<?php
/**
 * Prefix search of page names.
 *
 * 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\MediaWikiServices;

/**
 * Handles searching prefixes of titles and finding any page
 * names that match. Used largely by the OpenSearch implementation.
 * @deprecated Since 1.27, Use SearchEngine::defaultPrefixSearch or SearchEngine::completionSearch
 *
 * @stable to extend
 * @ingroup Search
 */
abstract class PrefixSearch {
	/**
	 * Do a prefix search of titles and return a list of matching page names.
	 *
	 * @param string $search
	 * @param int $limit
	 * @param array $namespaces Used if query is not explicitly prefixed
	 * @param int $offset How many results to offset from the beginning
	 * @return array Array of strings or Title objects
	 */
	public function search( $search, $limit, $namespaces = [], $offset = 0 ) {
		$search = trim( $search );
		if ( $search == '' ) {
			return []; // Return empty result
		}

		$hasNamespace = SearchEngine::parseNamespacePrefixes( $search, false, true );
		if ( $hasNamespace !== false ) {
			list( $search, $namespaces ) = $hasNamespace;
		}

		return $this->searchBackend( $namespaces, $search, $limit, $offset );
	}

	/**
	 * Do a prefix search for all possible variants of the prefix
	 * @param string $search
	 * @param int $limit
	 * @param array $namespaces
	 * @param int $offset How many results to offset from the beginning
	 *
	 * @return array
	 */
	public function searchWithVariants( $search, $limit, array $namespaces, $offset = 0 ) {
		$searches = $this->search( $search, $limit, $namespaces, $offset );

		// if the content language has variants, try to retrieve fallback results
		$fallbackLimit = $limit - count( $searches );
		if ( $fallbackLimit > 0 ) {
			$fallbackSearches = MediaWikiServices::getInstance()->getContentLanguage()->
				autoConvertToAllVariants( $search );
			$fallbackSearches = array_diff( array_unique( $fallbackSearches ), [ $search ] );

			foreach ( $fallbackSearches as $fbs ) {
				$fallbackSearchResult = $this->search( $fbs, $fallbackLimit, $namespaces );
				$searches = array_merge( $searches, $fallbackSearchResult );
				$fallbackLimit -= count( $fallbackSearchResult );

				if ( $fallbackLimit == 0 ) {
					break;
				}
			}
		}
		return $searches;
	}

	/**
	 * When implemented in a descendant class, receives an array of Title objects and returns
	 * either an unmodified array or an array of strings corresponding to titles passed to it.
	 *
	 * @param array $titles
	 * @return array
	 */
	abstract protected function titles( array $titles );

	/**
	 * When implemented in a descendant class, receives an array of titles as strings and returns
	 * either an unmodified array or an array of Title objects corresponding to strings received.
	 *
	 * @param string[] $strings
	 *
	 * @return array
	 */
	abstract protected function strings( array $strings );

	/**
	 * Do a prefix search of titles and return a list of matching page names.
	 * @param array $namespaces
	 * @param string $search
	 * @param int $limit
	 * @param int $offset How many results to offset from the beginning
	 * @return array Array of strings
	 */
	protected function searchBackend( $namespaces, $search, $limit, $offset ) {
		if ( count( $namespaces ) == 1 ) {
			$ns = $namespaces[0];
			if ( $ns == NS_MEDIA ) {
				$namespaces = [ NS_FILE ];
			} elseif ( $ns == NS_SPECIAL ) {
				return $this->titles( $this->specialSearch( $search, $limit, $offset ) );
			}
		}
		$srchres = [];
		if ( Hooks::runner()->onPrefixSearchBackend(
			$namespaces, $search, $limit, $srchres, $offset )
		) {
			return $this->titles( $this->defaultSearchBackend( $namespaces, $search, $limit, $offset ) );
		}
		return $this->strings(
			$this->handleResultFromHook( $srchres, $namespaces, $search, $limit, $offset ) );
	}

	private function handleResultFromHook( $srchres, $namespaces, $search, $limit, $offset ) {
		if ( $offset === 0 ) {
			// Only perform exact db match if offset === 0
			// This is still far from perfect but at least we avoid returning the
			// same title afain and again when the user is scrolling with a query
			// that matches a title in the db.
			$rescorer = new SearchExactMatchRescorer();
			$srchres = $rescorer->rescore( $search, $namespaces, $srchres, $limit );
		}
		return $srchres;
	}

	/**
	 * Prefix search special-case for Special: namespace.
	 *
	 * @param string $search Term
	 * @param int $limit Max number of items to return
	 * @param int $offset Number of items to offset
	 * @return array
	 */
	protected function specialSearch( $search, $limit, $offset ) {
		$searchParts = explode( '/', $search, 2 );
		$searchKey = $searchParts[0];
		$subpageSearch = $searchParts[1] ?? null;

		// Handle subpage search separately.
		$spFactory = MediaWikiServices::getInstance()->getSpecialPageFactory();
		if ( $subpageSearch !== null ) {
			// Try matching the full search string as a page name
			$specialTitle = Title::makeTitleSafe( NS_SPECIAL, $searchKey );
			if ( !$specialTitle ) {
				return [];
			}
			$special = $spFactory->getPage( $specialTitle->getText() );
			if ( $special ) {
				$subpages = $special->prefixSearchSubpages( $subpageSearch, $limit, $offset );
				return array_map( function ( $sub ) use ( $specialTitle ) {
					return $specialTitle->getSubpage( $sub );
				}, $subpages );
			} else {
				return [];
			}
		}

