37 lines
1.8 KiB
Scala
37 lines
1.8 KiB
Scala
package snake
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/**
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* m05 game: one `update` turns every action into a new state; replaying a game is a fold over its actions.
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* m10 adds pause, restart and a frame clock that speeds up as the score grows.
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*/
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object Game:
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/** How many frames pass between game steps: 8 at first, one fewer every 3 points, never fewer than 2. */
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def movesEvery(score: Int): Int = math.max(2, 8 - score / 3)
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// One animation frame: count it, and every `movesEvery(score)`-th frame run a game step.
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private def frame(state: GameState): GameState =
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if state.status != Status.Playing then state
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else
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val counted = state.copy(frame = state.frame + 1)
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if counted.frame % movesEvery(counted.score) == 0 then Spawn.tick(counted) else counted
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// Pause and resume only make sense in those two statuses; a finished game stays finished.
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private def togglePause(state: GameState): GameState = state.status match
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case Status.Playing => state.copy(status = Status.Paused)
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case Status.Paused => state.copy(status = Status.Playing)
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case Status.GameOver | Status.Won => state
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// Every case is listed (no `case _`): adding an Action later makes the compiler point here.
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def update(state: GameState, action: Action): GameState = action match
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case Action.Tick => Spawn.tick(state)
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case Action.Turn(dir) => Rules.turn(state, dir)
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case Action.TogglePause => togglePause(state)
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case Action.Restart => Spawn.newGame(state.seed)
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case Action.Frame => frame(state)
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def replay(state: GameState, actions: List[Action]): GameState = actions.foldLeft(state)(update)
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// scanLeft is foldLeft that keeps every intermediate result.
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def history(state: GameState, actions: List[Action]): List[GameState] = actions.scanLeft(state)(update)
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