day1_p2.exs

defmodule Day1P2 do
  @number_words %{
    "zero" => 0,
    "one" => 1,
    "two" => 2,
    "three" => 3,
    "four" => 4,
    "five" => 5,
    "six" => 6,
    "seven" => 7,
    "eight" => 8,
    "nine" => 9
  }

  # Replaces words representing numbers with the number itself
  def numberify(line) do
    String.replace(line, Map.keys(@number_words), fn word -> to_string(@number_words[word]) end)
  end

  def integers(codepoints) do
    codepoints
    |> Enum.flat_map(fn cp ->
      case Integer.parse(cp) do
        {i, _} -> [i]
        :error -> []
      end
    end)
  end

  def pairs(integers) do
    [List.first(integers), List.last(integers)]
  end
end

{:ok, file} = File.open("data/day1p1.txt")

file
|> IO.stream(:line)
|> Stream.map(&String.trim(&1))
|> Stream.map(&Day1P2.numberify(&1))
 |> Stream.map(&String.codepoints(&1))
 |> Stream.map(&Day1P2.integers/1)
 |> Stream.map(&Day1P2.pairs/1)
 |> Stream.map(fn [a, b] -> a * 10 + b end)
 |> Enum.sum()
 |> IO.puts