using System;
using static System.Console;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using Xunit;

namespace AdventOfCode {

  public class Day04 {

    static string[] requiredFields = {
      // "cid" not required because we are hackers
      "byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid"
    };

    static string[] validEyeColors = {
      "amb", "blu", "brn", "gry", "grn", "hzl", "oth"
    };

    static bool IsValidPassport1(string input) {
      string[] fields = input.Split(' ');
      var fieldsPresent = new HashSet<string>();
      foreach (string field in fields) {
        string[] tokens = field.Split(':');
        string key = tokens[0];
        fieldsPresent.Add(key);
      }
      return fieldsPresent.IsSupersetOf(requiredFields);
    }

    static int ParseInt(string value) {
      int result;
      if (!int.TryParse(value, out result)) {
        return -1;
      }
      return result;
    }

    static bool ValidateYear(string value, int min, int max) {
      int year = ParseInt(value);
      return year >= min && year <= max;
    }

    static bool ValidateHeight(string value) {
      string unit = value.Substring(value.Length - 2);
      int amount = ParseInt(value.Substring(0, value.Length - 2));
      if (unit == "cm") {
        return amount >= 150 && amount <= 193;
      } else if (unit == "in") {
        return amount >= 59 && amount <= 76;
      } else {  // not cm or in
        return false;
      }
    }

    static bool IsValidPassport2(string input) {
      string[] fields = input.Split(' ');
      var fieldsPresent = new HashSet<string>();
      foreach (string field in fields) {
        if (field.Length == 0) {
          continue;
        }
        string[] tokens = field.Split(':');
        string key = tokens[0];
        string value = tokens[1];
        bool valid = key switch {
          "byr" => ValidateYear(value, 1920, 2002),
          "iyr" => ValidateYear(value, 2010, 2020),
          "eyr" => ValidateYear(value, 2020, 2030),
          "hgt" => ValidateHeight(value),
          "hcl" => Regex.IsMatch(value, @"^#[0-9a-f]{6}$"),
          "ecl" => validEyeColors.Contains(value),
          "pid" => Regex.IsMatch(value, @"^[0-9]{9}$"),
          _ => false
        };
        if (valid) {
          fieldsPresent.Add(key);
        }
      }
      return fieldsPresent.IsSupersetOf(requiredFields);
    }

    static List<string> ParsePassports(string[] input) {
      var result = new List<string>();
      string passport = "";
      foreach (string line in input) {
        if (line == "") {
          result.Add(passport);
          passport = "";
        } else {
          passport += line + " ";
        }
      }
      result.Add(passport);
      return result;
    }

    static int CountValidPassports1(string[] input) {
      return ParsePassports(input).Count(IsValidPassport1);
    }

    static int CountValidPassports2(string[] input) {
      return ParsePassports(input).Count(IsValidPassport2);
    }

    static int Part1() {
      string[] input = File.ReadAllLines(Util.RootDir + "day04.txt");
      return CountValidPassports1(input);
    }

    static int Part2() {
      string[] input = File.ReadAllLines(Util.RootDir + "day04.txt");
      return CountValidPassports2(input);
    }

    [Fact]
    public static void Test() {
      string[] example =
@"ecl:gry pid:860033327 eyr:2020 hcl:#fffffd
byr:1937 iyr:2017 cid:147 hgt:183cm

iyr:2013 ecl:amb cid:350 eyr:2023 pid:028048884
hcl:#cfa07d byr:1929

hcl:#ae17e1 iyr:2013
eyr:2024
ecl:brn pid:760753108 byr:1931
hgt:179cm

hcl:#cfa07d eyr:2025 pid:166559648
iyr:2011 ecl:brn hgt:59in".Split('\n');

      Assert.Equal(2, CountValidPassports1(example));
      Assert.Equal(256, Part1());

      string[] invalidPassports =
@"eyr:1972 cid:100
hcl:#18171d ecl:amb hgt:170 pid:186cm iyr:2018 byr:1926

iyr:2019
hcl:#602927 eyr:1967 hgt:170cm
ecl:grn pid:012533040 byr:1946

hcl:dab227 iyr:2012
ecl:brn hgt:182cm pid:021572410 eyr:2020 byr:1992 cid:277

hgt:59cm ecl:zzz
eyr:2038 hcl:74454a iyr:2023
pid:3556412378 byr:2007".Split('\n');

      string[] validPassports =
@"pid:087499704 hgt:74in ecl:grn iyr:2012 eyr:2030 byr:1980
hcl:#623a2f

eyr:2029 ecl:blu cid:129 byr:1989
iyr:2014 pid:896056539 hcl:#a97842 hgt:165cm

hcl:#888785
hgt:164cm byr:2001 iyr:2015 cid:88
pid:545766238 ecl:hzl
eyr:2022

iyr:2010 hgt:158cm hcl:#b6652a ecl:blu byr:1944 eyr:2021 pid:093154719".Split('\n');

      List<string> invalid = ParsePassports(invalidPassports);
      Assert.Equal(4, invalid.Count);
      Assert.All(invalid, item => Assert.False(IsValidPassport2(item)));

      List<string> valid = ParsePassports(validPassports);
      Assert.Equal(4, valid.Count);
      Assert.All(valid, item => Assert.True(IsValidPassport2(item)));

      Assert.Equal(198, Part2());
    }
  }
}