defmodule ArcadiaCloud.Provisioning.Steps.ActivateDeployment do
  @moduledoc """
  Final step of the deployment-provisioning choreography: moves the
  deployment from `provisioning` to `active` now that its infra is up,
  registered, linked, and reachable by DNS.

  Idempotent: `transition_state/3` returns `{:ok, deployment}` when the
  deployment is already `active`.

  No compensation: this is the last step, so the saga only ever rolls
  back from a step BEFORE this one — meaning this step never ran and the
  deployment is still `provisioning` (cancelled by
  MarkDeploymentProvisioning's compensate).
  """

  @behaviour ArcadiaCloud.Provisioning.Step

  alias ArcadiaCloud.Deployments

  @impl true
  def name, do: "activate_deployment"

  @impl true
  def execute(state) do
    with {:ok, deployment} <- fetch_deployment(state) do
      case Deployments.transition_state(deployment, "active",
             reason: "provisioning_complete",
             actor: "saga:#{state.saga_id}"
           ) do
        {:ok, _} -> {:ok, state}
        {:error, reason} -> {:error, {:activate_failed, reason}}
      end
    end
  end

  defp fetch_deployment(state) do
    case state.saga && state.saga.deployment_id do
      nil ->
        {:error, :saga_has_no_deployment}

      id ->
        case Deployments.get_deployment(id) do
          nil -> {:error, :deployment_not_found}
          deployment -> {:ok, deployment}
        end
    end
  end
end