smartplaylist: allow exporting item fields

Allow generating extm3u playlists so that they contain additional item fields such as the `id`.

The feature is required by the mgoltzsche/beets-webm3u plugin (M3U server) to transform playlists using a request based item URI template which may require additional fields such as the `id`, e.g. `beets:library:track;$id`.

5 files changed, 83 insertions, 5 deletions

diff --git a/beetsplug/smartplaylist.py b/beetsplug/smartplaylist.py
index 12a1c9218..7e16d3390 100644
--- a/beetsplug/smartplaylist.py
+++ b/beetsplug/smartplaylist.py
@@ -16,6 +16,7 @@
 """
 
 
+import json
 import os
 from urllib.request import pathname2url
 
@@ -46,6 +47,7 @@ class SmartPlaylistPlugin(BeetsPlugin):
                 "auto": True,
                 "playlists": [],
                 "uri_format": None,
+                "fields": [],
                 "forward_slash": False,
                 "prefix": "",
                 "urlencode": False,
@@ -297,7 +299,7 @@ class SmartPlaylistPlugin(BeetsPlugin):
                     item_uri = prefix + item_uri
 
                 if item_uri not in m3us[m3u_name]:
-                    m3us[m3u_name].append({"item": item, "uri": item_uri})
+                    m3us[m3u_name].append(PlaylistItem(item, item_uri))
                     if pretend and self.config["pretend_paths"]:
                         print(displayable_path(item_uri))
                     elif pretend:
@@ -317,16 +319,23 @@ class SmartPlaylistPlugin(BeetsPlugin):
                     raise Exception(msg.format(pl_format))
                 m3u8 = pl_format == "m3u8"
                 with open(syspath(m3u_path), "wb") as f:
+                    keys = []
                     if m3u8:
+                        keys = self.config["fields"].get(list)
                         f.write(b"#EXTM3U\n")
                     for entry in m3us[m3u]:
-                        item = entry["item"]
+                        item = entry.item
                         comment = ""
                         if m3u8:
-                            comment = "#EXTINF:{},{} - {}\n".format(
-                                int(item.length), item.artist, item.title
+                            attr = [(k, entry.item[k]) for k in keys]
+                            al = [
+                                f" {a[0]}={json.dumps(str(a[1]))}" for a in attr
+                            ]
+                            attrs = "".join(al)
+                            comment = "#EXTINF:{}{},{} - {}\n".format(
+                                int(item.length), attrs, item.artist, item.title
                             )
-                        f.write(comment.encode("utf-8") + entry["uri"] + b"\n")
+                        f.write(comment.encode("utf-8") + entry.uri + b"\n")
             # Send an event when playlists were updated.
             send_event("smartplaylist_update")
 
@@ -339,3 +348,9 @@ class SmartPlaylistPlugin(BeetsPlugin):
             self._log.info(
                 "{0} playlists updated", len(self._matched_playlists)
             )
+
+
+class PlaylistItem:
+    def __init__(self, item, uri):
+        self.item = item
+        self.uri = uri
diff --git a/docs/changelog.rst b/docs/changelog.rst
index fad853fee..ce6442c3a 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -160,6 +160,7 @@ New features:
   like the other lossless formats.
 * Add support for `barcode` field.
   :bug:`3172`
+* :doc:`/plugins/smartplaylist`: Add new config option `smartplaylist.fields`.
 
 Bug fixes:
 
diff --git a/docs/plugins/index.rst b/docs/plugins/index.rst
index 0da487b03..06b4bd256 100644
--- a/docs/plugins/index.rst
+++ b/docs/plugins/index.rst
@@ -313,6 +313,9 @@ Interoperability
    Automatically notifies `Subsonic`_ whenever the beets
    library changes.
 
+`webm3u`_
+   Serves the (:doc:`smartplaylist <smartplaylist>` plugin generated) M3U
+   playlists via HTTP.
 
