module Maths
  ( dotP,
    lengthSquared,
    unitVector,
    randV3,
    rand,
    reflect,
    refract,
    reflectance,
    clamp,
  )
where

import Control.Monad.Random
import Linear.V3
import Linear.Vector
import System.Random

rand :: (RandomGen g) => Rand g Double
rand = getRandomR (-1.0, 1.0 :: Double)

randV3 :: (RandomGen g) => Rand g (V3 Double)
randV3 = do
  x <- rand
  y <- rand
  z <- rand
  if vectorLength (V3 x y z) >= 1.0
    then randV3
    else return $ unitVector (V3 x y z)

--  _ -> randV3

--inf = read "Infinity"

degToRadians :: Double -> Double
degToRadians d = (d * pi) / 180.0

dotP :: V3 Double -> V3 Double -> Double
dotP (V3 a b c) (V3 d e f) = a * d + b * e + c * f

lengthSquared :: V3 Double -> Double
lengthSquared (V3 x y z) = x ^ 2 + y ^ 2 + z ^ 2

vectorLength :: V3 Double -> Double
vectorLength v = sqrt (lengthSquared v)

unitVector :: V3 Double -> V3 Double
unitVector v = v ^/ vectorLength v

reflect :: V3 Double -> V3 Double -> V3 Double
reflect v n = v - (2 * (v `dotP` n)) *^ n

refract :: V3 Double -> V3 Double -> Double -> V3 Double
refract uv n etai_over_etat = perp ^+^ parallel
  where
    ct = min (uv `dotP` n) 1.0
    perp = etai_over_etat *^ ((-1.0 *^ uv) ^+^ (ct *^ n))
    parallel = -1.0 * sqrt (abs (1.0 - lengthSquared perp)) *^ n

reflectance :: Double -> Double -> Double
reflectance c r = r00 + (1 - r00) * (1 - c) ^ 5
  where
    r0 = (1 - r) / (1 + r)
    r00 = r0 * r0

clamp :: Double -> Double -> Double -> Double
clamp x mi ma
  | x < mi = mi
  | x > ma = ma
  | otherwise = x