player: make watch later/resume work when "playing" directories

If you do "mpv /bla/", and then branch out into sub-directories using
playlist navigation, and then used quit and watch later, then playing
the same directory did not resume from the previous point. This was
because resuming is based on the path hash, so a path prefix can't be
detected when resuming the parent directory.

Solve this by writing each path prefix when playing directories is
involved. (This includes all parent paths, so interestingly, "mpv /"
would also resume in the above example.)

Something like this was requested multiple times, and I want it too.

6 files changed, 98 insertions, 9 deletions

diff --git a/common/playlist.c b/common/playlist.c
index 9fd087be67..fe197a8ded 100644
--- a/common/playlist.c
+++ b/common/playlist.c
@@ -206,6 +206,18 @@ void playlist_add_base_path(struct playlist *pl, bstr base_path)
     }
 }
 
+// Add redirected_from as new redirect entry to each item in pl.
+void playlist_add_redirect(struct playlist *pl, const char *redirected_from)
+{
+    for (struct playlist_entry *e = pl->first; e; e = e->next) {
+        if (e->num_redirects >= 10) // arbitrary limit for sanity
+            break;
+        char *s = talloc_strdup(e, redirected_from);
+        if (s)
+            MP_TARRAY_APPEND(e, e->redirects, e->num_redirects, s);
+    }
+}
+
 // Move all entries from source_pl to pl, appending them after the current entry
 // of pl. source_pl will be empty, and all entries have changed ownership to pl.
 void playlist_transfer_entries(struct playlist *pl, struct playlist *source_pl)
diff --git a/common/playlist.h b/common/playlist.h
index be9fd991e2..b2861b5230 100644
--- a/common/playlist.h
+++ b/common/playlist.h
@@ -36,6 +36,11 @@ struct playlist_entry {
 
     char *title;
 
+    // If the user plays a playlist, then the playlist's URL will be appended
+    // as redirect to each entry. (Same for directories etc.)
+    char **redirects;
+    int num_redirects;
+
     // 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
@@ -88,6 +93,7 @@ void playlist_add_file(struct playlist *pl, const char *filename);
 void playlist_shuffle(struct playlist *pl);
 struct playlist_entry *playlist_get_next(struct playlist *pl, int direction);
 void playlist_add_base_path(struct playlist *pl, bstr base_path);
+void playlist_add_redirect(struct playlist *pl, const char *redirected_from);
 void playlist_transfer_entries(struct playlist *pl, struct playlist *source_pl);
 void playlist_append_entries(struct playlist *pl, struct playlist *source_pl);
 
diff --git a/options/path.c b/options/path.c
index 5072e7312c..adfd2ded3e 100644
--- a/options/path.c
+++ b/options/path.c
@@ -213,6 +213,21 @@ struct bstr mp_dirname(const char *path)
     return ret;
 }
 
+
+#if HAVE_DOS_PATHS
+static const char mp_path_separators[] = "\\/";
+#else
+static const char mp_path_separators[] = "/";
+#endif
+
+// Mutates path and removes a trailing '/' (or '\' on Windows)
+void mp_path_strip_trailing_separator(char *path)
+{
+    size_t len = strlen(path);
+    if (len > 0 && strchr(mp_path_separators, path[len - 1]))
+        path[len - 1] = '\0';
+}
+
 char *mp_splitext(const char *path, bstr *root)
 {
     assert(path);
diff --git a/options/path.h b/options/path.h
index 763a8dda54..203651a931 100644
--- a/options/path.h
+++ b/options/path.h
@@ -65,6 +65,8 @@ char *mp_splitext(const char *path, bstr *root);
  */
 struct bstr mp_dirname(const char *path);
 
+void mp_path_strip_trailing_separator(char *path);
+
 /* Join two path components and return a newly allocated string
  * for the result. '/' is inserted between the components if needed.
  * If p2 is an absolute path then the value of p1 is ignored.
diff --git a/player/configfiles.c b/player/configfiles.c
index db19685c0f..678d60ddc0 100644
--- a/player/configfiles.c
+++ b/player/configfiles.c
@@ -273,11 +273,35 @@ static bool needs_config_quoting(const char *s)
     return false;
 }
 
