linkButton( $text, array $attrs, array $modifiers = [] ) {
                return self::element( 'a',
                        self::buttonAttributes( $attrs, $modifiers ),
                        $text
                );
        }

        /**
         * Returns an HTML link element in a string styled as a button
         * (when $wgUseMediaWikiUIEverywhere is enabled).
         *
         * @param string $contents The raw HTML contents of the element: *not*
         *   escaped!
         * @param array $attrs Associative array of attributes, e.g., [
         *   'href' => 'https://www.mediawiki.org/' ]. See expandAttributes() for
         *   further documentation.
         * @param string[] $modifiers classes to add to the button
         * @see https://tools.wmflabs.org/styleguide/desktop/index.html for guidance on available modifiers
         * @return string Raw HTML
         */
        public static function submitButton( $contents, array $attrs, array $modifiers = [] ) {
                $attrs['type'] = 'submit';
                $attrs['value'] = $contents;
                return self::element( 'input', self::buttonAttributes( $attrs, $modifiers ) );
        }

        /**
         * Returns an HTML element in a string.  The major advantage here over
         * manually typing out the HTML is that it will escape all attribute
         * values.
         *
         * This is quite similar to Xml::tags(), but it implements some useful
         * HTML-specific logic.  For instance, there is no $allowShortTag
         * parameter: the closing tag is magically omitted if $element has an empty
         * content model.
         *
         * @param string $element The element's name, e.g., 'a'
         * @param array $attribs Associative array of attributes, e.g., [
         *   'href' => 'https://www.mediawiki.org/' ]. See expandAttributes() for
         *   further documentation.
         * @param string $contents The raw HTML contents of the element: *not*
         *   escaped!
         * @return string Raw HTML
         */
        public static function rawElement( $element, $attribs = [], $contents = '' ) {
                $start = self::openElement( $element, $attribs );
                if ( isset( self::$voidElements[$element] ) ) {
                        // Silly XML.
                        return substr( $start, 0, -1 ) . '/>';
                } else {
                        return $start . $contents . self::closeElement( $element );
                }
        }

        /**
         * Identical to rawElement(), but HTML-escapes $contents (like
         * Xml::element()).
         *
         * @param string $element Name of the element, e.g., 'a'
         * @param array $attribs Associative array of attributes, e.g., [
         *   'href' => 'https://www.mediawiki.org/' ]. See expandAttributes() for
         *   further documentation.
         * @param string $contents
         *
         * @return string
         */
        public static function element( $element, $attribs = [], $contents = '' ) {
                return self::rawElement( $element, $attribs, strtr( $contents, [
                        // There's no point in escaping quotes, >, etc. in the contents of
                        // elements.
                        '&' => '&amp;',
                        '<' => '&lt;'
                ] ) );
        }

        /**
         * Identical to rawElement(), but has no third parameter and omits the end
         * tag (and the self-closing '/' in XML mode for empty elements).
         *
         * @param string $element Name of the element, e.g., 'a'
         * @param array $attribs Associative array of attributes, e.g., [
         *   'href' => 'https://www.mediawiki.org/' ]. See expandAttributes() for
         *   further documentation.
         *
         * @return string
         */
        public static function openElement( $element, $attribs = [] ) {
                $attribs = (array)$attribs;
                // This is not required in HTML5, but let's do it anyway, for
                // consistency and better compression.
                $element = strtolower( $element );

                // Some people were abusing this by passing things like
                // 'h1 id="foo" to $element, which we don't want.
                if ( strpos( $element, ' ' ) !== false ) {
                        wfWarn( __METHOD__ . " given element name with space '$element'" );
                }

                // Remove invalid input types
                if ( $element == 'input' ) {
                        $validTypes = [
                                'hidden' => true,
                                'text' => true,
                                'password' => true,
                                'checkbox' => true,
                                'radio' => true,
                                'file' => true,
                                'submit' => true,
                                'image' => true,
                                'reset' => true,
                                'button' => true,

