namespace LivingVillage.Kernel

module Sim =

    type Vec2 =
        { X: float32
          Y: float32 }

    type Avatar =
        { Pos: Vec2 }

    type Input =
        { MoveX: float32
          MoveY: float32 }

    type TimeStep =
        { Dt: float32
          Input: Input }

    type World =
        { Tick: int64
          Avatar: Avatar }

    let mapWidthTiles = 64
    let mapHeightTiles = 48
    let tilePixels = 32
    let avatarSpeed = 160.0f

    let initialWorld () : World =
        let centerX = float32 (mapWidthTiles * tilePixels / 2 - tilePixels / 2)
        let centerY = float32 (mapHeightTiles * tilePixels / 2 - tilePixels / 2)
        { Tick = 0L
          Avatar = { Pos = { X = centerX; Y = centerY } } }

    let clamp v lo hi = if v < lo then lo elif v > hi then hi else v

    let step (ts: TimeStep) (world: World) : World =
        let maxX = float32 (mapWidthTiles * tilePixels - tilePixels)
        let maxY = float32 (mapHeightTiles * tilePixels - tilePixels)
        let dx = ts.Input.MoveX * avatarSpeed * ts.Dt
        let dy = ts.Input.MoveY * avatarSpeed * ts.Dt
        { Tick = world.Tick + 1L
          Avatar =
            { Pos =
                { X = clamp (world.Avatar.Pos.X + dx) 0.0f maxX
                  Y = clamp (world.Avatar.Pos.Y + dy) 0.0f maxY } } }