Add module to format numbers

lib/music_library/format_number.ex

@@ -0,0 +1,51 @@
+defmodule MusicLibrary.FormatNumber do
+  @moduledoc """
+  Provides utilities for formatting numbers with human-readable suffixes.
+
+  ## Examples
+
+      iex> MusicLibrary.FormatNumber.to_compact(96591)
+      "96.6k"
+
+      iex> MusicLibrary.FormatNumber.to_compact(1234)
+      "1.2k"
+
+      iex> MusicLibrary.FormatNumber.to_compact(999)
+      "999"
+
+      iex> MusicLibrary.FormatNumber.to_compact(1500000)
+      "1.5M"
+
+      iex> MusicLibrary.FormatNumber.to_compact(2000000000)
+      "2.0B"
+
+      iex> MusicLibrary.FormatNumber.to_compact(0)
+      "0"
+  """
+
+  @doc """
+  Converts an integer to a compact string representation using k, M, B suffixes.
+
+  Numbers less than 1,000 are returned as-is.
+  Numbers 1,000 and above are formatted with appropriate suffix and one decimal place.
+  """
+  def to_compact(number) when is_integer(number) and number < 1000 do
+    Integer.to_string(number)
+  end
+
+  def to_compact(number) when is_integer(number) and number < 1_000_000 do
+    format_with_suffix(number / 1000, "k")
+  end
+
+  def to_compact(number) when is_integer(number) and number < 1_000_000_000 do
+    format_with_suffix(number / 1_000_000, "M")
+  end
+
+  def to_compact(number) when is_integer(number) do
+    format_with_suffix(number / 1_000_000_000, "B")
+  end
+
+  defp format_with_suffix(value, suffix) do
+    "#{:erlang.float_to_binary(value, decimals: 1)}#{suffix}"
+  end
+end

test/music_library/format_number_test.exs

@@ -0,0 +1,4 @@
+defmodule MusicLibrary.FormatNumberTest do
+  use ExUnit.Case, async: true
+  doctest MusicLibrary.FormatNumber
+end