module Physics where

import Vec2 (..)

getNewPosAndSpeed : Float -> Vec2 -> (Float -> Float) -> (Vec2, Vec2) -> (Vec2, Vec2)
getNewPosAndSpeed dt dir computeSpeed (pos, speed) =
  let move = getMove (computeSpeed dt) dir
      acc = getAcc move speed
      newPos = getNewPos dt acc speed pos
      newSpeed = getNewSpeed dt acc speed
  in  ( newPos
      , newSpeed
      )

getMove : Float -> Vec2 -> Vec2
getMove speed dir =
  if (isNull dir)
    then {x = 0, y = 0}
    else
      let angle = atan2 dir.y dir.x
      in  { x = speed * cos angle
          , y = speed * sin angle
          }

getAcc : Vec2 -> Vec2 -> Vec2
getAcc move speed = (move `div` 800) `sub` (speed `div` 1000)

getNewPos : Float -> Vec2 -> Vec2 -> Vec2 -> Vec2
getNewPos dt acc speed pos =
  ((dt^2 / 2) `mul` acc) `add` ((dt `mul` speed) `add` pos)

getNewSpeed : Float -> Vec2 -> Vec2 -> Vec2
getNewSpeed dt acc speed = add (mul dt acc) speed