<?php
/**
 *
 *
 * Created on Oct 16, 2006
 *
 * Copyright © 2006 Yuri Astrakhan "<Firstname><Lastname>@gmail.com"
 *
 * 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
 */

/**
 * This is a three-in-one module to query:
 *   * backlinks  - links pointing to the given page,
 *   * embeddedin - what pages transclude the given page within themselves,
 *   * imageusage - what pages use the given image
 *
 * @ingroup API
 */
class ApiQueryBacklinks extends ApiQueryGeneratorBase {

	/**
	 * @var Title
	 */
	private $rootTitle;

	private $params, $contID, $redirID, $redirect;
	private $bl_ns, $bl_from, $bl_table, $bl_code, $bl_title, $bl_fields, $hasNS;

	/**
	 * Maps ns and title to pageid
	 *
	 * @var array
	 */
	private $pageMap = array();
	private $resultArr;

	private $redirTitles = array();
	private $continueStr = null;

	// output element name, database column field prefix, database table
	private $backlinksSettings = array(
		'backlinks' => array(
			'code' => 'bl',
			'prefix' => 'pl',
			'linktbl' => 'pagelinks',
			'helpurl' => 'https://www.mediawiki.org/wiki/API:Backlinks',
		),
		'embeddedin' => array(
			'code' => 'ei',
			'prefix' => 'tl',
			'linktbl' => 'templatelinks',
			'helpurl' => 'https://www.mediawiki.org/wiki/API:Embeddedin',
		),
		'imageusage' => array(
			'code' => 'iu',
			'prefix' => 'il',
			'linktbl' => 'imagelinks',
			'helpurl' => 'https://www.mediawiki.org/wiki/API:Imageusage',
		)
	);

	public function __construct( ApiQuery $query, $moduleName ) {
		$settings = $this->backlinksSettings[$moduleName];
		$prefix = $settings['prefix'];
		$code = $settings['code'];
		$this->resultArr = array();

		parent::__construct( $query, $moduleName, $code );
		$this->bl_ns = $prefix . '_namespace';
		$this->bl_from = $prefix . '_from';
		$this->bl_table = $settings['linktbl'];
		$this->bl_code = $code;
		$this->helpUrl = $settings['helpurl'];

		$this->hasNS = $moduleName !== 'imageusage';
		if ( $this->hasNS ) {
			$this->bl_title = $prefix . '_title';
			$this->bl_fields = array(
				$this->bl_ns,
				$this->bl_title
			);
		} else {
			$this->bl_title = $prefix . '_to';
			$this->bl_fields = array(
				$this->bl_title
			);
		}
	}

	public function execute() {
		$this->run();
	}

	public function getCacheMode( $params ) {
		return 'public';
	}

	public function executeGenerator( $resultPageSet ) {
		$this->run( $resultPageSet );
	}

	/**
	 * @param ApiPageSet $resultPageSet
	 * @return void
	 */
	private function prepareFirstQuery( $resultPageSet = null ) {
		/* SELECT page_id, page_title, page_namespace, page_is_redirect
		 * FROM pagelinks, page WHERE pl_from=page_id
		 * AND pl_title='Foo' AND pl_namespace=0
		 * LIMIT 11 ORDER BY pl_from
		 */
		$this->addTables( array( $this->bl_table, 'page' ) );
		$this->addWhere( "{$this->bl_from}=page_id" );
		if ( is_null( $resultPageSet ) ) {
			$this->addFields( array( 'page_id', 'page_title', 'page_namespace' ) );
		} else {
			$this->addFields( $resultPageSet->getPageTableFields() );
		}

