{-# LANGUAGE OverloadedStrings #-}

module AoC.Day3 where

import Data.Text (Text)
import Data.Maybe (fromMaybe)
import Data.Monoid (Sum(..), getSum)
import Data.List.Split (chunksOf)
import Data.Tuple.Extra (uncurry3)
import qualified Data.Text as T

valueMap :: [(Char, Int)]
valueMap = zip (['a'..'z']++['A'..'Z']) [1..]

breakInTwoEqualLengthSubStrings :: Text -> (Text,Text)
breakInTwoEqualLengthSubStrings txt = T.splitAt (T.length txt `div` 2) txt

findCommonItem :: Text -> Text -> Char
findCommonItem _ "" = undefined
findCommonItem compartment1 compartment2 =
  if (c `T.elem` compartment1)
  then c
  else findCommonItem compartment1 (T.tail compartment2)
  where
    c = T.head compartment2


solveAOnOne :: Text -> Int
solveAOnOne = fromMaybe undefined
            . flip lookup valueMap
            . uncurry findCommonItem
            . breakInTwoEqualLengthSubStrings

solveA :: Text -> Int
solveA = getSum . mconcat . map (Sum . solveAOnOne) . T.lines

--------------------------------------------------------------------------------
-- Part 2

findCommonItem3 :: Text -> Text -> Text -> Char
findCommonItem3 c1 c2 c3 = T.head $ go (go c1 c2) c3
  where
    go :: Text -> Text -> Text
    go t1 = T.foldl (\acc c -> if c `T.elem` t1 then T.cons c acc else acc) ""

tupleMeUp3 :: [[Text]] -> [(Text,Text,Text)]
tupleMeUp3 = go []
  where
    go :: [(Text,Text,Text)] -> [[Text]] -> [(Text,Text,Text)]
    go tuples [] = tuples
    go tuples ([t1, t2, t3]:xs) = go ((t1,t2,t3):tuples) xs
    go _ _ = undefined

solveBOnOne :: (Text,Text,Text) -> Int
solveBOnOne = fromMaybe undefined
            . flip lookup valueMap
            . uncurry3 findCommonItem3

solveB :: Text -> Int
solveB = getSum
       . mconcat
       . map (Sum . solveBOnOne)
       . tupleMeUp3
       . chunksOf 3
       . T.lines