module Main where

import System.Environment (getArgs)

import Data.List (sort)

import Text.Parsec (parse, many, char, endBy)
import Text.ParserCombinators.Parsec (GenParser)
import Text.ParserCombinators.Parsec.Number (decimal)

line :: GenParser Char st (Int, Int)
line = decimal >>= \l -> many (char ' ') >> decimal >>= \r -> return (l, r)

locationIDs :: GenParser Char st [(Int, Int)]
locationIDs = endBy line (char '\n')

computeDistance :: [Int] -> [Int] -> Int
computeDistance l r = sum (zipWith (curry (abs . uncurry (-))) l r)

main :: IO ()
main = do
    args <- getArgs
    (fp:_) <- return args
    content <- readFile fp
    case parse locationIDs fp content of
        Left e -> putStrLn ("Input file is incorrectly formatted : " ++ show e)
        Right ids -> let (l, r) = unzip ids
                     in putStrLn ("Solution (Part 1) : "
                         ++ show (computeDistance (sort l) (sort r)))