Merge "Import: Handle uploads with sha1 starting with 0 properly"

[mediawiki.git] / includes / changetags / ChangeTags.php

<?php
/**
 * Recent changes tagging.
 *
 * 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
 * @ingroup Change tagging
 */

class ChangeTags {
        /**
         * Can't delete tags with more than this many uses. Similar in intent to
         * the bigdelete user right
         * @todo Use the job queue for tag deletion to avoid this restriction
         */
        const MAX_DELETE_USES = 5000;

        /**
         * Creates HTML for the given tags
         *
         * @param string $tags Comma-separated list of tags
         * @param string $page A label for the type of action which is being displayed,
         *   for example: 'history', 'contributions' or 'newpages'
         * @return array Array with two items: (html, classes)
         *   - html: String: HTML for displaying the tags (empty string when param $tags is empty)
         *   - classes: Array of strings: CSS classes used in the generated html, one class for each tag
         */
        public static function formatSummaryRow( $tags, $page ) {
                global $wgLang;

                if ( !$tags ) {
                        return array( '', array() );
                }

                $classes = array();

                $tags = explode( ',', $tags );
                $displayTags = array();
                foreach ( $tags as $tag ) {
                        if ( !$tag ) {
                                continue;
                        }
                        $description = self::tagDescription( $tag );
                        if ( $description === false ) {
                                continue;
                        }
                        $displayTags[] = Xml::tags(
                                'span',
                                array( 'class' => 'mw-tag-marker ' .
                                                                Sanitizer::escapeClass( "mw-tag-marker-$tag" ) ),
                                $description
                        );
                        $classes[] = Sanitizer::escapeClass( "mw-tag-$tag" );
                }

                if ( !$displayTags ) {
                        return array( '', array() );
                }

                $markers = wfMessage( 'tag-list-wrapper' )
                        ->numParams( count( $displayTags ) )
                        ->rawParams( $wgLang->commaList( $displayTags ) )
                        ->parse();
                $markers = Xml::tags( 'span', array( 'class' => 'mw-tag-markers' ), $markers );

                return array( $markers, $classes );
        }

        /**
         * Get a short description for a tag.
         *
         * Checks if message key "mediawiki:tag-$tag" exists. If it does not,
         * returns the HTML-escaped tag name. Uses the message if the message
         * exists, provided it is not disabled. If the message is disabled,
         * we consider the tag hidden, and return false.
         *
         * @param string $tag Tag
         * @return string|bool Tag description or false if tag is to be hidden.
         * @since 1.25 Returns false if tag is to be hidden.
         */
        public static function tagDescription( $tag ) {
                $msg = wfMessage( "tag-$tag" );
                if ( !$msg->exists() ) {
                        // No such message, so return the HTML-escaped tag name.
                        return htmlspecialchars( $tag );
                }
                if ( $msg->isDisabled() ) {
                        // The message exists but is disabled, hide the tag.
                        return false;
                }

                // Message exists and isn't disabled, use it.
                return $msg->parse();
        }

        /**
         * Add tags to a change given its rc_id, rev_id and/or log_id
         *
         * @param string|array $tags Tags to add to the change
         * @param int|null $rc_id The rc_id of the change to add the tags to
         * @param int|null $rev_id The rev_id of the change to add the tags to
         * @param int|null $log_id The log_id of the change to add the tags to
         * @param string $params Params to put in the ct_params field of table 'change_tag'
         *
         * @throws MWException
         * @return bool False if no changes are made, otherwise true
         */
        public static function addTags( $tags, $rc_id = null, $rev_id = null,
                $log_id = null, $params = null
        ) {
                $result = self::updateTags( $tags, null, $rc_id, $rev_id, $log_id, $params );
                return (bool)$result[0];
        }

        /**
         * Add and remove tags to/from a change given its rc_id, rev_id and/or log_id,
         * without verifying that the tags exist or are valid. If a tag is present in
         * both $tagsToAdd and $tagsToRemove, it will be removed.
         *
         * This function should only be used by extensions to manipulate tags they
         * have registered using the ListDefinedTags hook. When dealing with user
         * input, call updateTagsWithChecks() instead.
         *
         * @param string|array|null $tagsToAdd Tags to add to the change
         * @param string|array|null $tagsToRemove Tags to remove from the change
         * @param int|null &$rc_id The rc_id of the change to add the tags to.
         * Pass a variable whose value is null if the rc_id is not relevant or unknown.
         * @param int|null &$rev_id The rev_id of the change to add the tags to.
         * Pass a variable whose value is null if the rev_id is not relevant or unknown.
         * @param int|null &$log_id The log_id of the change to add the tags to.
         * Pass a variable whose value is null if the log_id is not relevant or unknown.
         * @param string $params Params to put in the ct_params field of table
         * 'change_tag' when adding tags
         *
         * @throws MWException When $rc_id, $rev_id and $log_id are all null
         * @return array Index 0 is an array of tags actually added, index 1 is an
         * array of tags actually removed, index 2 is an array of tags present on the
         * revision or log entry before any changes were made
         *
         * @since 1.25
         */
        public static function updateTags(
                $tagsToAdd, $tagsToRemove,
                &$rc_id = null, &$rev_id = null, &$log_id = null, $params = null
        ) {

                $tagsToAdd = array_filter( (array)$tagsToAdd ); // Make sure we're submitting all tags...
                $tagsToRemove = array_filter( (array)$tagsToRemove );

                if ( !$rc_id && !$rev_id && !$log_id ) {
                        throw new MWException( 'At least one of: RCID, revision ID, and log ID MUST be ' .
                                'specified when adding or removing a tag from a change!' );
                }

                $dbw = wfGetDB( DB_MASTER );

