Main.hs

{-# LANGUAGE DeriveGeneric #-}

module Main where

import qualified Data.Char as Char
import qualified Data.HashMap.Strict as HM
import Data.Hashable
import qualified Data.List.Split as S
import Data.Maybe (mapMaybe)
import GHC.Generics (Generic)

main :: IO ()
main = do
  contents <- readFile "input.txt"
  let entries = map parseEntry (S.splitOn "\n\n" contents)
  print $ length $ filter isEntryValid entries

type PassportEntry = HM.HashMap PassportField String

data PassportField
  = BirthYear
  | IssueYear
  | ExpirationYear
  | Height
  | HairColor
  | EyeColor
  | PassportId
  | CountryId
  deriving (Eq, Show, Generic)

instance Hashable PassportField

parseEntry :: String -> PassportEntry
parseEntry line =
  HM.fromList $
    mapMaybe parseTag $
      S.splitWhen Char.isSpace line

parseTag :: String -> Maybe (PassportField, String)
parseTag value =
  case S.splitOn ":" value of
    ["byr", byr] ->
      Just (BirthYear, byr)
    ["iyr", iyr] ->
      Just (IssueYear, iyr)
    ["eyr", eyr] ->
      Just (ExpirationYear, eyr)
    ["hgt", height] ->
      Just (Height, height)
    ["hcl", color] ->
      Just (HairColor, color)
    ["ecl", color] ->
      Just (EyeColor, color)
    ["pid", pid] ->
      Just (PassportId, pid)
    ["cid", cid] ->
      Just (CountryId, cid)
    _ ->
      Nothing

requiredFields :: [PassportField]
requiredFields =
  [ BirthYear,
    IssueYear,
    ExpirationYear,
    Height,
    HairColor,
    EyeColor,
    PassportId
  ]

isEntryValid :: PassportEntry -> Bool
isEntryValid entry =
  all (`HM.member` entry) requiredFields