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+<?php
+/**
+ * Functions to help implement an external link filter for spam control.
+ *
+ * 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 Wikimedia\Rdbms\LikeMatch;
+
+/**
+ * Some functions to help implement an external link filter for spam control.
+ *
+ * @todo implement the filter. Currently these are just some functions to help
+ * maintenance/cleanupSpam.php remove links to a single specified domain. The
+ * next thing is to implement functions for checking a given page against a big
+ * list of domains.
+ *
+ * Another cool thing to do would be a web interface for fast spam removal.
+ */
+class LinkFilter {
+
+	/**
+	 * Check whether $content contains a link to $filterEntry
+	 *
+	 * @param Content $content Content to check
+	 * @param string $filterEntry Domainparts, see makeRegex() for more details
+	 * @return int 0 if no match or 1 if there's at least one match
+	 */
+	static function matchEntry( Content $content, $filterEntry ) {
+		if ( !( $content instanceof TextContent ) ) {
+			// TODO: handle other types of content too.
+			//      Maybe create ContentHandler::matchFilter( LinkFilter ).
+			//      Think about a common base class for LinkFilter and MagicWord.
+			return 0;
+		}
+
+		$text = $content->getNativeData();
+
+		$regex = self::makeRegex( $filterEntry );
+		return preg_match( $regex, $text );
+	}
+
+	/**
+	 * Builds a regex pattern for $filterEntry.
+	 *
+	 * @param string $filterEntry URL, if it begins with "*.", it'll be
+	 *        replaced to match any subdomain
+	 * @return string Regex pattern, for preg_match()
+	 */
+	private static function makeRegex( $filterEntry ) {
+		$regex = '!http://';
+		if ( substr( $filterEntry, 0, 2 ) == '*.' ) {
+			$regex .= '(?:[A-Za-z0-9.-]+\.|)';
+			$filterEntry = substr( $filterEntry, 2 );
+		}
+		$regex .= preg_quote( $filterEntry, '!' ) . '!Si';
+		return $regex;
+	}
+
+	/**
+	 * Make an array to be used for calls to Database::buildLike(), which
+	 * will match the specified string. There are several kinds of filter entry:
+	 *     *.domain.com    -  Produces http://com.domain.%, matches domain.com
+	 *                        and www.domain.com
+	 *     domain.com      -  Produces http://com.domain./%, matches domain.com
+	 *                        or domain.com/ but not www.domain.com
+	 *     *.domain.com/x  -  Produces http://com.domain.%/x%, matches
+	 *                        www.domain.com/xy
+	 *     domain.com/x    -  Produces http://com.domain./x%, matches
+	 *                        domain.com/xy but not www.domain.com/xy
+	 *
+	 * Asterisks in any other location are considered invalid.
+	 *
+	 * This function does the same as wfMakeUrlIndexes(), except it also takes care
+	 * of adding wildcards
+	 *
+	 * @param string $filterEntry Domainparts
+	 * @param string $protocol Protocol (default http://)
+	 * @return array|bool Array to be passed to Database::buildLike() or false on error
+	 */
+	public static function makeLikeArray( $filterEntry, $protocol = 'http://' ) {
+		$db = wfGetDB( DB_REPLICA );
+
+		$target = $protocol . $filterEntry;
+		$bits = wfParseUrl( $target );
+
+		if ( $bits == false ) {
+			// Unknown protocol?
+			return false;
+		}
+
+		if ( substr( $bits['host'], 0, 2 ) == '*.' ) {
+			$subdomains = true;
+			$bits['host'] = substr( $bits['host'], 2 );
+			if ( $bits['host'] == '' ) {
+				// We don't want to make a clause that will match everything,
+				// that could be dangerous
+				return false;
+			}
+		} else {
+			$subdomains = false;
+		}
+
+		// Reverse the labels in the hostname, convert to lower case
+		// For emails reverse domainpart only
+		if ( $bits['scheme'] === 'mailto' && strpos( $bits['host'], '@' ) ) {
+			// complete email address
+			$mailparts = explode( '@', $bits['host'] );
+			$domainpart = strtolower( implode( '.', array_reverse( explode( '.', $mailparts[1] ) ) ) );
+			$bits['host'] = $domainpart . '@' . $mailparts[0];
+		} elseif ( $bits['scheme'] === 'mailto' ) {
+			// domainpart of email address only, do not add '.'
+			$bits['host'] = strtolower( implode( '.', array_reverse( explode( '.', $bits['host'] ) ) ) );
+		} else {
+			$bits['host'] = strtolower( implode( '.', array_reverse( explode( '.', $bits['host'] ) ) ) );
+			if ( substr( $bits['host'], -1, 1 ) !== '.' ) {
+				$bits['host'] .= '.';
+			}
+		}
+
+		$like[] = $bits['scheme'] . $bits['delimiter'] . $bits['host'];
+
+		if ( $subdomains ) {
+			$like[] = $db->anyString();
+		}
+
+		if ( isset( $bits['port'] ) ) {
+			$like[] = ':' . $bits['port'];
+		}
+		if ( isset( $bits['path'] ) ) {
+			$like[] = $bits['path'];
+		} elseif ( !$subdomains ) {
+			$like[] = '/';
+		}
+		if ( isset( $bits['query'] ) ) {
+			$like[] = '?' . $bits['query'];
+		}
+		if ( isset( $bits['fragment'] ) ) {
+			$like[] = '#' . $bits['fragment'];
+		}
+
+		// Check for stray asterisks: asterisk only allowed at the start of the domain
+		foreach ( $like as $likepart ) {
+			if ( !( $likepart instanceof LikeMatch ) && strpos( $likepart, '*' ) !== false ) {
+				return false;
+			}
+		}
+
+		if ( !( $like[count( $like ) - 1] instanceof LikeMatch ) ) {
+			// Add wildcard at the end if there isn't one already
+			$like[] = $db->anyString();
+		}
+
+		return $like;
+	}
+
+	/**
+	 * Filters an array returned by makeLikeArray(), removing everything past first
+	 * pattern placeholder.
+	 *
+	 * @param array $arr Array to filter
+	 * @return array Filtered array
+	 */
+	public static function keepOneWildcard( $arr ) {
+		if ( !is_array( $arr ) ) {
+			return $arr;
+		}
+
+		foreach ( $arr as $key => $value ) {
+			if ( $value instanceof LikeMatch ) {
+				return array_slice( $arr, 0, $key + 1 );
+			}
+		}
+
+		return $arr;
+	}
+}