                // Might as well look for rcids and so on.
                if ( !$rc_id ) {
                        // Info might be out of date, somewhat fractionally, on slave.
                        // LogEntry/LogPage and WikiPage match rev/log/rc timestamps,
                        // so use that relation to avoid full table scans.
                        if ( $log_id ) {
                                $rc_id = $dbw->selectField(
                                        array( 'logging', 'recentchanges' ),
                                        'rc_id',
                                        array(
                                                'log_id' => $log_id,
                                                'rc_timestamp = log_timestamp',
                                                'rc_logid = log_id'
                                        ),
                                        __METHOD__
                                );
                        } elseif ( $rev_id ) {
                                $rc_id = $dbw->selectField(
                                        array( 'revision', 'recentchanges' ),
                                        'rc_id',
                                        array(
                                                'rev_id' => $rev_id,
                                                'rc_timestamp = rev_timestamp',
                                                'rc_this_oldid = rev_id'
                                        ),
                                        __METHOD__
                                );
                        }
                } elseif ( !$log_id && !$rev_id ) {
                        // Info might be out of date, somewhat fractionally, on slave.
                        $log_id = $dbw->selectField(
                                'recentchanges',
                                'rc_logid',
                                array( 'rc_id' => $rc_id ),
                                __METHOD__
                        );
                        $rev_id = $dbw->selectField(
                                'recentchanges',
                                'rc_this_oldid',
                                array( 'rc_id' => $rc_id ),
                                __METHOD__
                        );
                }

                // update the tag_summary row
                $prevTags = array();
                if ( !self::updateTagSummaryRow( $tagsToAdd, $tagsToRemove, $rc_id, $rev_id,
                        $log_id, $prevTags ) ) {

                        // nothing to do
                        return array( array(), array(), $prevTags );
                }

                // insert a row into change_tag for each new tag
                if ( count( $tagsToAdd ) ) {
                        $tagsRows = array();
                        foreach ( $tagsToAdd as $tag ) {
                                // Filter so we don't insert NULLs as zero accidentally.
                                // Keep in mind that $rc_id === null means "I don't care/know about the
                                // rc_id, just delete $tag on this revision/log entry". It doesn't
                                // mean "only delete tags on this revision/log WHERE rc_id IS NULL".
                                $tagsRows[] = array_filter(
                                        array(
                                                'ct_tag' => $tag,
                                                'ct_rc_id' => $rc_id,
                                                'ct_log_id' => $log_id,
                                                'ct_rev_id' => $rev_id,
                                                'ct_params' => $params
                                        )
                                );
                        }

                        $dbw->insert( 'change_tag', $tagsRows, __METHOD__, array( 'IGNORE' ) );
                }

                // delete from change_tag
                if ( count( $tagsToRemove ) ) {
                        foreach ( $tagsToRemove as $tag ) {
                                $conds = array_filter(
                                        array(
                                                'ct_tag' => $tag,
                                                'ct_rc_id' => $rc_id,
                                                'ct_log_id' => $log_id,
                                                'ct_rev_id' => $rev_id
                                        )
                                );
                                $dbw->delete( 'change_tag', $conds, __METHOD__ );
                        }
                }

                self::purgeTagUsageCache();
                return array( $tagsToAdd, $tagsToRemove, $prevTags );
        }

        /**
         * Adds or removes a given set of tags to/from the relevant row of the
         * tag_summary table. Modifies the tagsToAdd and tagsToRemove arrays to
         * reflect the tags that were actually added and/or removed.
         *
         * @param array &$tagsToAdd
         * @param array &$tagsToRemove If a tag is present in both $tagsToAdd and
         * $tagsToRemove, it will be removed
         * @param int|null $rc_id Null if not known or not applicable
         * @param int|null $rev_id Null if not known or not applicable
         * @param int|null $log_id Null if not known or not applicable
         * @param array &$prevTags Optionally outputs a list of the tags that were
         * in the tag_summary row to begin with
         * @return bool True if any modifications were made, otherwise false
         * @since 1.25
         */
        protected static function updateTagSummaryRow( &$tagsToAdd, &$tagsToRemove,
                $rc_id, $rev_id, $log_id, &$prevTags = array() ) {

                $dbw = wfGetDB( DB_MASTER );

                $tsConds = array_filter( array(
                        'ts_rc_id' => $rc_id,
                        'ts_rev_id' => $rev_id,
                        'ts_log_id' => $log_id
                ) );

                // Can't both add and remove a tag at the same time...
                $tagsToAdd = array_diff( $tagsToAdd, $tagsToRemove );

                // Update the summary row.
                // $prevTags can be out of date on slaves, especially when addTags is called consecutively,
                // causing loss of tags added recently in tag_summary table.
                $prevTags = $dbw->selectField( 'tag_summary', 'ts_tags', $tsConds, __METHOD__ );
                $prevTags = $prevTags ? $prevTags : '';
                $prevTags = array_filter( explode( ',', $prevTags ) );

                // add tags
                $tagsToAdd = array_values( array_diff( $tagsToAdd, $prevTags ) );
                $newTags = array_unique( array_merge( $prevTags, $tagsToAdd ) );

