smartplaylist: add --uri-template option

Beets web API already allows remote players to access audio files but it doesn't provide a way to expose the playlists defined using the smartplaylist plugin.
Now the smartplaylist plugin provides an option to generate ID-based item URIs/URLs instead of paths.
Once playlists are generated this way, they can be served using a regular HTTP server such as nginx.

To provide sufficient flexibility for the plethora of potential beets integrations (e.g. beets API, beets API with context path, AURA API, mopidy resource URI, etc), the new option has been defined as a template with an `$id` placeholder (assuming each integration requires a different path schema but they all rely on using the beets item `id` as identifier/path segment).

To prevent local path-related plugin configuration from leaking into a HTTP URL-based playlist generation (invoked with CLI option in addition to the local playlists generated into another directory), setting the new option makes the plugin ignore the other path-related options `prefix`, `relative_to`, `forward_slash` and `urlencode`.

Usage example: `beet splupdate --uri-template 'http://beets:8337/item/$id/file'`

(While it was already possible to generate playlists containing HTTP URLs previously using the `prefix` option, it did not allow to generate ID-based URLs pointing to the beets web API but required to expose the audio files using a web server directly and refer to them using their file system path.)

Relates to beetbox#5037

beetsplug/smartplaylist.py

@@ -45,6 +45,7 @@ def __init__(self):
                 "playlist_dir": ".",
                 "auto": True,
                 "playlists": [],
+                "uri_template": None,
                 "forward_slash": False,
                 "prefix": "",
                 "urlencode": False,
@@ -72,6 +73,13 @@ def commands(self):
             action="store_true",
             help="display query results but don't write playlist files.",
         )
+        spl_update.parser.add_option(
+            "--uri-template",
+            dest="uri_template",
+            metavar="TPL",
+            type="string",
+            help="playlist item URI template, e.g. http://beets/item/$id/file.",
+        )
         spl_update.parser.add_option(
             "--extm3u",
             action="store_true",
@@ -208,6 +216,7 @@ def update_playlists(self, lib, extm3u=None, pretend=False):
                 "Updating {0} smart playlists...", len(self._matched_playlists)
             )
 
+        tpl = self.config["uri_template"].get()
         playlist_dir = self.config["playlist_dir"].as_filename()
         playlist_dir = bytestring_path(playlist_dir)
         relative_to = self.config["relative_to"].get()
@@ -238,13 +247,22 @@ def update_playlists(self, lib, extm3u=None, pretend=False):
                 m3u_name = sanitize_path(m3u_name, lib.replacements)
                 if m3u_name not in m3us:
                     m3us[m3u_name] = []
-                item_path = item.path
-                if relative_to:
-                    item_path = os.path.relpath(item.path, relative_to)
-                if item_path not in m3us[m3u_name]:
-                    m3us[m3u_name].append({"item": item, "path": item_path})
+                item_uri = item.path
+                if tpl:
+                    item_uri = tpl.replace("$id", str(item.id)).encode("utf-8")
+                else:
+                    if relative_to:
+                        item_uri = os.path.relpath(item_uri, relative_to)
+                    if self.config["forward_slash"].get():
+                        item_uri = path_as_posix(item_uri)
+                    if self.config["urlencode"]:
+                        item_uri = bytestring_path(pathname2url(item_uri))
+                    item_uri = prefix + item_uri
+
+                if item_uri not in m3us[m3u_name]:
+                    m3us[m3u_name].append({"item": item, "uri": item_uri})
                     if pretend and self.config["pretend_paths"]:
-                        print(displayable_path(item_path))
+                        print(displayable_path(item_uri))
                     elif pretend:
                         print(item)
 
@@ -261,18 +279,13 @@ def update_playlists(self, lib, extm3u=None, pretend=False):
                     if extm3u:
                         f.write(b"#EXTM3U\n")
                     for entry in m3us[m3u]:
-                        path = entry["path"]
                         item = entry["item"]
-                        if self.config["forward_slash"].get():
-                            path = path_as_posix(path)
-                        if self.config["urlencode"]:
-                            path = bytestring_path(pathname2url(path))
                         comment = ""
                         if extm3u:
                             comment = "#EXTINF:{},{} - {}\n".format(
                                 int(item.length), item.artist, item.title
                             )
-                        f.write(comment.encode("utf-8") + prefix + path + b"\n")
+                        f.write(comment.encode("utf-8") + entry["uri"] + b"\n")
             # Send an event when playlists were updated.
             send_event("smartplaylist_update")
 

docs/changelog.rst

@@ -148,7 +148,8 @@ New features:
   `synced` option to prefer synced lyrics over plain lyrics.
 * :ref:`import-cmd`: Expose import.quiet_fallback as CLI option.
 * :ref:`import-cmd`: Expose `import.incremental_skip_later` as CLI option.
-* :doc:`/plugins/smartplaylist`: Add new config option `smartplaylist.extm3u`.
+* :doc:`/plugins/smartplaylist`: Add new option `smartplaylist.extm3u`.
+* :doc:`/plugins/smartplaylist`: Add new option `smartplaylist.uri_template`.
 
 Bug fixes:
 

docs/plugins/smartplaylist.rst

@@ -119,3 +119,7 @@ other configuration options are:
 - **pretend_paths**: When running with ``--pretend``, show the actual file
   paths that will be written to the m3u file. Default: ``false``.
 - **extm3u**: Generate extm3u/m3u8 playlists. Default ``ǹo``.
+- **uri_template**: Template with an ``$id`` placeholder used generate a
+  playlist item URI, e.g. ``http://beets/item/$id/file``.
+  When this option is specified, the local path-related options ``prefix``,
+  ``relative_to``, ``forward_slash`` and ``urlencode`` are ignored.