module Text.Format.Flags (

	FormatFlags,

	getFlag, hasFlag,

	baseFlag, preciseFlag

	) where



import Prelude.Unicode



import Control.Applicative

import Data.List (stripPrefix)

import Data.Maybe (listToMaybe, mapMaybe, fromMaybe)

import Text.Read



type FormatFlags = [String]



getFlag ∷ (String → Maybe a) → [String] → Maybe a

getFlag fn = listToMaybe ∘ mapMaybe fn



hasFlag ∷ String → [String] → Bool

hasFlag = (∈)



getFlagValue ∷ Read a ⇒ String → [String] → Maybe a

getFlagValue nm fmts = do

	f ← getFlag (stripPrefix (nm ++ "=")) fmts

	readMaybe f



baseFlag ∷ (Read a, Integral a) ⇒ [String] → a

baseFlag fmts

	| hasFlag "bin" fmts ∨ hasFlag "b" fmts = 2

	| hasFlag "octal" fmts ∨ hasFlag "o" fmts = 8

	| hasFlag "hex" fmts ∨ hasFlag "h" fmts = 16

	| otherwise = fromMaybe 10 (getFlagValue "base" fmts <|> getFlagValue "b" fmts)



preciseFlag ∷ [String] → Maybe Int

preciseFlag fmts = read <$> listToMaybe (mapMaybe preciseFlag' fmts) where

	preciseFlag' ('d':d) = Just d

	preciseFlag' _ = Nothing