defmodule Integrations.BoundaryProbe do
  @moduledoc """
  Watches a named metric from another monitor and emits a health signal based
  on configurable soft and hard boundaries.

  Headless by design — no dashboard card. The alert *is* the product here;
  see `#267` on the backlog for the reasoning. Configure alerting/handlers
  against this monitor's health signal directly.

  ## How it works

  Raven subscribes this monitor to metric events automatically (it's
  `CodeNameRaven.Probe`-shaped — see `probe_init/1`/`on_metric/3` below).
  When a metric event arrives matching the configured `monitor_id` and
  `metric_name`, it updates its cached value and immediately triggers a
  check cycle. `healthy?/1` compares the cached value against the
  configured thresholds.

  ## Params

    * `monitor_id`  — the id of the monitor whose metric to watch (required)
    * `metric_name` — the name of the metric to watch (required)
    * `soft`        — soft threshold (optional); crossing emits `:degraded`
    * `hard`        — hard threshold (optional); crossing emits `:down`

  Thresholds are upper bounds: a value *greater than* the threshold is a
  violation. Both are optional; if neither is set, the probe always returns
  `:up` when a value is present.

  ## Example

  An HTTP monitor publishes `latency_ms` on every check. A BoundaryProbe
  configured as:

      monitor_id  = "my-http-check"
      metric_name = "latency_ms"
      soft        = 500
      hard        = 2000

  returns `:up` when latency < 500ms, `:degraded` when 500–2000ms, and `:down`
  when > 2000ms.
  """

  use CodeNameRaven.Probe
  use CodeNameRaven.Display, size_hint: :small, category: :system

  @impl true
  def params_template do
    %{monitor_id: "", metric_name: "", soft: nil, hard: nil}
  end

  @impl true
  def probe_init(%{monitor_id: monitor_id, metric_name: metric_name} = params)
      when is_binary(monitor_id) and is_binary(metric_name) do
    {:ok,
     %{
       monitor_id: monitor_id,
       metric_name: metric_name,
       soft: params[:soft],
       hard: params[:hard],
       last_value: nil
     }}
  end

  def probe_init(_params), do: {:error, "monitor_id and metric_name are required"}

  @impl true
  def on_metric(
        %{monitor_id: mid, metric_name: name, value: value, node: msg_node},
        _params,
        %{monitor_id: mid, metric_name: name} = state
      ) do
    if msg_node in [nil, :nonode@nohost, node()] do
      {:ok, %{state | last_value: value}, :check_now}
    else
      {:ok, state}
    end
  end

  def on_metric(_metric, _params, state), do: {:ok, state}

  @impl true
  def healthy?(%{last_value: nil}), do: :unknown

  def healthy?(%{last_value: value, soft: soft, hard: hard}) when is_number(value) do
    cond do
      is_number(hard) and value > hard -> :down
      is_number(soft) and value > soft -> :degraded
      true -> :up
    end
  end

  @impl true
  def target_uri(%{monitor_id: mid, metric_name: name}),
    do: {:ok, "boundary://#{mid}/#{name}"}

  def target_uri(_), do: :none

  @impl CodeNameRaven.Display
  def compatible_monitors, do: [__MODULE__]

  @impl CodeNameRaven.Display
  def render(assigns) do
    ~H"""
    <div class="space-y-2">
      <div class="flex items-center gap-2">
        <CodeNameRaven.MonitorComponents.status_badge status={@status} />
        <CodeNameRaven.MonitorComponents.check_time checked_at={@last_checked_at} />
      </div>

      <div :if={@result} class="mt-2 text-sm text-base-content/80">
        <div><span class="font-semibold">Watching:</span> <code class="font-mono bg-base-200 px-1 rounded"><%= @result.monitor_id %>/<%= @result.metric_name %></code></div>
        <div class="mt-1"><span class="font-semibold">Last Value:</span> <span class="font-mono"><%= @result.last_value || "none" %></span></div>
        <div class="mt-1 text-xs text-base-content/50">
          Thresholds: 
          <%= if @result.soft, do: "Soft > #{@result.soft}", else: "" %>
          <%= if @result.hard, do: " | Hard > #{@result.hard}", else: "" %>
          <%= if not @result.soft and not @result.hard, do: "none" %>
        </div>
      </div>

      <CodeNameRaven.MonitorComponents.error_message message={@last_error} />
    </div>
    """
  end
end