defmodule Phoenix.FaultModel do
  @moduledoc """
  Comprehensive classification of failure modes in distributed agent systems.
  
  Failure Categories:
  1. **Process Failures**: Agent crashes, memory exhaustion, deadlocks
  2. **Node Failures**: Hardware failures, OS crashes, resource exhaustion  
  3. **Network Failures**: Partitions, high latency, packet loss
  4. **Software Failures**: Bugs, race conditions, resource leaks
  5. **Byzantine Failures**: Malicious behavior, corruption, inconsistent responses
  """
  
  @type failure_type ::
    :process_crash |
    :process_hang |
    :memory_exhaustion |
    :node_crash |
    :node_unreachable |
    :network_partition |
    :high_latency |
    :packet_loss |
    :software_bug |
    :resource_leak |
    :byzantine_behavior |
    :data_corruption
    
  @type failure_severity :: :low | :medium | :high | :critical
  @type failure_scope :: :local | :node | :cluster | :global
  
  defstruct [
    :type,
    :severity,
    :scope,
    :affected_components,
    :detection_time,
    :probable_cause,
    :recovery_strategy,
    :impact_assessment
  ]
  
  @doc """
  Classify detected failure and determine response strategy.
  """
  def classify_failure(failure_symptoms, context \\ %{}) do
    failure_type = determine_failure_type(failure_symptoms)
    severity = assess_severity(failure_type, failure_symptoms, context)
    scope = determine_scope(failure_type, failure_symptoms, context)
    
    %__MODULE__{
      type: failure_type,
      severity: severity,
      scope: scope,
      affected_components: identify_affected_components(failure_symptoms),
      detection_time: DateTime.utc_now(),
      probable_cause: analyze_probable_cause(failure_symptoms, context),
      recovery_strategy: select_recovery_strategy(failure_type, severity, scope),
      impact_assessment: assess_impact(failure_symptoms, context)
    }
  end
  
  @doc """
  Determine appropriate response based on failure classification.
  """
  def determine_response(failure_classification) do
    case {failure_classification.severity, failure_classification.scope} do
      {:critical, :global} -> :emergency_response
      {:critical, :cluster} -> :cluster_failover
      {:high, :node} -> :node_isolation
      {:medium, :local} -> :local_restart
      {:low, _} -> :graceful_degradation
    end
  end
  
  defp determine_failure_type(symptoms) do
    cond do
      symptoms.process_exit_reason -> classify_process_failure(symptoms)
      symptoms.node_down_event -> :node_crash
      symptoms.network_timeout -> classify_network_failure(symptoms)
      symptoms.resource_exhaustion -> classify_resource_failure(symptoms)
      symptoms.inconsistent_state -> :byzantine_behavior
      true -> :unknown_failure
    end
  end
  
  defp assess_severity(failure_type, symptoms, context) do
    base_severity = base_severity_for_type(failure_type)
    
    # Adjust severity based on context
    severity_adjustments = [
      criticality_adjustment(context),
      cascade_risk_adjustment(symptoms),
      recovery_difficulty_adjustment(failure_type)
    ]
    
    apply_severity_adjustments(base_severity, severity_adjustments)
  end
end

defmodule Phoenix.FailureDetector do
  @moduledoc """
  Comprehensive failure detection system using multiple detection mechanisms.
  
  Detection Methods:
  1. **Heartbeat Monitoring**: Regular health checks
  2. **Performance Monitoring**: Latency and throughput tracking
  3. **Resource Monitoring**: CPU, memory, disk usage
  4. **Network Monitoring**: Connection quality and reachability
  5. **Application Monitoring**: Business logic health indicators
  """
  
  use GenServer
  
  defstruct [
    :node_id,
    :monitored_components,
    :detection_thresholds,
    :failure_history,
    :active_detectors,
    :escalation_policies
  ]
  
  @heartbeat_interval 5_000  # 5 seconds
  @failure_threshold 3       # Failed checks before marking as failed
  @recovery_threshold 2      # Successful checks before marking as recovered
  
