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[mediawiki.git] / includes / cache / CacheHelper.php

<?php
/**
 * Cache of various elements in a single cache entry.
 *
 * 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
 * @license GNU GPL v2 or later
 * @author Jeroen De Dauw < jeroendedauw@gmail.com >
 */

/**
 * Interface for all classes implementing CacheHelper functionality.
 *
 * @since 1.20
 */
interface ICacheHelper {
        /**
         * Sets if the cache should be enabled or not.
         *
         * @since 1.20
         * @param bool $cacheEnabled
         */
        function setCacheEnabled( $cacheEnabled );

        /**
         * Initializes the caching.
         * Should be called before the first time anything is added via addCachedHTML.
         *
         * @since 1.20
         *
         * @param int|null $cacheExpiry Sets the cache expiry, either ttl in seconds or unix timestamp.
         * @param bool|null $cacheEnabled Sets if the cache should be enabled or not.
         */
        function startCache( $cacheExpiry = null, $cacheEnabled = null );

        /**
         * Get a cached value if available or compute it if not and then cache it if possible.
         * The provided $computeFunction is only called when the computation needs to happen
         * and should return a result value. $args are arguments that will be passed to the
         * compute function when called.
         *
         * @since 1.20
         *
         * @param callable $computeFunction
         * @param array|mixed $args
         * @param string|null $key
         *
         * @return mixed
         */
        function getCachedValue( $computeFunction, $args = array(), $key = null );

        /**
         * Saves the HTML to the cache in case it got recomputed.
         * Should be called after the last time anything is added via addCachedHTML.
         *
         * @since 1.20
         */
        function saveCache();

        /**
         * Sets the time to live for the cache, in seconds or a unix timestamp
         * indicating the point of expiry...
         *
         * @since 1.20
         *
         * @param int $cacheExpiry
         */
        function setExpiry( $cacheExpiry );
}

/**
 * Helper class for caching various elements in a single cache entry.
 *
 * To get a cached value or compute it, use getCachedValue like this:
 * $this->getCachedValue( $callback );
 *
 * To add HTML that should be cached, use addCachedHTML like this:
 * $this->addCachedHTML( $callback );
 *
 * The callback function is only called when needed, so do all your expensive
 * computations here. This function should returns the HTML to be cached.
 * It should not add anything to the PageOutput object!
 *
 * Before the first addCachedHTML call, you should call $this->startCache();
 * After adding the last HTML that should be cached, call $this->saveCache();
 *
 * @since 1.20
 */
class CacheHelper implements ICacheHelper {
        /**
         * The time to live for the cache, in seconds or a unix timestamp indicating the point of expiry.
         *
         * @since 1.20
         * @var int
         */
        protected $cacheExpiry = 3600;

        /**
         * List of HTML chunks to be cached (if !hasCached) or that where cached (of hasCached).
         * If not cached already, then the newly computed chunks are added here,
         * if it as cached already, chunks are removed from this list as they are needed.
         *
         * @since 1.20
         * @var array
         */
        protected $cachedChunks;

        /**
         * Indicates if the to be cached content was already cached.
         * Null if this information is not available yet.
         *
         * @since 1.20
         * @var bool|null
         */
        protected $hasCached = null;

        /**
         * If the cache is enabled or not.
         *
         * @since 1.20
         * @var bool
         */
        protected $cacheEnabled = true;

        /**
         * Function that gets called when initialization is done.
         *
         * @since 1.20
         * @var callable
         */
        protected $onInitHandler = false;

        /**
         * Elements to build a cache key with.
         *
         * @since 1.20
         * @var array
         */
        protected $cacheKey = array();

        /**
         * Sets if the cache should be enabled or not.
         *
         * @since 1.20
         * @param bool $cacheEnabled
         */
        public function setCacheEnabled( $cacheEnabled ) {
                $this->cacheEnabled = $cacheEnabled;
        }

        /**
         * Initializes the caching.
         * Should be called before the first time anything is added via addCachedHTML.
         *
         * @since 1.20
         *
         * @param int|null $cacheExpiry Sets the cache expiry, either ttl in seconds or unix timestamp.
         * @param bool|null $cacheEnabled Sets if the cache should be enabled or not.
         */
        public function startCache( $cacheExpiry = null, $cacheEnabled = null ) {
                if ( is_null( $this->hasCached ) ) {
                        if ( !is_null( $cacheExpiry ) ) {
                                $this->cacheExpiry = $cacheExpiry;
                        }

                        if ( !is_null( $cacheEnabled ) ) {
                                $this->setCacheEnabled( $cacheEnabled );
                        }

                        $this->initCaching();
                }
        }

        /**
         * Returns a message that notifies the user he/she is looking at
         * a cached version of the page, including a refresh link.
         *
         * @since 1.20
         *
         * @param IContextSource $context
         * @param bool $includePurgeLink
         *
         * @return string
         */
        public function getCachedNotice( IContextSource $context, $includePurgeLink = true ) {
                if ( $this->cacheExpiry < 86400 * 3650 ) {
                        $message = $context->msg(
                                'cachedspecial-viewing-cached-ttl',
                                $context->getLanguage()->formatDuration( $this->cacheExpiry )
                        )->escaped();
                } else {
                        $message = $context->msg(
                                'cachedspecial-viewing-cached-ts'
                        )->escaped();
                }

                if ( $includePurgeLink ) {
                        $refreshArgs = $context->getRequest()->getQueryValues();
                        unset( $refreshArgs['title'] );
                        $refreshArgs['action'] = 'purge';