                // remove tags
                $tagsToRemove = array_values( array_intersect( $tagsToRemove, $newTags ) );
                $newTags = array_values( array_diff( $newTags, $tagsToRemove ) );

                sort( $prevTags );
                sort( $newTags );
                if ( $prevTags == $newTags ) {
                        // No change.
                        return false;
                }

                if ( !$newTags ) {
                        // no tags left, so delete the row altogether
                        $dbw->delete( 'tag_summary', $tsConds, __METHOD__ );
                } else {
                        $dbw->replace( 'tag_summary',
                                array( 'ts_rev_id', 'ts_rc_id', 'ts_log_id' ),
                                array_filter( array_merge( $tsConds, array( 'ts_tags' => implode( ',', $newTags ) ) ) ),
                                __METHOD__
                        );
                }

                return true;
        }

        /**
         * Helper function to generate a fatal status with a 'not-allowed' type error.
         *
         * @param string $msgOne Message key to use in the case of one tag
         * @param string $msgMulti Message key to use in the case of more than one tag
         * @param array $tags Restricted tags (passed as $1 into the message, count of
         * $tags passed as $2)
         * @return Status
         * @since 1.25
         */
        protected static function restrictedTagError( $msgOne, $msgMulti, $tags ) {
                $lang = RequestContext::getMain()->getLanguage();
                $count = count( $tags );
                return Status::newFatal( ( $count > 1 ) ? $msgMulti : $msgOne,
                        $lang->commaList( $tags ), $count );
        }

        /**
         * Is it OK to allow the user to apply all the specified tags at the same time
         * as they edit/make the change?
         *
         * @param array $tags Tags that you are interested in applying
         * @param User|null $user User whose permission you wish to check, or null if
         * you don't care (e.g. maintenance scripts)
         * @return Status
         * @since 1.25
         */
        public static function canAddTagsAccompanyingChange( array $tags,
                User $user = null ) {

                if ( !is_null( $user ) ) {
                        if ( !$user->isAllowed( 'applychangetags' ) ) {
                                return Status::newFatal( 'tags-apply-no-permission' );
                        } elseif ( $user->isBlocked() ) {
                                return Status::newFatal( 'tags-apply-blocked' );
                        }
                }

                // to be applied, a tag has to be explicitly defined
                // @todo Allow extensions to define tags that can be applied by users...
                $allowedTags = self::listExplicitlyDefinedTags();
                $disallowedTags = array_diff( $tags, $allowedTags );
                if ( $disallowedTags ) {
                        return self::restrictedTagError( 'tags-apply-not-allowed-one',
                                'tags-apply-not-allowed-multi', $disallowedTags );
                }

                return Status::newGood();
        }

        /**
         * Adds tags to a given change, checking whether it is allowed first, but
         * without adding a log entry. Useful for cases where the tag is being added
         * along with the action that generated the change (e.g. tagging an edit as
         * it is being made).
         *
         * Extensions should not use this function, unless directly handling a user
         * request to add a particular tag. Normally, extensions should call
         * ChangeTags::updateTags() instead.
         *
         * @param array $tags Tags to apply
         * @param int|null $rc_id The rc_id of the change to add the tags to
         * @param int|null $rev_id The rev_id of the change to add the tags to
         * @param int|null $log_id The log_id of the change to add the tags to
         * @param string $params Params to put in the ct_params field of table
         * 'change_tag' when adding tags
         * @param User $user Who to give credit for the action
         * @return Status
         * @since 1.25
         */
        public static function addTagsAccompanyingChangeWithChecks(
                array $tags, $rc_id, $rev_id, $log_id, $params, User $user
        ) {

                // are we allowed to do this?
                $result = self::canAddTagsAccompanyingChange( $tags, $user );
                if ( !$result->isOK() ) {
                        $result->value = null;
                        return $result;
                }

                // do it!
                self::addTags( $tags, $rc_id, $rev_id, $log_id, $params );

                return Status::newGood( true );
        }

        /**
         * Is it OK to allow the user to adds and remove the given tags tags to/from a
         * change?
         *
         * @param array $tagsToAdd Tags that you are interested in adding
         * @param array $tagsToRemove Tags that you are interested in removing
         * @param User|null $user User whose permission you wish to check, or null if
         * you don't care (e.g. maintenance scripts)
         * @return Status
         * @since 1.25
         */
        public static function canUpdateTags( array $tagsToAdd, array $tagsToRemove,
                User $user = null ) {

                if ( !is_null( $user ) ) {
                        if ( !$user->isAllowed( 'changetags' ) ) {
                                return Status::newFatal( 'tags-update-no-permission' );
                        } elseif ( $user->isBlocked() ) {
                                return Status::newFatal( 'tags-update-blocked' );
                        }
                }

                if ( $tagsToAdd ) {
                        // to be added, a tag has to be explicitly defined
                        // @todo Allow extensions to define tags that can be applied by users...
                        $explicitlyDefinedTags = self::listExplicitlyDefinedTags();
                        $diff = array_diff( $tagsToAdd, $explicitlyDefinedTags );
                        if ( $diff ) {
                                return self::restrictedTagError( 'tags-update-add-not-allowed-one',
                                        'tags-update-add-not-allowed-multi', $diff );
                        }
                }

                if ( $tagsToRemove ) {
                        // to be removed, a tag must not be defined by an extension, or equivalently it
                        // has to be either explicitly defined or not defined at all
                        // (assuming no edge case of a tag both explicitly-defined and extension-defined)
                        $extensionDefinedTags = self::listExtensionDefinedTags();
                        $intersect = array_intersect( $tagsToRemove, $extensionDefinedTags );
                        if ( $intersect ) {
                                return self::restrictedTagError( 'tags-update-remove-not-allowed-one',
                                        'tags-update-remove-not-allowed-multi', $intersect );
                        }
                }

