module Parse.Expression (def,term,typeAnnotation,expr) where

import Control.Applicative ((<$>), (<*>))
import Data.List (foldl')
import Text.Parsec hiding (newline,spaces)
import Text.Parsec.Indent

import Parse.Binop
import Parse.Helpers
import Parse.Literal
import qualified Parse.Pattern as Pattern
import qualified Parse.Type as Type

import SourceSyntax.Annotation as Annotation
import qualified SourceSyntax.Pattern as P
import qualified SourceSyntax.Literal as L
import SourceSyntax.Expression


--------  Basic Terms  --------

varTerm :: IParser ParseExpr'
varTerm = toVar <$> var <?> "variable"

toVar :: String -> ParseExpr'
toVar v = case v of "True"  -> Literal (L.Boolean True)
                    "False" -> Literal (L.Boolean False)
                    _       -> rawVar v

accessor :: IParser ParseExpr'
accessor = do
  (start, lbl, end) <- located (try (string "." >> rLabel))
  let loc e = Annotation.at start end e
  return (Lambda (P.Var "_") (loc $ Access (loc $ rawVar "_") lbl))

negative :: IParser ParseExpr'
negative = do
  (start, nTerm, end) <-
      located (try (char '-' >> notFollowedBy (char '.' <|> char '-')) >> term)
  let loc e = Annotation.at start end e
  return (Binop "-" (loc $ Literal (L.IntNum 0)) nTerm)


--------  Complex Terms  --------

listTerm :: IParser ParseExpr'
listTerm = markdown' <|> braces (try range <|> ExplicitList <$> commaSep expr)
  where
    range = do
      lo <- expr
      padded (string "..")
      Range lo <$> expr

    markdown' = do
      pos <- getPosition
      let uid = show (sourceLine pos) ++ ":" ++ show (sourceColumn pos)
      (rawText, exprs) <- markdown (interpolation uid)
      return (Markdown uid (filter (/='\r') rawText) exprs)

    span uid index =
        "<span id=\"md-" ++ uid ++ "-" ++ show index ++ "\">{{ markdown interpolation is in the pipeline, but still needs more testing }}</span>"

    interpolation uid exprs = do
      try (string "{{")
      e <- padded expr
      string "}}"
      return (span uid (length exprs), exprs ++ [e])

parensTerm :: IParser ParseExpr
parensTerm = try (parens opFn) <|> parens (tupleFn <|> parened)
  where
    opFn = do
      (start, op, end) <- located anyOp
      let loc = Annotation.at start end
      return . loc . Lambda (P.Var "x") . loc . Lambda (P.Var "y") . loc $
             Binop op (loc $ rawVar "x") (loc $ rawVar "y")

    tupleFn = do
      let comma = char ',' <?> "comma ','"
      (start, commas, end) <- located (comma >> many (whitespace >> comma))
      let vars = map (('v':) . show) [ 0 .. length commas + 1 ]
          loc = Annotation.at start end
      return $ foldr (\x e -> loc $ Lambda x e)
                 (loc . tuple $ map (loc . rawVar) vars) (map P.Var vars)
    
    parened = do
      (start, es, end) <- located (commaSep expr)
      return $ case es of
                 [e] -> e
                 _   -> Annotation.at start end (tuple es)

recordTerm :: IParser ParseExpr
recordTerm = brackets $ choice [ misc, addLocation record ]
    where
      field = do
        label <- rLabel
        patterns <- spacePrefix Pattern.term
        padded equals
        body <- expr
        return (label, makeFunction patterns body)
              
      record = Record <$> commaSep field

      change = do
        lbl <- rLabel
        padded (string "<-")
        (,) lbl <$> expr

      remove r = addLocation (string "-" >> whitespace >> Remove r <$> rLabel)

      insert r = addLocation $ do
                   string "|" >> whitespace
                   Insert r <$> rLabel <*> (padded equals >> expr)

      modify r =
          addLocation (string "|" >> whitespace >> Modify r <$> commaSep1 change)

      misc = try $ do
               record <- addLocation (rawVar <$> rLabel)
               opt <- padded (optionMaybe (remove record))
               case opt of
                 Just e  -> try (insert e) <|> return e
                 Nothing -> try (insert record) <|> try (modify record)
                        

term :: IParser ParseExpr
term =  addLocation (choice [ Literal <$> literal, listTerm, accessor, negative ])
    <|> accessible (addLocation varTerm <|> parensTerm <|> recordTerm)
    <?> "basic term (4, x, 'c', etc.)"

