player: add loadfile insert-next commands

This commit adds two new commands (`insert-next` and `insert-next-play`)
which mirror the existing commands, `append` and `append-play` in
functionality, with the difference that they insert directly after the
current playlist entry, rather than at the end of the playlist.

This change gives MPV a piece of functionality already found in (for
example) Spotify's media player: "play next". Additionally, using the
new `insert-next` command, users can trivially write a script to play a
new piece of media immediately without otherwise clearing or altering
the remainder of the playlist.

DOCS/man/input.rst

@@ -469,6 +469,12 @@ Remember to quote string arguments in input.conf (see `Flat command syntax`_).
         Append the file, and if nothing is currently playing, start playback.
         (Always starts with the added file, even if the playlist was not empty
         before running this command.)
+    <insert-next>
+        Insert the file into the playlist, directly after the current entry.
+    <insert-next-play>
+        Insert the file next, and if nothing is currently playing, start playback.
+        (Always starts with the added file, even if the playlist was not empty
+        before running this command.)
 
     The third argument is a list of options and values which should be set
     while the file is playing. It is of the form ``opt1=value1,opt2=value2,..``.

common/playlist.c

@@ -70,6 +70,25 @@ void playlist_add(struct playlist *pl, struct playlist_entry *add)
     talloc_steal(pl, add);
 }
 
+// Inserts the entry so that it comes directly after "at" (or move to end, if at==NULL).
+void playlist_insert_next(struct playlist *pl, struct playlist_entry *add,
+                          struct playlist_entry *at)
+{
+    assert(add->filename);
+    assert(!at || at->pl == pl);
+
+    int index = at ? at->pl_index + 1 : pl->num_entries;
+    MP_TARRAY_INSERT_AT(pl, pl->entries, pl->num_entries, index, add);
+
+    add->pl = pl;
+    add->pl_index = index;
+    add->id = ++pl->id_alloc;
+
+    playlist_update_indexes(pl, index, pl->num_entries);
+
+    talloc_steal(pl, add);
+}
+
 void playlist_entry_unref(struct playlist_entry *e)
 {
     e->reserved--;

common/playlist.h

@@ -82,6 +82,10 @@ void playlist_entry_add_params(struct playlist_entry *e,
 struct playlist_entry *playlist_entry_new(const char *filename);
 
 void playlist_add(struct playlist *pl, struct playlist_entry *add);
+
+void playlist_insert_next(struct playlist *pl, struct playlist_entry *entry,
+                          struct playlist_entry *at);
+
 void playlist_remove(struct playlist *pl, struct playlist_entry *entry);
 void playlist_clear(struct playlist *pl);
 void playlist_clear_except_current(struct playlist *pl);

player/command.c

@@ -5527,9 +5527,13 @@ static void cmd_loadfile(void *p)
     struct mp_cmd_ctx *cmd = p;
     struct MPContext *mpctx = cmd->mpctx;
     char *filename = cmd->args[0].v.s;
-    int append = cmd->args[1].v.i;
+    int action = cmd->args[1].v.i;
 
-    if (!append)
+    bool replace = (action == 0);
+    bool insert_next = (action == 3 || action == 4);
+    bool play = (action == 2 || action == 4);
+
+    if (replace)
         playlist_clear(mpctx->playlist);
 
     struct playlist_entry *entry = playlist_entry_new(filename);
@@ -5538,13 +5542,18 @@ static void cmd_loadfile(void *p)
         for (int i = 0; pairs[i] && pairs[i + 1]; i += 2)
             playlist_entry_add_param(entry, bstr0(pairs[i]), bstr0(pairs[i + 1]));
     }
-    playlist_add(mpctx->playlist, entry);
+
+    if (insert_next) {
+        playlist_insert_next(mpctx->playlist, entry, mpctx->playlist->current);
+    } else {
+        playlist_add(mpctx->playlist, entry);
+    }
 
     struct mpv_node *res = &cmd->result;
     node_init(res, MPV_FORMAT_NODE_MAP, NULL);
     node_map_add_int64(res, "playlist_entry_id", entry->id);
 
-    if (!append || (append == 2 && !mpctx->playlist->current)) {
+    if (replace || (play && !mpctx->playlist->current)) {
         if (mpctx->opts->position_save_on_quit) // requested in issue #1148
             mp_write_watch_later_conf(mpctx);
         mp_set_playlist_entry(mpctx, entry);
@@ -6681,7 +6690,9 @@ const struct mp_cmd_def mp_cmds[] = {
             {"flags", OPT_CHOICE(v.i,
                 {"replace", 0},
                 {"append", 1},
-                {"append-play", 2}),
+                {"append-play", 2},
+                {"insert-next", 3},
+                {"insert-next-play", 4}),
                 .flags = MP_CMD_OPT_ARG},
             {"options", OPT_KEYVALUELIST(v.str_list), .flags = MP_CMD_OPT_ARG},
         },