defmodule ArcadiaCloud.Provisioning.Steps.PointDeploymentDns do
  @moduledoc """
  Points a deployment's hostname at its droplet by upserting an A record.

  Reads the droplet's public IPv4 from context (`droplet_public_ip`, set
  by WaitDropletActive) — the IP isn't known at saga-start, so this can't
  be a generic UpsertDnsRecord with the data baked into inputs.

  Saga inputs:
    dns_domain       — the zone (e.g. "sky-ai.com"); when absent the
                       step is a no-op (deployment opted out of DNS)
    dns_record_name  — subdomain; defaults handled by the assembler
    dns_record_ttl   — optional, defaults 1800

  Behaviour mirrors UpsertDnsRecord: create / no-op / update, with the
  prior record stashed for compensation.
  """

  @behaviour ArcadiaCloud.Provisioning.Step

  alias ArcadiaCloud.DigitalOcean.Client
  alias ArcadiaCloud.Provisioning.SagaState

  @default_ttl 1800
  @type_a "A"

  @impl true
  def name, do: "point_deployment_dns"

  @impl true
  def execute(state) do
    domain = SagaState.get_input(state, :dns_domain)
    rname = SagaState.get_input(state, :dns_record_name)
    ip = SagaState.get_output(state, :droplet_public_ip)
    ttl = SagaState.get_input(state, :dns_record_ttl) || @default_ttl

    cond do
      is_nil(domain) or domain == "" ->
        {:ok, SagaState.put_output(state, :dns_outcome, "skipped")}

      is_nil(rname) or rname == "" ->
        {:error, :missing_dns_record_name}

      is_nil(ip) ->
        {:error, :no_droplet_public_ip_in_context}

      true ->
        upsert(state, domain, rname, ip, ttl)
    end
  end

  @impl true
  def compensate(state) do
    domain = SagaState.get_input(state, :dns_domain)
    outcome = SagaState.get_output(state, :dns_outcome)
    record_id = SagaState.get_output(state, :dns_record_id)

    case outcome do
      "created" -> delete_record(domain, record_id)
      "updated" -> restore_record(state, domain, record_id)
      _ -> :ok
    end
  end

  # ---- execute helpers ------------------------------------------------------

  defp upsert(state, domain, rname, ip, ttl) do
    case find_record(domain, rname) do
      {:ok, nil} ->
        create(state, domain, rname, ip, ttl)

      {:ok, existing} ->
        if normalize(existing["data"]) == normalize(ip) and existing["ttl"] == ttl do
          {:ok, record_outcome(state, existing["id"], "noop", nil)}
        else
          update(state, domain, existing, rname, ip, ttl)
        end

      {:error, reason} ->
        {:error, reason}
    end
  end

  defp create(state, domain, rname, ip, ttl) do
    case Client.create_domain_record(domain, %{type: @type_a, name: rname, data: ip, ttl: ttl}) do
      {:ok, %{"id" => id}} -> {:ok, record_outcome(state, id, "created", nil)}
      {:error, reason} -> {:error, reason}
    end
  end

  defp update(state, domain, existing, rname, ip, ttl) do
    prior = %{
      "type" => existing["type"],
      "name" => existing["name"],
      "data" => existing["data"],
      "ttl" => existing["ttl"]
    }

    case Client.update_domain_record(domain, existing["id"], %{
           type: @type_a,
           name: rname,
           data: ip,
           ttl: ttl
         }) do
      {:ok, %{"id" => id}} -> {:ok, record_outcome(state, id, "updated", prior)}
      {:error, reason} -> {:error, reason}
    end
  end

  defp record_outcome(state, record_id, outcome, prior) do
    state
    |> SagaState.put_output(:dns_record_id, record_id)
    |> SagaState.put_output(:dns_outcome, outcome)
    |> SagaState.put_output(:dns_prior, prior)
  end

  # ---- compensate helpers ---------------------------------------------------

  defp delete_record(domain, record_id) do
    case Client.delete_domain_record(domain, record_id) do
      {:ok, _} -> :ok
      {:error, {:http, 404, _}} -> :ok
      {:error, reason} -> {:error, reason}
    end
  end

  defp restore_record(state, domain, record_id) do
    case SagaState.get_output(state, :dns_prior) do
      nil ->
        :ok

      prior ->
        case Client.update_domain_record(domain, record_id, %{
               type: prior["type"],
               name: prior["name"],
               data: prior["data"],
               ttl: prior["ttl"]
             }) do
          {:ok, _} -> :ok
          {:error, {:http, 404, _}} -> :ok
          {:error, reason} -> {:error, reason}
        end
    end
  end

  # ---- shared ---------------------------------------------------------------

  defp find_record(domain, rname) do
    case Client.list_domain_records(domain) do
      {:ok, records} ->
        {:ok, Enum.find(records, &(&1["type"] == @type_a and &1["name"] == rname))}

      {:error, reason} ->
        {:error, reason}
    end
  end

  defp normalize(nil), do: ""
  defp normalize(v) when is_binary(v), do: v |> String.trim() |> String.trim_trailing(".")
  defp normalize(v), do: to_string(v)
end