{-# LANGUAGE ForeignFunctionInterface #-}
module Q.Options.ImpliedVol.LetsBeRational (
  euImpliedVol
) where

import           Data.Coerce                    (coerce)
import           Data.Number.Erf
import           Foreign.C.Types
import           Numeric.IEEE                   (epsilon, maxFinite, minNormal)
import           Q.Options.BlackScholes
import           Q.Options
import           Q.Types
import           Statistics.Distribution        (cumulative, density, quantile)
import           Statistics.Distribution.Normal (standard)

foreign import ccall
   "lets_be_rational.h implied_volatility_from_a_transformed_rational_guess" c_lbr ::
     CDouble -> CDouble  -> CDouble -> CDouble  -> CDouble  -> CDouble

euImpliedVol :: OptionType -> Forward -> Strike -> YearFrac -> Rate -> Premium -> Vol
euImpliedVol cp (Forward f) (Strike k) (YearFrac t) (Rate r) (Premium p) =
  coerce $ c_lbr (CDouble p) (CDouble f) (CDouble k) (CDouble t) (CDouble (cpi cp))