                                // HTML input types
                                'datetime' => true,
                                'datetime-local' => true,
                                'date' => true,
                                'month' => true,
                                'time' => true,
                                'week' => true,
                                'number' => true,
                                'range' => true,
                                'email' => true,
                                'url' => true,
                                'search' => true,
                                'tel' => true,
                                'color' => true,
                        ];
                        if ( isset( $attribs['type'] ) && !isset( $validTypes[$attribs['type']] ) ) {
                                unset( $attribs['type'] );
                        }
                }

                // According to standard the default type for <button> elements is "submit".
                // Depending on compatibility mode IE might use "button", instead.
                // We enforce the standard "submit".
                if ( $element == 'button' && !isset( $attribs['type'] ) ) {
                        $attribs['type'] = 'submit';
                }

                return "<$element" . self::expandAttributes(
                        self::dropDefaults( $element, $attribs ) ) . '>';
        }

        /**
         * Returns "</$element>"
         *
         * @since 1.17
         * @param string $element Name of the element, e.g., 'a'
         * @return string A closing tag
         */
        public static function closeElement( $element ) {
                $element = strtolower( $element );

                return "</$element>";
        }

        /**
         * Given an element name and an associative array of element attributes,
         * return an array that is functionally identical to the input array, but
         * possibly smaller.  In particular, attributes might be stripped if they
         * are given their default values.
         *
         * This method is not guaranteed to remove all redundant attributes, only
         * some common ones and some others selected arbitrarily at random.  It
         * only guarantees that the output array should be functionally identical
         * to the input array (currently per the HTML 5 draft as of 2009-09-06).
         *
         * @param string $element Name of the element, e.g., 'a'
         * @param array $attribs Associative array of attributes, e.g., [
         *   'href' => 'https://www.mediawiki.org/' ].  See expandAttributes() for
         *   further documentation.
         * @return array An array of attributes functionally identical to $attribs
         */
        private static function dropDefaults( $element, array $attribs ) {
                // Whenever altering this array, please provide a covering test case
                // in HtmlTest::provideElementsWithAttributesHavingDefaultValues
                static $attribDefaults = [
                        'area' => [ 'shape' => 'rect' ],
                        'button' => [
                                'formaction' => 'GET',
                                'formenctype' => 'application/x-www-form-urlencoded',
                        ],
                        'canvas' => [
                                'height' => '150',
                                'width' => '300',
                        ],
                        'form' => [
                                'action' => 'GET',
                                'autocomplete' => 'on',
                                'enctype' => 'application/x-www-form-urlencoded',
                        ],
                        'input' => [
                                'formaction' => 'GET',
                                'type' => 'text',
                        ],
                        'keygen' => [ 'keytype' => 'rsa' ],
                        'link' => [ 'media' => 'all' ],
                        'menu' => [ 'type' => 'list' ],
                        'script' => [ 'type' => 'text/javascript' ],
                        'style' => [
                                'media' => 'all',
                                'type' => 'text/css',
                        ],
                        'textarea' => [ 'wrap' => 'soft' ],
                ];

                foreach ( $attribs as $attrib => $value ) {
                        if ( $attrib === 'class' ) {
                                if ( $value === '' || $value === [] || $value === [ '' ] ) {
                                        unset( $attribs[$attrib] );
                                }
                        } elseif ( isset( $attribDefaults[$element][$attrib] ) ) {
                                if ( is_array( $value ) ) {
                                        $value = implode( ' ', $value );
                                } else {
                                        $value = strval( $value );
                                }
                                if ( $attribDefaults[$element][$attrib] == $value ) {
                                        unset( $attribs[$attrib] );
                                }
                        }
                }

