DatabasePlugin: add method GetStats()

Optimize the ProxyDatabase by invoking "stats" on the peer, instead of
visiting all songs.

src/DatabaseHelpers.cxx

@@ -76,3 +76,59 @@ VisitUniqueTags(const Database &db, const DatabaseSelection &selection,
 
 	return true;
 }
+
+static void
+StatsVisitTag(DatabaseStats &stats, StringSet &artists, StringSet &albums,
+	      const struct tag &tag)
+{
+	if (tag.time > 0)
+		stats.total_duration += tag.time;
+
+	for (unsigned i = 0; i < tag.num_items; ++i) {
+		const struct tag_item &item = *tag.items[i];
+
+		switch (item.type) {
+		case TAG_ARTIST:
+			artists.insert(item.value);
+			break;
+
+		case TAG_ALBUM:
+			albums.insert(item.value);
+			break;
+
+		default:
+			break;
+		}
+	}
+}
+
+static bool
+StatsVisitSong(DatabaseStats &stats, StringSet &artists, StringSet &albums,
+	       song &song)
+{
+	++stats.song_count;
+
+	if (song.tag != nullptr)
+		StatsVisitTag(stats, artists, albums, *song.tag);
+
+	return true;
+}
+
+bool
+GetStats(const Database &db, const DatabaseSelection &selection,
+	 DatabaseStats &stats, GError **error_r)
+{
+	stats.Clear();
+
+	StringSet artists, albums;
+	using namespace std::placeholders;
+	const auto f = std::bind(StatsVisitSong,
+				 std::ref(stats), std::ref(artists),
+				 std::ref(albums), _1);
+	if (!db.Visit(selection, f, error_r))
+		return false;
+
+	stats.artist_count = artists.size();
+	stats.album_count = albums.size();
+	return true;
+}

src/DatabaseHelpers.hxx

@@ -26,6 +26,7 @@
 
 class Database;
 struct DatabaseSelection;
+struct DatabaseStats;
 
 bool
 VisitUniqueTags(const Database &db, const DatabaseSelection &selection,
@@ -33,4 +34,8 @@ VisitUniqueTags(const Database &db, const DatabaseSelection &selection,
 		VisitString visit_string,
 		GError **error_r);
 
+bool
+GetStats(const Database &db, const DatabaseSelection &selection,
+	 DatabaseStats &stats, GError **error_r);
+
 #endif

src/DatabasePlugin.hxx

@@ -37,6 +37,34 @@ 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:
 	/**
@@ -94,6 +122,10 @@ public:
 				     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 {

src/Stats.cxx

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2011 The Music Player Daemon Project
+ * Copyright (C) 2003-2012 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -22,11 +22,8 @@
 extern "C" {
 #include "stats.h"
 #include "database.h"
-#include "tag.h"
-#include "song.h"
 #include "client.h"
 #include "player_control.h"
-#include "strset.h"
 #include "client_internal.h"
 }
 
@@ -34,9 +31,6 @@ extern "C" {
 #include "DatabaseGlue.hxx"
 #include "DatabasePlugin.hxx"
 
-#include <functional>
-#include <set>
-
 struct stats stats;
 
 void stats_global_init(void)
@@ -49,66 +43,27 @@ void stats_global_finish(void)
 	g_timer_destroy(stats.timer);
 }
 
-struct StringLess {
-	gcc_pure
-	bool operator()(const char *a, const char *b) const {
-		return strcmp(a, b) < 0;
-	}
-};
-
-typedef std::set<const char *, StringLess> StringSet;
-
-static void
-visit_tag(StringSet &artists, StringSet &albums, const struct tag *tag)
-{
-	if (tag->time > 0)
-		stats.song_duration += tag->time;
-
-	for (unsigned i = 0; i < tag->num_items; ++i) {
-		const struct tag_item *item = tag->items[i];
-
-		switch (item->type) {
-		case TAG_ARTIST:
-			artists.insert(item->value);
-			break;
-
-		case TAG_ALBUM:
-			albums.insert(item->value);
-			break;
-
-		default:
-			break;
-		}
-	}
-}
-
-static bool
-collect_stats_song(StringSet &artists, StringSet &albums, song &song)
-{
-	++stats.song_count;
-
-	if (song.tag != NULL)
-		visit_tag(artists, albums, song.tag);
-
-	return true;
-}
-
 void stats_update(void)
 {
-	stats.song_count = 0;
-	stats.song_duration = 0;
-	stats.artist_count = 0;
+	GError *error = nullptr;
+
+	DatabaseStats stats2;
 