--------  Applications  --------

appExpr :: IParser ParseExpr
appExpr = do
  t <- term
  ts <- constrainedSpacePrefix term $ \str ->
            if null str then notFollowedBy (char '-') else return ()
  return $ case ts of
             [] -> t
             _  -> foldl' (\f x -> Annotation.merge f x $ App f x) t ts

--------  Normal Expressions  --------

binaryExpr :: IParser ParseExpr
binaryExpr = binops appExpr lastExpr anyOp
  where lastExpr = addLocation (choice [ ifExpr, letExpr, caseExpr ])
                <|> lambdaExpr

ifExpr :: IParser ParseExpr'
ifExpr = reserved "if" >> whitespace >> (normal <|> multiIf)
    where
      normal = do
        bool <- expr
        padded (reserved "then")
        thenBranch <- expr
        whitespace <?> "an 'else' branch" ; reserved "else" <?> "an 'else' branch" ; whitespace
        elseBranch <- expr
        return $ MultiIf [(bool, thenBranch),
                          (Annotation.sameAs elseBranch (Literal . L.Boolean $ True), elseBranch)]
      multiIf = MultiIf <$> spaceSep1 iff
          where iff = do string "|" ; whitespace
                         b <- expr ; padded arrow
                         (,) b <$> expr

lambdaExpr :: IParser ParseExpr
lambdaExpr = do char '\\' <|> char '\x03BB' <?> "anonymous function"
                whitespace
                args <- spaceSep1 Pattern.term
                padded arrow
                body <- expr
                return (makeFunction args body)

defSet :: IParser [ParseDef]
defSet = block (do d <- def ; whitespace ; return d)

letExpr :: IParser ParseExpr'
letExpr = do
  reserved "let" ; whitespace
  defs <- defSet
  padded (reserved "in")
  Let defs <$> expr

caseExpr :: IParser ParseExpr'
caseExpr = do
  reserved "case"; e <- padded expr; reserved "of"; whitespace
  Case e <$> (with <|> without)
    where case_ = do p <- Pattern.expr
                     padded arrow
                     (,) p <$> expr
          with    = brackets (semiSep1 (case_ <?> "cases { x -> ... }"))
          without = block (do c <- case_ ; whitespace ; return c)

expr :: IParser ParseExpr
expr = addLocation (choice [ ifExpr, letExpr, caseExpr ])
    <|> lambdaExpr
    <|> binaryExpr 
    <?> "an expression"

defStart :: IParser [P.Pattern]
defStart =
    choice [ do p1 <- try Pattern.term
                infics p1 <|> func p1
           , func =<< (P.Var <$> parens symOp)
           , (:[]) <$> Pattern.expr
           ] <?> "the definition of a variable (x = ...)"
    where
      func pattern =
          case pattern of
            P.Var _ -> (pattern:) <$> spacePrefix Pattern.term
            _ -> do try (lookAhead (whitespace >> string "="))
                    return [pattern]

      infics p1 = do
        o:p <- try (whitespace >> anyOp)
        p2  <- (whitespace >> Pattern.term)
        return $ if o == '`' then [ P.Var $ takeWhile (/='`') p, p1, p2 ]
                             else [ P.Var (o:p), p1, p2 ]

makeFunction :: [P.Pattern] -> ParseExpr -> ParseExpr
makeFunction args body@(A ann _) =
    foldr (\arg body' -> A ann $ Lambda arg body') body args

definition :: IParser ParseDef
definition = withPos $ do
  (name:args) <- defStart
  padded equals
  body <- expr
  return . Def name $ makeFunction args body

typeAnnotation :: IParser ParseDef
typeAnnotation = TypeAnnotation <$> try start <*> Type.expr
  where
    start = do
      v <- lowVar <|> parens symOp
      padded hasType
      return v

def :: IParser ParseDef
def = typeAnnotation <|> definition