                // More subtle checks
                if ( $element === 'link'
                        && isset( $attribs['type'] ) && strval( $attribs['type'] ) == 'text/css'
                ) {
                        unset( $attribs['type'] );
                }
                if ( $element === 'input' ) {
                        $type = $attribs['type'] ?? null;
                        $value = $attribs['value'] ?? null;
                        if ( $type === 'checkbox' || $type === 'radio' ) {
                                // The default value for checkboxes and radio buttons is 'on'
                                // not ''. By stripping value="" we break radio boxes that
                                // actually wants empty values.
                                if ( $value === 'on' ) {
                                        unset( $attribs['value'] );
                                }
                        } elseif ( $type === 'submit' ) {
                                // The default value for submit appears to be "Submit" but
                                // let's not bother stripping out localized text that matches
                                // that.
                        } else {
                                // The default value for nearly every other field type is ''
                                // The 'range' and 'color' types use different defaults but
                                // stripping a value="" does not hurt them.
                                if ( $value === '' ) {
                                        unset( $attribs['value'] );
                                }
                        }
                }
                if ( $element === 'select' && isset( $attribs['size'] ) ) {
                        if ( in_array( 'multiple', $attribs )
                                || ( isset( $attribs['multiple'] ) && $attribs['multiple'] !== false )
                        ) {
                                // A multi-select
                                if ( strval( $attribs['size'] ) == '4' ) {
                                        unset( $attribs['size'] );
                                }
                        } else {
                                // Single select
                                if ( strval( $attribs['size'] ) == '1' ) {
                                        unset( $attribs['size'] );
                                }
                        }
                }

                return $attribs;
        }

        /**
         * Given an associative array of element attributes, generate a string
         * to stick after the element name in HTML output.  Like [ 'href' =>
         * 'https://www.mediawiki.org/' ] becomes something like
         * ' href="https://www.mediawiki.org"'.  Again, this is like
         * Xml::expandAttributes(), but it implements some HTML-specific logic.
         *
         * Attributes that can contain space-separated lists ('class', 'accesskey' and 'rel') array
         * values are allowed as well, which will automagically be normalized
         * and converted to a space-separated string. In addition to a numerical
         * array, the attribute value may also be an associative array. See the
         * example below for how that works.
         *
         * @par Numerical array
         * @code
         *     Html::element( 'em', [
         *         'class' => [ 'foo', 'bar' ]
         *     ] );
         *     // gives '<em class="foo bar"></em>'
         * @endcode
         *
         * @par Associative array
         * @code
         *     Html::element( 'em', [
         *         'class' => [ 'foo', 'bar', 'foo' => false, 'quux' => true ]
         *     ] );
         *     // gives '<em class="bar quux"></em>'
         * @endcode
         *
         * @param array $attribs Associative array of attributes, e.g., [
         *   'href' => 'https://www.mediawiki.org/' ].  Values will be HTML-escaped.
         *   A value of false or null means to omit the attribute.  For boolean attributes,
         *   you can omit the key, e.g., [ 'checked' ] instead of
         *   [ 'checked' => 'checked' ] or such.
         *
         * @throws MWException If an attribute that doesn't allow lists is set to an array
         * @return string HTML fragment that goes between element name and '>'
         *   (starting with a space if at least one attribute is output)
         */
        public static function expandAttributes( array $attribs ) {
                $ret = '';
                foreach ( $attribs as $key => $value ) {
                        // Support intuitive [ 'checked' => true/false ] form
                        if ( $value === false || $value === null ) {
                                continue;
                        }

                        // For boolean attributes, support [ 'foo' ] instead of
                        // requiring [ 'foo' => 'meaningless' ].
                        if ( is_int( $key ) && isset( self::$boolAttribs[strtolower( $value )] ) ) {
                                $key = $value;
                        }

                        // Not technically required in HTML5 but we'd like consistency
                        // and better compression anyway.
                        $key = strtolower( $key );

                        // https://www.w3.org/TR/html401/index/attributes.html ("space-separated")
                        // https://www.w3.org/TR/html5/index.html#attributes-1 ("space-separated")
                        $spaceSeparatedListAttributes = [
                                'class' => true, // html4, html5
                                'accesskey' => true, // as of html5, multiple space-separated values allowed
                                // html4-spec doesn't document rel= as space-separated
                                // but has been used like that and is now documented as such
                                // in the html5-spec.
                                'rel' => true,
                        ];

                        // Specific features for attributes that allow a list of space-separated values
                        if ( isset( $spaceSeparatedListAttributes[$key] ) ) {
                                // Apply some normalization and remove duplicates

