{-# OPTIONS -fvia-C -O2 -optc-O3 #-}
-- ^ required to get results. -fasm seems to slow(!)
--
-- | Pointfree programming fun
--
-- A catalogue of refactorings is at:
--      http://www.cs.kent.ac.uk/projects/refactor-fp/catalogue/
--      http://www.cs.kent.ac.uk/projects/refactor-fp/catalogue/RefacIdeasAug03.html
--
-- Use more Arrow stuff
--
-- TODO would be to plug into HaRe and use some of their refactorings.
--
module Plugin.Pl (theModule) where

import Plugin

import Plugin.Pl.Common          (TopLevel, mapTopLevel, getExpr)
import Plugin.Pl.Parser          (parsePF)
import Plugin.Pl.PrettyPrinter   (Expr)
import Plugin.Pl.Transform       (transform)
import Plugin.Pl.Optimize        (optimize)

import Message( Nick )

import Control.Concurrent.Chan    (Chan, newChan, isEmptyChan, readChan, writeList2Chan)

-- firstTimeout is the timeout when the expression is simplified for the first
-- time. After each unsuccessful attempt, this number is doubled until it hits
-- maxTimeout.
firstTimeout, maxTimeout :: Int
firstTimeout =  3000000 --  3 seconds
maxTimeout   = 15000000 -- 15 seconds

type PlState = GlobalPrivate () (Int, TopLevel)

PLUGIN Pl

type Pl = ModuleLB PlState

instance Module PlModule PlState where

    moduleCmds _   = ["pointless","pl-resume","pl"]

    moduleHelp _ "pl-resume" = "pl-resume. Resume a suspended pointless transformation."
    moduleHelp _ _           = "pointless <expr>. Play with pointfree code."

    moduleDefState _ = return $ mkGlobalPrivate 15 ()

    process _ _ target "pointless" rest = pf target rest
    process _ _ target "pl"        rest = pf target rest
    process _ _ target "pl-resume" _    = res target

------------------------------------------------------------------------

res :: Nick -> Pl
res target = do
  d <- readPS target
  case d of
    Nothing -> return ["pointless: sorry, nothing to resume."]
    Just d' -> optimizeTopLevel target d'

-- | Convert a string to pointfree form
pf :: Nick -> String -> Pl
pf target inp = case parsePF inp of
  Right d  -> optimizeTopLevel target (firstTimeout, mapTopLevel transform d)
  Left err -> return [err]

optimizeTopLevel :: Nick -> (Int, TopLevel) -> Pl
optimizeTopLevel target (to, d) = do
  let (e,decl) = getExpr d
  (e', finished) <- io $ optimizeIO to e
  extra <- if finished
           then do writePS target Nothing
                   return []
           else do writePS target $ Just (min (2*to) maxTimeout, decl e')
                   return ["optimization suspended, use @pl-resume to continue."]
  return $ (show $ decl e') : extra

------------------------------------------------------------------------

optimizeIO :: Int -> Expr -> IO (Expr, Bool)
optimizeIO to e = do
  chan <- newChan
  result <- timeout to $ writeList2Chan chan $ optimize e
  e' <- getChanLast chan e
  return $ case result of
    Nothing -> (e', False)
    Just _  -> (e', True)

getChanLast :: Chan a -> a -> IO a
getChanLast c x = do
  b <- isEmptyChan c
  if b then return x else getChanLast c =<< readChan c