fix: m3u file reappended everything when re-downloading the same playlist.

deezspot/libutils/write_m3u.py

@@ -88,32 +88,125 @@ def _get_track_info(track: Track) -> tuple:
         return 'Unknown Artist', 'Unknown Title'
 
 
+def _read_m3u_entries(m3u_path: str) -> List[tuple]:
+    """Parse existing m3u into a list of (extinf_line, path_line) entries after header."""
+    entries: List[tuple] = []
+    if not os.path.exists(m3u_path):
+        return entries
+    try:
+        with open(m3u_path, "r", encoding="utf-8") as f:
+            lines = [line.rstrip('\n') for line in f]
+    except OSError:
+        return entries
+    # Skip header if present
+    idx = 0
+    if idx < len(lines) and lines[idx].strip() == "#EXTM3U":
+        idx += 1
+    while idx < len(lines):
+        line = lines[idx]
+        if not line:
+            idx += 1
+            continue
+        if line.startswith("#EXTINF:"):
+            extinf = line
+            path = ""
+            if idx + 1 < len(lines):
+                path = lines[idx + 1]
+            entries.append((extinf, path))
+            idx += 2
+        else:
+            # Path-only entry
+            entries.append(("", line))
+            idx += 1
+    return entries
+
+
+def _write_m3u_entries(m3u_path: str, entries: List[tuple]) -> None:
+    """Write header and provided entries back to file."""
+    # Ensure folder exists
+    os.makedirs(os.path.dirname(m3u_path), exist_ok=True)
+    with open(m3u_path, "w", encoding="utf-8") as m3u_file:
+        m3u_file.write("#EXTM3U\n")
+        for extinf, path in entries:
+            # Skip empty placeholders
+            if not path and not extinf:
+                continue
+            if extinf:
+                m3u_file.write(f"{extinf}\n")
+            if path:
+                m3u_file.write(f"{path}\n")
+
+
 def append_track_to_m3u(m3u_path: str, track: Union[str, Track]) -> None:
-    """Append a single track to m3u with EXTINF and a resolved path."""
+    """Append a single track to m3u with EXTINF and a resolved path.
+    Idempotent behavior: if entry for same path exists, it is updated/moved to the desired position; if an entry exists at the desired position but differs, it is overwritten.
+    """
     ensure_m3u_header(m3u_path)
+    # Prepare entries and base dir
+    playlist_m3u_dir = os.path.dirname(m3u_path)
+    entries = _read_m3u_entries(m3u_path)
+
+    # Handle simple string path case: dedupe by path, append if new
     if isinstance(track, str):
         resolved = _resolve_existing_song_path(track)
         if not resolved:
             return
-        playlist_m3u_dir = os.path.dirname(m3u_path)
         relative_path = os.path.relpath(resolved, start=playlist_m3u_dir)
-        with open(m3u_path, "a", encoding="utf-8") as m3u_file:
-            m3u_file.write(f"{relative_path}\n")
-    else:
+        # Remove existing entries with same path
+        new_entries = [(e, p) for (e, p) in entries if p != relative_path]
+        # If nothing changed and path already existed identically, skip write
+        if len(new_entries) == len(entries) and any(p == relative_path for _, p in entries):
+            return
+        new_entries.append(("", relative_path))
+        _write_m3u_entries(m3u_path, new_entries)
+        return
+
+    # Validate Track object
     if (not isinstance(track, Track) or 
         not track.success or 
         not hasattr(track, 'song_path')):
         return
+
     resolved = _resolve_existing_song_path(track.song_path)
     if not resolved:
         return
-        playlist_m3u_dir = os.path.dirname(m3u_path)
+
     relative_path = os.path.relpath(resolved, start=playlist_m3u_dir)
     duration = _get_track_duration_seconds(track)
     artist, title = _get_track_info(track)
-        with open(m3u_path, "a", encoding="utf-8") as m3u_file:
-            m3u_file.write(f"#EXTINF:{duration},{artist} - {title}\n")
-            m3u_file.write(f"{relative_path}\n")
+    extinf_line = f"#EXTINF:{duration},{artist} - {title}"
+    new_entry = (extinf_line, relative_path)
+
+    # Determine target playlist position (1-based). Fallback to 0 (append behavior) if missing/invalid.
+    position = 0
+    try:
+        if hasattr(track, 'tags') and track.tags:
+            raw_pos = track.tags.get('playlistnum')
+            if raw_pos is not None:
+                position = int(raw_pos)
+    except (ValueError, TypeError):
+        position = 0
+
+    # Remove duplicates by path first (to avoid multiple occurrences upon re-download)
+    entries = [(e, p) for (e, p) in entries if p != relative_path]
+
+    if position >= 1 and position - 1 < len(entries):
+        # If there is already something at that position, only overwrite if different
+        current = entries[position - 1]
+        if current != new_entry:
+            entries[position - 1] = new_entry
+        else:
+            # Exact match at the correct position: nothing to do
+            return
+    else:
+        # If position beyond current length or not provided: append unless identical exists (path dedup above already handled)
+        # Avoid appending if an identical entry already exists (by both extinf and path)
+        if any(e == new_entry for e in entries):
+            return
+        # If position is within range but entries is shorter, we won't insert placeholders; we simply append to end.
+        entries.append(new_entry)
+
+    _write_m3u_entries(m3u_path, entries)
 
 
 def write_tracks_to_m3u(output_dir: str, playlist_name: str, tracks: List[Track]) -> str: