defmodule Argos.Parallel.Leader do
  @moduledoc """
  Coordinador que supervisa el ciclo de vida lógico de los workers.

  Arranca workers a través del `DynamicSupervisor`, recibe sus eventos y los
  retransmite a los suscriptores, además de mantener un estado mínimo por worker.
  """

  use GenServer
  require Logger

  alias Argos.Parallel.{LeaderState, Worker, WorkerState}
  alias Argos.Parallel.Logger, as: ParallelLogger

  @default_call_timeout 30_000

  def start_link(opts \\ []) do
    name = Keyword.get(opts, :name, __MODULE__)
    GenServer.start_link(__MODULE__, opts, name: name)
  end

  @doc """
  Inicia múltiples workers con las especificaciones dadas.

  ## Opciones

    * `:timeout` - Timeout para la llamada GenServer (por defecto: 30 segundos)

  ## Ejemplos

      iex> Argos.Parallel.Leader.start_workers([%{id: :w1, tasks: [fn -> :ok end]}])
      [{:ok, #PID<0.123.0>}]
  """
  @spec start_workers(GenServer.server(), [term()], keyword()) :: [term()]
  def start_workers(server \\ __MODULE__, worker_specs, opts \\ [])
      when is_list(worker_specs) do
    timeout = Keyword.get(opts, :timeout, @default_call_timeout)
    GenServer.call(server, {:start_workers, worker_specs}, timeout)
  end

  @doc """
  Suscribe el proceso actual para recibir eventos de workers.

  ## Opciones

    * `:timeout` - Timeout para la llamada GenServer (por defecto: 30 segundos)
  """
  @spec subscribe(GenServer.server(), keyword()) :: :ok
  def subscribe(server \\ __MODULE__, opts \\ []) do
    timeout = Keyword.get(opts, :timeout, @default_call_timeout)
    GenServer.call(server, {:subscribe, self()}, timeout)
  end

  @doc """
  Desuscribe el proceso actual de los eventos de workers.

  ## Opciones

    * `:timeout` - Timeout para la llamada GenServer (por defecto: 30 segundos)
  """
  @spec unsubscribe(GenServer.server(), keyword()) :: :ok
  def unsubscribe(server \\ __MODULE__, opts \\ []) do
    timeout = Keyword.get(opts, :timeout, @default_call_timeout)
    GenServer.call(server, {:unsubscribe, self()}, timeout)
  end

  @doc """
  Obtiene el estado interno del líder.

  ## Opciones

    * `:timeout` - Timeout para la llamada GenServer (por defecto: 30 segundos)
  """
  @spec get_state(GenServer.server(), keyword()) :: map()
  def get_state(server \\ __MODULE__, opts \\ []) do
    timeout = Keyword.get(opts, :timeout, @default_call_timeout)
    GenServer.call(server, :get_state, timeout)
  end

  def stop(server \\ __MODULE__) do
    GenServer.stop(server, :normal)
  end

  @doc """
  Detiene un worker específico por su ID.

  ## Opciones

    * `:timeout` - Timeout para la llamada GenServer (por defecto: 30 segundos)

  ## Retorna

    `{:ok, :stopped}` si el worker se detuvo correctamente,
    `{:error, :not_found}` si el worker no existe, o `{:error, reason}` si hubo otro error.
  """
  @spec stop_worker(GenServer.server(), term(), keyword()) ::
          {:ok, :stopped} | {:error, term()}
  def stop_worker(server \\ __MODULE__, worker_id, opts \\ []) do
    timeout = Keyword.get(opts, :timeout, @default_call_timeout)
    GenServer.call(server, {:stop_worker, worker_id}, timeout)
  end

  @impl true
  def init(opts) do
    dyn_sup = Keyword.get(opts, :dyn_sup_name, Argos.Parallel.DynamicSupervisor)
    name = Keyword.get(opts, :name, __MODULE__)

    state = %LeaderState{dyn_sup: dyn_sup, name: name}
    {:ok, state}
  end

  @impl true
  def handle_call({:subscribe, pid}, _from, %LeaderState{subscribers: subs} = state) do
    Process.monitor(pid)
    {:reply, :ok, %{state | subscribers: MapSet.put(subs, pid)}}
  end

  def handle_call({:unsubscribe, pid}, _from, %LeaderState{subscribers: subs} = state) do
    {:reply, :ok, %{state | subscribers: MapSet.delete(subs, pid)}}
  end

  def handle_call(:get_state, _from, state) do
    public_state =
      state
      |> Map.from_struct()
      |> Map.update!(:workers, & &1)

    {:reply, public_state, state}
  end

  def handle_call({:start_workers, worker_specs}, _from, %LeaderState{dyn_sup: dyn_sup} = state) do
    :telemetry.execute(
      [:argos, :parallel, :workers, :start],
      %{count: length(worker_specs)},
      %{leader: state.name}
    )