                return Status::newGood();
        }

        /**
         * Adds and/or removes tags to/from a given change, checking whether it is
         * allowed first, and adding a log entry afterwards.
         *
         * Includes a call to ChangeTag::canUpdateTags(), so your code doesn't need
         * to do that. However, it doesn't check whether the *_id parameters are a
         * valid combination. That is up to you to enforce. See ApiTag::execute() for
         * an example.
         *
         * @param array|null $tagsToAdd If none, pass array() or null
         * @param array|null $tagsToRemove If none, pass array() or null
         * @param int|null $rc_id The rc_id of the change to add the tags to
         * @param int|null $rev_id The rev_id of the change to add the tags to
         * @param int|null $log_id The log_id of the change to add the tags to
         * @param string $params Params to put in the ct_params field of table
         * 'change_tag' when adding tags
         * @param string $reason Comment for the log
         * @param User $user Who to give credit for the action
         * @return Status If successful, the value of this Status object will be an
         * object (stdClass) with the following fields:
         *  - logId: the ID of the added log entry, or null if no log entry was added
         *    (i.e. no operation was performed)
         *  - addedTags: an array containing the tags that were actually added
         *  - removedTags: an array containing the tags that were actually removed
         * @since 1.25
         */
        public static function updateTagsWithChecks( $tagsToAdd, $tagsToRemove,
                $rc_id, $rev_id, $log_id, $params, $reason, User $user ) {

                if ( is_null( $tagsToAdd ) ) {
                        $tagsToAdd = array();
                }
                if ( is_null( $tagsToRemove ) ) {
                        $tagsToRemove = array();
                }
                if ( !$tagsToAdd && !$tagsToRemove ) {
                        // no-op, don't bother
                        return Status::newGood( (object)array(
                                'logId' => null,
                                'addedTags' => array(),
                                'removedTags' => array(),
                        ) );
                }

                // are we allowed to do this?
                $result = self::canUpdateTags( $tagsToAdd, $tagsToRemove, $user );
                if ( !$result->isOK() ) {
                        $result->value = null;
                        return $result;
                }

                // basic rate limiting
                if ( $user->pingLimiter( 'changetag' ) ) {
                        return Status::newFatal( 'actionthrottledtext' );
                }

                // do it!
                list( $tagsAdded, $tagsRemoved, $initialTags ) = self::updateTags( $tagsToAdd,
                        $tagsToRemove, $rc_id, $rev_id, $log_id, $params );
                if ( !$tagsAdded && !$tagsRemoved ) {
                        // no-op, don't log it
                        return Status::newGood( (object)array(
                                'logId' => null,
                                'addedTags' => array(),
                                'removedTags' => array(),
                        ) );
                }

                // log it
                $logEntry = new ManualLogEntry( 'tag', 'update' );
                $logEntry->setPerformer( $user );
                $logEntry->setComment( $reason );

                // find the appropriate target page
                if ( $rev_id ) {
                        $rev = Revision::newFromId( $rev_id );
                        if ( $rev ) {
                                $logEntry->setTarget( $rev->getTitle() );
                        }
                } elseif ( $log_id ) {
                        // This function is from revision deletion logic and has nothing to do with
                        // change tags, but it appears to be the only other place in core where we
                        // perform logged actions on log items.
                        $logEntry->setTarget( RevDelLogList::suggestTarget( 0, array( $log_id ) ) );
                }

                if ( !$logEntry->getTarget() ) {
                        // target is required, so we have to set something
                        $logEntry->setTarget( SpecialPage::getTitleFor( 'Tags' ) );
                }

                $logParams = array(
                        '4::revid' => $rev_id,
                        '5::logid' => $log_id,
                        '6:list:tagsAdded' => $tagsAdded,
                        '7:number:tagsAddedCount' => count( $tagsAdded ),
                        '8:list:tagsRemoved' => $tagsRemoved,
                        '9:number:tagsRemovedCount' => count( $tagsRemoved ),
                        'initialTags' => $initialTags,
                );
                $logEntry->setParameters( $logParams );
                $logEntry->setRelations( array( 'Tag' => array_merge( $tagsAdded, $tagsRemoved ) ) );

                $dbw = wfGetDB( DB_MASTER );
                $logId = $logEntry->insert( $dbw );
                // Only send this to UDP, not RC, similar to patrol events
                $logEntry->publish( $logId, 'udp' );

                return Status::newGood( (object)array(
                        'logId' => $logId,
                        'addedTags' => $tagsAdded,
                        'removedTags' => $tagsRemoved,
                ) );
        }

        /**
         * Applies all tags-related changes to a query.
         * Handles selecting tags, and filtering.
         * Needs $tables to be set up properly, so we can figure out which join conditions to use.
         *
         * @param string|array $tables Table names, see DatabaseBase::select
         * @param string|array $fields Fields used in query, see DatabaseBase::select
         * @param string|array $conds Conditions used in query, see DatabaseBase::select
         * @param array $join_conds Join conditions, see DatabaseBase::select
         * @param array $options Options, see Database::select
         * @param bool|string $filter_tag Tag to select on
         *
         * @throws MWException When unable to determine appropriate JOIN condition for tagging
         */
        public static function modifyDisplayQuery( &$tables, &$fields, &$conds,
                                                                                &$join_conds, &$options, $filter_tag = false ) {
                global $wgRequest, $wgUseTagFilter;

                if ( $filter_tag === false ) {
                        $filter_tag = $wgRequest->getVal( 'tagfilter' );
                }

                // Figure out which conditions can be done.
                if ( in_array( 'recentchanges', $tables ) ) {
                        $join_cond = 'ct_rc_id=rc_id';
                } elseif ( in_array( 'logging', $tables ) ) {
                        $join_cond = 'ct_log_id=log_id';
                } elseif ( in_array( 'revision', $tables ) ) {
                        $join_cond = 'ct_rev_id=rev_id';
                } elseif ( in_array( 'archive', $tables ) ) {
                        $join_cond = 'ct_rev_id=ar_rev_id';
                } else {
                        throw new MWException( 'Unable to determine appropriate JOIN condition for tagging.' );
                }