		$this->addFields( 'page_is_redirect' );
		$this->addWhereFld( $this->bl_title, $this->rootTitle->getDBkey() );

		if ( $this->hasNS ) {
			$this->addWhereFld( $this->bl_ns, $this->rootTitle->getNamespace() );
		}
		$this->addWhereFld( 'page_namespace', $this->params['namespace'] );

		if ( !is_null( $this->contID ) ) {
			$op = $this->params['dir'] == 'descending' ? '<' : '>';
			$this->addWhere( "{$this->bl_from}$op={$this->contID}" );
		}

		if ( $this->params['filterredir'] == 'redirects' ) {
			$this->addWhereFld( 'page_is_redirect', 1 );
		} elseif ( $this->params['filterredir'] == 'nonredirects' && !$this->redirect ) {
			// bug 22245 - Check for !redirect, as filtering nonredirects, when
			// getting what links to them is contradictory
			$this->addWhereFld( 'page_is_redirect', 0 );
		}

		$this->addOption( 'LIMIT', $this->params['limit'] + 1 );
		$sort = ( $this->params['dir'] == 'descending' ? ' DESC' : '' );
		$this->addOption( 'ORDER BY', $this->bl_from . $sort );
		$this->addOption( 'STRAIGHT_JOIN' );
	}

	/**
	 * @param ApiPageSet $resultPageSet
	 * @return void
	 */
	private function prepareSecondQuery( $resultPageSet = null ) {
		/* SELECT page_id, page_title, page_namespace, page_is_redirect, pl_title, pl_namespace
		   FROM pagelinks, page WHERE pl_from=page_id
		   AND (pl_title='Foo' AND pl_namespace=0) OR (pl_title='Bar' AND pl_namespace=1)
		   ORDER BY pl_namespace, pl_title, pl_from LIMIT 11
		 */
		$db = $this->getDB();
		$this->addTables( array( 'page', $this->bl_table ) );
		$this->addWhere( "{$this->bl_from}=page_id" );

		if ( is_null( $resultPageSet ) ) {
			$this->addFields( array( 'page_id', 'page_title', 'page_namespace', 'page_is_redirect' ) );
		} else {
			$this->addFields( $resultPageSet->getPageTableFields() );
		}

		$this->addFields( $this->bl_title );
		if ( $this->hasNS ) {
			$this->addFields( $this->bl_ns );
		}

		// We can't use LinkBatch here because $this->hasNS may be false
		$titleWhere = array();
		$allRedirNs = array();
		$allRedirDBkey = array();
		/** @var $t Title */
		foreach ( $this->redirTitles as $t ) {
			$redirNs = $t->getNamespace();
			$redirDBkey = $t->getDBkey();
			$titleWhere[] = "{$this->bl_title} = " . $db->addQuotes( $redirDBkey ) .
				( $this->hasNS ? " AND {$this->bl_ns} = {$redirNs}" : '' );
			$allRedirNs[] = $redirNs;
			$allRedirDBkey[] = $redirDBkey;
		}
		$this->addWhere( $db->makeList( $titleWhere, LIST_OR ) );
		$this->addWhereFld( 'page_namespace', $this->params['namespace'] );

		if ( !is_null( $this->redirID ) ) {
			$op = $this->params['dir'] == 'descending' ? '<' : '>';
			/** @var $first Title */
			$first = $this->redirTitles[0];
			$title = $db->addQuotes( $first->getDBkey() );
			$ns = $first->getNamespace();
			$from = $this->redirID;
			if ( $this->hasNS ) {
				$this->addWhere( "{$this->bl_ns} $op $ns OR " .
					"({$this->bl_ns} = $ns AND " .
					"({$this->bl_title} $op $title OR " .
					"({$this->bl_title} = $title AND " .
					"{$this->bl_from} $op= $from)))" );
			} else {
				$this->addWhere( "{$this->bl_title} $op $title OR " .
					"({$this->bl_title} = $title AND " .
					"{$this->bl_from} $op= $from)" );
			}
		}
		if ( $this->params['filterredir'] == 'redirects' ) {
			$this->addWhereFld( 'page_is_redirect', 1 );
		} elseif ( $this->params['filterredir'] == 'nonredirects' ) {
			$this->addWhereFld( 'page_is_redirect', 0 );
		}