    {results, new_workers} =
      Enum.map_reduce(worker_specs, %{}, fn spec, acc ->
        {id, tasks, log_enabled} = normalize_spec(spec)

        if log_enabled do
          try do
            ParallelLogger.register_worker(id, true)
          rescue
            e ->
              Logger.warning("Failed to register worker logger: worker_id=#{inspect(id)}, error=#{inspect(e)}")

              :ok
          end
        end

        child_spec = %{
          id: {:parallel_worker, id},
          start:
            {Worker, :start_link,
             [
               %{
                 leader: self(),
                 id: id,
                 tasks: tasks
               }
             ]},
          restart: :transient,
          shutdown: 5_000,
          type: :worker
        }

        case DynamicSupervisor.start_child(dyn_sup, child_spec) do
          {:ok, pid} ->
            Logger.debug("Started worker #{inspect(id)} -> #{inspect(pid)}")

            worker_state = WorkerState.new(id) |> WorkerState.running(0, length(tasks), nil)
            {{:ok, pid}, Map.put(acc, id, worker_state)}

          {:ok, pid, _info} ->
            Logger.debug("Started worker #{inspect(id)} (info) -> #{inspect(pid)}")

            worker_state = WorkerState.new(id) |> WorkerState.running(0, length(tasks), nil)
            {{:ok, pid}, Map.put(acc, id, worker_state)}

          {:error, reason} ->
            Logger.warning("Could not start worker #{inspect(id)}: #{inspect(reason)}")

            maybe_unregister_logger(log_enabled, id)

            worker_state = WorkerState.new(id) |> WorkerState.error(reason, nil)
            {{:error, reason}, Map.put(acc, id, worker_state)}
        end
      end)

    new_state = %{state | workers: Map.merge(state.workers, new_workers)}

    successful = Enum.count(results, fn {status, _} -> status == :ok end)
    failed = length(results) - successful

    :telemetry.execute(
      [:argos, :parallel, :workers, :started],
      %{successful: successful, failed: failed, total: length(results)},
      %{leader: state.name}
    )

    {:reply, results, new_state}
  end

  def handle_call(
        {:stop_worker, worker_id},
        _from,
        %LeaderState{dyn_sup: dyn_sup, workers: workers, subscribers: subs, name: name} = state
      ) do
    child_id = {:parallel_worker, worker_id}
    result = stop_worker_internal(dyn_sup, child_id, worker_id, name, subs)
    new_workers = update_workers_after_stop(workers, worker_id, result)
    new_state = %{state | workers: new_workers}
    {:reply, result, new_state}
  end

  defp stop_worker_internal(dyn_sup, child_id, worker_id, name, subs) do
    children = DynamicSupervisor.which_children(dyn_sup)
    find_and_stop_worker(children, child_id, worker_id, dyn_sup, name, subs)
  end

  defp find_and_stop_worker(children, child_id, worker_id, dyn_sup, name, subs) do
    case Enum.find(children, fn {id, _pid, _type, _modules} -> id == child_id end) do
      {^child_id, pid, _type, _modules} when is_pid(pid) ->
        terminate_and_notify(dyn_sup, worker_id, pid, name, subs)

      nil ->
        Logger.warning("Worker #{inspect(worker_id)} not found")
        {:error, :not_found}
    end
  end

  defp terminate_and_notify(dyn_sup, worker_id, pid, name, subs) do
    case DynamicSupervisor.terminate_child(dyn_sup, pid) do
      :ok ->
        Logger.debug("Stopped worker #{inspect(worker_id)} -> #{inspect(pid)}")

        try do
          ParallelLogger.unregister_worker(worker_id)
        rescue
          e ->
            Logger.warning("Failed to unregister worker logger during stop: worker_id=#{inspect(worker_id)}, error=#{inspect(e)}")

            :ok
        end

        notify_subscribers(subs, name, worker_id)
        {:ok, :stopped}

      {:error, :not_found} ->
        Logger.warning("Worker #{inspect(worker_id)} not found in supervisor")
        {:error, :not_found}
    end
  end

  defp notify_subscribers(subs, name, worker_id) do
    event = %{
      worker_id: worker_id,
      type: :stopped,
      data: %{reason: :stopped_manually},
      leader: name,
      timestamp: DateTime.utc_now()
    }

    Enum.each(subs, fn sub_pid ->
      send(sub_pid, {:parallel_event, name, event})
    end)
  end

  defp update_workers_after_stop(workers, worker_id, result) do
    case result do
      {:ok, :stopped} ->
        Map.update(workers, worker_id, nil, fn worker ->
          current_task = worker.current_task || 0
          WorkerState.error(worker, :stopped_manually, current_task)
        end)

