defmodule AdventCode2024 do
  @moduledoc """
  Documentation for `AdventCode2024`.
  """

  @doc """
  Reads the input file for day 1 and calculates the total distance between the two lists.
  Returns {:ok, result} if successful, {:error, reason} if there's an error.
  """
  def solve_day1(input_file \\ "day1/input.txt") do
    case File.read(input_file) do
      {:ok, content} ->
        {left_list, right_list} = parse_input(content)
        result = calculate_total_distance(left_list, right_list)
        {:ok, result}
      {:error, reason} -> {:error, reason}
    end
  end

  @doc """
  Parses the input string into two lists of numbers.
  Input format is expected to be tab-separated numbers, one pair per line.
  """
  def parse_input(content) do
    {left, right} =
      content
      |> String.split("\n", trim: true)
      |> Enum.map(&String.split(&1, ~r/\s+/, trim: true))
      |> Enum.map(fn [left, right] -> 
        {String.to_integer(left), String.to_integer(right)}
      end)
      |> Enum.unzip()

    {left, right}
  end

  @doc """
  Calculates the total distance between two lists of numbers.
  Lists are first sorted, then paired up, and the absolute differences are summed.

  ## Examples

      iex> AdventCode2024.calculate_total_distance([3, 4, 2, 1, 3, 3], [4, 3, 5, 3, 9, 3])
      11
      iex> AdventCode2024.calculate_total_distance([], [])
      0
      iex> AdventCode2024.calculate_total_distance([1], [3])
      2

  """
  def calculate_total_distance(left_list, right_list) do
    Enum.zip(Enum.sort(left_list), Enum.sort(right_list))
    |> Enum.map(fn {a, b} -> abs(a - b) end)
    |> Enum.sum()
  end
end