From 5a261507173d28c762ba4f605d7983d928d4bf24 Mon Sep 17 00:00:00 2001
From: wm4 <wm4@nowhere>
Date: Sat, 28 Dec 2019 21:32:03 +0100
Subject: command: add a playlist-unshuffle command

Has a number of restrictions.

See: #2491, #7294
---
 DOCS/man/input.rst |  6 ++++++
 common/playlist.c  | 22 ++++++++++++++++++++++
 common/playlist.h  |  4 ++++
 player/command.c   | 10 ++++++++++
 4 files changed, 42 insertions(+)

diff --git a/DOCS/man/input.rst b/DOCS/man/input.rst
index 1d66dc47bc..d6430581a8 100644
--- a/DOCS/man/input.rst
+++ b/DOCS/man/input.rst
@@ -426,6 +426,12 @@ Remember to quote string arguments in input.conf (see `Flat command syntax`_).
     Shuffle the playlist. This is similar to what is done on start if the
     ``--shuffle`` option is used.
 
+``playlist-unshuffle``
+    Attempt to revert the previous ``playlist-shuffle`` command. This works
+    only once (multiple successive ``playlist-unshuffle`` commands do nothing).
+    May not work correctly if new recursive playlists have been opened since
+    a ``playlist-shuffle`` command.
+
 ``run <command> [<arg1> [<arg2> [...]]]``
     Run the given command. Unlike in MPlayer/mplayer2 and earlier versions of
     mpv (0.2.x and older), this doesn't call the shell. Instead, the command
diff --git a/common/playlist.c b/common/playlist.c
index 300fc48bf9..1fd202b98f 100644
--- a/common/playlist.c
+++ b/common/playlist.c
@@ -33,6 +33,7 @@ struct playlist_entry *playlist_entry_new(const char *filename)
     char *local_filename = mp_file_url_to_filename(e, bstr0(filename));
     e->filename = local_filename ? local_filename : talloc_strdup(e, filename);
     e->stream_flags = STREAM_ORIGIN_DIRECT;
+    e->original_index = -1;
     return e;
 }
 
@@ -141,6 +142,8 @@ void playlist_add_file(struct playlist *pl, const char *filename)
 
 void playlist_shuffle(struct playlist *pl)
 {
+    for (int n = 0; n < pl->num_entries; n++)
+        pl->entries[n]->original_index = n;
     for (int n = 0; n < pl->num_entries - 1; n++) {
         int j = (int)((double)(pl->num_entries - n) * rand() / (RAND_MAX + 1.0));
         MPSWAP(struct playlist_entry *, pl->entries[n], pl->entries[n + j]);
@@ -148,6 +151,25 @@ void playlist_shuffle(struct playlist *pl)
     playlist_update_indexes(pl, 0, -1);
 }
 
+#define CMP_INT(a, b) ((a) == (b) ? 0 : ((a) > (b) ? 1 : -1))
+
+static int cmp_unshuffle(const void *a, const void *b)
+{
+    struct playlist_entry *ea = *(struct playlist_entry **)a;
+    struct playlist_entry *eb = *(struct playlist_entry **)b;
+
+    if (ea->original_index >= 0 && ea->original_index != eb->original_index)
+        return CMP_INT(ea->original_index, eb->original_index);
+    return CMP_INT(ea->pl_index, eb->pl_index);
+}
+
+void playlist_unshuffle(struct playlist *pl)
+{
+    if (pl->num_entries)
+        qsort(pl->entries, pl->num_entries, sizeof(pl->entries[0]), cmp_unshuffle);
+    playlist_update_indexes(pl, 0, -1);
+}
+
 // (Explicitly ignores current_was_replaced.)
 struct playlist_entry *playlist_get_first(struct playlist *pl)
 {
diff --git a/common/playlist.h b/common/playlist.h
index d0f17e315f..8b014e864d 100644
--- a/common/playlist.h
+++ b/common/playlist.h
@@ -42,6 +42,9 @@ struct playlist_entry {
     char **redirects;
     int num_redirects;
 
+    // Used for unshuffling: the pl_index before it was shuffled. -1 => unknown.
+    int original_index;
+
     // Set to true if playback didn't seem to work, or if the file could be
     // played only for a very short time. This is used to make playlist
     // navigation just work in case the user has unplayable files in the
@@ -87,6 +90,7 @@ void playlist_move(struct playlist *pl, struct playlist_entry *entry,
 
 void playlist_add_file(struct playlist *pl, const char *filename);
 void playlist_shuffle(struct playlist *pl);
+void playlist_unshuffle(struct playlist *pl);
 struct playlist_entry *playlist_get_first(struct playlist *pl);
 struct playlist_entry *playlist_get_last(struct playlist *pl);
 struct playlist_entry *playlist_get_next(struct playlist *pl, int direction);
diff --git a/player/command.c b/player/command.c
index 084fd0fc4e..0a17a1def4 100644
--- a/player/command.c
+++ b/player/command.c
@@ -4916,6 +4916,15 @@ static void cmd_playlist_shuffle(void *p)
     mp_notify(mpctx, MP_EVENT_CHANGE_PLAYLIST, NULL);
 }
 
+static void cmd_playlist_unshuffle(void *p)
+{
+    struct mp_cmd_ctx *cmd = p;
+    struct MPContext *mpctx = cmd->mpctx;
+
+    playlist_unshuffle(mpctx->playlist);
+    mp_notify(mpctx, MP_EVENT_CHANGE_PLAYLIST, NULL);
+}
+
 static void cmd_stop(void *p)
 {
     struct mp_cmd_ctx *cmd = p;
@@ -5629,6 +5638,7 @@ const struct mp_cmd_def mp_cmds[] = {
         .priv = &(const int){-1},
     },
     { "playlist-shuffle", cmd_playlist_shuffle, },
+    { "playlist-unshuffle", cmd_playlist_unshuffle, },
     { "sub-step", cmd_sub_step_seek, { OPT_INT("skip", v.i, 0) },
         .allow_auto_repeat = true, .priv = &(const bool){true} },
     { "sub-seek", cmd_sub_step_seek, { OPT_INT("skip", v.i, 0) },
-- 
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