                $fields['ts_tags'] = wfGetDB( DB_SLAVE )->buildGroupConcatField(
                        ',', 'change_tag', 'ct_tag', $join_cond
                );

                if ( $wgUseTagFilter && $filter_tag ) {
                        // Somebody wants to filter on a tag.
                        // Add an INNER JOIN on change_tag

                        $tables[] = 'change_tag';
                        $join_conds['change_tag'] = array( 'INNER JOIN', $join_cond );
                        $conds['ct_tag'] = $filter_tag;
                }
        }

        /**
         * Build a text box to select a change tag
         *
         * @param string $selected Tag to select by default
         * @param bool $fullForm Affects return value, see below
         * @param Title $title Title object to send the form to. Used only if $fullForm is true.
         * @param bool $ooui Use an OOUI TextInputWidget as selector instead of a non-OOUI input field
         *        You need to call OutputPage::enableOOUI() yourself.
         * @return string|array
         *        - if $fullForm is false: an array of (label, selector).
         *        - if $fullForm is true: HTML of entire form built around the selector.
         */
        public static function buildTagFilterSelector( $selected = '',
                $fullForm = false, Title $title = null, $ooui = false
        ) {
                global $wgUseTagFilter;

                if ( !$wgUseTagFilter || !count( self::listDefinedTags() ) ) {
                        return $fullForm ? '' : array();
                }

                $data = array(
                        Html::rawElement(
                                'label',
                                array( 'for' => 'tagfilter' ),
                                wfMessage( 'tag-filter' )->parse()
                        )
                );

                if ( $ooui ) {
                        $data[] = new OOUI\TextInputWidget( array(
                                'id' => 'tagfilter',
                                'name' => 'tagfilter',
                                'value' => $selected,
                                'classes' => 'mw-tagfilter-input',
                        ) );
                } else {
                        $data[] = Xml::input(
                                'tagfilter',
                                20,
                                $selected,
                                array( 'class' => 'mw-tagfilter-input mw-ui-input mw-ui-input-inline', 'id' => 'tagfilter' )
                        );
                }

                if ( !$fullForm ) {
                        return $data;
                }

                $html = implode( '&#160;', $data );
                $html .= "\n" .
                        Xml::element(
                                'input',
                                array( 'type' => 'submit', 'value' => wfMessage( 'tag-filter-submit' )->text() )
                        );
                $html .= "\n" . Html::hidden( 'title', $title->getPrefixedText() );
                $html = Xml::tags(
                        'form',
                        array( 'action' => $title->getLocalURL(), 'class' => 'mw-tagfilter-form', 'method' => 'get' ),
                        $html
                );

                return $html;
        }

        /**
         * Defines a tag in the valid_tag table, without checking that the tag name
         * is valid.
         * Extensions should NOT use this function; they can use the ListDefinedTags
         * hook instead.
         *
         * @param string $tag Tag to create
         * @since 1.25
         */
        public static function defineTag( $tag ) {
                $dbw = wfGetDB( DB_MASTER );
                $dbw->replace( 'valid_tag',
                        array( 'vt_tag' ),
                        array( 'vt_tag' => $tag ),
                        __METHOD__ );

                // clear the memcache of defined tags
                self::purgeTagCacheAll();
        }

        /**
         * Removes a tag from the valid_tag table. The tag may remain in use by
         * extensions, and may still show up as 'defined' if an extension is setting
         * it from the ListDefinedTags hook.
         *
         * @param string $tag Tag to remove
         * @since 1.25
         */
        public static function undefineTag( $tag ) {
                $dbw = wfGetDB( DB_MASTER );
                $dbw->delete( 'valid_tag', array( 'vt_tag' => $tag ), __METHOD__ );

                // clear the memcache of defined tags
                self::purgeTagCacheAll();
        }

        /**
         * Writes a tag action into the tag management log.
         *
         * @param string $action
         * @param string $tag
         * @param string $reason
         * @param User $user Who to attribute the action to
         * @param int $tagCount For deletion only, how many usages the tag had before
         * it was deleted.
         * @return int ID of the inserted log entry
         * @since 1.25
         */
        protected static function logTagManagementAction( $action, $tag, $reason,
                User $user, $tagCount = null ) {

                $dbw = wfGetDB( DB_MASTER );

                $logEntry = new ManualLogEntry( 'managetags', $action );
                $logEntry->setPerformer( $user );
                // target page is not relevant, but it has to be set, so we just put in
                // the title of Special:Tags
                $logEntry->setTarget( Title::newFromText( 'Special:Tags' ) );
                $logEntry->setComment( $reason );

                $params = array( '4::tag' => $tag );
                if ( !is_null( $tagCount ) ) {
                        $params['5:number:count'] = $tagCount;
                }
                $logEntry->setParameters( $params );
                $logEntry->setRelations( array( 'Tag' => $tag ) );

                $logId = $logEntry->insert( $dbw );
                $logEntry->publish( $logId );
                return $logId;
        }

        /**
         * Is it OK to allow the user to activate this tag?
         *
         * @param string $tag Tag that you are interested in activating
         * @param User|null $user User whose permission you wish to check, or null if
         * you don't care (e.g. maintenance scripts)
         * @return Status
         * @since 1.25
         */
        public static function canActivateTag( $tag, User $user = null ) {
                if ( !is_null( $user ) ) {
                        if ( !$user->isAllowed( 'managechangetags' ) ) {
                                return Status::newFatal( 'tags-manage-no-permission' );
                        } elseif ( $user->isBlocked() ) {
                                return Status::newFatal( 'tags-manage-blocked' );
                        }
                }

