Add CollectionChat StreamProvider

lib/music_library/chats/collection_chat.ex

@@ -0,0 +1,38 @@
+defmodule MusicLibrary.Chats.CollectionChat do
+  @moduledoc """
+  Chat implementation for the music collection using OpenAI streaming with web search.
+  """
+
+  @behaviour MusicLibrary.Chats.StreamProvider
+
+  alias MusicLibrary.Chats.Prompt
+
+  @impl true
+  @spec stream_response([map()], String.t(), (String.t() -> any())) :: :ok | {:error, term()}
+  def stream_response(messages, collection_summary, callback) do
+    instructions = build_instructions(collection_summary)
+
+    OpenAI.chat_stream(messages, on_chunk: callback, instructions: instructions)
+  end
+
+  defp build_instructions(collection_summary) do
+    record_count = count_records(collection_summary)
+
+    Prompt.build("""
+    Answer questions about the user's music collection. \
+    Use the provided collection catalog as your primary reference. \
+    The collection contains #{record_count} records.
+
+    Collection catalog:
+    #{collection_summary}\
+    """)
+  end
+
+  defp count_records(""), do: 0
+
+  defp count_records(summary) do
+    summary
+    |> String.split("\n")
+    |> length()
+  end
+end