module PrettyJSON
    (
      renderJValue
    ) where

import Data.Char (ord)
import Data.Bits (shiftR, (.&.))
import Numeric (showHex)
import SimpleJSON (JValue(..))
import Prettify (Doc, (<>), char, double, fsep, hcat, punctuate, text, compact, pretty)

renderJValue :: JValue -> Doc
renderJValue (JBool True)  = text "true"
renderJValue (JBool False) = text "false"
renderJValue JNull         = text "null"
renderJValue (JNumber num) = double num
renderJValue (JString str) = string str
renderJValue (JArray ary)  = series '[' ']' renderJValue ary
renderJValue (JObject obj) = series '{' '}' field obj
    where field (name,val) = string name
                           <> text ": "
                           <> renderJValue val

series :: Char -> Char -> (a -> Doc) -> [a] -> Doc
series open close item =
    enclose open close . fsep . punctuate (char ',') . map item

string :: String -> Doc
string = enclose '"' '"' . hcat . map oneChar

enclose :: Char -> Char -> Doc -> Doc
enclose left right x = char left <> x <> char right

oneChar :: Char -> Doc
oneChar c =
    case lookup c simpleEscapes of
        Just r                 -> text r
        Nothing | mustEscape c -> hexEscape c
                | otherwise    -> char c
    where mustEscape c = c < ' ' || c == '\x7f' || c > '\xff'

simpleEscapes :: [(Char, String)]
simpleEscapes = zipWith ch "\b\n\f\r\t\\\"/" "bnfrt\\\"/"
    where ch a b = (a, ['\\',b])

hexEscape :: Char -> Doc
hexEscape c | d < 0x10000 = smallHex d
            | otherwise   = astral (d - 0x10000)
    where d = ord c

smallHex :: Int -> Doc
smallHex x = text "\\u"
             <> text (replicate (4 - length h) '0')
             <> text h
    where h = showHex x ""

astral :: Int -> Doc
astral n = smallHex (a + 0xd800) <> smallHex (b + 0xdc00)
    where a = (n `shiftR` 10) .&. 0x3ff
          b = n .&. 0x3ff