      {:error, _reason} ->
        workers
    end
  end

  @impl true
  def handle_cast({:worker_msg, worker_id, msg}, %LeaderState{subscribers: subs} = state) do
    new_state = update_state_with_worker_msg(state, worker_id, msg)
    event = build_event(state.name, worker_id, msg)

    Enum.each(subs, fn pid ->
      send(pid, {:parallel_event, state.name, event})
    end)

    {:noreply, new_state}
  end

  @impl true
  def handle_info({:DOWN, _ref, :process, pid, _reason}, %LeaderState{subscribers: subs} = state) do
    {:noreply, %{state | subscribers: MapSet.delete(subs, pid)}}
  end

  def handle_info(msg, state) do
    Logger.debug("Leader received unexpected message: #{inspect(msg)}")
    {:noreply, state}
  end

  defp normalize_spec({id, tasks}) when is_list(tasks), do: {id, tasks, false}

  defp normalize_spec(%{id: id, tasks: tasks} = spec) when is_list(tasks) do
    log_enabled = Map.get(spec, :log, false)
    {id, tasks, log_enabled}
  end

  defp normalize_spec(tasks) when is_list(tasks), do: {make_ref(), tasks, false}
  defp normalize_spec(other), do: {make_ref(), [other], false}

  defp build_event(leader_name, worker_id, {:progress, task_index, total, percent}) do
    %{
      worker_id: worker_id,
      type: :progress,
      data: %{task_index: task_index, total: total, percent: percent},
      leader: leader_name,
      timestamp: DateTime.utc_now()
    }
  end

  defp build_event(leader_name, worker_id, {:result, task_index, result}) do
    %{
      worker_id: worker_id,
      type: :result,
      data: %{task_index: task_index, result: result},
      leader: leader_name,
      timestamp: DateTime.utc_now()
    }
  end

  defp build_event(leader_name, worker_id, {:error, task_index, reason}) do
    %{
      worker_id: worker_id,
      type: :error,
      data: %{task_index: task_index, reason: inspect(reason)},
      leader: leader_name,
      timestamp: DateTime.utc_now()
    }
  end

  defp build_event(leader_name, worker_id, :started) do
    %{
      worker_id: worker_id,
      type: :started,
      data: %{},
      leader: leader_name,
      timestamp: DateTime.utc_now()
    }
  end

  defp build_event(leader_name, worker_id, :finished) do
    %{
      worker_id: worker_id,
      type: :finished,
      data: %{},
      leader: leader_name,
      timestamp: DateTime.utc_now()
    }
  end

  defp update_state_with_worker_msg(
         %LeaderState{workers: workers} = state,
         worker_id,
         {:progress, task_index, total, percent}
       ) do
    workers =
      Map.update(
        workers,
        worker_id,
        WorkerState.new(worker_id) |> WorkerState.running(percent, total, task_index),
        fn worker ->
          WorkerState.running(worker, percent, total, task_index)
        end
      )

    %{state | workers: workers}
  end

  defp update_state_with_worker_msg(
         %LeaderState{workers: workers} = state,
         worker_id,
         {:result, task_index, result}
       ) do
    workers =
      Map.update(
        workers,
        worker_id,
        WorkerState.new(worker_id) |> WorkerState.add_result(task_index, result),
        fn worker ->
          WorkerState.add_result(worker, task_index, result)
        end
      )

    %{state | workers: workers}
  end

  defp update_state_with_worker_msg(
         %LeaderState{workers: workers} = state,
         worker_id,
         {:error, task_index, reason}
       ) do
    workers =
      Map.update(
        workers,
        worker_id,
        WorkerState.new(worker_id) |> WorkerState.error(reason, task_index),
        fn worker ->
          WorkerState.error(worker, reason, task_index)
        end
      )

    %{state | workers: workers}
  end

  defp update_state_with_worker_msg(state, worker_id, :started) do
    workers = Map.put_new_lazy(state.workers, worker_id, fn -> WorkerState.new(worker_id) end)
    %{state | workers: workers}
  end

  defp update_state_with_worker_msg(state, worker_id, :finished) do
    workers =
      Map.update(state.workers, worker_id, WorkerState.new(worker_id), fn worker ->
        WorkerState.finished(worker)
      end)

    %{state | workers: workers}
  end

  defp maybe_unregister_logger(false, _id), do: :ok

  defp maybe_unregister_logger(true, id) do
    ParallelLogger.unregister_worker(id)
  rescue
    e ->
      Logger.warning("Failed to unregister worker logger: worker_id=#{inspect(id)}, error=#{inspect(e)}")

      :ok
  end
end