defmodule Integrations.HttpAbsent do
  @moduledoc """
  HTTP absence check.

  The inverse of the HTTP integration: healthy when the URL is *not* reachable,
  down when it is. Useful for verifying a decommissioned service is gone, a
  firewall rule is blocking a destination, or a site is intentionally offline.

  Collection only — see `Integrations.HttpAbsent.Display` (same package) for
  the dashboard panel. `Display.BundledDefault` auto-hooks it whenever this
  monitor starts, same as a single-module package would; a release without
  `raven_web` simply never compiles the display half and runs this monitor
  headless.

  ## Params

    * `:url`        — The URL to check. Required.
    * `:timeout_ms` — Request timeout in milliseconds. Defaults to `10_000`.

  ## Example config

      %CodeNameRaven.Monitor.Config{
        id:          "old-api-gone",
        name:        "Old API Decommissioned",
        module:      Integrations.HttpAbsent,
        params:      %{url: "https://old-api.example.com"},
        interval_ms: 300_000,
        enabled:     true,
        tags:        ["infra"]
      }

  ## Health signal

    * `:up`   — Connection failed or timed out (site is unreachable — expected)
    * `:down` — Site responded with any HTTP status (site is reachable — unexpected)
  """

  use CodeNameRaven.Monitor

  @default_timeout_ms 10_000

  @impl true
  def params_template, do: %{url: "https://"}

  @impl true
  def params_schema do
    [
      url:        [type: :string,          required: true,  doc: "URL that should be unreachable (healthy when 4xx/5xx or no response)"],
      timeout_ms: [type: :non_neg_integer, default: 10_000, doc: "Request timeout in milliseconds"]
    ]
  end


  @impl true
  def target_uri(%{url: url}) when is_binary(url), do: {:ok, url}
  def target_uri(_params), do: :none

  @impl true
  def collect(%{url: _} = params, state), do: do_collect(params, state)
  def collect(params, state),
    do: {:error, "missing required param :url — got: #{inspect(params)}", state}

  defp do_collect(%{url: url} = params, state) do
    timeout_ms = Map.get(params, :timeout_ms, @default_timeout_ms)

    result =
      case Req.get(url, receive_timeout: timeout_ms, max_retries: 1) do
        {:ok, %{status: code}} -> %{url: url, reachable: true,  status_code: code}
        {:error, _reason}      -> %{url: url, reachable: false, status_code: nil}
      end

    {:ok, result, state}
  end

  @impl true
  def healthy?(%{reachable: false}), do: :up
  def healthy?(%{reachable: true}),  do: :down
end