+static void write_filename(struct MPContext *mpctx, FILE *file, char *filename)
+{
+    if (mpctx->opts->write_filename_in_watch_later_config) {
+        char write_name[1024] = {0};
+        for (int n = 0; filename[n] && n < sizeof(write_name) - 1; n++)
+            write_name[n] = (unsigned char)filename[n] < 32 ? '_' : filename[n];
+        fprintf(file, "# %s\n", write_name);
+    }
+}
+
+static void write_redirect(struct MPContext *mpctx, char *path)
+{
+    char *conffile = mp_get_playback_resume_config_filename(mpctx, path);
+    if (conffile) {
+        FILE *file = fopen(conffile, "wb");
+        if (file) {
+            fprintf(file, "# redirect entry\n");
+            write_filename(mpctx, file, path);
+            fclose(file);
+        }
+        talloc_free(conffile);
+    }
+}
+
 void mp_write_watch_later_conf(struct MPContext *mpctx)
 {
-    char *filename = mpctx->filename;
+    struct playlist_entry *cur = mpctx->playing;
     char *conffile = NULL;
-    if (!filename)
+    if (!cur)
         goto exit;
 
     struct demuxer *demux = mpctx->demuxer;
@@ -288,7 +312,7 @@ void mp_write_watch_later_conf(struct MPContext *mpctx)
 
     mp_mk_config_dir(mpctx->global, MP_WATCH_LATER_CONF);
 
-    conffile = mp_get_playback_resume_config_filename(mpctx, filename);
+    conffile = mp_get_playback_resume_config_filename(mpctx, cur->filename);
     if (!conffile)
         goto exit;
 
@@ -297,12 +321,9 @@ void mp_write_watch_later_conf(struct MPContext *mpctx)
     FILE *file = fopen(conffile, "wb");
     if (!file)
         goto exit;
-    if (mpctx->opts->write_filename_in_watch_later_config) {
-        char write_name[1024] = {0};
-        for (int n = 0; filename[n] && n < sizeof(write_name) - 1; n++)
-            write_name[n] = (unsigned char)filename[n] < 32 ? '_' : filename[n];
-        fprintf(file, "# %s\n", write_name);
-    }
+
+    write_filename(mpctx, file, cur->filename);
+
     double pos = get_current_time(mpctx);
     if (pos != MP_NOPTS_VALUE)
         fprintf(file, "start=%f\n", pos);
@@ -328,6 +349,37 @@ void mp_write_watch_later_conf(struct MPContext *mpctx)
     }
     fclose(file);
 
+    // This allows us to recursively resume directories etc., whose entries are
+    // expanded the first time it's "played". For example, if "/a/b/c.mkv" is
+    // the current entry, then we want to resume this file if the user does
+    // "mpv /a". This would expand to the directory entries in "/a", and if
+    // "/a/a.mkv" is not the first entry, this would be played.
+    // Here, we write resume entries for "/a" and "/a/b".
+    // (Unfortunately, this will leave stray resume files on resume, because
+    // obviously it resumes only from one of those paths.)
+    for (int n = 0; n < cur->num_redirects; n++)
+        write_redirect(mpctx, cur->redirects[n]);
+    // And at last, for local directories, we write an entry for each path
+    // prefix, so the user can resume from an arbitrary directory. This starts
+    // with the first redirect (all other redirects are further prefixes).
+    if (cur->num_redirects) {
+        char *path = cur->redirects[0];
+        char tmp[4096];
+        if (!mp_is_url(bstr0(path)) && strlen(path) < sizeof(tmp)) {
+            snprintf(tmp, sizeof(tmp), "%s", path);
+            for (;;) {
+                bstr dir = mp_dirname(tmp);
+                if (dir.len == strlen(tmp) || !dir.len || bstr_equals0(dir, "."))
+                    break;
+
+                tmp[dir.len] = '\0';
+                if (strlen(tmp) >= 2) // keep "/"
+                    mp_path_strip_trailing_separator(tmp);
+                write_redirect(mpctx, tmp);
+            }
+        }
+    }
+
 exit:
     talloc_free(conffile);
 }
diff --git a/player/loadfile.c b/player/loadfile.c
index 4a7a71f421..ec4d19d3c5 100644
--- a/player/loadfile.c
+++ b/player/loadfile.c
@@ -836,6 +836,8 @@ static void transfer_playlist(struct MPContext *mpctx, struct playlist *pl)
     if (pl->first) {
         prepare_playlist(mpctx, pl);
         struct playlist_entry *new = pl->current;
+        if (mpctx->playlist->current)
+            playlist_add_redirect(pl, mpctx->playlist->current->filename);
         playlist_transfer_entries(mpctx->playlist, pl);
         // current entry is replaced
         if (mpctx->playlist->current)