		# normalize searchKey, so aliases with spaces can be found - T27675
		$contLang = MediaWikiServices::getInstance()->getContentLanguage();
		$searchKey = str_replace( ' ', '_', $searchKey );
		$searchKey = $contLang->caseFold( $searchKey );

		// Unlike SpecialPage itself, we want the canonical forms of both
		// canonical and alias title forms...
		$keys = [];
		foreach ( $spFactory->getNames() as $page ) {
			$keys[$contLang->caseFold( $page )] = [ 'page' => $page, 'rank' => 0 ];
		}

		foreach ( $contLang->getSpecialPageAliases() as $page => $aliases ) {
			if ( !in_array( $page, $spFactory->getNames() ) ) {# T22885
				continue;
			}

			foreach ( $aliases as $key => $alias ) {
				$keys[$contLang->caseFold( $alias )] = [ 'page' => $alias, 'rank' => $key ];
			}
		}
		ksort( $keys );

		$matches = [];
		foreach ( $keys as $pageKey => $page ) {
			if ( $searchKey === '' || strpos( $pageKey, $searchKey ) === 0 ) {
				// T29671: Don't use SpecialPage::getTitleFor() here because it
				// localizes its input leading to searches for e.g. Special:All
				// returning Spezial:MediaWiki-Systemnachrichten and returning
				// Spezial:Alle_Seiten twice when $wgLanguageCode == 'de'
				$matches[$page['rank']][] = Title::makeTitleSafe( NS_SPECIAL, $page['page'] );

				if ( isset( $matches[0] ) && count( $matches[0] ) >= $limit + $offset ) {
					// We have enough items in primary rank, no use to continue
					break;
				}
			}

		}

		// Ensure keys are in order
		ksort( $matches );
		// Flatten the array
		$matches = array_reduce( $matches, 'array_merge', [] );

		return array_slice( $matches, $offset, $limit );
	}

	/**
	 * Unless overridden by PrefixSearchBackend hook...
	 * This is case-sensitive (First character may
	 * be automatically capitalized by Title::secureAndSpit()
	 * later on depending on $wgCapitalLinks)
	 *
	 * @param array|null $namespaces Namespaces to search in
	 * @param string $search Term
	 * @param int $limit Max number of items to return
	 * @param int $offset Number of items to skip
	 * @return Title[] Array of Title objects
	 */
	public function defaultSearchBackend( $namespaces, $search, $limit, $offset ) {
		// Backwards compatability with old code. Default to NS_MAIN if no namespaces provided.
		if ( $namespaces === null ) {
			$namespaces = [];
		}
		if ( !$namespaces ) {
			$namespaces[] = NS_MAIN;
		}

		// Construct suitable prefix for each namespace. They differ in cases where
		// some namespaces always capitalize and some don't.
		$prefixes = [];
		foreach ( $namespaces as $namespace ) {
			// For now, if special is included, ignore the other namespaces
			if ( $namespace == NS_SPECIAL ) {
				return $this->specialSearch( $search, $limit, $offset );
			}

			$title = Title::makeTitleSafe( $namespace, $search );
			// Why does the prefix default to empty?
			$prefix = $title ? $title->getDBkey() : '';
			$prefixes[$prefix][] = $namespace;
		}

		$dbr = wfGetDB( DB_REPLICA );
		// Often there is only one prefix that applies to all requested namespaces,
		// but sometimes there are two if some namespaces do not always capitalize.
		$conds = [];
		foreach ( $prefixes as $prefix => $namespaces ) {
			$condition = [
				'page_namespace' => $namespaces,
				'page_title' . $dbr->buildLike( $prefix, $dbr->anyString() ),
			];
			$conds[] = $dbr->makeList( $condition, LIST_AND );
		}

		$table = 'page';
		$fields = [ 'page_id', 'page_namespace', 'page_title' ];
		$conds = $dbr->makeList( $conds, LIST_OR );
		$options = [
			'LIMIT' => $limit,
			'ORDER BY' => [ 'page_title', 'page_namespace' ],
			'OFFSET' => $offset
		];

		$res = $dbr->select( $table, $fields, $conds, __METHOD__, $options );

		return iterator_to_array( TitleArray::newFromResult( $res ) );
	}

	/**
	 * Validate an array of numerical namespace indexes
	 *
	 * @param array $namespaces
	 * @return array (default: contains only NS_MAIN)
	 */
	protected function validateNamespaces( $namespaces ) {
		// We will look at each given namespace against content language namespaces
		$validNamespaces = MediaWikiServices::getInstance()->getContentLanguage()->getNamespaces();
		if ( is_array( $namespaces ) && count( $namespaces ) > 0 ) {
			$valid = [];
			foreach ( $namespaces as $ns ) {
				if ( is_numeric( $ns ) && array_key_exists( $ns, $validNamespaces ) ) {
					$valid[] = $ns;
				}
			}
			if ( count( $valid ) > 0 ) {
				return $valid;
			}
		}

		return [ NS_MAIN ];
	}
}