 	const DatabaseSelection selection("", true);
+	if (GetDatabase()->GetStats(selection, stats2, &error)) {
+		stats.song_count = stats2.song_count;
+		stats.song_duration = stats2.total_duration;
+		stats.artist_count = stats2.artist_count;
+		stats.album_count = stats2.album_count;
+	} else {
+		g_warning("%s", error->message);
+		g_error_free(error);
 
-	StringSet artists, albums;
-	using namespace std::placeholders;
-	const auto f = std::bind(collect_stats_song,
-				 std::ref(artists), std::ref(albums), _1);
-	GetDatabase()->Visit(selection, f, NULL);
-
-	stats.artist_count = artists.size();
-	stats.album_count = albums.size();
+		stats.song_count = 0;
+		stats.song_duration = 0;
+		stats.artist_count = 0;
+		stats.album_count = 0;
+	}
 }
 
 int stats_print(struct client *client)

src/db/ProxyDatabasePlugin.cxx

@@ -67,6 +67,10 @@ public:
 				     VisitString visit_string,
 				     GError **error_r) const override;
 
+	virtual bool GetStats(const DatabaseSelection &selection,
+			      DatabaseStats &stats,
+			      GError **error_r) const override;
+
 protected:
 	bool Configure(const struct config_param *param, GError **error_r);
 };
@@ -420,6 +424,27 @@ ProxyDatabase::VisitUniqueTags(const DatabaseSelection &selection,
 		result;
 }
 
+bool
+ProxyDatabase::GetStats(const DatabaseSelection &selection,
+			DatabaseStats &stats, GError **error_r) const
+{
+	// TODO: match
+	(void)selection;
+
+	struct mpd_stats *stats2 =
+		mpd_run_stats(connection);
+	if (stats2 == nullptr)
+		return CheckError(connection, error_r);
+
+	stats.song_count = mpd_stats_get_number_of_songs(stats2);
+	stats.total_duration = mpd_stats_get_db_play_time(stats2);
+	stats.artist_count = mpd_stats_get_number_of_artists(stats2);
+	stats.album_count = mpd_stats_get_number_of_albums(stats2);
+	mpd_stats_free(stats2);
+
+	return true;
+}
+
 const DatabasePlugin proxy_db_plugin = {
 	"proxy",
 	ProxyDatabase::Create,

src/db/SimpleDatabasePlugin.cxx

@@ -280,6 +280,13 @@ SimpleDatabase::VisitUniqueTags(const DatabaseSelection &selection,
 				 error_r);
 }
 
+bool
+SimpleDatabase::GetStats(const DatabaseSelection &selection,
+			 DatabaseStats &stats, GError **error_r) const
+{
+	return ::GetStats(*this, selection, stats, error_r);
+}
+
 bool
 SimpleDatabase::Save(GError **error_r)
 {

src/db/SimpleDatabasePlugin.hxx

@@ -58,6 +58,7 @@ public:
 
 	virtual bool Open(GError **error_r) override;
 	virtual void Close() override;
+
 	virtual struct song *GetSong(const char *uri_utf8,
 				     GError **error_r) const override;
 	virtual bool Visit(const DatabaseSelection &selection,
@@ -71,6 +72,10 @@ public:
 				     VisitString visit_string,
 				     GError **error_r) const override;
 
+	virtual bool GetStats(const DatabaseSelection &selection,
+			      DatabaseStats &stats,
+			      GError **error_r) const override;
+
 protected:
 	bool Configure(const struct config_param *param, GError **error_r);