-- | Analysis of a context-free grammar
{-# LANGUAGE ScopedTypeVariables #-}

module Data.Cfg.Analysis
  ( Analysis(..)
  , mkAnalysis
  , Prediction
  , Predictions
  ) where

import Data.Cfg.Augment
import qualified Data.Cfg.Cfg as Cfg
import Data.Cfg.FreeCfg
import qualified Data.Cfg.Internal.FirstSet as I
import qualified Data.Cfg.Internal.FollowSet as I
import qualified Data.Cfg.Internal.Nullable as I
import qualified Data.Cfg.Internal.PredictSet as I
import Data.Cfg.Internal.PredictSet (Prediction, Predictions)
import Data.Cfg.LookaheadSet
import qualified Data.Map.Strict as M
import qualified Data.Set as S

-- | Analysis of a context-free grammar
data Analysis t nt = Analysis
  { baseCfg :: FreeCfg t nt
    -- ^ (a 'FreeCfg' equivalent to) the source grammar
  , augmentedCfg :: FreeCfg (AugT t) (AugNT nt)
    -- ^ the augmented grammar
  , nullables :: S.Set (AugNT nt)
    -- ^ the nonterminals in the grammar that can produce the
    -- empty string
  , firstSet :: AugNT nt -> LookaheadSet t
    -- ^ the first set of the nonterminal for the grammar
  , firstsOfVs :: AugVs t nt -> LookaheadSet t
    -- ^ the first set of a list of symbols
  , followSet :: AugNT nt -> LookaheadSet t
    -- ^ the follow set of the nonterminal for the grammar
  , predictSet :: AugProduction t nt -> LookaheadSet t
    -- ^ the predict set of the production
  , isLL1 :: Bool
    -- ^ 'True' iff the grammar is LL(1)
  , ll1Info :: AugNT nt -> Predictions t nt
    -- ^ the productions for this nonterminal and the lookaheads
    -- that predict them
  }

-- | Analyzes a context-free grammar
mkAnalysis ::
     forall cfg t nt. (Cfg.Cfg cfg t nt, Ord nt, Ord t)
  => cfg t nt
  -> Analysis t nt
mkAnalysis cfg =
  Analysis
    { baseCfg = bcfg
    , augmentedCfg = cfg'
    , nullables = ns
    , firstSet = fs
    , firstsOfVs = I.firstsOfVs fs
    , followSet = fols
    , predictSet = predict
    , isLL1 = isLL1'
    , ll1Info = (ll1InfoMap M.!)
    }
  where
    bcfg = toFreeCfg cfg
    cfg' = augmentCfg bcfg
    ns = I.nullables cfg'
    fsm = I.firstSetMap cfg'
    fs nt = fsm M.! nt
    folm = I.followSetMap cfg' fs
    fols nt = folm M.! nt
    predict = I.predictSet fs fols
    ll1InfoMap = I.ll1InfoMap cfg' predict
    isLL1' = I.isLL1 ll1InfoMap