refactored state -> screen

game/screens/__init__.py

@@ -0,0 +1,99 @@
+"""Package for game state stuff."""
+
+from __future__ import annotations
+
+from typing import Protocol, TypeAlias
+
+import attrs
+import tcod.console
+import tcod.event
+
+import g
+
+
+class Screen(Protocol):
+    """An abstract game screen."""
+
+    __slots__ = ()
+
+    def on_event(self, event: tcod.event.Event) -> ScreenResult:
+        """Called on events."""
+
+    def on_draw(self, console: tcod.console.Console) -> None:
+        """Called when the screen is being drawn."""
+
+
+@attrs.define()
+class Push:
+    """Push a new screen on top of the stack."""
+
+    screen: Screen
+
+
+@attrs.define()
+class Pop:
+    """Remove the current screen from the stack."""
+
+
+@attrs.define()
+class Reset:
+    """Replace the entire stack with a new screen."""
+
+    screen: Screen
+
+
+ScreenResult: TypeAlias = "Push | Pop | Reset | None"
+"""Union of screen results."""
+
+
+def main_draw() -> None:
+    """Render and present the active screen."""
+    if not g.screens:
+        return
+    g.console.clear()
+    g.screens[-1].on_draw(g.console)
+    g.context.present(g.console)
+
+
+def apply_state_result(result: ScreenResult) -> None:
+    """Apply a StateResult to `g.states`."""
+    match result:
+        case Push(screen=screen):
+            g.screens.append(screen)
+        case Pop():
+            g.screens.pop()
+        case Reset(screen=screen):
+            while g.screens:
+                apply_state_result(Pop())
+            apply_state_result(Push(screen))
+        case None:
+            pass
+        case _:
+            raise TypeError(result)
+
+
+def main_loop() -> None:
+    """Run the active state forever."""
+    while g.screens:
+        main_draw()
+        for event in tcod.event.wait():
+            tile_event = g.context.convert_event(event)
+            if g.screens:
+                apply_state_result(g.screens[-1].on_event(tile_event))
+
+
+def get_previous_screen(screen: Screen) -> Screen | None:
+    """Return the state before `state` in the stack if it exists."""
+    current_index = next(index for index, value in enumerate(g.screens) if value is screen)
+    return g.screens[current_index - 1] if current_index > 0 else None
+
+
+def draw_previous_screens(screen: Screen, console: tcod.console.Console, dim: bool = True) -> None:
+    """Draw previous states, optionally dimming all but the active state."""
+    prev_screen = get_previous_screen(screen)
+    if prev_screen is None:
+        return
+    prev_screen.on_draw(console)
+    if dim and screen is g.screens[-1]:
+        console.rgb["fg"] //= 4
+        console.rgb["bg"] //= 4