module Glyph.Key.Count where

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import qualified Data.Char                 as Char
import qualified Data.List                 as List

import           Glyph.Class.Stringable    ( Stringable (..) )
import           Glyph.Key.Chord           ( Chord (..) )

import           Graphics.Vty.Input.Events ( Key (..) )

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data Count
  -- Nada
  = NoCount
  -- Digits are being collected, newest last.
  | Reading (List Char)
  -- Digits finished and folded into a number.
  | Counted Natural
  deriving (Eq, Show)

instance Stringable Count where
  toString NoCount         = ""
  toString (Reading chars) = chars
  toString (Counted num)   = show num

  -- One way
  fromString _ = Nothing

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canCount :: Count -> List Chord -> Key -> Bool
canCount count [] (KChar c) =
  case count of
    NoCount   -> Char.isDigit c
    Reading _ -> Char.isDigit c
    Counted _ -> False
canCount _ _ _ = False

pushDigit :: Key -> Count -> Count
pushDigit (KChar c) count =
  case count of
    NoCount        -> Reading [c]
    Reading digits -> Reading (digits <> [c])
    Counted _      -> Reading [c]
pushDigit _ count = Counted <| settle count

settle :: Count -> Natural
settle =
  \case
    NoCount -> 1
    Reading digits ->
      List.foldl' (\accum char -> accum * 10 + digitValue char) 0 digits
    Counted value -> value

digitValue :: Char -> Natural
digitValue char
  | Char.isDigit char = Char.ord char - Char.ord '0' |> toEnum
  | otherwise = 0