module Text.Json where

import Data.Either (Either(..))
import Data.Eq (class Eq, (==), (/=))
import Control.Monad ((<|>))
import Text.Parsec (Parsec, parse, combine, many, fixP, between, trimP, spacesP, idP, charP, 
  predP, stringP, floatP, withPos, (.>>), (>>.), (.>>.), (|>>), (>>%), (<?>))

data JsonValue = JsonNull
               | JsonString String
               | JsonNum    Float
               | JsonBool   Boolean
               | JsonList   [JsonValue]
               | JsonObject [(String, JsonValue)]

instance Eq JsonValue where
  eq  JsonNull       JsonNull      = true
  eq (JsonString x) (JsonString y) = x == y
  eq (JsonNum    x) (JsonNum    y) = x == y
  eq (JsonBool   x) (JsonBool   y) = x == y
  eq (JsonList   x) (JsonList   y) = x == y
  eq (JsonObject x) (JsonObject y) = x == y
  eq  _              _             = false

jsonNullP :: Parsec JsonValue
jsonNullP = trimP (stringP "null" >>% JsonNull) <?> "Expect null"

escapeP :: Parsec Char
escapeP = stringP "\\n" >>% '\n' <|>
          stringP "\\t" >>% '\t' <|>
          --stringP "\\b" >>% '\b' <|>
          --stringP "\\v" >>% '\v' <|>
          --stringP "\\f" >>% '\f' <|>
          stringP "\\r" >>% '\r' <|>
          --stringP "\\e" >>% '\e' <|>
          charP '\\' >>. idP

jsonStringP' :: Parsec String
jsonStringP' = withPos (trimP (charP '\'' >>. many jsonCharP1 .>> (charP '\'' <?> "Unclosed '" ) <|>
                               charP '"'  >>. many jsonCharP2 .>> (charP '"'  <?> "Unclosed \"")))
  where jsonCharP1 = escapeP <|> predP (\c -> c /= '\'') -- '
        jsonCharP2 = escapeP <|> predP (\c -> c /= '"' ) -- "

jsonStringP :: Parsec JsonValue
jsonStringP = jsonStringP' |>> JsonString

jsonNumP :: Parsec JsonValue
jsonNumP = trimP (floatP |>> JsonNum)

jsonBoolP :: Parsec JsonValue
jsonBoolP = trimP (stringP "true"  >>% JsonBool true <|>
                   stringP "false" >>% JsonBool false) <?> "Expect true/false"

jsonListP :: Parsec JsonValue -> Parsec JsonValue
jsonListP p = trimP (between (charP '[') (charP ']' <?> "Unclosed []") sepP) |>> JsonList
  where sepP = (combine (\a b -> Right [a|b]) p (many (charP ',' >>. p))) <|>
               (spacesP >>% [])

jsonObjectP :: Parsec JsonValue -> Parsec JsonValue
jsonObjectP p = trimP (between (charP '{') (charP '}' <?> "Unclosed {}") sepP) |>> JsonObject
  where kvP = (jsonStringP' .>> charP ':') .>>. p
        sepP = (combine (\a b -> Right [a|b]) kvP (many (charP ',' >>. kvP))) <|>
               (spacesP >>% [])

jsonValueP :: Parsec JsonValue
jsonValueP = fixP (\p -> jsonNullP <|> jsonStringP <|> jsonBoolP <|> jsonNumP <|> jsonListP p <|> jsonObjectP p)

parseJson :: String -> Either [String] JsonValue
parseJson s = parse jsonValueP s