                                // Convert into correct array. Array can contain space-separated
                                // values. Implode/explode to get those into the main array as well.
                                if ( is_array( $value ) ) {
                                        // If input wasn't an array, we can skip this step
                                        $arrayValue = [];
                                        foreach ( $value as $k => $v ) {
                                                if ( is_string( $v ) ) {
                                                        // String values should be normal `[ 'foo' ]`
                                                        // Just append them
                                                        if ( !isset( $value[$v] ) ) {
                                                                // As a special case don't set 'foo' if a
                                                                // separate 'foo' => true/false exists in the array
                                                                // keys should be authoritative
                                                                foreach ( explode( ' ', $v ) as $part ) {
                                                                        // Normalize spacing by fixing up cases where people used
                                                                        // more than 1 space and/or a trailing/leading space
                                                                        if ( $part !== '' && $part !== ' ' ) {
                                                                                $arrayValue[] = $part;
                                                                        }
                                                                }
                                                        }
                                                } elseif ( $v ) {
                                                        // If the value is truthy but not a string this is likely
                                                        // an [ 'foo' => true ], falsy values don't add strings
                                                        $arrayValue[] = $k;
                                                }
                                        }
                                } else {
                                        $arrayValue = explode( ' ', $value );
                                        // Normalize spacing by fixing up cases where people used
                                        // more than 1 space and/or a trailing/leading space
                                        $arrayValue = array_diff( $arrayValue, [ '', ' ' ] );
                                }

                                // Remove duplicates and create the string
                                $value = implode( ' ', array_unique( $arrayValue ) );

                                // Optimization: Skip below boolAttribs check and jump straight
                                // to its `else` block. The current $spaceSeparatedListAttributes
                                // block is mutually exclusive with $boolAttribs.
                                // phpcs:ignore Generic.PHP.DiscourageGoto
                                goto not_bool; // NOSONAR
                        } elseif ( is_array( $value ) ) {
                                throw new MWException( "HTML attribute $key can not contain a list of values" );
                        }

                        if ( isset( self::$boolAttribs[$key] ) ) {
                                $ret .= " $key=\"\"";
                        } else {
                                // phpcs:ignore Generic.PHP.DiscourageGoto
                                not_bool:
                                // Inlined from Sanitizer::encodeAttribute() for improved performance
                                $encValue = htmlspecialchars( $value, ENT_QUOTES );
                                // Whitespace is normalized during attribute decoding,
                                // so if we've been passed non-spaces we must encode them
                                // ahead of time or they won't be preserved.
                                $encValue = strtr( $encValue, [
                                        "\n" => '&#10;',
                                        "\r" => '&#13;',
                                        "\t" => '&#9;',
                                ] );
                                $ret .= " $key=\"$encValue\"";
                        }
                }
                return $ret;
        }

        /**
         * Output an HTML script tag with the given contents.
         *
         * It is unsupported for the contents to contain the sequence `<script` or `</script`
         * (case-insensitive). This ensures the script can be terminated easily and consistently.
         * It is the responsibility of the caller to avoid such character sequence by escaping
         * or avoiding it. If found at run-time, the contents are replaced with a comment, and
         * a warning is logged server-side.
         *
         * @param string $contents JavaScript
         * @param string|null $nonce Nonce for CSP header, from OutputPage->getCSP()->getNonce()
         * @return string Raw HTML
         */
        public static function inlineScript( $contents, $nonce = null ) {
                $attrs = [];
                if ( $nonce !== null ) {
                        $attrs['nonce'] = $nonce;
                } elseif ( ContentSecurityPolicy::isNonceRequired( MediaWikiServices::getInstance()->getMainConfig() ) ) {
                        wfWarn( "no nonce set on script. CSP will break it" );
                }

                if ( preg_match( '/<\/?script/i', $contents ) ) {
                        wfLogWarning( __METHOD__ . ': Illegal character sequence found in inline script.' );
                        $contents = '/* ERROR: Invalid script */';
                }

