feat: added action for updating state to Delivery resource

TODO: add missing state transitions

tololo/lib/tololo/deliveries/delivery.ex

@@ -19,8 +19,19 @@ defmodule Tololo.Deliveries.Delivery do
     repo Tololo.Repo
   end
 
+  code_interface do
+    define :update_state, args: [:state], action: :update_state
+  end
+
   actions do
-    defaults [:read]
+    defaults [:read, :create, :update, :destroy]
+
+    update :update_state do
+      accept [:state]
+      require_atomic? false
+
+      change Tololo.Deliveries.UpdateHistory
+    end
   end
 
   attributes do

tololo/lib/tololo/deliveries/delivery_state_changes.ex

@@ -1,6 +1,6 @@
 defmodule Tololo.Deliveries.DeliveryStateChanges do
   @moduledoc """
-  Stores the state changes of a delivery.
+  Resource that stores the state changes of a delivery.
   """
   use Ash.Resource,
     otp_app: :tololo,
@@ -17,8 +17,13 @@ defmodule Tololo.Deliveries.DeliveryStateChanges do
     repo Tololo.Repo
   end
 
+  code_interface do
+    define :add_to_state_history, args: [:delivery_id, :old_state, :new_state, :comment], action: :create
+  end
+
   actions do
-    defaults [:read]
+    defaults [:read, :create, :destroy]
+    default_accept [:delivery_id, :old_state, :new_state, :comment]
   end
 
   attributes do

tololo/lib/tololo/deliveries/transitions.ex

@@ -0,0 +1,23 @@
+defmodule Tololo.Deliveries.Transitions do
+  @moduledoc """
+  Functions related to delivery state transitions and comments.
+  """
+
+  @state_transitions %{
+    {nil, "In_Preparation"} => "La orden está siendo preparada.",
+    {"In_Preparation", "In_Delivery"} => "La orden está en tránsito."
+    # TODO add all possible states
+  }
+
+  @doc """
+  Generates a comment for a state transition, based on the old and new state.
+  """
+  def generate_comment(old_state, new_state),
+    do: Map.get(@state_transitions, {old_state, new_state})
+
+  @doc """
+  Checks if a state transition is valid.
+  """
+  def valid?(old_state, new_state),
+    do: Map.has_key?(@state_transitions, {old_state, new_state})
+end

tololo/lib/tololo/deliveries/update_history.ex

@@ -0,0 +1,27 @@
+defmodule Tololo.Deliveries.UpdateHistory do
+  @moduledoc """
+  Checks validity of state transition and also adds it to the state history.
+  """
+  alias Tololo.Deliveries.Transitions
+  alias Tololo.Deliveries.DeliveryStateChanges
+
+  use Ash.Resource.Change
+
+  @impl true
+  def change(changeset, _opts, _context) do
+    %{id: id, state: old_state} = changeset.data
+    {:ok, new_state} = Ash.Changeset.fetch_change(changeset, :state)
+
+    case Transitions.valid?(old_state, new_state) do
+      true ->
+        comment = Transitions.generate_comment(old_state, new_state)
+        DeliveryStateChanges.add_to_state_history!(id, old_state, new_state, comment)
+
+        changeset
+
+      false ->
+        changeset
+        |> Ash.Changeset.add_error(field: :state, message: "invalid state transition")
+    end
+  end
+end