                // defined tags cannot be activated (a defined tag is either extension-
                // defined, in which case the extension chooses whether or not to active it;
                // or user-defined, in which case it is considered active)
                $definedTags = self::listDefinedTags();
                if ( in_array( $tag, $definedTags ) ) {
                        return Status::newFatal( 'tags-activate-not-allowed', $tag );
                }

                // non-existing tags cannot be activated
                $tagUsage = self::tagUsageStatistics();
                if ( !isset( $tagUsage[$tag] ) ) { // we already know the tag is undefined
                        return Status::newFatal( 'tags-activate-not-found', $tag );
                }

                return Status::newGood();
        }

        /**
         * Activates a tag, checking whether it is allowed first, and adding a log
         * entry afterwards.
         *
         * Includes a call to ChangeTag::canActivateTag(), so your code doesn't need
         * to do that.
         *
         * @param string $tag
         * @param string $reason
         * @param User $user Who to give credit for the action
         * @param bool $ignoreWarnings Can be used for API interaction, default false
         * @return Status If successful, the Status contains the ID of the added log
         * entry as its value
         * @since 1.25
         */
        public static function activateTagWithChecks( $tag, $reason, User $user,
                $ignoreWarnings = false ) {

                // are we allowed to do this?
                $result = self::canActivateTag( $tag, $user );
                if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
                        $result->value = null;
                        return $result;
                }

                // do it!
                self::defineTag( $tag );

                // log it
                $logId = self::logTagManagementAction( 'activate', $tag, $reason, $user );
                return Status::newGood( $logId );
        }

        /**
         * Is it OK to allow the user to deactivate this tag?
         *
         * @param string $tag Tag that you are interested in deactivating
         * @param User|null $user User whose permission you wish to check, or null if
         * you don't care (e.g. maintenance scripts)
         * @return Status
         * @since 1.25
         */
        public static function canDeactivateTag( $tag, User $user = null ) {
                if ( !is_null( $user ) ) {
                        if ( !$user->isAllowed( 'managechangetags' ) ) {
                                return Status::newFatal( 'tags-manage-no-permission' );
                        } elseif ( $user->isBlocked() ) {
                                return Status::newFatal( 'tags-manage-blocked' );
                        }
                }

                // only explicitly-defined tags can be deactivated
                $explicitlyDefinedTags = self::listExplicitlyDefinedTags();
                if ( !in_array( $tag, $explicitlyDefinedTags ) ) {
                        return Status::newFatal( 'tags-deactivate-not-allowed', $tag );
                }
                return Status::newGood();
        }

        /**
         * Deactivates a tag, checking whether it is allowed first, and adding a log
         * entry afterwards.
         *
         * Includes a call to ChangeTag::canDeactivateTag(), so your code doesn't need
         * to do that.
         *
         * @param string $tag
         * @param string $reason
         * @param User $user Who to give credit for the action
         * @param bool $ignoreWarnings Can be used for API interaction, default false
         * @return Status If successful, the Status contains the ID of the added log
         * entry as its value
         * @since 1.25
         */
        public static function deactivateTagWithChecks( $tag, $reason, User $user,
                $ignoreWarnings = false ) {

                // are we allowed to do this?
                $result = self::canDeactivateTag( $tag, $user );
                if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
                        $result->value = null;
                        return $result;
                }

                // do it!
                self::undefineTag( $tag );

                // log it
                $logId = self::logTagManagementAction( 'deactivate', $tag, $reason, $user );
                return Status::newGood( $logId );
        }

        /**
         * Is it OK to allow the user to create this tag?
         *
         * @param string $tag Tag that you are interested in creating
         * @param User|null $user User whose permission you wish to check, or null if
         * you don't care (e.g. maintenance scripts)
         * @return Status
         * @since 1.25
         */
        public static function canCreateTag( $tag, User $user = null ) {
                if ( !is_null( $user ) ) {
                        if ( !$user->isAllowed( 'managechangetags' ) ) {
                                return Status::newFatal( 'tags-manage-no-permission' );
                        } elseif ( $user->isBlocked() ) {
                                return Status::newFatal( 'tags-manage-blocked' );
                        }
                }

                // no empty tags
                if ( $tag === '' ) {
                        return Status::newFatal( 'tags-create-no-name' );
                }

                // tags cannot contain commas (used as a delimiter in tag_summary table) or
                // slashes (would break tag description messages in MediaWiki namespace)
                if ( strpos( $tag, ',' ) !== false || strpos( $tag, '/' ) !== false ) {
                        return Status::newFatal( 'tags-create-invalid-chars' );
                }

                // could the MediaWiki namespace description messages be created?
                $title = Title::makeTitleSafe( NS_MEDIAWIKI, "Tag-$tag-description" );
                if ( is_null( $title ) ) {
                        return Status::newFatal( 'tags-create-invalid-title-chars' );
                }

                // does the tag already exist?
                $tagUsage = self::tagUsageStatistics();
                if ( isset( $tagUsage[$tag] ) || in_array( $tag, self::listDefinedTags() ) ) {
                        return Status::newFatal( 'tags-create-already-exists', $tag );
                }

                // check with hooks
                $canCreateResult = Status::newGood();
                Hooks::run( 'ChangeTagCanCreate', array( $tag, $user, &$canCreateResult ) );
                return $canCreateResult;
        }

        /**
         * Creates a tag by adding a row to the `valid_tag` table.
         *
         * Includes a call to ChangeTag::canDeleteTag(), so your code doesn't need to
         * do that.
         *
         * @param string $tag
         * @param string $reason
         * @param User $user Who to give credit for the action
         * @param bool $ignoreWarnings Can be used for API interaction, default false
         * @return Status If successful, the Status contains the ID of the added log
         * entry as its value
         * @since 1.25
         */
        public static function createTagWithChecks( $tag, $reason, User $user,
                $ignoreWarnings = false ) {

