day 2 part 2

2021/lib/advent_of_code/day02.ex

@@ -2,6 +2,10 @@ defmodule AdventOfCode.Day02 do
   @moduledoc """
   Day 2
   """
+
+  def parse_action("forward " <> v), do: {:forward, String.to_integer(v)}
+  def parse_action("down " <> v), do: {:down, String.to_integer(v)}
+  def parse_action("up " <> v), do: {:up, String.to_integer(v)}
 end
 
 defmodule AdventOfCode.Day02.Part1 do
@@ -23,10 +27,6 @@ defmodule AdventOfCode.Day02.Part1 do
     |> product()
   end
 
-  defp parse_action("forward " <> v), do: {:forward, String.to_integer(v)}
-  defp parse_action("down " <> v), do: {:down, String.to_integer(v)}
-  defp parse_action("up " <> v), do: {:up, String.to_integer(v)}
-
   defp apply_action({:forward, v}, {horiz, depth}), do: {horiz + v, depth}
   defp apply_action({:down, v}, {horiz, depth}), do: {horiz, depth + v}
   defp apply_action({:up, v}, {horiz, depth}), do: {horiz, depth - v}
@@ -45,8 +45,18 @@ defmodule AdventOfCode.Day02.Part2 do
   import AdventOfCode.Day02, warn: false
 
   @impl PuzzleSolver
-  def solve(_input_stream) do
-    :ok |> to_string()
+  def solve(input_stream) do
+    input_stream
+    |> Stream.map(&String.trim/1)
+    |> Stream.map(&parse_action/1)
+    |> Enum.reduce({0, 0, 0}, &apply_action/2)
+    |> product()
   end
+
+  defp apply_action({:forward, v}, {horiz, depth, aim}), do: {horiz + v, depth + aim * v, aim}
+  defp apply_action({:down, v}, {horiz, depth, aim}), do: {horiz, depth, aim + v}
+  defp apply_action({:up, v}, {horiz, depth, aim}), do: {horiz, depth, aim - v}
+
+  defp product({x, y, _z}), do: x * y
 end
 

2021/test/advent_of_code/day02/part_2_test.exs

@@ -1,11 +1,16 @@
 defmodule AdventOfCode.Day02.Part2Test do
   use AdventOfCode.PuzzleCase, module: AdventOfCode.Day02.Part2
 
-  test "returns :ok" do
+  test "returns the product of horizontal position and depth" do
     input = ~S"""
-    input
+    forward 5
+    down 5
+    forward 8
+    up 3
+    down 8
+    forward 2
     """
 
-    assert_solution(input, "ok")
+    assert_solution(input, 900)
   end
 end