module Parse.Pattern (term, expr) where

import Control.Applicative ((<$>))
import Data.Char (isUpper)
import qualified Data.List as List
import Text.Parsec ((<|>), (<?>), char, choice, optionMaybe, try)

import Parse.Helpers
import qualified Parse.Literal as Literal
import qualified AST.Literal as L
import qualified AST.Pattern as P
import qualified AST.Variable as Var

basic :: IParser P.RawPattern
basic = choice
    [ char '_' >> return P.Anything
    , stringToPattern <$> var
    , P.Literal <$> Literal.literal
    ]
  where
    stringToPattern v =
        case v of
          "True"          -> P.Literal (L.Boolean True)
          "False"         -> P.Literal (L.Boolean False)
          c:_ | isUpper c -> P.Data (Var.Raw v) []
          _               -> P.Var v


asPattern :: P.RawPattern -> IParser P.RawPattern
asPattern pattern =
  do  var <- optionMaybe (try (whitespace >> reserved "as") >> whitespace >> lowVar)
      case var of
        Just v ->
          return (P.Alias v pattern)

        Nothing ->
          return pattern


record :: IParser P.RawPattern
record = P.Record <$> brackets (commaSep1 lowVar)

tuple :: IParser P.RawPattern
tuple = do
  ps <- parens (commaSep expr)
  return $ case ps of
             [p] -> p
             _ -> P.tuple ps

list :: IParser P.RawPattern
list = P.list <$> braces (commaSep expr)

term :: IParser P.RawPattern
term =
     (choice [ record, tuple, list, basic ]) <?> "pattern"

patternConstructor :: IParser P.RawPattern
patternConstructor = do
  v <- List.intercalate "." <$> dotSep1 capVar
  case v of
    "True"  -> return $ P.Literal (L.Boolean True)
    "False" -> return $ P.Literal (L.Boolean False)
    _       -> P.Data (Var.Raw v) <$> spacePrefix term

expr :: IParser P.RawPattern
expr = do
  patterns <- consSep1 (patternConstructor <|> term)
  asPattern (foldr1 P.cons patterns) <?> "pattern"