module Main where

import System.Environment (getArgs)

import Text.Parsec (parse, many1, char, sepBy, endBy)
import Text.Parsec.Char (endOfLine)
import Text.ParserCombinators.Parsec (GenParser)
import Text.ParserCombinators.Parsec.Number (decimal)

type Report = [Level]
type Level = Int

reports :: GenParser Char st [Report]
reports = endBy report endOfLine

report :: GenParser Char st Report
report = sepBy level (many1 (char ' '))

level :: GenParser Char st Level
level = decimal

pairUp :: [a] -> [(a, a)]
pairUp (a:b:tl) = (a, b) : pairUp (b:tl)
pairUp _ = []

allIncOrDec :: Report -> Bool
allIncOrDec (a:b:tl)
    | a /= b = all (uncurry (if a < b then (<) else (>))) $ pairUp $ b:tl
    | otherwise = False
allIncOrDec _ = True

notTooDifferent :: Report -> Bool
notTooDifferent (a:b:tl) = let dif = abs (a - b)
                           in (1 <= dif) && (dif <= 3) && notTooDifferent (b:tl)
notTooDifferent _ = True

part1 :: [Report] -> Int
part1 = length . filter allIncOrDec . filter notTooDifferent

main :: IO ()
main = do
    args <- getArgs
    (fp:_) <- return args
    content <- readFile fp
    case parse reports fp content of
        Left e -> putStrLn ("Input file is incorrectly formatted : " ++ show e)
        Right r -> do
            putStrLn ("Solution (Part 1) : " ++ show (part1 r))
            -- putStrLn ("Solution (Part 2) : " ++ show (part2 r))