		$this->addOption( 'LIMIT', $this->params['limit'] + 1 );
		$orderBy = array();
		$sort = ( $this->params['dir'] == 'descending' ? ' DESC' : '' );
		// Don't order by namespace/title if it's constant in the WHERE clause
		if ( $this->hasNS && count( array_unique( $allRedirNs ) ) != 1 ) {
			$orderBy[] = $this->bl_ns . $sort;
		}
		if ( count( array_unique( $allRedirDBkey ) ) != 1 ) {
			$orderBy[] = $this->bl_title . $sort;
		}
		$orderBy[] = $this->bl_from . $sort;
		$this->addOption( 'ORDER BY', $orderBy );
		$this->addOption( 'USE INDEX', array( 'page' => 'PRIMARY' ) );
	}

	/**
	 * @param ApiPageSet $resultPageSet
	 * @return void
	 */
	private function run( $resultPageSet = null ) {
		$this->params = $this->extractRequestParams( false );
		$this->redirect = isset( $this->params['redirect'] ) && $this->params['redirect'];
		$userMax = ( $this->redirect ? ApiBase::LIMIT_BIG1 / 2 : ApiBase::LIMIT_BIG1 );
		$botMax = ( $this->redirect ? ApiBase::LIMIT_BIG2 / 2 : ApiBase::LIMIT_BIG2 );

		$result = $this->getResult();

		if ( $this->params['limit'] == 'max' ) {
			$this->params['limit'] = $this->getMain()->canApiHighLimits() ? $botMax : $userMax;
			$result->setParsedLimit( $this->getModuleName(), $this->params['limit'] );
		} else {
			$this->params['limit'] = intval( $this->params['limit'] );
			$this->validateLimit( 'limit', $this->params['limit'], 1, $userMax, $botMax );
		}

		$this->processContinue();
		$this->prepareFirstQuery( $resultPageSet );

		$res = $this->select( __METHOD__ . '::firstQuery' );

		$count = 0;

		foreach ( $res as $row ) {
			if ( ++$count > $this->params['limit'] ) {
				// We've reached the one extra which shows that there are
				// additional pages to be had. Stop here...
				// Continue string preserved in case the redirect query doesn't pass the limit
				$this->continueStr = $this->getContinueStr( $row->page_id );
				break;
			}

			if ( is_null( $resultPageSet ) ) {
				$this->extractRowInfo( $row );
			} else {
				$this->pageMap[$row->page_namespace][$row->page_title] = $row->page_id;
				if ( $row->page_is_redirect ) {
					$this->redirTitles[] = Title::makeTitle( $row->page_namespace, $row->page_title );
				}

				$resultPageSet->processDbRow( $row );
			}
		}

		if ( $this->redirect && count( $this->redirTitles ) ) {
			$this->resetQueryParams();
			$this->prepareSecondQuery( $resultPageSet );
			$res = $this->select( __METHOD__ . '::secondQuery' );
			$count = 0;
			foreach ( $res as $row ) {
				if ( ++$count > $this->params['limit'] ) {
					// We've reached the one extra which shows that there are
					// additional pages to be had. Stop here...
					// We need to keep the parent page of this redir in
					if ( $this->hasNS ) {
						$parentID = $this->pageMap[$row->{$this->bl_ns}][$row->{$this->bl_title}];
					} else {
						$parentID = $this->pageMap[NS_FILE][$row->{$this->bl_title}];
					}
					$this->continueStr = $this->getContinueRedirStr( $parentID, $row->page_id );
					break;
				}

				if ( is_null( $resultPageSet ) ) {
					$this->extractRedirRowInfo( $row );
				} else {
					$resultPageSet->processDbRow( $row );
				}
			}
		}
		if ( is_null( $resultPageSet ) ) {
			// Try to add the result data in one go and pray that it fits
			$fit = $result->addValue( 'query', $this->getModuleName(), array_values( $this->resultArr ) );
			if ( !$fit ) {
				// It didn't fit. Add elements one by one until the
				// result is full.
				foreach ( $this->resultArr as $pageID => $arr ) {
					// Add the basic entry without redirlinks first
					$fit = $result->addValue(
						array( 'query', $this->getModuleName() ),
						null, array_diff_key( $arr, array( 'redirlinks' => '' ) ) );
					if ( !$fit ) {
						$this->continueStr = $this->getContinueStr( $pageID );
						break;
					}

