argos

defmodule Argos.Command.CircuitBreaker do
  @moduledoc """
  Circuit Breaker para comandos del sistema.

  Implementa el patrón Circuit Breaker para prevenir la ejecución de comandos
  cuando hay demasiados fallos consecutivos. Esto mejora la resiliencia del sistema.

  ## Estados

  - `:closed` - Circuito cerrado, comandos se ejecutan normalmente
  - `:open` - Circuito abierto, comandos se rechazan inmediatamente
  - `:half_open` - Circuito semi-abierto, permite un intento de prueba

  ## Configuración

      config :argos, :circuit_breaker,
        threshold: 5,
        timeout: 60_000,
        enabled: true

  ## Uso

      # Ejecutar comando con circuit breaker
      Argos.Command.exec("risky_command", circuit_breaker: true)
  """

  use GenServer

  require Logger

  @default_threshold 5
  @default_timeout 60_000
  @default_enabled true

  defstruct [
    :state,
    :failure_count,
    :last_failure_time,
    :threshold,
    :timeout,
    :enabled
  ]

  @type state :: :closed | :open | :half_open
  @type t :: %__MODULE__{
          state: state(),
          failure_count: non_neg_integer(),
          last_failure_time: integer() | nil,
          threshold: non_neg_integer(),
          timeout: non_neg_integer(),
          enabled: boolean()
        }

  @doc """
  Inicia el Circuit Breaker.
  """
  @spec start_link(keyword()) :: GenServer.on_start()
  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end

  @doc """
  Verifica si el circuito permite ejecutar un comando.
  """
  @spec call(atom(), (-> result)) :: {:ok, result} | {:error, :circuit_open} | {:error, term()}
        when result: term()
  def call(key, fun) when is_function(fun, 0) do
    GenServer.call(__MODULE__, {:call, key, fun}, :infinity)
  end

  @doc """
  Registra un éxito en el circuito.
  """
  @spec success(atom()) :: :ok
  def success(key) do
    GenServer.cast(__MODULE__, {:success, key})
  end

  @doc """
  Registra un fallo en el circuito.
  """
  @spec failure(atom()) :: :ok
  def failure(key) do
    GenServer.cast(__MODULE__, {:failure, key})
  end

  @doc """
  Obtiene el estado actual del circuito.
  """
  @spec get_state(atom()) :: state()
  def get_state(key) do
    GenServer.call(__MODULE__, {:get_state, key}, :infinity)
  end

  @doc """
  Resetea el circuito a estado cerrado.
  """
  @spec reset(atom()) :: :ok
  def reset(key) do
    GenServer.cast(__MODULE__, {:reset, key})
  end

  @impl true
  def init(opts) do
    threshold = Keyword.get(opts, :threshold, @default_threshold)
    timeout = Keyword.get(opts, :timeout, @default_timeout)
    enabled = Keyword.get(opts, :enabled, @default_enabled)

    state = %__MODULE__{
      state: :closed,
      failure_count: 0,
      last_failure_time: nil,
      threshold: threshold,
      timeout: timeout,
      enabled: enabled
    }

    {:ok, %{default: state}}
  end

  @impl true
  def handle_call({:call, key, fun}, _from, state) do
    circuit = Map.get(state, key, state.default)

    if circuit.enabled do
      handle_enabled_circuit(circuit, key, fun, state)
    else
      execute_without_circuit_breaker(fun, state)
    end
  end

  def handle_call({:get_state, key}, _from, state) do
    circuit = Map.get(state, key, state.default)
    {:reply, circuit.state, state}
  end

  defp execute_without_circuit_breaker(fun, state) do
    result = fun.()
    {:reply, {:ok, result}, state}
  rescue
    e -> {:reply, {:error, e}, state}
  catch
    :exit, reason -> {:reply, {:error, {:exit, reason}}, state}
    :throw, reason -> {:reply, {:error, {:throw, reason}}, state}
  end

  defp handle_enabled_circuit(circuit, key, fun, state) do
    case circuit.state do
      :closed -> handle_closed_circuit(circuit, key, fun, state)
      :open -> handle_open_circuit(circuit, key, fun, state)
      :half_open -> handle_half_open_circuit(circuit, key, fun, state)
    end
  end

  defp handle_closed_circuit(circuit, key, fun, state) do
    result = fun.()
    new_circuit = %{circuit | failure_count: 0}
    new_state = Map.put(state, key, new_circuit)
    {:reply, {:ok, result}, new_state}
  rescue
    e ->
      new_circuit = record_failure(circuit)
      new_state = Map.put(state, key, new_circuit)
      {:reply, {:error, e}, new_state}
  catch
    :exit, reason ->
      new_circuit = record_failure(circuit)
      new_state = Map.put(state, key, new_circuit)
      {:reply, {:error, {:exit, reason}}, new_state}

