Add a soundtrack by picking or dropping a folder (#50)

"Add soundtrack…" in the statistics toolbar, or a folder dropped anywhere on
the window, opens a popup that lists the folder's songs and uploads them to
the server, which adds the soundtrack at once (Sansan/MusicServer#33).

- The name comes from the folder and can be changed; characters the server
  refuses are replaced.
- Only MP3s are uploaded, as the server takes no other; other song files
  are listed greyed out as left out. Hidden files are skipped.
- Disc folders are flattened with the disc's number first ("1-01 Title.mp3"),
  as the server wants one folder. With one disc folder, names stay as
  they are.
- Songs are sent one at a time with a progress bar, reading one file at a
  time. A failed song is sent again twice, then the upload is cancelled
  and the server's reason shown. Closing the popup cancels it too.
- Not offered while the server syncs, offline, or without MP3s.
- Afterwards search, the inspiration list and the statistics reload.

The API types come from the server's spec (Upload, UploadFile,
UploadRequest).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/music_server_client.gd

@@ -30,6 +30,8 @@ const CLIENT_TYPE: String = "godot"
 const QUEUE_HEADER: String = "X-Queue-Id"
 ## The type of the JSON bodies sent.
 const JSON_TYPE: String = "application/json"
+## The type of uploaded songs.
+const MP3_TYPE: String = "audio/mpeg"
 ## The files of a MusicPlayer release that can be downloaded: the Windows game, the Linux
 ## game, and the Linux package with an installer.
 const DOWNLOAD_ASSETS: Array[String] = ["windows", "linux", "linux-package"]
@@ -179,6 +181,43 @@ func delete_soundtrack_cover(
 			on_failed)
 
 
+## Starts uploading a new soundtrack called [param name], which is also its folder name on
+## the server, and calls [param on_done] with the [Upload]. Refused when the name is taken
+## or not a valid folder name, or while the server syncs; see [member last_error].
+func start_upload(name: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
+	var request: UploadRequest = UploadRequest.new()
+	request.name = name
+	var path: String = "/soundtracks/uploads"
+	_request(path, HTTPClient.METHOD_POST,
+			_parse_json.bind(path, _as_object.bind(Upload, on_done, on_failed), on_failed),
+			on_failed, true, JSON.stringify(request.to_dict()).to_utf8_buffer())
+
+
+## Sends the MP3 [param song] as [param file_name] in the upload [param upload_id]. A song
+## of the same name is replaced, so a failed song can be sent again.
+func upload_song(upload_id: String, file_name: String, song: PackedByteArray,
+		on_done: Callable, on_failed: Callable = Callable()) -> void:
+	_request(_upload_path(upload_id) + "/files/" + file_name.uri_encode(),
+			HTTPClient.METHOD_PUT, _call_ignoring_body.bind(on_done), on_failed, true, song,
+			MP3_TYPE)
+
+
+## Adds the uploaded songs to the server's library as a new soundtrack and calls
+## [param on_done] with it as a [SoundtrackWithSongList].
+func finish_upload(upload_id: String, on_done: Callable,
+		on_failed: Callable = Callable()) -> void:
+	var path: String = _upload_path(upload_id) + "/finish"
+	_request(path, HTTPClient.METHOD_POST, _parse_json.bind(path,
+			_as_object.bind(SoundtrackWithSongList, on_done, on_failed), on_failed), on_failed)
+
+
+## Deletes the unfinished upload [param upload_id] and its songs.
+func cancel_upload(upload_id: String, on_done: Callable = Callable(),
+		on_failed: Callable = Callable()) -> void:
+	_request(_upload_path(upload_id), HTTPClient.METHOD_DELETE,
+			_call_ignoring_body.bind(on_done), on_failed)
+
+
 ## Replaces the alternative names of the soundtrack with [param uuid] with
 ## [param names]. The server trims them, drops duplicates and the soundtrack's own name,
 ## and calls [param on_done] with the updated [Soundtrack].
@@ -637,6 +676,20 @@ static func header_value(headers: PackedStringArray, header_name: String) -> Str
 	return ""
 
 
+static func _upload_path(upload_id: String) -> String:
+	return "/soundtracks/uploads/" + upload_id.uri_encode()
+
+
+# Calls [param on_done] with [param data] read as [param type], or [param on_failed] when
+# it is not a JSON object
+static func _as_object(data: Variant, type: GDScript, on_done: Callable,
+		on_failed: Callable) -> void:
+	if !(data is Dictionary):
+		_call_if_valid(on_failed)
+		return
+	on_done.call(type.from_dict(data))
+
+
 static func _cover_path(uuid: String) -> String:
 	return "/soundtracks/%s/cover" % uuid.uri_encode()