DetachedSong: fork of struct Song

From now on, struct Song will be used by the database only, and
DetachedSong will be used by everybody else.  DetachedSong is easier
to use, but Song has lower overhead.

src/DetachedSong.cxx

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2003-2014 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.
+ */
+
+#include "config.h"
+#include "DetachedSong.hxx"
+#include "Song.hxx"
+#include "util/UriUtil.hxx"
+#include "fs/Traits.hxx"
+
+DetachedSong::DetachedSong(const Song &other)
+	:uri(other.GetURI().c_str()),
+	 tag(other.tag != nullptr ? *other.tag : Tag()),
+	 mtime(other.mtime),
+	 start_ms(other.start_ms), end_ms(other.end_ms) {}
+
+bool
+DetachedSong::IsRemote() const
+{
+	return uri_has_scheme(uri.c_str());
+}
+
+bool
+DetachedSong::IsAbsoluteFile() const
+{
+	return PathTraitsUTF8::IsAbsolute(uri.c_str());
+}
+
+double
+DetachedSong::GetDuration() const
+{
+	if (end_ms > 0)
+		return (end_ms - start_ms) / 1000.0;
+
+	return tag.time - start_ms / 1000.0;
+}