 .. _AURA: https://auraspec.readthedocs.io
 .. _Emby: https://emby.media
@@ -321,6 +324,7 @@ Interoperability
 .. _Kodi: https://kodi.tv
 .. _Sonos: https://sonos.com
 .. _Subsonic: http://www.subsonic.org/
+.. _webm3u: https://github.com/mgoltzsche/beets-webm3u
 
 Miscellaneous
 -------------
diff --git a/docs/plugins/smartplaylist.rst b/docs/plugins/smartplaylist.rst
index a40d18882..057f9910d 100644
--- a/docs/plugins/smartplaylist.rst
+++ b/docs/plugins/smartplaylist.rst
@@ -123,6 +123,12 @@ other configuration options are:
   When this option is specified, the local path-related options ``prefix``,
   ``relative_to``, ``forward_slash`` and ``urlencode`` are ignored.
 - **output**: Specify the playlist format: m3u|m3u8. Default ``m3u``.
+- **fields**: Specify the names of the additional item fields to export into
+  the playlist. This allows using e.g. the ``id`` field within other tools such
+  as the `webm3u`_ plugin.
+  To use this option, you must set the ``output`` option to ``m3u8``.
+
+.. _webm3u: https://github.com/mgoltzsche/beets-webm3u
 
 For many configuration options, there is a corresponding CLI option, e.g.
 ``--playlist-dir``, ``--relative-to``, ``--prefix``, ``--forward-slash``,
diff --git a/test/plugins/test_smartplaylist.py b/test/plugins/test_smartplaylist.py
index ee3bfb8ce..15841640b 100644
--- a/test/plugins/test_smartplaylist.py
+++ b/test/plugins/test_smartplaylist.py
@@ -241,6 +241,58 @@ class SmartPlaylistTest(_common.TestCase):
             + b"http://beets:8337/files/tagada.mp3\n",
         )
 
+    def test_playlist_update_output_m3u8_fields(self):
+        spl = SmartPlaylistPlugin()
+
+        i = MagicMock()
+        type(i).artist = PropertyMock(return_value="Fake Artist")
+        type(i).title = PropertyMock(return_value="fake Title")
+        type(i).length = PropertyMock(return_value=300.123)
+        type(i).path = PropertyMock(return_value=b"/tagada.mp3")
+        a = {"id": 456, "genre": "Fake Genre"}
+        i.__getitem__.side_effect = a.__getitem__
+        i.evaluate_template.side_effect = lambda pl, _: pl.replace(
+            b"$title",
+            b"ta:ga:da",
+        ).decode()
+
+        lib = Mock()
+        lib.replacements = CHAR_REPLACE
+        lib.items.return_value = [i]
+        lib.albums.return_value = []
+
+        q = Mock()
+        a_q = Mock()
+        pl = b"$title-my<playlist>.m3u", (q, None), (a_q, None)
+        spl._matched_playlists = [pl]
+
+        dir = bytestring_path(mkdtemp())
+        config["smartplaylist"]["output"] = "m3u8"
+        config["smartplaylist"]["relative_to"] = False
+        config["smartplaylist"]["playlist_dir"] = py3_path(dir)
+        config["smartplaylist"]["fields"] = ["id", "genre"]
+        try:
+            spl.update_playlists(lib)
+        except Exception:
+            rmtree(syspath(dir))
+            raise
+
+        lib.items.assert_called_once_with(q, None)
+        lib.albums.assert_called_once_with(a_q, None)
+
+        m3u_filepath = path.join(dir, b"ta_ga_da-my_playlist_.m3u")
+        self.assertExists(m3u_filepath)
+        with open(syspath(m3u_filepath), "rb") as f:
+            content = f.read()
+        rmtree(syspath(dir))
+
+        self.assertEqual(
+            content,
+            b"#EXTM3U\n"
+            + b'#EXTINF:300 id="456" genre="Fake Genre",Fake Artist - fake Title\n'
+            + b"/tagada.mp3\n",
+        )
+
     def test_playlist_update_uri_format(self):
         spl = SmartPlaylistPlugin()