Remove after_start/0 and update tests and docs

guides/Events.md

@@ -87,8 +87,8 @@ This will ensure the handler only receives events appended to that stream.
 
 ### Event handler callbacks
 
-- `c:Commanded.Event.Handler.init/0` - (optional) initialisation callback function called when the handler starts.
 - `c:Commanded.Event.Handler.init/1` - (optional) used to configure the handler before it starts.
+- `c:Commanded.Event.Handler.after_start/1` - (optional) initialisation callback function called in the process of the started handler.
 - `c:Commanded.Event.Handler.error/3` - (optional) called when an event handle/2 callback returns an error.
 
 ### Metadata

guides/Usage.md

@@ -104,7 +104,7 @@ Here's an example bank account opening feature built using Commanded to demonstr
         application: BankApp,
         name: __MODULE__
 
-      def init do
+      def after_start(_state) do
         with {:ok, _pid} <- Agent.start_link(fn -> 0 end, name: __MODULE__) do
           :ok
         end

lib/commanded/event/handler.ex

@@ -344,7 +344,7 @@ defmodule Commanded.Event.Handler do
   @type subscribe_from :: :origin | :current | non_neg_integer()
   @type consistency :: :eventual | :strong
 
-  @doc deprecated: "Use the initialize/1 callback instead."
+  @doc deprecated: "Use the after_start/1 callback instead."
   @callback init() :: :ok | {:stop, reason :: any()}
 
   @doc """
@@ -364,7 +364,7 @@ defmodule Commanded.Event.Handler do
           name: "ExampleHandler"
 
         # Optional initialisation
-        def initialize(_handler_state) do
+        def after_start(_handler_state) do
           :ok
         end
 
@@ -375,7 +375,7 @@ defmodule Commanded.Event.Handler do
       end
 
   """
-  @callback initialize(handler_state :: term()) :: :ok | {:stop, reason :: any()}
+  @callback after_start(handler_state :: term()) :: :ok | {:stop, reason :: any()}
 
   @doc """
   Optional callback function called to configure the handler before it starts.
@@ -603,18 +603,15 @@ defmodule Commanded.Event.Handler do
       end
 
       @doc false
-      def init, do: :ok
-
-      @doc false
-      def initialize(_state), do: init()
+      def after_start(_state), do: :ok
 
       @doc false
       def init(config), do: {:ok, config}
 
       @doc false
       def before_reset, do: :ok
 
-      defoverridable init: 0, init: 1, initialize: 1, before_reset: 0
+      defoverridable init: 1, after_start: 1, before_reset: 0
     end
   end
 
@@ -782,12 +779,17 @@ defmodule Commanded.Event.Handler do
 
     %Handler{handler_module: handler_module} = state
 
-    case handler_module.initialize(state.handler_state) do
+    if function_exported?(handler_module, :init, 0) do
+      IO.warn("#{inspect(handler_module)}.init/0 is deprecated, use after_start/1 instead")
+      :ok = handler_module.init()
+    end
+
+    case handler_module.after_start(state.handler_state) do
       :ok ->
         {:noreply, state}
 
       {:stop, reason} ->
-        Logger.debug(describe(state) <> " `init/0` callback has requested to stop")
+        Logger.debug(describe(state) <> " `after_start/1` callback has requested to stop")
 
         {:stop, reason, state}
     end

test/event/support/appending_event_handler.ex

@@ -5,7 +5,7 @@ defmodule Commanded.Event.AppendingEventHandler do
     application: Commanded.DefaultApp,
     name: __MODULE__
 
-  def init do
+  def after_start(_state) do
     with {:ok, _pid} <- Agent.start_link(fn -> %{events: [], metadata: []} end, name: __MODULE__) do
       :ok
     end

test/event/support/concurrency/concurrent_event_handler.ex

@@ -8,7 +8,7 @@ defmodule Commanded.Event.ConcurrentEventHandler do
     concurrency: 5
 
   @impl Commanded.Event.Handler
-  def init do
+  def after_start(_state) do
     Process.send(:test, {:init, self()}, [])
   end
 

test/event/support/concurrency/partition_event_handler.ex

@@ -8,7 +8,7 @@ defmodule Commanded.Event.PartitionEventHandler do
     concurrency: 5
 
   @impl Commanded.Event.Handler
-  def init do
+  def after_start(_state) do
     Process.send(:test, {:init, self()}, [])
   end
 

test/event/support/init/after_start_handler.ex

@@ -0,0 +1,9 @@
+defmodule Commanded.Event.AfterStartHandler do
+  use Commanded.Event.Handler,
+    application: Commanded.MockedApp,
+    name: __MODULE__
+
+  def after_start(_state) do
+    Process.send(:test, {:after_start, self()}, [])
+  end
+end

test/event_handler_after_start_test.exs

@@ -0,0 +1,37 @@
+defmodule Commanded.Event.HandlerAfterStartTest do
+  use Commanded.MockEventStoreCase
+
+  import Mox
+
+  alias Commanded.Event.AfterStartHandler
+  alias Commanded.EventStore.Adapters.Mock, as: MockEventStore
+
+  describe "event handler `after_start/1` callback" do
+    setup do
+      true = Process.register(self(), :test)
+
+      expect(MockEventStore, :subscribe_to, fn
+        _event_store, :all, handler_name, handler, _subscribe_from, _opts ->
+          assert is_binary(handler_name)
+
+          {:ok, handler}
+      end)
+
+      handler = start_supervised!(AfterStartHandler)
+
+      [handler: handler]
+    end
+
+    test "should be called after subscription subscribed", %{handler: handler} do
+      refute_receive {:after_start, ^handler}
+
+      send_subscribed(handler)
+
+      assert_receive {:after_start, ^handler}
+    end
+  end
+
+  defp send_subscribed(handler) do
+    send(handler, {:subscribed, handler})
+  end
+end

test/example_domain/bank_account/account_balance_handler.ex

@@ -9,7 +9,7 @@ defmodule Commanded.ExampleDomain.BankAccount.AccountBalanceHandler do
   alias Commanded.ExampleDomain.BankAccount.Events.MoneyDeposited
   alias Commanded.ExampleDomain.BankAccount.Events.MoneyWithdrawn
 
-  def init do
+  def after_start(_state) do
     with {:ok, _pid} <- Agent.start_link(fn -> 0 end, name: __MODULE__) do
       :ok
     end

test/example_domain/bank_account/bank_account_handler.ex

@@ -8,7 +8,7 @@ defmodule Commanded.ExampleDomain.BankAccount.BankAccountHandler do
 
   alias Commanded.ExampleDomain.BankAccount.Events.BankAccountOpened
 
-  def init do
+  def after_start(_state) do
     case Agent.start_link(fn -> %{prefix: "", accounts: []} end, name: __MODULE__) do
       {:ok, _} -> :ok
       {:error, {:already_started, _}} -> :ok