					$hasRedirs = false;
					$redirLinks = isset( $arr['redirlinks'] ) ? $arr['redirlinks'] : array();
					foreach ( (array)$redirLinks as $key => $redir ) {
						$fit = $result->addValue(
							array( 'query', $this->getModuleName(), $pageID, 'redirlinks' ),
							$key, $redir );
						if ( !$fit ) {
							$this->continueStr = $this->getContinueRedirStr( $pageID, $redir['pageid'] );
							break;
						}
						$hasRedirs = true;
					}
					if ( $hasRedirs ) {
						$result->setIndexedTagName_internal(
							array( 'query', $this->getModuleName(), $pageID, 'redirlinks' ),
							$this->bl_code );
					}
					if ( !$fit ) {
						break;
					}
				}
			}

			$result->setIndexedTagName_internal(
				array( 'query', $this->getModuleName() ),
				$this->bl_code
			);
		}
		if ( !is_null( $this->continueStr ) ) {
			$this->setContinueEnumParameter( 'continue', $this->continueStr );
		}
	}

	private function extractRowInfo( $row ) {
		$this->pageMap[$row->page_namespace][$row->page_title] = $row->page_id;
		$t = Title::makeTitle( $row->page_namespace, $row->page_title );
		$a = array( 'pageid' => intval( $row->page_id ) );
		ApiQueryBase::addTitleInfo( $a, $t );
		if ( $row->page_is_redirect ) {
			$a['redirect'] = '';
			$this->redirTitles[] = $t;
		}
		// Put all the results in an array first
		$this->resultArr[$a['pageid']] = $a;
	}

	private function extractRedirRowInfo( $row ) {
		$a['pageid'] = intval( $row->page_id );
		ApiQueryBase::addTitleInfo( $a, Title::makeTitle( $row->page_namespace, $row->page_title ) );
		if ( $row->page_is_redirect ) {
			$a['redirect'] = '';
		}
		$ns = $this->hasNS ? $row->{$this->bl_ns} : NS_FILE;
		$parentID = $this->pageMap[$ns][$row->{$this->bl_title}];
		// Put all the results in an array first
		$this->resultArr[$parentID]['redirlinks'][] = $a;
		$this->getResult()->setIndexedTagName(
			$this->resultArr[$parentID]['redirlinks'],
			$this->bl_code
		);
	}

	protected function processContinue() {
		if ( !is_null( $this->params['continue'] ) ) {
			$this->parseContinueParam();
		} else {
			$this->rootTitle = $this->getTitleOrPageId( $this->params )->getTitle();
		}

		// only image titles are allowed for the root in imageinfo mode
		if ( !$this->hasNS && $this->rootTitle->getNamespace() !== NS_FILE ) {
			$this->dieUsage(
				"The title for {$this->getModuleName()} query must be an image",
				'bad_image_title'
			);
		}
	}

	protected function parseContinueParam() {
		$continueList = explode( '|', $this->params['continue'] );
		// expected format:
		// ns | key | id1 [| id2]
		// ns+key: root title
		// id1: first-level page ID to continue from
		// id2: second-level page ID to continue from

		// null stuff out now so we know what's set and what isn't
		$this->rootTitle = $this->contID = $this->redirID = null;
		$rootNs = intval( $continueList[0] );
		$this->dieContinueUsageIf( $rootNs === 0 && $continueList[0] !== '0' );

		$this->rootTitle = Title::makeTitleSafe( $rootNs, $continueList[1] );
		$this->dieContinueUsageIf( !$this->rootTitle );

		$contID = intval( $continueList[2] );
		$this->dieContinueUsageIf( $contID === 0 && $continueList[2] !== '0' );