                return self::rawElement( 'script', $attrs, $contents );
        }

        /**
         * Output a "<script>" tag linking to the given URL, e.g.,
         * "<script src=foo.js></script>".
         *
         * @param string $url
         * @param string|null $nonce Nonce for CSP header, from OutputPage->getCSP()->getNonce()
         * @return string Raw HTML
         */
        public static function linkedScript( $url, $nonce = null ) {
                $attrs = [ 'src' => $url ];
                if ( $nonce !== null ) {
                        $attrs['nonce'] = $nonce;
                } elseif ( ContentSecurityPolicy::isNonceRequired( MediaWikiServices::getInstance()->getMainConfig() ) ) {
                        wfWarn( "no nonce set on script. CSP will break it" );
                }

                return self::element( 'script', $attrs );
        }

        /**
         * Output a "<style>" tag with the given contents for the given media type
         * (if any).  TODO: do some useful escaping as well, like if $contents
         * contains literal "</style>" (admittedly unlikely).
         *
         * @param string $contents CSS
         * @param string $media A media type string, like 'screen'
         * @param array $attribs (since 1.31) Associative array of attributes, e.g., [
         *   'href' => 'https://www.mediawiki.org/' ]. See expandAttributes() for
         *   further documentation.
         * @return string Raw HTML
         */
        public static function inlineStyle( $contents, $media = 'all', $attribs = [] ) {
                // Don't escape '>' since that is used
                // as direct child selector.
                // Remember, in css, there is no "x" for hexadecimal escapes, and
                // the space immediately after an escape sequence is swallowed.
                $contents = strtr( $contents, [
                        '<' => '\3C ',
                        // CDATA end tag for good measure, but the main security
                        // is from escaping the '<'.
                        ']]>' => '\5D\5D\3E '
                ] );

                if ( preg_match( '/[<&]/', $contents ) ) {
                        $contents = "/*<![CDATA[*/$contents/*]]>*/";
                }

                return self::rawElement( 'style', [
                        'media' => $media,
                ] + $attribs, $contents );
        }

        /**
         * Output a "<link rel=stylesheet>" linking to the given URL for the given
         * media type (if any).
         *
         * @param string $url
         * @param string $media A media type string, like 'screen'
         * @return string Raw HTML
         */
        public static function linkedStyle( $url, $media = 'all' ) {
                return self::element( 'link', [
                        'rel' => 'stylesheet',
                        'href' => $url,
                        'media' => $media,
                ] );
        }

        /**
         * Convenience function to produce an "<input>" element.  This supports the
         * new HTML5 input types and attributes.
         *
         * @param string $name Name attribute
         * @param string $value Value attribute
         * @param string $type Type attribute
         * @param array $attribs Associative array of miscellaneous extra
         *   attributes, passed to Html::element()
         * @return string Raw HTML
         */
        public static function input( $name, $value = '', $type = 'text', array $attribs = [] ) {
                $attribs['type'] = $type;
                $attribs['value'] = $value;
                $attribs['name'] = $name;
                $textInputAttributes = [
                        'text' => true,
                        'search' => true,
                        'email' => true,
                        'password' => true,
                        'number' => true
                ];
                if ( isset( $textInputAttributes[$type] ) ) {
                        $attribs = self::getTextInputAttributes( $attribs );
                }
                $buttonAttributes = [
                        'button' => true,
                        'reset' => true,
                        'submit' => true
                ];
                if ( isset( $buttonAttributes[$type] ) ) {
                        $attribs = self::buttonAttributes( $attribs );
                }
                return self::element( 'input', $attribs );
        }

        /**
         * Convenience function to produce a checkbox (input element with type=checkbox)
         *
         * @param string $name Name attribute
         * @param bool $checked Whether the checkbox is checked or not
         * @param array $attribs Array of additional attributes
         * @return string Raw HTML
         */
        public static function check( $name, $checked = false, array $attribs = [] ) {
                if ( isset( $attribs['value'] ) ) {
                        $value = $attribs['value'];
                        unset( $attribs['value'] );
                } else {
                        $value = 1;
                }

                if ( $checked ) {
                        $attribs[] = 'checked';
                }

                return self::input( $name, $value, 'checkbox', $attribs );
        }

        /**
         * Return the HTML for a message box.
         * @since 1.31
         * @param string $html of contents of box
         * @param string|array $className corresponding to box
         * @param string $heading (optional)
         * @return string of HTML representing a box.
         */
        private static function messageBox( $html, $className, $heading = '' ) {
                if ( $heading !== '' ) {
                        $html = self::element( 'h2', [], $heading ) . $html;
                }
                if ( is_array( $className ) ) {
                        $className[] = 'mw-message-box';
                } else {
                        $className .= ' mw-message-box';
                }
                return self::rawElement( 'div', [ 'class' => $className ], $html );
        }

