mpdclient: rewrite the "fancy swap" code

This is a trick to keep playlist swaps cheap: ncmpc tries to predict
the new playlist.

diff --git a/src/mpdclient.c b/src/mpdclient.c
index d60436946a378753538c1711cb653d0ce4bc9c16..9efb5b5a5fc81702c6a61b0b6bcec0e04fc5fe7c 100644 (file)
--- a/src/mpdclient.c
+++ b/src/mpdclient.c
@@ -32,8 +32,6 @@
 #include <time.h>
 #include <string.h>
 
-#define ENABLE_FANCY_PLAYLIST_MANAGMENT_CMD_MOVE
-
 #define BUFSIZE 1024
 
 static bool
@@ -592,8 +590,8 @@ mpdclient_cmd_delete_range(struct mpdclient *c, unsigned start, unsigned end)
 gint
 mpdclient_cmd_move(struct mpdclient *c, gint old_index, gint new_index)
 {
-       gint n;
-       struct mpd_song *song1, *song2;
+       const struct mpd_song *song1, *song2;
+       struct mpd_status *status;
 
        if (MPD_ERROR(c))
                return -1;
@@ -605,22 +603,39 @@ mpdclient_cmd_move(struct mpdclient *c, gint old_index, gint new_index)
        song1 = playlist_get(&c->playlist, old_index);
        song2 = playlist_get(&c->playlist, new_index);
 
-       /* send the move command to mpd */
-       mpd_send_swap_id(c->connection,
-                        mpd_song_get_id(song1), mpd_song_get_id(song2));
-       if( (n=mpdclient_finish_command(c)) )
-               return n;
-
-#ifdef ENABLE_FANCY_PLAYLIST_MANAGMENT_CMD_MOVE
-       /* update the playlist */
-       playlist_swap(&c->playlist, old_index, new_index);
+       /* send the delete command to mpd; at the same time, get the
+          new status (to verify the playlist id) */
 
-       /* increment the playlist id, so we don't retrieve a new playlist */
-       c->playlist.version++;
-#endif
+       if (!mpd_command_list_begin(c->connection, false) ||
+           !mpd_send_swap_id(c->connection, mpd_song_get_id(song1),
+                             mpd_song_get_id(song2)) ||
+           !mpd_send_status(c->connection) ||
+           !mpd_command_list_end(c->connection))
+               return mpdclient_handle_error(c);
 
        c->events |= MPD_IDLE_PLAYLIST;
 
+       status = mpd_recv_status(c->connection);
+       if (status != NULL) {
+               if (c->status != NULL)
+                       mpd_status_free(c->status);
+               c->status = status;
+       }
+
+       if (!mpd_response_finish(c->connection))
+               return mpdclient_handle_error(c);
+
+       if (mpd_status_get_queue_length(status) == playlist_length(&c->playlist) &&
+           mpd_status_get_queue_version(status) == c->playlist.version + 1) {
+               /* the cheap route: match on the new playlist length
+                  and its version, we can keep our local playlist
+                  copy in sync */
+               c->playlist.version = mpd_status_get_queue_version(status);
+
+               /* swap songs in the local playlist */
+               playlist_swap(&c->playlist, old_index, new_index);
+       }
+
        return 0;
 }