/// m13 life rules: the next generation is a function of the whole old board, and nothing else.
module Snake.Life.Rules

open Snake
open Snake.Model
open Snake.Life.Model

/// One generation of Conway's Life on the LW x LH board (B3/S23), from a canonical list of live cells to a canonical
/// list (sorted row-major: by `Y`, then `X`; no duplicates).
/// - A live cell with 2 or 3 live neighbours stays alive; a dead cell with exactly 3 live neighbours is born;
///   every other cell is dead in the next generation.
/// - The neighbours of a cell are the up to 8 cells around it that are on the board: the edges are dead,
///   nothing wraps around.
/// - Every cell is judged by the *old* board only.
let lifeStep (cells: Point list) : Point list = failwith "TODO m13"

/// The one function that says how the world changes.
/// - `Frame`: when running, the next generation (`lifeStep`) and `Generation + 1`; when paused, unchanged.
/// - `Step`: when paused, the next generation and `Generation + 1`; when running, unchanged.
/// - `TogglePause`: `Running` flips.
/// - `Toggle cell`: a dead cell becomes alive, a live one dead, whether the world runs or not; `Cells` stays canonical
///   (insert the new cell at its row-major place). A cell off the board changes nothing. `Generation` is unchanged.
/// - `Clear`: no live cells, generation 0; `Running` and `Seed` are kept.
/// - `Randomize`: draw `Random.intBelow 4` (Module 4) once for every cell of the board, in row-major order
///   (y = 0..LH-1, and within a row x = 0..LW-1), threading the seed from `state.Seed`; a cell is alive when its draw
///   is 0. The state gets those cells, the seed after the last draw, and generation 0; `Running` is kept.
let lifeUpdate (state: LifeState) (action: LifeAction) : LifeState = failwith "TODO m13"