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+<?php
+/**
+ * Recent changes filtering by category.
+ *
+ * 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\IDatabase;
+
+/**
+ * The "CategoryFinder" class takes a list of articles, creates an internal
+ * representation of all their parent categories (as well as parents of
+ * parents etc.). From this representation, it determines which of these
+ * articles are in one or all of a given subset of categories.
+ *
+ * Example use :
+ * @code
+ *     # Determines whether the article with the page_id 12345 is in both
+ *     # "Category 1" and "Category 2" or their subcategories, respectively
+ *
+ *     $cf = new CategoryFinder;
+ *     $cf->seed(
+ *         [ 12345 ],
+ *         [ 'Category 1', 'Category 2' ],
+ *         'AND'
+ *     );
+ *     $a = $cf->run();
+ *     print implode( ',' , $a );
+ * @endcode
+ *
+ * @deprecated since 1.31
+ */
+class CategoryFinder {
+	/** @var int[] The original article IDs passed to the seed function */
+	protected $articles = [];
+
+	/** @var array Array of DBKEY category names for categories that don't have a page */
+	protected $deadend = [];
+
+	/** @var array Array of [ ID => [] ] */
+	protected $parents = [];
+
+	/** @var array Array of article/category IDs */
+	protected $next = [];
+
+	/** @var int Max layer depth **/
+	protected $maxdepth = -1;
+
+	/** @var array Array of DBKEY category names */
+	protected $targets = [];
+
+	/** @var array */
+	protected $name2id = [];
+
+	/** @var string "AND" or "OR" */
+	protected $mode;
+
+	/** @var IDatabase Read-DB replica DB */
+	protected $dbr;
+
+	/**
+	 * Initializes the instance. Do this prior to calling run().
+	 * @param array $articleIds Array of article IDs
+	 * @param array $categories FIXME
+	 * @param string $mode FIXME, default 'AND'.
+	 * @param int $maxdepth Maximum layer depth. Where:
+	 * 	-1 means deep recursion (default);
+	 * 	 0 means no-parents;
+	 * 	 1 means one parent layer, etc.
+	 * @todo FIXME: $categories/$mode
+	 */
+	public function seed( $articleIds, $categories, $mode = 'AND', $maxdepth = -1 ) {
+		$this->articles = $articleIds;
+		$this->next = $articleIds;
+		$this->mode = $mode;
+		$this->maxdepth = $maxdepth;
+
+		# Set the list of target categories; convert them to DBKEY form first
+		$this->targets = [];
+		foreach ( $categories as $c ) {
+			$ct = Title::makeTitleSafe( NS_CATEGORY, $c );
+			if ( $ct ) {
+				$c = $ct->getDBkey();
+				$this->targets[$c] = $c;
+			}
+		}
+	}
+
+	/**
+	 * Iterates through the parent tree starting with the seed values,
+	 * then checks the articles if they match the conditions
+	 * @return array Array of page_ids (those given to seed() that match the conditions)
+	 */
+	public function run() {
+		$this->dbr = wfGetDB( DB_REPLICA );
+
+		$i = 0;
+		$dig = true;
+		while ( count( $this->next ) && $dig ) {
+			$this->scanNextLayer();
+
+			// Is there any depth limit?
+			if ( $this->maxdepth !== -1 ) {
+				$dig = $i < $this->maxdepth;
+				$i++;
+			}
+		}
+
+		# Now check if this applies to the individual articles
+		$ret = [];
+
+		foreach ( $this->articles as $article ) {
+			$conds = $this->targets;
+			if ( $this->check( $article, $conds ) ) {
+				# Matches the conditions
+				$ret[] = $article;
+			}
+		}
+		return $ret;
+	}
+
+	/**
+	 * Get the parents. Only really useful if run() has been called already
+	 * @return array
+	 */
+	public function getParents() {
+		return $this->parents;
+	}
+
+	/**
+	 * This functions recurses through the parent representation, trying to match the conditions
+	 * @param int $id The article/category to check
+	 * @param array $conds The array of categories to match
+	 * @param array $path Used to check for recursion loops
+	 * @return bool Does this match the conditions?
+	 */
+	private function check( $id, &$conds, $path = [] ) {
+		// Check for loops and stop!
+		if ( in_array( $id, $path ) ) {
+			return false;
+		}
+
+		$path[] = $id;
+
+		# Shortcut (runtime paranoia): No conditions=all matched
+		if ( count( $conds ) == 0 ) {
+			return true;
+		}
+
+		if ( !isset( $this->parents[$id] ) ) {
+			return false;
+		}
+
+		# iterate through the parents
+		foreach ( $this->parents[$id] as $p ) {
+			$pname = $p->cl_to;
+
+			# Is this a condition?
+			if ( isset( $conds[$pname] ) ) {
+				# This key is in the category list!
+				if ( $this->mode == 'OR' ) {
+					# One found, that's enough!
+					$conds = [];
+					return true;
+				} else {
+					# Assuming "AND" as default
+					unset( $conds[$pname] );
+					if ( count( $conds ) == 0 ) {
+						# All conditions met, done
+						return true;
+					}
+				}
+			}
+
+			# Not done yet, try sub-parents
+			if ( !isset( $this->name2id[$pname] ) ) {
+				# No sub-parent
+				continue;
+			}
+			$done = $this->check( $this->name2id[$pname], $conds, $path );
+			if ( $done || count( $conds ) == 0 ) {
+				# Subparents have done it!
+				return true;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * Scans a "parent layer" of the articles/categories in $this->next
+	 */
+	private function scanNextLayer() {
+		# Find all parents of the article currently in $this->next
+		$layer = [];
+		$res = $this->dbr->select(
+			/* FROM   */ 'categorylinks',
+			/* SELECT */ [ 'cl_to', 'cl_from' ],
+			/* WHERE  */ [ 'cl_from' => $this->next ],
+			__METHOD__ . '-1'
+		);
+		foreach ( $res as $o ) {
+			$k = $o->cl_to;
+
+			# Update parent tree
+			if ( !isset( $this->parents[$o->cl_from] ) ) {
+				$this->parents[$o->cl_from] = [];
+			}
+			$this->parents[$o->cl_from][$k] = $o;
+
+			# Ignore those we already have
+			if ( in_array( $k, $this->deadend ) ) {
+				continue;
+			}
+
+			if ( isset( $this->name2id[$k] ) ) {
+				continue;
+			}
+
+			# Hey, new category!
+			$layer[$k] = $k;
+		}
+
+		$this->next = [];
+
+		# Find the IDs of all category pages in $layer, if they exist
+		if ( count( $layer ) > 0 ) {
+			$res = $this->dbr->select(
+				/* FROM   */ 'page',
+				/* SELECT */ [ 'page_id', 'page_title' ],
+				/* WHERE  */ [ 'page_namespace' => NS_CATEGORY, 'page_title' => $layer ],
+				__METHOD__ . '-2'
+			);
+			foreach ( $res as $o ) {
+				$id = $o->page_id;
+				$name = $o->page_title;
+				$this->name2id[$name] = $id;
+				$this->next[] = $id;
+				unset( $layer[$name] );
+			}
+		}
+
+		# Mark dead ends
+		foreach ( $layer as $v ) {
+			$this->deadend[$v] = $v;
+		}
+	}
+}