        /**
         * Return the HTML for a notice message box.
         * @since 1.38
         * @param string $html of contents of notice
         * @param string|array $className corresponding to notice
         * @return string of HTML representing the notice
         */
        public static function noticeBox( $html, $className ) {
                return self::messageBox( $html, [ 'mw-message-box-notice', $className ] );
        }

        /**
         * Return a warning box.
         * @since 1.31
         * @since 1.34 $className optional parameter added
         * @param string $html of contents of box
         * @param string $className (optional) corresponding to box
         * @return string of HTML representing a warning box.
         */
        public static function warningBox( $html, $className = '' ) {
                return self::messageBox( $html, [ 'mw-message-box-warning', $className ] );
        }

        /**
         * Return an error box.
         * @since 1.31
         * @since 1.34 $className optional parameter added
         * @param string $html of contents of error box
         * @param string $heading (optional)
         * @param string $className (optional) corresponding to box
         * @return string of HTML representing an error box.
         */
        public static function errorBox( $html, $heading = '', $className = '' ) {
                return self::messageBox( $html, [ 'mw-message-box-error', $className ], $heading );
        }

        /**
         * Return a success box.
         * @since 1.31
         * @since 1.34 $className optional parameter added
         * @param string $html of contents of box
         * @param string $className (optional) corresponding to box
         * @return string of HTML representing a success box.
         */
        public static function successBox( $html, $className = '' ) {
                return self::messageBox( $html, [ 'mw-message-box-success', $className ] );
        }

        /**
         * Convenience function to produce a radio button (input element with type=radio)
         *
         * @param string $name Name attribute
         * @param bool $checked Whether the radio button is checked or not
         * @param array $attribs Array of additional attributes
         * @return string Raw HTML
         */
        public static function radio( $name, $checked = false, array $attribs = [] ) {
                if ( isset( $attribs['value'] ) ) {
                        $value = $attribs['value'];
                        unset( $attribs['value'] );
                } else {
                        $value = 1;
                }

                if ( $checked ) {
                        $attribs[] = 'checked';
                }

                return self::input( $name, $value, 'radio', $attribs );
        }

        /**
         * Convenience function for generating a label for inputs.
         *
         * @param string $label Contents of the label
         * @param string $id ID of the element being labeled
         * @param array $attribs Additional attributes
         * @return string Raw HTML
         */
        public static function label( $label, $id, array $attribs = [] ) {
                $attribs += [
                        'for' => $id
                ];
                return self::element( 'label', $attribs, $label );
        }

        /**
         * Convenience function to produce an input element with type=hidden
         *
         * @param string $name Name attribute
         * @param mixed $value Value attribute
         * @param array $attribs Associative array of miscellaneous extra
         *   attributes, passed to Html::element()
         * @return string Raw HTML
         */
        public static function hidden( $name, $value, array $attribs = [] ) {
                return self::input( $name, $value, 'hidden', $attribs );
        }

        /**
         * Convenience function to produce a <textarea> element.
         *
         * This supports leaving out the cols= and rows= which Xml requires and are
         * required by HTML4/XHTML but not required by HTML5.
         *
         * @param string $name Name attribute
         * @param string $value Value attribute
         * @param array $attribs Associative array of miscellaneous extra
         *   attributes, passed to Html::element()
         * @return string Raw HTML
         */
        public static function textarea( $name, $value = '', array $attribs = [] ) {
                $attribs['name'] = $name;

                if ( substr( $value, 0, 1 ) == "\n" ) {
                        // Workaround for T14130: browsers eat the initial newline
                        // assuming that it's just for show, but they do keep the later
                        // newlines, which we may want to preserve during editing.
                        // Prepending a single newline
                        $spacedValue = "\n" . $value;
                } else {
                        $spacedValue = $value;
                }
                return self::element( 'textarea', self::getTextInputAttributes( $attribs ), $spacedValue );
        }

