[Enhancement] Support Multiple YouTube API Keys (#606)

* feat: multiple YouTube API keys

* fix: requested changes

lib/pinchflat/fast_indexing/youtube_api.ex

@@ -12,6 +12,8 @@ defmodule Pinchflat.FastIndexing.YoutubeApi do
 
   @behaviour YoutubeBehaviour
 
+  @agent_name {:global, __MODULE__.KeyIndex}
+
   @doc """
   Determines if the YouTube API is enabled for fast indexing by checking
   if the user has an API key set
@@ -19,7 +21,7 @@ defmodule Pinchflat.FastIndexing.YoutubeApi do
   Returns boolean()
   """
   @impl YoutubeBehaviour
-  def enabled?(), do: is_binary(api_key())
+  def enabled?, do: Enum.any?(api_keys())
 
   @doc """
   Fetches the recent media IDs from the YouTube API for a given source.
@@ -74,8 +76,45 @@ defmodule Pinchflat.FastIndexing.YoutubeApi do
     |> FunctionUtils.wrap_ok()
   end
 
-  defp api_key do
-    Settings.get!(:youtube_api_key)
+  defp api_keys do
+    case Settings.get!(:youtube_api_key) do
+      nil ->
+        []
+
+      keys ->
+        keys
+        |> String.split(",")
+        |> Enum.map(&String.trim/1)
+        |> Enum.reject(&(&1 == ""))
+    end
+  end
+
+  defp get_or_start_api_key_agent do
+    case Agent.start(fn -> 0 end, name: @agent_name) do
+      {:ok, pid} -> pid
+      {:error, {:already_started, pid}} -> pid
+    end
+  end
+
+  # Gets the next API key in round-robin fashion
+  defp next_api_key do
+    keys = api_keys()
+
+    case keys do
+      [] ->
+        nil
+
+      keys ->
+        pid = get_or_start_api_key_agent()
+
+        current_index =
+          Agent.get_and_update(pid, fn current ->
+            {current, rem(current + 1, length(keys))}
+          end)
+
+        Logger.debug("Using YouTube API key: #{Enum.at(keys, current_index)}")
+        Enum.at(keys, current_index)
+    end
   end
 
   defp construct_api_endpoint(playlist_id) do
@@ -83,7 +122,7 @@ defmodule Pinchflat.FastIndexing.YoutubeApi do
     property_type = "contentDetails"
     max_results = 50
 
-    "#{api_base}?part=#{property_type}&maxResults=#{max_results}&playlistId=#{playlist_id}&key=#{api_key()}"
+    "#{api_base}?part=#{property_type}&maxResults=#{max_results}&playlistId=#{playlist_id}&key=#{next_api_key()}"
   end
 
   defp http_client do

lib/pinchflat_web/controllers/settings/setting_html/setting_form.html.heex

@@ -34,9 +34,9 @@
 
       <.input
         field={f[:youtube_api_key]}
-        placeholder="ABC123"
+        placeholder="ABC123,DEF456"
         type="text"
-        label="YouTube API Key"
+        label="YouTube API Key(s)"
         help={youtube_api_help()}
         html_help={true}
         inputclass="font-mono text-sm mr-4"