document_update_pipeline.ex

defmodule Document.UpdatePipeline do
  use Opus.Pipeline
  
  check :validate_params, with: &match(%{"id" => id} when is_number(id), &1.params)
  step :fetch_document,   with: &(put_in &1[:document], Document.get(get_in(&1, [:params, "id"])), error_message: :not_found
  check :can_view?,       with: &Authorizer.can_view(&1.document, &1.user)
  check :can_edit?,       with: &Authorizer.can_view(&1.document, &1.user)
  step :update,           with: &(put_in &1[:updated_document], Documents.update(&1.document, &1.params))
  tee :notify,            with: &Notifications.push_document_updated(&1.updated_document)
  step :finalize,         with: &(&1.updated_document)
end

# Controller Code
def update(conn, params \\ %{}) do
  case Document.UpdatePipeline.call(%{user: conn.assigns.user, params: params}) do
    {:ok, document} -> json(conn, document)
    {:error, %{error: error, stage: stage}} when error == :not_found or stage: :can_view? -> 
      render(conn, ErrorView, :"404")
      
    {:error, %{stage: :can_edit?}} ->
      render(conn, ErrorView, :"403")
      
    {:error, %{error: %Ecto.Changeset{} = changeset}}
     render(conn, ErrorView, :"400", changeset)
  end
end