        /**
         * Helper for Html::namespaceSelector().
         * @param array $params See Html::namespaceSelector()
         * @return array
         */
        public static function namespaceSelectorOptions( array $params = [] ) {
                if ( !isset( $params['exclude'] ) || !is_array( $params['exclude'] ) ) {
                        $params['exclude'] = [];
                }

                if ( $params['in-user-lang'] ?? false ) {
                        global $wgLang;
                        $lang = $wgLang;
                } else {
                        $lang = MediaWikiServices::getInstance()->getContentLanguage();
                }

                $optionsOut = [];
                if ( isset( $params['all'] ) ) {
                        // add an option that would let the user select all namespaces.
                        // Value is provided by user, the name shown is localized for the user.
                        $optionsOut[$params['all']] = wfMessage( 'namespacesall' )->text();
                }
                // Add all namespaces as options
                $options = $lang->getFormattedNamespaces();
                // Filter out namespaces below 0 and massage labels
                foreach ( $options as $nsId => $nsName ) {
                        if ( $nsId < NS_MAIN || in_array( $nsId, $params['exclude'] ) ) {
                                continue;
                        }
                        if ( $nsId === NS_MAIN ) {
                                // For other namespaces use the namespace prefix as label, but for
                                // main we don't use "" but the user message describing it (e.g. "(Main)" or "(Article)")
                                $nsName = wfMessage( 'blanknamespace' )->text();
                        } elseif ( is_int( $nsId ) ) {
                                $converter = MediaWikiServices::getInstance()->getLanguageConverterFactory()
                                        ->getLanguageConverter( $lang );
                                $nsName = $converter->convertNamespace( $nsId );
                        }
                        $optionsOut[$nsId] = $nsName;
                }

                return $optionsOut;
        }

        /**
         * Build a drop-down box for selecting a namespace
         *
         * @param array $params Params to set.
         * - selected: [optional] Id of namespace which should be pre-selected
         * - all: [optional] Value of item for "all namespaces". If null or unset,
         *   no "<option>" is generated to select all namespaces.
         * - label: text for label to add before the field.
         * - exclude: [optional] Array of namespace ids to exclude.
         * - disable: [optional] Array of namespace ids for which the option should
         *   be disabled in the selector.
         * @param array $selectAttribs HTML attributes for the generated select element.
         * - id:   [optional], default: 'namespace'.
         * - name: [optional], default: 'namespace'.
         * @return string HTML code to select a namespace.
         */
        public static function namespaceSelector( array $params = [],
                array $selectAttribs = []
        ) {
                ksort( $selectAttribs );

                // Is a namespace selected?
                if ( isset( $params['selected'] ) ) {
                        // If string only contains digits, convert to clean int. Selected could also
                        // be "all" or "" etc. which needs to be left untouched.
                        if ( !is_int( $params['selected'] ) && ctype_digit( (string)$params['selected'] ) ) {
                                $params['selected'] = (int)$params['selected'];
                        }
                        // else: leaves it untouched for later processing
                } else {
                        $params['selected'] = '';
                }

                if ( !isset( $params['disable'] ) || !is_array( $params['disable'] ) ) {
                        $params['disable'] = [];
                }

                // Associative array between option-values and option-labels
                $options = self::namespaceSelectorOptions( $params );

                // Convert $options to HTML
                $optionsHtml = [];
                foreach ( $options as $nsId => $nsName ) {
                        $optionsHtml[] = self::element(
                                'option', [
                                        'disabled' => in_array( $nsId, $params['disable'] ),
                                        'value' => $nsId,
                                        'selected' => $nsId === $params['selected'],
                                ], $nsName
                        );
                }

                if ( !array_key_exists( 'id', $selectAttribs ) ) {
                        $selectAttribs['id'] = 'namespace';
                }

                if ( !array_key_exists( 'name', $selectAttribs ) ) {
                        $selectAttribs['name'] = 'namespace';
                }

