{-# LANGUAGE OverloadedStrings #-}

-- | Linearisation-only grammar format.
-- Closely follows description in Section 2 of Angelov, Bringert, Ranta (2009):
-- "PGF: A Portable Run-Time Format for Type-Theoretical Grammars".
module LPGF where

import PGF (Language)
import PGF.CId
import PGF.Expr (Expr)
import PGF.Tree (Tree (..), expr2tree, prTree)

import Data.Binary (Binary, get, put, encodeFile, decodeFile)
import qualified Data.Map as Map
import Data.Text (Text)
import qualified Data.Text as T
import Text.Printf (printf)

import Prelude hiding ((!!))
import qualified Prelude

-- | Linearisation-only PGF
data LPGF = LPGF {
  absname   :: CId,
  abstract  :: Abstract,
  concretes :: Map.Map CId Concrete
} deriving (Show)

-- | Abstract syntax (currently empty)
data Abstract = Abstract {
} deriving (Show)

-- | Concrete syntax
data Concrete = Concrete {
  -- lincats :: Map.Map CId LinType, -- ^ a linearization type for each category
  lins    :: Map.Map CId LinFun  -- ^ a linearization function for each function
} deriving (Show)

-- | Abstract function type
-- data Type = Type [CId] CId
--   deriving (Show)

-- -- | Linearisation type
-- data LinType =
--     LTStr
--   | LTInt Int
--   | LTProduct [LinType]
--   deriving (Show)

-- | Linearisation function
data LinFun =
  -- Additions
    LFError String -- ^ a runtime error, should probably not be supported at all
  | LFBind -- ^ join adjacent tokens
  | LFSpace -- ^ space between adjacent tokens
  | LFCapit -- ^ capitalise next character
  | LFAllCapit -- ^ capitalise next word
  | LFPre [([Text], LinFun)] LinFun

  -- From original definition in paper
  | LFEmpty
  | LFToken Text
  | LFConcat LinFun LinFun
  | LFInt Int
  | LFTuple [LinFun]
  | LFProjection LinFun LinFun
  | LFArgument Int
  deriving (Show, Read)

instance Binary LPGF where
  put lpgf = do
    put (absname lpgf)
    put (abstract lpgf)
    put (concretes lpgf)
  get = do
    an <- get
    abs <- get
    concs <- get
    return $ LPGF {
      absname = an,
      abstract = abs,
      concretes = concs
    }

instance Binary Abstract where
  put abs = return ()
  get = return $ Abstract {}

instance Binary Concrete where
  put concr = put (lins concr)
  get = do
    ls <- get
    return $ Concrete {
      lins = ls
    }

instance Binary LinFun where
  put = put . show
  get = read <$> get

abstractName :: LPGF -> CId
abstractName = absname

encodeFile :: FilePath -> LPGF -> IO ()
encodeFile = Data.Binary.encodeFile

readLPGF :: FilePath -> IO LPGF
readLPGF = Data.Binary.decodeFile

-- | Main linearize function, to 'String'
linearize :: LPGF -> Language -> Expr -> String
linearize lpgf lang expr = T.unpack $ linearizeText lpgf lang expr

-- | Main linearize function, to 'Data.Text.Text'
linearizeText :: LPGF -> Language -> Expr -> Text
linearizeText lpgf lang =
  case Map.lookup lang (concretes lpgf) of
    Just concr -> linearizeConcreteText concr
    Nothing -> error $ printf "Unknown language: %s" (showCId lang)

-- | Language-specific linearize function, to 'String'
linearizeConcrete :: Concrete -> Expr -> String
linearizeConcrete concr expr = T.unpack $ linearizeConcreteText concr expr

-- | Language-specific linearize function, to 'Data.Text.Text'
linearizeConcreteText :: Concrete -> Expr -> Text
linearizeConcreteText concr expr = lin2string $ lin (expr2tree expr)
  where
    lin :: Tree -> LinFun
    lin tree = case tree of
      Fun f as ->
        case Map.lookup f (lins concr) of
          Just t -> eval (map lin as) t
          _ -> error $ printf "Lookup failed for function: %s" (showCId f)
      x -> error $ printf "Cannot lin: %s" (prTree x)

-- | Evaluation context is a sequence of terms
type Context = [LinFun]

-- | Operational semantics
eval :: Context -> LinFun -> LinFun
eval cxt t = case t of
  LFError err -> error err
  LFPre pts df -> LFPre pts' df'
    where
      pts' = [ (strs, eval cxt t) | (strs,t) <- pts]
      df' = eval cxt df
  LFConcat s t -> LFConcat v w
    where
      v = eval cxt s
      w = eval cxt t
  LFTuple ts -> LFTuple vs
    where vs = map (eval cxt) ts
  LFProjection t u ->
    case (eval cxt t, eval cxt u) of
      (LFTuple vs, LFInt i) -> vs !! (i-1)
      (tp@(LFTuple _), LFTuple is) | all isInt is -> foldl (\(LFTuple vs) (LFInt i) -> vs !! (i-1)) tp is
      (t',u') -> error $ printf "Incompatible projection:\n%s\n%s" (show t) (show u)
  LFArgument i -> cxt !! (i-1)
  _ -> t

-- | Turn concrete syntax terms into an actual string
lin2string :: LinFun -> Text
lin2string l = case l of
  LFEmpty -> ""
  LFBind -> "" -- when encountered at beginning/end
  LFSpace -> "" -- when encountered at beginning/end
  LFToken tok -> tok
  LFTuple [l] -> lin2string l
  LFConcat (LFPre pts df) l2 -> lin2string $ LFConcat l1 l2
    where
      l2' = lin2string l2
      matches = [ l | (pfxs, l) <- pts, any (`T.isPrefixOf` l2') pfxs ]
      l1 = if null matches then df else head matches
  LFConcat l1 (LFConcat LFBind l2) -> lin2string l1 `T.append` lin2string l2
  LFConcat l1 (LFConcat LFSpace l2) -> lin2string $ LFConcat l1 l2
  LFConcat LFCapit l2 -> let l = lin2string l2 in T.toUpper (T.take 1 l) `T.append` T.drop 1 l
  LFConcat LFAllCapit l2 -> let tks = T.words (lin2string l2) in T.unwords $ T.toUpper (head tks) : tail tks
  LFConcat l1 l2 -> T.unwords $ filter (not.T.null) [lin2string l1, lin2string l2]
  x -> T.pack $ printf "[%s]" (show x)

-- | List indexing with more verbose error messages
(!!) :: (Show a) => [a] -> Int -> a
(!!) xs i
  | i < 0 = error $ printf "!!: index %d too small for list: %s" i (show xs)
  | i > length xs - 1 = error $ printf "!!: index %d too large for list: %s" i (show xs)
  | otherwise = xs Prelude.!! i

isInt :: LinFun -> Bool
isInt (LFInt _) = True
isInt _ = False