defmodule AOC.Day5 do
  @upper 'BR'
  @lower 'FL'

  def search_range([], x, x), do: x

  def search_range([hd | tl], low, high) when hd in @lower do
    search_range(tl, low, div(high + 1 + low, 2) - 1)
  end

  def search_range([hd | tl], low, high) when hd in @upper do
    search_range(tl, div(low + high + 1, 2), high)
  end

  def search_seat({row_search, col_search}) do
    row = search_range(row_search, 0, 127)
    column = search_range(col_search, 0, 7)
    {row, column}
  end

  def part1 do
    AOC.Util.input_lines(5, 1)
    |> Enum.map(&String.to_charlist/1)
    |> Enum.map(&Enum.split(&1, 7))
    |> Enum.map(&search_seat/1)
    |> Enum.map(fn {r, c} -> r * 8 + c end)
    |> Enum.max()
  end

  def find_missing_seat([l, r | _]) when r != l + 1, do: l + 1
  def find_missing_seat([_ | tl]), do: find_missing_seat(tl)

  def part2 do
    AOC.Util.input_lines(5, 1)
    |> Enum.map(&String.to_charlist/1)
    |> Enum.map(&Enum.split(&1, 7))
    |> Enum.map(&search_seat/1)
    |> Enum.map(fn {r, c} -> r * 8 + c end)
    |> Enum.sort()
    |> find_missing_seat()
  end
end