generic 'play file' API route

app.py

@@ -202,15 +202,15 @@ def api_nowplaying():
     return jsonify(response)
 
 
-@app.route("/api/isengard", methods=["POST"])
-def api_isengard():
+@app.route("/api/play/<filename>", methods=["POST"])
+def api_play_file(filename: str, error_str: str = "Could not play file '{filename}'"):
     if not is_playing():
         playback_start()
 
     sock = mpv_socket_open()
     if sock is not None:
         mpv_socket_command(
-            sock, {"command": ["loadfile", str(music_path.joinpath("isengard.mp3"))]}
+            sock, {"command": ["loadfile", str(music_path.joinpath(filename))]}
         )
         sock.close()
 
@@ -218,7 +218,14 @@ def api_isengard():
         if is_playing():
             return jsonify("ok")
 
-    return jsonify("Could not take the hobbits to Isengard"), 500
+    return jsonify(error_str.format(filename=filename)), 500
+
+
+@app.route("/api/isengard", methods=["POST"])
+def api_isengard():
+    return api_play_file(
+        "isengard.mp3", error_str="Could not take the hobbits to Isengard"
+    )
 
 
 signal.signal(signal.SIGTERM, sigh)