/// m05 game: one `update` turns every action into a new state; replaying a game is a fold over its actions.
module Snake.Game

open Snake.Model

/// How many frames pass between game steps (m10): `max 2 (8 - score / 3)` (integer division).
/// Score 0-2 -> 8, 3-5 -> 7, ..., 18 and up -> 2.
let movesEvery (score: int) : int = failwith "TODO m10"

/// The one function that says how the game changes: `state -> action -> state`.
///
/// m05: `Tick` runs a game step (`Spawn.tick`), `Turn` asks to change direction (`Rules.turn`);
/// every other action returns the state unchanged.
///
/// (m10) `TogglePause` switches Playing <-> Paused and does nothing in any other status.
/// (m10) `Restart` gives `Spawn.newGame state.Seed`, whatever the status.
/// (m10) `Frame` does nothing unless Playing; otherwise it adds 1 to `Frame`, and when the new `Frame` is a multiple of
/// `movesEvery Score` it also runs a game step (`Spawn.tick`) on that incremented state.
/// In m10, match every case of `Action` explicitly (no `| _ ->`), so the compiler tells you if one is forgotten.
let update (state: GameState) (action: Action) : GameState = failwith "TODO m05"

/// Apply all actions in order, starting from `state`, and return the final state.
let replay (state: GameState) (actions: Action list) : GameState = failwith "TODO m05"

/// Like `replay`, but keep every state: `[state; afterFirst; afterSecond; ...]`, so its length is `List.length actions + 1`.
let history (state: GameState) (actions: Action list) : GameState list = failwith "TODO m05"