/// m04 spawn: placing apples with the Random from Random.fs.
module Snake.Spawn

open Snake.Model

let freeCells (state: GameState) : Point list =
    [ for y in Util.range state.Height do
          for x in Util.range state.Width do
              let p = { X = x; Y = y }
              if not (Util.contains state.Snake p (=)) then
                  yield p ]

let spawnApple (state: GameState) : GameState =
    if state.Apple.IsSome || state.Status <> Playing then
        state
    else
        match freeCells state with
        | [] -> { state with Status = Won }
        | cells ->
            let i, seed = Random.run state.Seed (Random.intBelow (List.length cells))
            { state with Apple = Some(List.item i cells); Seed = seed }

let tick (state: GameState) : GameState = spawnApple (Rules.advance state)

let newGame (seed: uint32) : GameState = spawnApple (initialState seed)