adding store for temp change on aggregate that reflects emitted event…

…s during command excution

lib/helios/aggregate.ex

@@ -18,6 +18,8 @@ defmodule Helios.Aggregate do
 
   @type init_args :: [otp_app: atom, id: aggregate_id]
 
+  @type t :: struct
+
   @doc """
   Returns unique identifier for stream to which events will be persisted.
 
@@ -37,9 +39,9 @@ defmodule Helios.Aggregate do
   struct is defined in different module.
   """
   @callback new(args :: init_args) ::
-        {:ok, aggregate}
-        | {:stop, term}
-        | :ignore
+              {:ok, aggregate}
+              | {:stop, term}
+              | :ignore
 
   @doc """
   Applies single event to aggregate when replied or after `handle_exec/3` is executed.
@@ -92,7 +94,49 @@ defmodule Helios.Aggregate do
     end
   end
 
+  @doc """
+  Returns aggregate state from context.
+
+  State can be only accessed once pipeline enters in aggregate process.
+  """
+  @spec state(Helios.Context.t()) :: t | nil
   def state(%Context{assigns: %{aggregate: aggregate}}), do: aggregate
 
   def state(_ctx), do: nil
+
+  @change_key :helios_aggregate_change
+
+  @spec get_change(Helios.Context.t()) :: struct
+  def get_change(ctx) do
+    Map.get(ctx.private, @change_key, state(ctx))
+  end
+
+  @spec put_change(Context.t(), struct) :: Context.t()
+  def put_change(ctx, change) do
+    private = Map.put(ctx.private, @change_key, change)
+    %{ctx | private: private}
+  end
+
+
+
+  #
+  # Validators
+  #
+
+  @doc """
+  Validates required parameters
+
+
+  """
+  def validate_required(ctx, fields, opts \\ []) do
+    fields =
+      fields
+      |> List.wrap()
+      |> Enum.map(fn key ->
+        case key do
+          k when is_atom(k) -> Atom.to_string(k)
+          k -> k
+        end
+      end)
+  end
 end