                // are we allowed to do this?
                $result = self::canCreateTag( $tag, $user );
                if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
                        $result->value = null;
                        return $result;
                }

                // do it!
                self::defineTag( $tag );

                // log it
                $logId = self::logTagManagementAction( 'create', $tag, $reason, $user );
                return Status::newGood( $logId );
        }

        /**
         * Permanently removes all traces of a tag from the DB. Good for removing
         * misspelt or temporary tags.
         *
         * This function should be directly called by maintenance scripts only, never
         * by user-facing code. See deleteTagWithChecks() for functionality that can
         * safely be exposed to users.
         *
         * @param string $tag Tag to remove
         * @return Status The returned status will be good unless a hook changed it
         * @since 1.25
         */
        public static function deleteTagEverywhere( $tag ) {
                $dbw = wfGetDB( DB_MASTER );
                $dbw->startAtomic( __METHOD__ );

                // delete from valid_tag
                self::undefineTag( $tag );

                // find out which revisions use this tag, so we can delete from tag_summary
                $result = $dbw->select( 'change_tag',
                        array( 'ct_rc_id', 'ct_log_id', 'ct_rev_id', 'ct_tag' ),
                        array( 'ct_tag' => $tag ),
                        __METHOD__ );
                foreach ( $result as $row ) {
                        // remove the tag from the relevant row of tag_summary
                        $tagsToAdd = array();
                        $tagsToRemove = array( $tag );
                        self::updateTagSummaryRow( $tagsToAdd, $tagsToRemove, $row->ct_rc_id,
                                $row->ct_rev_id, $row->ct_log_id );
                }

                // delete from change_tag
                $dbw->delete( 'change_tag', array( 'ct_tag' => $tag ), __METHOD__ );

                $dbw->endAtomic( __METHOD__ );

                // give extensions a chance
                $status = Status::newGood();
                Hooks::run( 'ChangeTagAfterDelete', array( $tag, &$status ) );
                // let's not allow error results, as the actual tag deletion succeeded
                if ( !$status->isOK() ) {
                        wfDebug( 'ChangeTagAfterDelete error condition downgraded to warning' );
                        $status->ok = true;
                }

                // clear the memcache of defined tags
                self::purgeTagCacheAll();

                return $status;
        }

        /**
         * Is it OK to allow the user to delete this tag?
         *
         * @param string $tag Tag that you are interested in deleting
         * @param User|null $user User whose permission you wish to check, or null if
         * you don't care (e.g. maintenance scripts)
         * @return Status
         * @since 1.25
         */
        public static function canDeleteTag( $tag, User $user = null ) {
                $tagUsage = self::tagUsageStatistics();

                if ( !is_null( $user ) ) {
                        if ( !$user->isAllowed( 'managechangetags' ) ) {
                                return Status::newFatal( 'tags-manage-no-permission' );
                        } elseif ( $user->isBlocked() ) {
                                return Status::newFatal( 'tags-manage-blocked' );
                        }
                }

                if ( !isset( $tagUsage[$tag] ) && !in_array( $tag, self::listDefinedTags() ) ) {
                        return Status::newFatal( 'tags-delete-not-found', $tag );
                }

                if ( isset( $tagUsage[$tag] ) && $tagUsage[$tag] > self::MAX_DELETE_USES ) {
                        return Status::newFatal( 'tags-delete-too-many-uses', $tag, self::MAX_DELETE_USES );
                }

                $extensionDefined = self::listExtensionDefinedTags();
                if ( in_array( $tag, $extensionDefined ) ) {
                        // extension-defined tags can't be deleted unless the extension
                        // specifically allows it
                        $status = Status::newFatal( 'tags-delete-not-allowed' );
                } else {
                        // user-defined tags are deletable unless otherwise specified
                        $status = Status::newGood();
                }

                Hooks::run( 'ChangeTagCanDelete', array( $tag, $user, &$status ) );
                return $status;
        }

        /**
         * Deletes a tag, checking whether it is allowed first, and adding a log entry
         * afterwards.
         *
         * Includes a call to ChangeTag::canDeleteTag(), so your code doesn't need to
         * do that.
         *
         * @param string $tag
         * @param string $reason
         * @param User $user Who to give credit for the action
         * @param bool $ignoreWarnings Can be used for API interaction, default false
         * @return Status If successful, the Status contains the ID of the added log
         * entry as its value
         * @since 1.25
         */
        public static function deleteTagWithChecks( $tag, $reason, User $user,
                $ignoreWarnings = false ) {

                // are we allowed to do this?
                $result = self::canDeleteTag( $tag, $user );
                if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
                        $result->value = null;
                        return $result;
                }

                // store the tag usage statistics
                $tagUsage = self::tagUsageStatistics();
                $hitcount = isset( $tagUsage[$tag] ) ? $tagUsage[$tag] : 0;

                // do it!
                $deleteResult = self::deleteTagEverywhere( $tag );
                if ( !$deleteResult->isOK() ) {
                        return $deleteResult;
                }

                // log it
                $logId = self::logTagManagementAction( 'delete', $tag, $reason, $user, $hitcount );
                $deleteResult->value = $logId;
                return $deleteResult;
        }

        /**
         * Lists those tags which extensions report as being "active".
         *
         * @return array
         * @since 1.25
         */
        public static function listExtensionActivatedTags() {
                return ObjectCache::getMainWANInstance()->getWithSetCallback(
                        wfMemcKey( 'active-tags' ),
                        300,
                        function ( $oldValue, &$ttl, array &$setOpts ) {
                                $setOpts += Database::getCacheSetOptions( wfGetDB( DB_SLAVE ) );

