/// m02 model: the data the whole game is built from. Records and unions are immutable.
module Snake.Model

/// A grid cell. Records compare structurally: two points with the same X and Y are `=`.
type Point = { X: int; Y: int }

type Direction =
    | Up
    | Down
    | Left
    | Right

type Status =
    | Playing
    | Paused
    | GameOver
    | Won

/// Everything that can happen to the game, as data.
type Action =
    | Tick
    | Turn of Direction
    | TogglePause
    | Restart
    | Frame

/// The whole game. `Snake` is head first; `Seed` is the unsigned 32-bit random seed.
type GameState =
    { Width: int
      Height: int
      Snake: Point list
      Dir: Direction
      NextDir: Direction
      Apple: Point option
      Seed: uint32
      Score: int
      Status: Status
      Frame: int }

let delta (dir: Direction) : Point =
    match dir with
    | Up -> { X = 0; Y = -1 }
    | Down -> { X = 0; Y = 1 }
    | Left -> { X = -1; Y = 0 }
    | Right -> { X = 1; Y = 0 }

let opposite (dir: Direction) : Direction =
    match dir with
    | Up -> Down
    | Down -> Up
    | Left -> Right
    | Right -> Left

let initialState (seed: uint32) : GameState =
    { Width = 20
      Height = 20
      Snake = [ { X = 10; Y = 10 }; { X = 9; Y = 10 }; { X = 8; Y = 10 } ]
      Dir = Right
      NextDir = Right
      Apple = None
      Seed = seed
      Score = 0
      Status = Playing
      Frame = 0 }