From dc9c8fca8e4794faa3c1008cc8ee0ed7b5d4708b Mon Sep 17 00:00:00 2001
From: Claudio Ortolina <cloud8421@gmail.com>
Date: Wed, 17 Sep 2025 09:33:13 +0300
Subject: [PATCH] Add Asset.Transform module

Allows building URLs with embedded transformation options
---
 lib/music_library/assets/transform.ex        | 39 ++++++++++++++++++++
 test/music_library/assets/transform_test.exs |  5 +++
 2 files changed, 44 insertions(+)
 create mode 100644 lib/music_library/assets/transform.ex
 create mode 100644 test/music_library/assets/transform_test.exs

diff --git a/lib/music_library/assets/transform.ex b/lib/music_library/assets/transform.ex
new file mode 100644
index 00000000..037c56fa
--- /dev/null
+++ b/lib/music_library/assets/transform.ex
@@ -0,0 +1,39 @@
+defmodule MusicLibrary.Assets.Transform do
+  @derive JSON.Encoder
+  defstruct [:hash, :width]
+
+  @type t :: %__MODULE__{}
+  @type payload :: String.t()
+
+  @doc """
+    iex> alias MusicLibrary.Assets.Transform
+    iex> transform = %Transform{hash: "abc123", width: 300}
+    iex> Transform.encode!(transform)
+    "eyJoYXNoIjoiYWJjMTIzIiwid2lkdGgiOjMwMH0"
+  """
+  @spec encode!(t()) :: payload()
+  def encode!(transform) do
+    transform
+    |> JSON.encode!()
+    |> Base.url_encode64(padding: false)
+  end
+
+  @doc """
+    iex> alias MusicLibrary.Assets.Transform
+    iex> payload = "eyJoYXNoIjoiYWJjMTIzIiwid2lkdGgiOjMwMH0"
+    iex> Transform.decode!(payload)
+    %Transform{hash: "abc123", width: 300}
+  """
+  @spec decode!(payload()) :: t()
+  def decode!(payload) do
+    params =
+      payload
+      |> Base.url_decode64!(padding: false)
+      |> JSON.decode!()
+
+    struct!(__MODULE__, %{
+      hash: params["hash"],
+      width: params["width"]
+    })
+  end
+end
diff --git a/test/music_library/assets/transform_test.exs b/test/music_library/assets/transform_test.exs
new file mode 100644
index 00000000..8e61be3b
--- /dev/null
+++ b/test/music_library/assets/transform_test.exs
@@ -0,0 +1,5 @@
+defmodule MusicLibrary.Assets.TransformTest do
+  use ExUnit.Case, async: true
+
+  doctest MusicLibrary.Assets.Transform
+end