                        $subPage = $context->getTitle()->getFullText();
                        $subPage = explode( '/', $subPage, 2 );
                        $subPage = count( $subPage ) > 1 ? $subPage[1] : false;

                        $message .= ' ' . Linker::link(
                                $context->getTitle( $subPage ),
                                $context->msg( 'cachedspecial-refresh-now' )->escaped(),
                                array(),
                                $refreshArgs
                        );
                }

                return $message;
        }

        /**
         * Initializes the caching if not already done so.
         * Should be called before any of the caching functionality is used.
         *
         * @since 1.20
         */
        protected function initCaching() {
                if ( $this->cacheEnabled && is_null( $this->hasCached ) ) {
                        $cachedChunks = wfGetCache( CACHE_ANYTHING )->get( $this->getCacheKeyString() );

                        $this->hasCached = is_array( $cachedChunks );
                        $this->cachedChunks = $this->hasCached ? $cachedChunks : array();

                        if ( $this->onInitHandler !== false ) {
                                call_user_func( $this->onInitHandler, $this->hasCached );
                        }
                }
        }

        /**
         * Get a cached value if available or compute it if not and then cache it if possible.
         * The provided $computeFunction is only called when the computation needs to happen
         * and should return a result value. $args are arguments that will be passed to the
         * compute function when called.
         *
         * @since 1.20
         *
         * @param callable $computeFunction
         * @param array|mixed $args
         * @param string|null $key
         *
         * @return mixed
         */
        public function getCachedValue( $computeFunction, $args = array(), $key = null ) {
                $this->initCaching();

                if ( $this->cacheEnabled && $this->hasCached ) {
                        $value = null;

                        if ( is_null( $key ) ) {
                                $itemKey = array_keys( array_slice( $this->cachedChunks, 0, 1 ) );
                                $itemKey = array_shift( $itemKey );

                                if ( !is_integer( $itemKey ) ) {
                                        wfWarn( "Attempted to get item with non-numeric key while " .
                                                "the next item in the queue has a key ($itemKey) in " . __METHOD__ );
                                } elseif ( is_null( $itemKey ) ) {
                                        wfWarn( "Attempted to get an item while the queue is empty in " . __METHOD__ );
                                } else {
                                        $value = array_shift( $this->cachedChunks );
                                }
                        } else {
                                if ( array_key_exists( $key, $this->cachedChunks ) ) {
                                        $value = $this->cachedChunks[$key];
                                        unset( $this->cachedChunks[$key] );
                                } else {
                                        wfWarn( "There is no item with key '$key' in this->cachedChunks in " . __METHOD__ );
                                }
                        }
                } else {
                        if ( !is_array( $args ) ) {
                                $args = array( $args );
                        }

                        $value = call_user_func_array( $computeFunction, $args );

                        if ( $this->cacheEnabled ) {
                                if ( is_null( $key ) ) {
                                        $this->cachedChunks[] = $value;
                                } else {
                                        $this->cachedChunks[$key] = $value;
                                }
                        }
                }

                return $value;
        }

        /**
         * Saves the HTML to the cache in case it got recomputed.
         * Should be called after the last time anything is added via addCachedHTML.
         *
         * @since 1.20
         */
        public function saveCache() {
                if ( $this->cacheEnabled && $this->hasCached === false && !empty( $this->cachedChunks ) ) {
                        wfGetCache( CACHE_ANYTHING )->set(
                                $this->getCacheKeyString(),
                                $this->cachedChunks,
                                $this->cacheExpiry
                        );
                }
        }

        /**
         * Sets the time to live for the cache, in seconds or a unix timestamp
         * indicating the point of expiry...
         *
         * @since 1.20
         *
         * @param int $cacheExpiry
         */
        public function setExpiry( $cacheExpiry ) {
                $this->cacheExpiry = $cacheExpiry;
        }

        /**
         * Returns the cache key to use to cache this page's HTML output.
         * Is constructed from the special page name and language code.
         *
         * @since 1.20
         *
         * @return string
         * @throws MWException
         */
        protected function getCacheKeyString() {
                if ( $this->cacheKey === array() ) {
                        throw new MWException( 'No cache key set, so cannot obtain or save the CacheHelper values.' );
                }

                return call_user_func_array( 'wfMemcKey', $this->cacheKey );
        }

        /**
         * Sets the cache key that should be used.
         *
         * @since 1.20
         *
         * @param array $cacheKey
         */
        public function setCacheKey( array $cacheKey ) {
                $this->cacheKey = $cacheKey;
        }

        /**
         * Rebuild the content, even if it's already cached.
         * This effectively has the same effect as purging the cache,
         * since it will be overridden with the new value on the next request.
         *
         * @since 1.20
         */
        public function rebuildOnDemand() {
                $this->hasCached = false;
        }

        /**
         * Sets a function that gets called when initialization of the cache is done.
         *
         * @since 1.20
         *
         * @param callable $handlerFunction
         */
        public function setOnInitializedHandler( $handlerFunction ) {
                $this->onInitHandler = $handlerFunction;
        }
}