defmodule ToweropsWeb.Api.AgentController do
  @moduledoc """
  API controller for remote agent communication.

  Provides endpoints for agents to:
  - Fetch polling configuration
  - Submit metrics
  - Send heartbeats
  """

  use ToweropsWeb, :controller

  alias Towerops.Agent.MetricBatch
  alias Towerops.Agents
  alias Towerops.Snmp

  @doc """
  GET /api/v1/agent/config

  Returns polling configuration for all equipment that should be polled by this agent.
  This includes directly assigned equipment plus equipment that inherits the agent
  from site or organization defaults.
  """
  def get_config(conn, _params) do
    agent_token = conn.assigns.current_agent_token
    equipment_list = Agents.list_agent_polling_targets(agent_token.id)

    config = %{
      version: "1.0",
      poll_interval_seconds: 60,
      equipment: Enum.map(equipment_list, &build_equipment_config/1)
    }

    json(conn, config)
  end

  @doc """
  POST /api/v1/agent/metrics

  Accepts a batch of metrics from the agent and processes them asynchronously.
  Supports both JSON (legacy) and Protocol Buffers (efficient).
  """
  def submit_metrics(conn, params) do
    agent_token = conn.assigns.current_agent_token

    metrics =
      case get_req_header(conn, "content-type") do
        ["application/x-protobuf" | _] ->
          # Decode protobuf
          {:ok, body, _conn} = Plug.Conn.read_body(conn)
          batch = MetricBatch.decode(body)
          convert_protobuf_metrics(batch.metrics)

        _ ->
          # JSON format (fallback)
          Map.get(params, "metrics", [])
      end

    _ =
      Task.start(fn ->
        process_metrics(agent_token, metrics)
      end)

    json(conn, %{status: "accepted", received: length(metrics)})
  end

  @doc """
  POST /api/v1/agent/heartbeat

  Updates the agent's last_seen_at timestamp and metadata.
  """
  def heartbeat(conn, params) do
    agent_token = conn.assigns.current_agent_token
    ip = to_string(:inet_parse.ntoa(conn.remote_ip))

    metadata = %{
      "version" => Map.get(params, "version"),
      "hostname" => Map.get(params, "hostname"),
      "uptime_seconds" => Map.get(params, "uptime_seconds")
    }

    # Update synchronously in the heartbeat endpoint
    Agents.update_agent_token_heartbeat(agent_token.id, ip, metadata)

    json(conn, %{status: "ok"})
  end

  # Private helpers

  defp build_equipment_config(equipment) do
    device = equipment.snmp_device

    %{
      id: equipment.id,
      name: equipment.name,
      ip_address: equipment.ip_address,
      snmp: %{
        enabled: equipment.snmp_enabled,
        version: equipment.snmp_version,
        community: equipment.snmp_community,
        port: equipment.snmp_port || 161
      },
      poll_interval_seconds: equipment.check_interval_seconds || 60,
      sensors: build_sensor_config(device),
      interfaces: build_interface_config(device)
    }
  end

  defp build_sensor_config(nil), do: []

  defp build_sensor_config(device) do
    Enum.map(device.sensors, fn sensor ->
      %{
        id: sensor.id,
        type: sensor.sensor_type,
        oid: sensor.sensor_oid,
        divisor: sensor.sensor_divisor,
        unit: sensor.sensor_unit,
        metadata: sensor.metadata
      }
    end)
  end

  defp build_interface_config(nil), do: []

  defp build_interface_config(device) do
    Enum.map(device.interfaces, fn interface ->
      %{
        id: interface.id,
        if_index: interface.if_index,
        if_name: interface.if_name
      }
    end)
  end

  defp process_metrics(_agent_token, metrics) do
    Enum.each(metrics, fn metric ->
      case metric do
        %{"type" => "sensor_reading"} = m ->
          Snmp.create_sensor_reading(%{
            sensor_id: m["sensor_id"],
            value: m["value"],
            status: m["status"] || "ok",
            checked_at: parse_timestamp(m["timestamp"])
          })

        %{"type" => "interface_stat"} = m ->
          Snmp.create_interface_stat(%{
            interface_id: m["interface_id"],
            if_in_octets: m["if_in_octets"],
            if_out_octets: m["if_out_octets"],
            if_in_errors: m["if_in_errors"],
            if_out_errors: m["if_out_errors"],
            if_in_discards: m["if_in_discards"],
            if_out_discards: m["if_out_discards"],
            checked_at: parse_timestamp(m["timestamp"])
          })

        _ ->
          :ok
      end
    end)
  end

  defp convert_protobuf_metrics(metrics) do
    metrics
    |> Enum.map(fn metric ->
      case metric.metric_type do
        {:sensor_reading, sr} ->
          %{
            "type" => "sensor_reading",
            "sensor_id" => sr.sensor_id,
            "value" => sr.value,
            "status" => sr.status,
            "timestamp" => sr.timestamp
          }

        {:interface_stat, is} ->
          %{
            "type" => "interface_stat",
            "interface_id" => is.interface_id,
            "if_in_octets" => is.if_in_octets,
            "if_out_octets" => is.if_out_octets,
            "if_in_errors" => is.if_in_errors,
            "if_out_errors" => is.if_out_errors,
            "if_in_discards" => is.if_in_discards,
            "if_out_discards" => is.if_out_discards,
            "timestamp" => is.timestamp
          }

        _ ->
          nil
      end
    end)
    |> Enum.reject(&is_nil/1)
  end

  defp parse_timestamp(nil), do: DateTime.truncate(DateTime.utc_now(), :second)

  defp parse_timestamp(ts) when is_integer(ts) do
    ts
    |> DateTime.from_unix!(:second)
    |> DateTime.truncate(:second)
  end

  defp parse_timestamp(ts) when is_binary(ts) do
    case DateTime.from_iso8601(ts) do
      {:ok, dt, _} -> DateTime.truncate(dt, :second)
      _ -> DateTime.truncate(DateTime.utc_now(), :second)
    end
  end
end