core/tags/track: Add a function to look up tracks using only the path

I'm struggling to come up with a good way to combine code for this with
code for track_add(), since the lookup mechanism is basically the same.
I'll keep them separate for now and think on it some more.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

core/tags/track.c

@@ -285,6 +285,23 @@ struct track *track_get(const unsigned int index)
 	return TRACK(db_at(&track_db, index));
 }
 
+struct track *track_lookup(const gchar *filepath)
+{
+	struct library *library = library_lookup(filepath);
+	unsigned int offset;
+	struct track *track;
+	gchar *key;
+
+	if (!library)
+		return NULL;
+
+	offset = strlen(library->li_path) + 1;
+	key    = __track_key(library, g_strdup(filepath + offset));
+	track  = TRACK(db_get(&track_db, key));
+	g_free(key);
+	return track;
+}
+
 int track_compare(struct track *lhs, struct track *rhs, enum compare_t compare)
 {
 	switch (compare) {

include/core/tags/track.h

@@ -99,6 +99,9 @@ void track_remove_all(struct library *);
 /* Called to get a track tag with a specific index. */
 struct track *track_get(const unsigned int);
 
+/* Called to look up a track tag using only a filepath. */
+struct track *track_lookup(const gchar *);
+
 /* Called to compare two track tags */
 int track_compare(struct track *, struct track *, enum compare_t);
 

tests/core/tags/track.c

@@ -209,8 +209,14 @@ static void __test_track_db_subprocess()
 	g_assert_cmpuint(track_db_count_unplayed(), ==, 0);
 	g_assert_cmpuint(track_db_count_plays(), ==, 0);
 	g_assert_cmpuint(track_db_average_plays(), ==, 0);
+
+	g_assert_null(track_lookup(NULL));
+	g_assert_null(track_lookup("/home/Zelda/Music/ocarina.ogg"));
+	g_assert_null(track_lookup(path));
+
 	track = track_add(library, path);
 	test_verify_track(track);
+	g_assert(track_lookup(path) == track);
 	g_assert_cmpuint(track_db_count_unplayed(), ==, 1);
 
 	g_assert_null(track_add(library, path));