{-# LANGUAGE CPP #-}
{-# LANGUAGE PatternGuards #-}

module Agda.Utils.Suffix where

import Data.Char

#include "../undefined.h"
import Agda.Utils.Impossible

------------------------------------------------------------------------
-- Subscript digits

-- | Is the character one of the subscripts @'₀'@-@'₉'@?

isSubscriptDigit :: Char -> Bool
isSubscriptDigit c = '₀' <= c && c <= '₉'

-- | Converts @'0'@-@'9'@ to @'₀'@-@'₉'@.
--
-- Precondition: The digit needs to be in range.

toSubscriptDigit :: Char -> Char
toSubscriptDigit d
  | isDigit d = toEnum (fromEnum '₀' + (fromEnum d - fromEnum '0'))
  | otherwise = __IMPOSSIBLE__

-- | Converts @'₀'@-@'₉'@ to @'0'@-@'9'@.
--
-- Precondition: The digit needs to be in range.

fromSubscriptDigit :: Char -> Char
fromSubscriptDigit d
  | isSubscriptDigit d =
      toEnum (fromEnum '0' + (fromEnum d - fromEnum '₀'))
  | otherwise          = __IMPOSSIBLE__

------------------------------------------------------------------------
-- Suffices

data Suffix = NoSuffix | Prime Int | Index Int | Subscript Int

nextSuffix NoSuffix      = Subscript 1
nextSuffix (Prime i)     = Prime $ i + 1
nextSuffix (Index i)     = Index $ i + 1
nextSuffix (Subscript i) = Subscript $ i + 1

suffixView :: String -> (String, Suffix)
suffixView s
    | (ps@(_:_), s') <- span (=='\'') rs         = (reverse s', Prime $ length ps)
    | (ns@(_:_), s') <- span isDigit rs          = (reverse s', Index $ read $ reverse ns)
    | (ns@(_:_), s') <- span isSubscriptDigit rs = (reverse s',
                                                    Subscript $ read $
                                                      map fromSubscriptDigit $ reverse ns)
    | otherwise                                  = (s, NoSuffix)
    where rs = reverse s

addSuffix :: String -> Suffix -> String
addSuffix s NoSuffix      = s
addSuffix s (Prime n)     = s ++ replicate n '\''
addSuffix s (Index i)     = s ++ show i
addSuffix s (Subscript i) = s ++ map toSubscriptDigit (show i)