                                // Ask extensions which tags they consider active
                                $extensionActive = array();
                                Hooks::run( 'ChangeTagsListActive', array( &$extensionActive ) );
                                return $extensionActive;
                        },
                        array(
                                'checkKeys' => array( wfMemcKey( 'active-tags' ) ),
                                'lockTSE' => 300,
                                'pcTTL' => 30
                        )
                );
        }

        /**
         * Basically lists defined tags which count even if they aren't applied to anything.
         * It returns a union of the results of listExplicitlyDefinedTags() and
         * listExtensionDefinedTags().
         *
         * @return string[] Array of strings: tags
         */
        public static function listDefinedTags() {
                $tags1 = self::listExplicitlyDefinedTags();
                $tags2 = self::listExtensionDefinedTags();
                return array_values( array_unique( array_merge( $tags1, $tags2 ) ) );
        }

        /**
         * Lists tags explicitly defined in the `valid_tag` table of the database.
         * Tags in table 'change_tag' which are not in table 'valid_tag' are not
         * included.
         *
         * Tries memcached first.
         *
         * @return string[] Array of strings: tags
         * @since 1.25
         */
        public static function listExplicitlyDefinedTags() {
                $fname = __METHOD__;

                return ObjectCache::getMainWANInstance()->getWithSetCallback(
                        wfMemcKey( 'valid-tags-db' ),
                        300,
                        function ( $oldValue, &$ttl, array &$setOpts ) use ( $fname ) {
                                $dbr = wfGetDB( DB_SLAVE );

                                $setOpts += Database::getCacheSetOptions( $dbr );

                                $tags = $dbr->selectFieldValues( 'valid_tag', 'vt_tag', array(), $fname );

                                return array_filter( array_unique( $tags ) );
                        },
                        array(
                                'checkKeys' => array( wfMemcKey( 'valid-tags-db' ) ),
                                'lockTSE' => 300,
                                'pcTTL' => 30
                        )
                );
        }

        /**
         * Lists tags defined by extensions using the ListDefinedTags hook.
         * Extensions need only define those tags they deem to be in active use.
         *
         * Tries memcached first.
         *
         * @return string[] Array of strings: tags
         * @since 1.25
         */
        public static function listExtensionDefinedTags() {
                return ObjectCache::getMainWANInstance()->getWithSetCallback(
                        wfMemcKey( 'valid-tags-hook' ),
                        300,
                        function ( $oldValue, &$ttl, array &$setOpts ) {
                                $setOpts += Database::getCacheSetOptions( wfGetDB( DB_SLAVE ) );

                                $tags = array();
                                Hooks::run( 'ListDefinedTags', array( &$tags ) );
                                return array_filter( array_unique( $tags ) );
                        },
                        array(
                                'checkKeys' => array( wfMemcKey( 'valid-tags-hook' ) ),
                                'lockTSE' => 300,
                                'pcTTL' => 30
                        )
                );
        }

        /**
         * Invalidates the short-term cache of defined tags used by the
         * list*DefinedTags functions, as well as the tag statistics cache.
         * @since 1.25
         */
        public static function purgeTagCacheAll() {
                $cache = ObjectCache::getMainWANInstance();

                $cache->touchCheckKey( wfMemcKey( 'active-tags' ) );
                $cache->touchCheckKey( wfMemcKey( 'valid-tags-db' ) );
                $cache->touchCheckKey( wfMemcKey( 'valid-tags-hook' ) );

                self::purgeTagUsageCache();
        }

        /**
         * Invalidates the tag statistics cache only.
         * @since 1.25
         */
        public static function purgeTagUsageCache() {
                $cache = ObjectCache::getMainWANInstance();

                $cache->touchCheckKey( wfMemcKey( 'change-tag-statistics' ) );
        }

        /**
         * Returns a map of any tags used on the wiki to number of edits
         * tagged with them, ordered descending by the hitcount.
         * This does not include tags defined somewhere that have never been applied.
         *
         * Keeps a short-term cache in memory, so calling this multiple times in the
         * same request should be fine.
         *
         * @return array Array of string => int
         */
        public static function tagUsageStatistics() {
                $fname = __METHOD__;
                return ObjectCache::getMainWANInstance()->getWithSetCallback(
                        wfMemcKey( 'change-tag-statistics' ),
                        300,
                        function ( $oldValue, &$ttl, array &$setOpts ) use ( $fname ) {
                                $dbr = wfGetDB( DB_SLAVE, 'vslow' );

                                $setOpts += Database::getCacheSetOptions( $dbr );

                                $res = $dbr->select(
                                        'change_tag',
                                        array( 'ct_tag', 'hitcount' => 'count(*)' ),
                                        array(),
                                        $fname,
                                        array( 'GROUP BY' => 'ct_tag', 'ORDER BY' => 'hitcount DESC' )
                                );

                                $out = array();
                                foreach ( $res as $row ) {
                                        $out[$row->ct_tag] = $row->hitcount;
                                }

                                return $out;
                        },
                        array(
                                'checkKeys' => array( wfMemcKey( 'change-tag-statistics' ) ),
                                'lockTSE' => 300,
                                'pcTTL' => 30
                        )
                );
        }

        /**
         * Indicate whether change tag editing UI is relevant
         *
         * Returns true if the user has the necessary right and there are any
         * editable tags defined.
         *
         * This intentionally doesn't check "any addable || any deletable", because
         * it seems like it would be more confusing than useful if the checkboxes
         * suddenly showed up because some abuse filter stopped defining a tag and
         * then suddenly disappeared when someone deleted all uses of that tag.
         *
         * @param User $user
         * @return bool
         */
        public static function showTagEditingUI( User $user ) {
                return $user->isAllowed( 'changetags' ) && (bool)self::listExplicitlyDefinedTags();
        }
}