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diff --git a/src/DatabasePlugin.hxx b/src/DatabasePlugin.hxx
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+/*
+ * Copyright (C) 2003-2011 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * 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.
+ */
+
+/** \file
+ *
+ * This header declares the db_plugin class.  It describes a
+ * plugin API for databases of song metadata.
+ */
+
+#ifndef MPD_DATABASE_PLUGIN_HXX
+#define MPD_DATABASE_PLUGIN_HXX
+
+#include "DatabaseVisitor.hxx"
+#include "gcc.h"
+
+extern "C" {
+#include "tag.h"
+}
+
+struct config_param;
+struct DatabaseSelection;
+struct db_visitor;
+
+struct DatabaseStats {
+	/**
+	 * Number of songs.
+	 */
+	unsigned song_count;
+
+	/**
+	 * Total duration of all songs (in seconds).
+	 */
+	unsigned long total_duration;
+
+	/**
+	 * Number of distinct artist names.
+	 */
+	unsigned artist_count;
+
+	/**
+	 * Number of distinct album names.
+	 */
+	unsigned album_count;
+
+	void Clear() {
+		song_count = 0;
+		total_duration = 0;
+		artist_count = album_count = 0;
+	}
+};
+
+class Database {
+public:
+	/**
+	 * Free instance data.
+         */
+	virtual ~Database() {}
+
+	/**
+         * Open the database.  Read it into memory if applicable.
+	 */
+	virtual bool Open(gcc_unused GError **error_r) {
+		return true;
+	}
+
+	/**
+         * Close the database, free allocated memory.
+	 */
+	virtual void Close() {}
+
+	/**
+         * Look up a song (including tag data) in the database.  When
+         * you don't need this anymore, call ReturnSong().
+	 *
+	 * @param uri_utf8 the URI of the song within the music
+	 * directory (UTF-8)
+	 */
+	virtual struct song *GetSong(const char *uri_utf8,
+				     GError **error_r) const = 0;
+
+	/**
+	 * Mark the song object as "unused".  Call this on objects
+	 * returned by GetSong().
+	 */
+	virtual void ReturnSong(struct song *song) const = 0;
+
+	/**
+	 * Visit the selected entities.
+	 */
+	virtual bool Visit(const DatabaseSelection &selection,
+			   VisitDirectory visit_directory,
+			   VisitSong visit_song,
+			   VisitPlaylist visit_playlist,
+			   GError **error_r) const = 0;
+
+	bool Visit(const DatabaseSelection &selection,
+		   VisitDirectory visit_directory,
+		   VisitSong visit_song,
+		   GError **error_r) const {
+		return Visit(selection, visit_directory, visit_song,
+			     VisitPlaylist(), error_r);
+	}
+
+	bool Visit(const DatabaseSelection &selection, VisitSong visit_song,
+		   GError **error_r) const {
+		return Visit(selection, VisitDirectory(), visit_song, error_r);
+	}
+
+	/**
+	 * Visit all unique tag values.
+	 */
+	virtual bool VisitUniqueTags(const DatabaseSelection &selection,
+				     enum tag_type tag_type,
+				     VisitString visit_string,
+				     GError **error_r) const = 0;
+
+	virtual bool GetStats(const DatabaseSelection &selection,
+			      DatabaseStats &stats,
+			      GError **error_r) const = 0;
+};
+
+struct DatabasePlugin {
+	const char *name;
+
+	/**
+	 * Allocates and configures a database.
+	 */
+	Database *(*create)(const struct config_param *param,
+			    GError **error_r);
+};
+
+#endif