workload-service/lib/workload_service/aggregates/task.ex

defmodule WorkloadService.Aggregates.Task do
  @moduledoc """
  Behaviour and __using__ macro for task aggregates.
  Each task type can override validation and add specific behavior.

  Usage:
    defmodule WorkloadService.Aggregates.QuoteTask do
      use WorkloadService.Aggregates.Task,
        task_type: "quote"
    end

  ## With custom submission type

    defmodule QuoteTaskWithCustomSubmission do
      defmodule CustomSubmission do
        @type t :: %{...custom_fields: term()}
      end

      use WorkloadService.Aggregates.Task,
        task_type: "quote",
        submission_type: CustomSubmission.t()
    end
  """

  @callback validate_submission(map()) :: :ok | {:error, term()}

  defmacro __using__(opts) do
    task_type = Keyword.fetch!(opts, :task_type)
    commands_module = Keyword.get(opts, :commands, WorkloadService.Commands.Task)
    submission_type = Keyword.get(opts, :submission_type, quote(do: map()))

    quote do
      @type t :: %__MODULE__{
              id: WorkloadService.Aggregates.TaskId.t() | nil,
              application_id: WorkloadService.Aggregates.ApplicationId.t() | nil,
              task_info: map() | nil,
              submission: unquote(submission_type) | nil,
              attachments: [String.t()],
              status: String.t() | nil
            }

      @behaviour Commanded.Aggregates.Aggregate
      @task_type unquote(task_type)

      alias unquote(commands_module).CreateTask
      alias unquote(commands_module).SubmitResponse
      alias unquote(commands_module).RequestApproval
      alias unquote(commands_module).ApproveSubmission
      alias unquote(commands_module).CompleteTask

      alias Commanded.Aggregates.Aggregate

      @derive Jason.Encoder
      defstruct [
        :id,
        :application_id,
        :task_info,
        :submission,
        :attachments,
        :status
      ]

      @impl Aggregate
      def execute(%__MODULE__{status: nil}, %CreateTask{} = cmd) do
        %WorkloadService.Events.TaskCreated{
          id: cmd.id,
          application_id: cmd.application_id,
          task_info: cmd.task_info,
          attachments: cmd.attachments || []
        }
      end

      @impl Aggregate
      def execute(%__MODULE__{}, %CreateTask{}) do
        {:error, :task_already_exists}
      end

      @impl Aggregate
      def execute(%__MODULE__{status: status}, %SubmitResponse{} = cmd)
          when status in [nil, "created", "draft", "approved"] do
        with :ok <- validate_submission(cmd.submission) do
          %WorkloadService.Events.SubmissionUpdated{
            id: cmd.id,
            submission: cmd.submission,
            attachments: cmd.attachments
          }
        end
      end

      @impl Aggregate
      def execute(%__MODULE__{status: "draft"}, %RequestApproval{} = cmd) do
        %WorkloadService.Events.ApprovalRequested{
          id: cmd.id
        }
      end

      @impl Aggregate
      def execute(%__MODULE__{status: status}, %RequestApproval{}) do
        {:error, {:invalid_state, "cannot request approval in state: #{status}"}}
      end

      @impl Aggregate
      def execute(%__MODULE__{id: id, status: "draft"}, %ApproveSubmission{}) do
        %WorkloadService.Events.SubmissionApproved{
          id: id
        }
      end

      @impl Aggregate
      def execute(%__MODULE__{status: status}, %ApproveSubmission{}) do
        {:error, {:invalid_state, "cannot approve in state: #{status}"}}
      end

      @impl Aggregate
      def execute(%__MODULE__{status: "approved", id: id}, %CompleteTask{} = cmd) do
        %WorkloadService.Events.TaskCompleted{
          id: id,
          completed_by: cmd.completed_by
        }
      end

      @impl Aggregate
      def execute(%__MODULE__{status: status}, %CompleteTask{}) do
        {:error, {:invalid_state, "cannot complete in state: #{status}"}}
      end

      @impl Aggregate
      def apply(%__MODULE__{} = agg, %WorkloadService.Events.TaskCreated{} = e) do
        %{
          agg
          | id: e.id,
            application_id: e.application_id,
            task_info: e.task_info,
            attachments: e.attachments,
            status: "created"
        }
      end

      @impl Aggregate
      def apply(%__MODULE__{} = agg, %WorkloadService.Events.SubmissionUpdated{} = e) do
        %{
          agg
          | submission: e.submission,
            attachments: e.attachments || [],
            status: "draft"
        }
      end

      @impl Aggregate
      def apply(%__MODULE__{} = agg, %WorkloadService.Events.SubmissionApproved{}) do
        %{
          agg
          | status: "approved"
        }
      end

      @impl Aggregate
      def apply(%__MODULE__{} = agg, %WorkloadService.Events.ApprovalRequested{}) do
        %{
          agg
          | status: "approval_requested"
        }
      end

      @impl Aggregate
      def apply(%__MODULE__{} = agg, %WorkloadService.Events.TaskCompleted{}) do
        %{
          agg
          | status: "completed"
        }
      end

      defoverridable execute: 2, apply: 2
    end
  end
end