{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE BlockArguments #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE TupleSections #-}

module PPL.Sampling
  ( mh,
  )
where

import Control.DeepSeq
import Control.Exception (evaluate)
import Control.Monad.IO.Class
import Control.Monad.Trans.State
import Data.Bifunctor
import qualified Data.HashMap.Strict as M
import Data.Monoid
import GHC.Exts.Heap
import Numeric.Log
import PPL.Distr
import PPL.Internal
import qualified Streaming as S
import Streaming.Prelude (Of, Stream, yield)
import System.IO.Unsafe
import System.Random (StdGen, random, randoms)
import qualified System.Random as R
import Data.IORef
import Control.Monad
import Debug.Trace

mh :: (MonadIO m) => StdGen -> Double -> Meas a -> Stream (Of (a, Log Double)) m ()
mh g p m = do
    let (g0, g1) = R.split g
    omega <- liftIO $ newIORef (mempty, g0)
    let (x, w) = head $ samples m $ newTree omega
    step g1 omega x w
  where

    step !g0 !omega !x !w = do 
      let (Exp . log -> r, R.split -> (g1, g2)) = R.random g0
      omega' <- mutate g1 omega
      let (!x', !w') = head $ samples m $ newTree omega'
          ratio = w' / w
          (omega'', x'', w'') =
            if r < ratio
              then (omega', x', w')
              else (omega, x, w)
      yield (x'', w'')
      step g2 omega'' x'' w''
    
    mutate :: MonadIO m => StdGen -> IORef (M.HashMap [Int] Double, StdGen) ->  m (IORef (M.HashMap [Int] Double, StdGen))
    mutate g omega = do
      (m, g0) <- liftIO $ readIORef omega
      {-let (r:q:_) = R.randoms g
          ks = M.keys m
          k = ks !! floor (r * join traceShow (fromIntegral (length ks)))
          m' = M.insert k q m
      liftIO $ newIORef $ (m',g0)-}
      liftIO $ newIORef $ (,g0) $ flip evalState g $ mapM go m
      
     where
      go x = do
        g <- get
        let (r, g1) = R.random g
            (y, g2) = R.random g1
        if r < p 
          then do
            put g2
            pure y
          else do
            put g1
            pure x