defmodule Symbiont.Heartbeat do
  @moduledoc """
  Periodic health check and queue processor.

  Runs on a configurable interval (default: 5 minutes).
  Each tick:
    1. Checks system health (API responding, disk space, ledger writable)
    2. Processes pending tasks from the queue
    3. Logs a health snapshot to heartbeat.jsonl
  """
  use GenServer

  require Logger

  # -- Client API --

  def start_link(opts) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end

  @doc "Trigger a heartbeat manually (useful for testing)."
  def pulse do
    GenServer.call(__MODULE__, :pulse, 60_000)
  end

  @doc "Get the last recorded health snapshot."
  def last_snapshot do
    GenServer.call(__MODULE__, :last_snapshot)
  end

  # -- Server Callbacks --

  @impl true
  def init(_opts) do
    interval = Application.get_env(:symbiont, :heartbeat_interval_ms, 300_000)
    data_dir = Application.get_env(:symbiont, :data_dir, "data")
    heartbeat_path = Path.join(data_dir, "heartbeat.jsonl")

    unless File.exists?(heartbeat_path), do: File.write!(heartbeat_path, "")

    # Schedule first heartbeat after a short delay (let other services start)
    Process.send_after(self(), :tick, 5_000)

    state = %{
      interval: interval,
      heartbeat_path: heartbeat_path,
      last_snapshot: nil,
      started_at: DateTime.utc_now()
    }

    {:ok, state}
  end

  @impl true
  def handle_info(:tick, state) do
    snapshot = run_heartbeat(state)
    schedule_next(state.interval)
    {:noreply, %{state | last_snapshot: snapshot}}
  end

  @impl true
  def handle_call(:pulse, _from, state) do
    snapshot = run_heartbeat(state)
    {:reply, snapshot, %{state | last_snapshot: snapshot}}
  end

  @impl true
  def handle_call(:last_snapshot, _from, state) do
    {:reply, state.last_snapshot, state}
  end

  # -- Private --

  defp run_heartbeat(state) do
    Logger.info("Heartbeat: running health check")

    # 1. Check health
    queue_size = Symbiont.Queue.size()
    ledger_stats = Symbiont.Ledger.stats()

    # 2. Process pending tasks
    max_batch = Application.get_env(:symbiont, :max_queue_batch, 5)
    tasks_processed = process_queue(max_batch)

    # 3. Build snapshot
    snapshot = %{
      "timestamp" => DateTime.utc_now() |> DateTime.to_iso8601(),
      "status" => "healthy",
      "queue_size" => queue_size,
      "tasks_processed" => tasks_processed,
      "total_calls" => ledger_stats["total_calls"],
      "total_cost" => ledger_stats["total_cost_estimated_usd"],
      "uptime_seconds" =>
        DateTime.diff(DateTime.utc_now(), state.started_at, :second)
    }

    # 4. Log snapshot
    line = Jason.encode!(snapshot) <> "\n"
    File.write!(state.heartbeat_path, line, [:append])

    Logger.info(
      "Heartbeat: queue=#{queue_size} processed=#{tasks_processed} " <>
        "total_cost=$#{ledger_stats["total_cost_estimated_usd"]}"
    )

    snapshot
  end

  defp process_queue(max_batch) do
    tasks = Symbiont.Queue.take(max_batch)

    Enum.each(tasks, fn task ->
      Task.Supervisor.start_child(Symbiont.TaskSupervisor, fn ->
        case Symbiont.Router.route_and_execute(task["task"]) do
          {:ok, result} ->
            text = result[:result] || ""

            if blocked_result?(text) do
              Logger.warning(
                "Heartbeat: task #{task["id"]} returned but self-reported blocked — marking blocked"
              )
              Symbiont.Queue.block(task["id"], text)
            else
              Symbiont.Queue.complete(task["id"], text)
            end

          {:error, reason} ->
            Symbiont.Queue.fail(task["id"], inspect(reason))
        end
      end)
    end)

    length(tasks)
  end

  # Heuristic: the LLM ran successfully but its text indicates an
  # unresolved obstacle rather than completed work. Without this the
  # queue marks every CLI success as `done`, which is what produced
  # the false-done loop fixed in 767ab4d (permission errors recorded
  # as task results). The patterns below are conservative — only
  # explicit, opening-position self-reports of blockage qualify.
  defp blocked_result?(text) when is_binary(text) do
    head =
      text
      |> String.trim_leading()
      |> String.slice(0, 400)
      |> String.downcase()

    patterns = [
      "i need permission",
      "i need write permission",
      "i need read permission",
      "i need access",
      "i don't have permission",
      "i do not have permission",
      "i don't have access",
      "i do not have access",
      "could you approve",
      "could you grant",
      "please approve",
      "please grant",
      "would you approve",
      "would you grant",
      "i'm blocked",
      "i am blocked",
      "i'm unable to",
      "i am unable to",
      "i cannot proceed",
      "i can't proceed",
      "permission denied",
      "write permission is blocked",
      "the edit tool keeps getting blocked",
      "blocked on writes",
      "blocked on permission",
      "blocked on write",
      "blocked on read",
      "blocked by the permission system",
      "blocked by the sandbox"
    ]

    Enum.any?(patterns, &String.contains?(head, &1))
  end

  defp blocked_result?(_), do: false

  defp schedule_next(interval) do
    Process.send_after(self(), :tick, interval)
  end
end