                $ret = '';
                if ( isset( $params['label'] ) ) {
                        $ret .= self::element(
                                'label', [
                                        'for' => $selectAttribs['id'] ?? null,
                                ], $params['label']
                        ) . "\u{00A0}";
                }

                // Wrap options in a <select>
                $ret .= self::openElement( 'select', $selectAttribs )
                        . "\n"
                        . implode( "\n", $optionsHtml )
                        . "\n"
                        . self::closeElement( 'select' );

                return $ret;
        }

        /**
         * Constructs the opening html-tag with necessary doctypes depending on
         * global variables.
         *
         * @param array $attribs Associative array of miscellaneous extra
         *   attributes, passed to Html::element() of html tag.
         * @return string Raw HTML
         */
        public static function htmlHeader( array $attribs = [] ) {
                $ret = '';
                $mainConfig = MediaWikiServices::getInstance()->getMainConfig();
                $html5Version = $mainConfig->get( MainConfigNames::Html5Version );
                $mimeType = $mainConfig->get( MainConfigNames::MimeType );
                $xhtmlNamespaces = $mainConfig->get( MainConfigNames::XhtmlNamespaces );

                $isXHTML = self::isXmlMimeType( $mimeType );

                if ( $isXHTML ) { // XHTML5
                        // XML MIME-typed markup should have an xml header.
                        // However a DOCTYPE is not needed.
                        $ret .= "<?xml version=\"1.0\" encoding=\"UTF-8\" ?>\n";

                        // Add the standard xmlns
                        $attribs['xmlns'] = 'http://www.w3.org/1999/xhtml';

                        // And support custom namespaces
                        foreach ( $xhtmlNamespaces as $tag => $ns ) {
                                $attribs["xmlns:$tag"] = $ns;
                        }
                } else { // HTML5
                        $ret .= "<!DOCTYPE html>\n";
                }

                if ( $html5Version ) {
                        $attribs['version'] = $html5Version;
                }

                $ret .= self::openElement( 'html', $attribs );

                return $ret;
        }

        /**
         * Determines if the given MIME type is xml.
         *
         * @param string $mimetype
         * @return bool
         */
        public static function isXmlMimeType( $mimetype ) {
                # https://html.spec.whatwg.org/multipage/infrastructure.html#xml-mime-type
                # * text/xml
                # * application/xml
                # * Any MIME type with a subtype ending in +xml (this implicitly includes application/xhtml+xml)
                return (bool)preg_match( '!^(text|application)/xml$|^.+/.+\+xml$!', $mimetype );
        }

        /**
         * Generate a srcset attribute value.
         *
         * Generates a srcset attribute value from an array mapping pixel densities
         * to URLs. A trailing 'x' in pixel density values is optional.
         *
         * @note srcset width and height values are not supported.
         *
         * @see https://html.spec.whatwg.org/#attr-img-srcset
         *
         * @par Example:
         * @code
         *     Html::srcSet( [
         *         '1x'   => 'standard.jpeg',
         *         '1.5x' => 'large.jpeg',
         *         '3x'   => 'extra-large.jpeg',
         *     ] );
         *     // gives 'standard.jpeg 1x, large.jpeg 1.5x, extra-large.jpeg 2x'
         * @endcode
         *
         * @param string[] $urls
         * @return string
         */
        public static function srcSet( array $urls ) {
                $candidates = [];
                foreach ( $urls as $density => $url ) {
                        // Cast density to float to strip 'x', then back to string to serve
                        // as array index.
                        $density = (string)(float)$density;
                        $candidates[$density] = $url;
                }

                // Remove duplicates that are the same as a smaller value
                ksort( $candidates, SORT_NUMERIC );
                $candidates = array_unique( $candidates );

                // Append density info to the url
                foreach ( $candidates as $density => $url ) {
                        $candidates[$density] = $url . ' ' . $density . 'x';
                }

                return implode( ", ", $candidates );
        }
}