    :throw, reason ->
      new_circuit = record_failure(circuit)
      new_state = Map.put(state, key, new_circuit)
      {:reply, {:error, {:throw, reason}}, new_state}
  end

  defp handle_open_circuit(circuit, key, fun, state) do
    if should_transition_to_half_open?(circuit) do
      new_circuit = %{circuit | state: :half_open, failure_count: 0}
      new_state = Map.put(state, key, new_circuit)

      try do
        result = fun.()
        new_circuit = %{new_circuit | state: :closed, failure_count: 0}
        new_state = Map.put(new_state, key, new_circuit)
        {:reply, {:ok, result}, new_state}
      rescue
        e ->
          new_circuit = %{new_circuit | state: :open, last_failure_time: System.system_time(:millisecond)}
          new_state = Map.put(new_state, key, new_circuit)
          {:reply, {:error, e}, new_state}
      catch
        :exit, reason ->
          new_circuit = %{new_circuit | state: :open, last_failure_time: System.system_time(:millisecond)}
          new_state = Map.put(new_state, key, new_circuit)
          {:reply, {:error, {:exit, reason}}, new_state}

        :throw, reason ->
          new_circuit = %{new_circuit | state: :open, last_failure_time: System.system_time(:millisecond)}
          new_state = Map.put(new_state, key, new_circuit)
          {:reply, {:error, {:throw, reason}}, new_state}
      end
    else
      {:reply, {:error, :circuit_open}, state}
    end
  end

  defp handle_half_open_circuit(circuit, key, fun, state) do
    result = fun.()
    new_circuit = %{circuit | state: :closed, failure_count: 0}
    new_state = Map.put(state, key, new_circuit)
    {:reply, {:ok, result}, new_state}
  rescue
    e ->
      new_circuit = %{circuit | state: :open, last_failure_time: System.system_time(:millisecond)}
      new_state = Map.put(state, key, new_circuit)
      {:reply, {:error, e}, new_state}
  catch
    :exit, reason ->
      new_circuit = %{circuit | state: :open, last_failure_time: System.system_time(:millisecond)}
      new_state = Map.put(state, key, new_circuit)
      {:reply, {:error, {:exit, reason}}, new_state}

    :throw, reason ->
      new_circuit = %{circuit | state: :open, last_failure_time: System.system_time(:millisecond)}
      new_state = Map.put(state, key, new_circuit)
      {:reply, {:error, {:throw, reason}}, new_state}
  end

  @impl true
  def handle_cast({:success, key}, state) do
    circuit = Map.get(state, key, state.default)
    new_circuit = %{circuit | failure_count: 0, state: :closed}
    new_state = Map.put(state, key, new_circuit)
    {:noreply, new_state}
  end

  def handle_cast({:failure, key}, state) do
    circuit = Map.get(state, key, state.default)
    new_circuit = record_failure(circuit)
    new_state = Map.put(state, key, new_circuit)
    {:noreply, new_state}
  end

  def handle_cast({:reset, key}, state) do
    circuit = Map.get(state, key, state.default)
    new_circuit = %{circuit | state: :closed, failure_count: 0, last_failure_time: nil}
    new_state = Map.put(state, key, new_circuit)
    {:noreply, new_state}
  end

  defp record_failure(circuit) do
    new_count = circuit.failure_count + 1
    new_state = if new_count >= circuit.threshold, do: :open, else: circuit.state

    %{
      circuit
      | failure_count: new_count,
        last_failure_time: System.system_time(:millisecond),
        state: new_state
    }
  end

  defp should_transition_to_half_open?(circuit) do
    case circuit.last_failure_time do
      nil -> true
      last_time -> System.system_time(:millisecond) - last_time >= circuit.timeout
    end
  end
end