feat: Add file reading and parsing functions for Day 1 puzzle solution

lib/advent_code2024.ex

@@ -3,6 +3,37 @@ defmodule AdventCode2024 do
   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.

test/advent_code2024_test.exs

@@ -3,6 +3,19 @@ defmodule AdventCode2024Test do
   doctest AdventCode2024
 
   describe "Day 1: Historian Hysteria" do
+    test "solves day 1 puzzle with actual input file" do
+      assert {:ok, result} = AdventCode2024.solve_day1()
+      assert is_integer(result)
+    end
+
+    test "handles missing input file" do
+      assert {:error, :enoent} = AdventCode2024.solve_day1("nonexistent.txt")
+    end
+
+    test "parses input string correctly" do
+      input = "1\t2\n3\t4\n5\t6"
+      assert {[1, 3, 5], [2, 4, 6]} = AdventCode2024.parse_input(input)
+    end
     test "calculates total distance between two lists using example input" do
       left_list = [3, 4, 2, 1, 3, 3]
       right_list = [4, 3, 5, 3, 9, 3]