module PGF.Generate 
         ( generateAll,         generateAllDepth
         , generateFrom,        generateFromDepth
         , generateRandom,      generateRandomDepth
         , generateRandomFrom,  generateRandomFromDepth
         , prove
         ) where

import PGF.CId
import PGF.Data
import PGF.Expr
import PGF.Macros
import PGF.TypeCheck
import PGF.Probabilistic

import Data.Maybe (fromMaybe)
import qualified Data.Map as Map
import qualified Data.IntMap as IntMap
import Control.Monad
import Control.Monad.Identity
import System.Random


------------------------------------------------------------------------------
-- The API

-- | Generates an exhaustive possibly infinite list of
-- abstract syntax expressions.
generateAll :: PGF -> Type -> [Expr]
generateAll pgf ty = generateAllDepth pgf ty Nothing

-- | A variant of 'generateAll' which also takes as argument
-- the upper limit of the depth of the generated expression.
generateAllDepth :: PGF -> Type -> Maybe Int -> [Expr]
generateAllDepth pgf ty dp = generate () pgf ty dp

-- | Generates a list of abstract syntax expressions
-- in a way similar to 'generateAll' but instead of
-- generating all instances of a given type, this
-- function uses a template. 
generateFrom :: PGF -> Expr -> [Expr]
generateFrom pgf ex = generateFromDepth pgf ex Nothing

-- | A variant of 'generateFrom' which also takes as argument
-- the upper limit of the depth of the generated subexpressions.
generateFromDepth :: PGF -> Expr -> Maybe Int -> [Expr]
generateFromDepth pgf e dp = 
  [e | (_,_,e) <- snd $ runTcM (abstract pgf)
                               (generateForMetas (prove dp) e)
                               emptyMetaStore ()]

-- | Generates an infinite list of random abstract syntax expressions.
-- This is usefull for tree bank generation which after that can be used
-- for grammar testing.
generateRandom :: RandomGen g => g -> PGF -> Type -> [Expr]
generateRandom g pgf ty = generateRandomDepth g pgf ty Nothing

-- | A variant of 'generateRandom' which also takes as argument
-- the upper limit of the depth of the generated expression.
generateRandomDepth :: RandomGen g => g -> PGF -> Type -> Maybe Int -> [Expr]
generateRandomDepth g pgf ty dp = restart g (\g -> generate (Identity g) pgf ty dp)

-- | Random generation based on template
generateRandomFrom :: RandomGen g => g -> PGF -> Expr -> [Expr]
generateRandomFrom g pgf e = generateRandomFromDepth g pgf e Nothing

-- | Random generation based on template with a limitation in the depth.
generateRandomFromDepth :: RandomGen g => g -> PGF -> Expr -> Maybe Int -> [Expr]
generateRandomFromDepth g pgf e dp = 
  restart g (\g -> [e | (_,ms,e) <- snd $ runTcM (abstract pgf)
                                                 (generateForMetas (prove dp) e)
                                                 emptyMetaStore (Identity g)])


------------------------------------------------------------------------------
-- The main generation algorithm

generate :: Selector sel => sel -> PGF -> Type -> Maybe Int -> [Expr]
generate sel pgf ty dp =
  [e | (_,ms,e) <- snd $ runTcM (abstract pgf)
                                (prove dp emptyScope (TTyp [] ty) >>= checkResolvedMetaStore emptyScope)
                                emptyMetaStore sel]

prove :: Selector sel => Maybe Int -> Scope -> TType -> TcM sel Expr
prove dp scope (TTyp env1 (DTyp hypos1 cat es1)) = do
  vs1 <- mapM (PGF.TypeCheck.eval env1) es1
  let scope' = exScope scope env1 hypos1
  (fe,TTyp env2 (DTyp hypos2 _ es2)) <- select cat scope' dp
  case dp of
    Just 0 | not (null hypos2) -> mzero
    _                          -> return ()
  (env2,args) <- mkEnv scope' env2 hypos2
  vs2 <- mapM (PGF.TypeCheck.eval env2) es2
  sequence_ [eqValue mzero suspend (scopeSize scope') v1 v2 | (v1,v2) <- zip vs1 vs2]
  es <- mapM (descend scope') args
  return (abs hypos1 (foldl EApp fe es))
  where
    suspend i c = do
      mv <- getMeta i
      case mv of
        MBound e -> c e
        MUnbound x scope tty cs -> setMeta i (MUnbound x scope tty (c:cs))

    abs []                e = e
    abs ((bt,x,ty):hypos) e = EAbs bt x (abs hypos e)

    exScope scope env []                = scope
    exScope scope env ((bt,x,ty):hypos) = 
       let env' | x /= wildCId = VGen (scopeSize scope) [] : env
                | otherwise    = env
       in exScope (addScopedVar x (TTyp env ty) scope) env' hypos

    mkEnv scope env []                = return (env,[])
    mkEnv scope env ((bt,x,ty):hypos) = do
      (env,arg) <- if x /= wildCId
                    then do i <- newMeta scope (TTyp env ty)
                            return (VMeta i (scopeEnv scope) [] : env,Right (EMeta i))
                    else return (env,Left (TTyp env ty))
      (env,args) <- mkEnv scope env hypos
      return (env,(bt,arg):args)

    descend scope (bt,arg) = do
      let dp' = fmap (flip (-) 1) dp
      e <- case arg of
             Right e  -> return e
             Left tty -> prove dp' scope tty
      e <- case bt of
             Implicit -> return (EImplArg e)
             Explicit -> return e
      return e


-- Helper function for random generation. After every
-- success we must restart the search to find sufficiently different solution.
restart :: RandomGen g => g -> (g -> [a]) -> [a]
restart g f =
  let (g1,g2) = split g
  in case f g1 of
       []     -> []
       (x:xs) -> x : restart g2 f


------------------------------------------------------------------------------
-- Selectors

instance Selector () where
  splitSelector s = (s,s)
  select cat scope dp = do
    gens <- typeGenerators scope cat
    TcM (\abstr k h -> iter k gens)
    where
      iter k []              ms s = id
      iter k ((_,e,tty):fns) ms s = k (e,tty) ms s . iter k fns ms s


instance RandomGen g => Selector (Identity g) where
  splitSelector (Identity g) = let (g1,g2) = split g
                               in (Identity g1, Identity g2)

  select cat scope dp = do
    gens <- typeGenerators scope cat
    TcM (\abstr k h -> iter k 1.0 gens)
    where
      iter k p []   ms (Identity g) = id
      iter k p gens ms (Identity g) = let (d,g')    = randomR (0.0,p) g
                                          (g1,g2)   = split g'
                                          (p',e_ty,gens') = hit d gens
                                      in k e_ty ms (Identity g1) . iter k (p-p') gens' ms (Identity g2)

      hit :: Double -> [(Double,Expr,TType)] -> (Double,(Expr,TType),[(Double,Expr,TType)])
      hit d (gen@(p,e,ty):gens)
        | d < p     = (p,(e,ty),gens)
        | otherwise = let (p',e_ty',gens') = hit (d-p) gens
                      in (p',e_ty',gen:gens')