		$this->contID = $contID;
		$id2 = isset( $continueList[3] ) ? $continueList[3] : null;
		$redirID = intval( $id2 );

		if ( $redirID === 0 && $id2 !== '0' ) {
			// This one isn't required
			return;
		}
		$this->redirID = $redirID;
	}

	protected function getContinueStr( $lastPageID ) {
		return $this->rootTitle->getNamespace() .
		'|' . $this->rootTitle->getDBkey() .
		'|' . $lastPageID;
	}

	protected function getContinueRedirStr( $lastPageID, $lastRedirID ) {
		return $this->getContinueStr( $lastPageID ) . '|' . $lastRedirID;
	}

	public function getAllowedParams() {
		$retval = array(
			'title' => array(
				ApiBase::PARAM_TYPE => 'string',
			),
			'pageid' => array(
				ApiBase::PARAM_TYPE => 'integer',
			),
			'continue' => null,
			'namespace' => array(
				ApiBase::PARAM_ISMULTI => true,
				ApiBase::PARAM_TYPE => 'namespace'
			),
			'dir' => array(
				ApiBase::PARAM_DFLT => 'ascending',
				ApiBase::PARAM_TYPE => array(
					'ascending',
					'descending'
				)
			),
			'filterredir' => array(
				ApiBase::PARAM_DFLT => 'all',
				ApiBase::PARAM_TYPE => array(
					'all',
					'redirects',
					'nonredirects'
				)
			),
			'limit' => array(
				ApiBase::PARAM_DFLT => 10,
				ApiBase::PARAM_TYPE => 'limit',
				ApiBase::PARAM_MIN => 1,
				ApiBase::PARAM_MAX => ApiBase::LIMIT_BIG1,
				ApiBase::PARAM_MAX2 => ApiBase::LIMIT_BIG2
			)
		);
		if ( $this->getModuleName() == 'embeddedin' ) {
			return $retval;
		}
		$retval['redirect'] = false;

		return $retval;
	}

	public function getParamDescription() {
		$retval = array(
			'title' => "Title to search. Cannot be used together with {$this->bl_code}pageid",
			'pageid' => "Pageid to search. Cannot be used together with {$this->bl_code}title",
			'continue' => 'When more results are available, use this to continue',
			'namespace' => 'The namespace to enumerate',
			'dir' => 'The direction in which to list',
		);
		if ( $this->getModuleName() != 'embeddedin' ) {
			return array_merge( $retval, array(
				'redirect' => 'If linking page is a redirect, find all pages ' .
					'that link to that redirect as well. Maximum limit is halved.',
				'filterredir' => 'How to filter for redirects. If set to ' .
					"nonredirects when {$this->bl_code}redirect is enabled, " .
					'this is only applied to the second level',
				'limit' => 'How many total pages to return. If ' .
					"{$this->bl_code}redirect is enabled, limit applies to each " .
					'level separately (which means you may get up to 2 * limit results).'
			) );
		}

		return array_merge( $retval, array(
			'filterredir' => 'How to filter for redirects',
			'limit' => 'How many total pages to return'
		) );
	}

	public function getDescription() {
		switch ( $this->getModuleName() ) {
			case 'backlinks':
				return 'Find all pages that link to the given page.';
			case 'embeddedin':
				return 'Find all pages that embed (transclude) the given title.';
			case 'imageusage':
				return 'Find all pages that use the given image title.';
			default:
				ApiBase::dieDebug( __METHOD__, 'Unknown module name.' );
		}
	}

	public function getExamples() {
		static $examples = array(
			'backlinks' => array(
				'api.php?action=query&list=backlinks&bltitle=Main%20Page',
				'api.php?action=query&generator=backlinks&gbltitle=Main%20Page&prop=info'
			),
			'embeddedin' => array(
				'api.php?action=query&list=embeddedin&eititle=Template:Stub',
				'api.php?action=query&generator=embeddedin&geititle=Template:Stub&prop=info'
			),
			'imageusage' => array(
				'api.php?action=query&list=imageusage&iutitle=File:Albert%20Einstein%20Head.jpg',
				'api.php?action=query&generator=imageusage&giutitle=File:Albert%20Einstein%20Head.jpg&prop=info'
			)
		);

		return $examples[$this->getModuleName()];
	}

	public function getHelpUrls() {
		return $this->helpUrl;
	}
}
