From cbee3ae795c1a5f316069df3245cfd4b6ded9b7e Mon Sep 17 00:00:00 2001
From: Alexandra Wolf <alexwolf1991@proton.me>
Date: Thu, 5 Oct 2023 01:09:23 +0200
Subject: [PATCH] :construction: subscriber: Comment out handle_batch/4 and add
 a generic message passing based subscriber

---
 lib/gazet/subscriber.ex         | 30 +++++++------
 lib/gazet/subscriber/generic.ex | 75 +++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+), 13 deletions(-)
 create mode 100644 lib/gazet/subscriber/generic.ex

diff --git a/lib/gazet/subscriber.ex b/lib/gazet/subscriber.ex
index d9a182c..77cff95 100644
--- a/lib/gazet/subscriber.ex
+++ b/lib/gazet/subscriber.ex
@@ -41,19 +41,20 @@ defmodule Gazet.Subscriber do
   @type implementation :: module
 
   @type opts :: [unquote(Gazet.Options.typespec(schema))]
+  # TODO: Allow state modification?
   @type result :: :ok | :skip | {:error, reason :: any}
 
   @callback init(spec) :: {:ok, config()} | {:error, reason :: any}
 
-  @callback handle_batch(
-              topic :: Gazet.topic(),
-              batch ::
-                nonempty_list({
-                  Gazet.Message.data(),
-                  Gazet.Message.metadata()
-                }),
-              config :: config
-            ) :: result
+  # @callback handle_batch(
+  #             topic :: Gazet.topic(),
+  #             batch ::
+  #               nonempty_list({
+  #                 Gazet.Message.data(),
+  #                 Gazet.Message.metadata()
+  #               }),
+  #             config :: config
+  #           ) :: result
 
   @callback handle_message(
               topic :: Gazet.topic(),
@@ -70,8 +71,6 @@ defmodule Gazet.Subscriber do
               config :: config
             ) :: result
 
-  @optional_callbacks handle_message: 4, handle_error: 5
-
   @spec spec(spec | opts) :: Gazet.Spec.result(__MODULE__)
   def spec(values), do: Gazet.Spec.build(__MODULE__, values)
   @spec spec!(spec | opts) :: spec | no_return
@@ -119,9 +118,14 @@ defmodule Gazet.Subscriber do
       end
 
       @impl Gazet.Subscriber
-      def init(%Gazet.Subscriber{extra: extra}), do: {:ok, extra}
+      def init(%Gazet.Subscriber{config: config}), do: {:ok, config}
+
+      @impl Gazet.Subscriber
+      def handle_error(reason, _topic, _message, _metadata, _config) do
+        {:error, reason}
+      end
 
-      defoverridable init: 1
+      defoverridable init: 1, handle_error: 5
     end
   end
 end
diff --git a/lib/gazet/subscriber/generic.ex b/lib/gazet/subscriber/generic.ex
new file mode 100644
index 0000000..aad506f
--- /dev/null
+++ b/lib/gazet/subscriber/generic.ex
@@ -0,0 +1,75 @@
+defmodule Gazet.Subscriber.Generic do
+  use GenServer
+
+  alias Gazet.Subscriber
+
+  def child_spec(%Subscriber{adapter_opts: opts} = subscriber) do
+    Supervisor.child_spec(
+      %{
+        id: subscriber.id,
+        start: {__MODULE__, :start_link, [subscriber]}
+      },
+      opts[:child_spec] || []
+    )
+  end
+
+  def start_link(%Subscriber{} = subscriber) do
+    GenServer.start_link(__MODULE__, subscriber, subscriber.adapter_opts[:start_opts] || [])
+  end
+
+  def init(%Subscriber{module: module} = subscriber) do
+    with {:ok, config} <- module.init(subscriber) do
+      {
+        :ok,
+        %{subscriber | config: config},
+        {:continue, {:on_start, subscriber.adapter_opts[:on_start]}}
+      }
+    end
+  end
+
+  def handle_continue({:on_start, nil}, %Subscriber{} = subscriber) do
+    {:noreply, subscriber}
+  end
+
+  def handle_continue({:on_start, on_start}, %Subscriber{} = subscriber) do
+    on_start
+    |> case do
+      function when is_function(function, 0) ->
+        function.()
+
+      function when is_function(function, 1) ->
+        function.(subscriber)
+
+      {module, function, args} ->
+        apply(module, function, [subscriber | args])
+    end
+    |> case do
+      :ok -> {:noreply, subscriber}
+      {:ok, %Subscriber{} = subscriber} -> {:noreply, subscriber}
+      {:error, reason} -> {:stop, reason}
+    end
+  end
+
+  def handle_info(
+        {:message, topic, %Gazet.Message{} = message},
+        %Subscriber{module: module} = subscriber
+      ) do
+    case module.handle_message(topic, message.data, message.metadata, subscriber.config) do
+      fine when fine in [:ok, :skip] ->
+        {:noreply, subscriber}
+
+      {:error, reason} ->
+        handle_error(reason, topic, message, subscriber)
+    end
+  end
+
+  defp handle_error(reason, topic, message, %{module: module} = subscriber) do
+    case module.handle_error(reason, topic, message.data, message.metadata, subscriber.config) do
+      fine when fine in [:ok, :skip] ->
+        {:noreply, subscriber}
+
+      {:error, reason} ->
+        {:stop, reason}
+    end
+  end
+end