defmodule Day4 do
  @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
  """

  def part1(example \\ false) do
    count_all_valid(example, false)
  end

  def part2(example \\ false) do
    count_all_valid(example, true)
  end

  def count_all_valid(example, check_values) do
    if(example, do: @example, else: File.read!("lib/day4/input.txt"))
    |> String.trim()
    |> String.split("\n\n")
    |> parse_input()
    |> count_valid(check_values)
  end

  def parse_input(inputs) do
    Enum.map(inputs, fn input ->
      input
      |> String.split()
      |> Enum.reduce(%{}, fn pair, acc ->
        [k, v] = String.split(pair, ":")
        Map.put(acc, k, v)
      end)
    end)
  end

  @doc """
    iex> Day4.validate_byr("2002")
    true
    iex> Day4.validate_byr("2003")
    false
  """
  def validate_byr(v) do
    Regex.match?(~r/(^19[2-9][0-9]|200[0-2])$/, v)
  end

  @doc """
    iex> Day4.validate_iyr("2010")
    true
    iex> Day4.validate_iyr("2009")
    false
    iex> Day4.validate_iyr("2021")
    false
  """
  def validate_iyr(v) do
    Regex.match?(~r/^(201\d|2020)$/, v)
  end

  @doc """
    iex> Day4.validate_eyr("2020")
    true
    iex> Day4.validate_eyr("2030")
    true
    iex> Day4.validate_eyr("2019")
    false
    iex> Day4.validate_eyr("2031")
    false
  """
  def validate_eyr(v) do
    Regex.match?(~r/^(202\d|2030)$/, v)
  end

  @doc """
    iex> Day4.validate_hgt("60in")
    true
    iex> Day4.validate_hgt("190cm")
    true
    iex> Day4.validate_hgt("190in")
    false
    iex> Day4.validate_hgt("190")
    false
  """
  def validate_hgt(v) do
    Regex.match?(~r/^(1[5-8]\dcm|19[0-9]cm|59in|6\din|7[0-6]in)$/, v)
  end

  @doc """
    iex> Day4.validate_hcl("#123abc")
    true
    iex> Day4.validate_hcl("#123ABC")
    true
    iex> Day4.validate_hcl("#123abz")
    false
    iex> Day4.validate_hcl("123abc")
    false
  """
  def validate_hcl(v) do
    Regex.match?(~r/#[0-9a-f]{6}/i, v)
  end

  @doc """
    iex> Day4.validate_ecl("brn")
    true
    iex> Day4.validate_ecl("wat")
    false
  """
  def validate_ecl(v) do
    Regex.match?(~r/^(amb|b(lu|rn)|gr[yn]|hzl|oth)$/i, v)
  end

  @doc """
    iex> Day4.validate_pid("000000001")
    true
    iex> Day4.validate_pid("0123456789")
    true
  """
  def validate_pid(v) do
    Regex.match?(~r/^\d{9}$/, v)
  end

  @required_keys ["byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid"]

  def count_valid(data, check_values) do
    Enum.count(data, fn passport ->
      is_valid(passport, check_values)
    end)
  end

  def is_valid(data, check_values) do
    Enum.all?(@required_keys, fn k ->
      Map.has_key?(data, k) &&
        (!check_values ||
           apply(Day4, String.to_atom("validate_#{k}"), [Map.fetch!(data, k)]))
    end)
  end
end