phantomcastle: add background music

pygame-wasm/phantomcastle/common.py

@@ -12,6 +12,15 @@ import pygame
 from coords import Coords
 
 
+class SingletonMeta(type):
+    _instances = {}
+
+    def __call__(cls, *args, **kwargs):
+        if cls not in cls._instances:
+            cls._instances[cls] = super(SingletonMeta, cls).__call__(*args, **kwargs)
+        return cls._instances[cls]
+
+
 class SurfaceWithRect(NamedTuple):
     surface: pygame.Surface
     rect: pygame.Rect