Initial support for embedded cue sheets found in flac files

So far only seekpoints are supported, so no proper tagging yet
except for track number and track length.
Tagging should be done by parsing the cue sheet which
is often embedded as vorbis comment in flac files.
Furthermore the pathname should be configurable like "%A - %t - %T",
where %A means Artist, %t track number and %T Title or so.

src/decoder/_flac_common.c

@@ -23,9 +23,6 @@
 
 #include <glib.h>
 
-#include <FLAC/format.h>
-#include <FLAC/metadata.h>
-
 #include <assert.h>
 
 void
@@ -349,3 +346,54 @@ flac_common_write(struct flac_data *data, const FLAC__Frame * frame,
 
 	return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
 }
+
+#if defined(FLAC_API_VERSION_CURRENT) && FLAC_API_VERSION_CURRENT > 7
+
+char*
+flac_cue_track(	const char* pathname,
+		const unsigned int tnum)
+{
+	FLAC__StreamMetadata* cs = FLAC__metadata_object_new(FLAC__METADATA_TYPE_CUESHEET);
+
+	FLAC__metadata_get_cuesheet(pathname, &cs);
+
+	if (cs == NULL)
+		return NULL;
+
+	if (cs->data.cue_sheet.num_tracks <= 1)
+	{
+		FLAC__metadata_object_delete(cs);
+		return NULL;
+	}
+
+	if (tnum > 0 && tnum < cs->data.cue_sheet.num_tracks)
+	{
+		char* track = g_strdup_printf("track_%03u.flac", tnum);
+
+		FLAC__metadata_object_delete(cs);
+
+		return track;
+	}
+	else
+	{
+		FLAC__metadata_object_delete(cs);
+		return NULL;
+	}
+}
+
+unsigned int
+flac_vtrack_tnum(const char* fname)
+{
+	/* find last occurrence of '_' in fname
+	 * which is hopefully something like track_xxx.flac
+	 * another/better way would be to use tag struct
+	 */
+	char* ptr = strrchr(fname, '_');
+
+	// copy ascii tracknumber to int
+	char vtrack[4];
+	g_strlcpy(vtrack, ++ptr, 4);
+	return (unsigned int)strtol(vtrack, NULL, 10);
+}
+
+#endif /* FLAC_API_VERSION_CURRENT >= 7 */