  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end
  
  def init(opts) do
    state = %__MODULE__{
      node_id: Keyword.get(opts, :node_id, node()),
      monitored_components: %{},
      detection_thresholds: default_thresholds(),
      failure_history: [],
      active_detectors: %{},
      escalation_policies: default_escalation_policies()
    }
    
    # Start monitoring subsystems
    start_heartbeat_monitoring()
    start_performance_monitoring()
    start_resource_monitoring()
    
    {:ok, state}
  end
  
  @doc """
  Register component for failure detection monitoring.
  """
  def monitor_component(component_id, component_spec) do
    GenServer.call(__MODULE__, {:monitor_component, component_id, component_spec})
  end
  
  @doc """
  Report suspected failure for investigation.
  """
  def report_suspected_failure(component_id, symptoms) do
    GenServer.cast(__MODULE__, {:suspected_failure, component_id, symptoms})
  end
  
  @doc """
  Get current health status of all monitored components.
  """
  def health_status() do
    GenServer.call(__MODULE__, :health_status)
  end
  
  def handle_call({:monitor_component, component_id, component_spec}, _from, state) do
    # Add component to monitoring
    new_monitored = Map.put(state.monitored_components, component_id, %{
      spec: component_spec,
      status: :healthy,
      last_check: DateTime.utc_now(),
      failure_count: 0,
      recovery_count: 0
    })
    
    # Start detector for this component
    detector_pid = start_component_detector(component_id, component_spec)
    new_detectors = Map.put(state.active_detectors, component_id, detector_pid)
    
    new_state = %{state | 
      monitored_components: new_monitored,
      active_detectors: new_detectors
    }
    
    {:reply, :ok, new_state}
  end
  
  def handle_call(:health_status, _from, state) do
    health_report = state.monitored_components
    |> Enum.map(fn {component_id, component_info} ->
      {component_id, %{
        status: component_info.status,
        last_check: component_info.last_check,
        failure_count: component_info.failure_count
      }}
    end)
    |> Enum.into(%{})
    
    {:reply, health_report, state}
  end
  
  def handle_cast({:suspected_failure, component_id, symptoms}, state) do
    # Investigate suspected failure
    case Map.get(state.monitored_components, component_id) do
      nil ->
        # Unknown component, ignore
        {:noreply, state}
        
      component_info ->
        # Verify failure and update state
        new_state = investigate_failure(component_id, symptoms, component_info, state)
        {:noreply, new_state}
    end
  end
  
  def handle_info({:heartbeat_timeout, component_id}, state) do
    # Component failed to respond to heartbeat
    symptoms = %{
      type: :heartbeat_timeout,
      component_id: component_id,
      timestamp: DateTime.utc_now()
    }
    
    new_state = handle_heartbeat_failure(component_id, symptoms, state)
    {:noreply, new_state}
  end
  
  def handle_info({:performance_degradation, component_id, metrics}, state) do
    # Component showing performance issues
    symptoms = %{
      type: :performance_degradation,
      component_id: component_id,
      metrics: metrics,
      timestamp: DateTime.utc_now()
    }
    
    new_state = investigate_failure(component_id, symptoms, Map.get(state.monitored_components, component_id), state)
    {:noreply, new_state}
  end
  
  defp investigate_failure(component_id, symptoms, component_info, state) do
    # Classify the failure
    failure_classification = Phoenix.FaultModel.classify_failure(symptoms, %{
      component_type: component_info.spec.type,
      criticality: component_info.spec.criticality
    })
    
    # Update failure count
    new_failure_count = component_info.failure_count + 1
    
    # Determine if component should be marked as failed
    if new_failure_count >= @failure_threshold do
      # Mark component as failed and trigger response
      new_component_info = %{component_info | 
        status: :failed,
        failure_count: new_failure_count,
        last_check: DateTime.utc_now()
      }
      
      # Trigger failure response
      trigger_failure_response(component_id, failure_classification)
      
      # Update state
      new_monitored = Map.put(state.monitored_components, component_id, new_component_info)
      new_history = [failure_classification | state.failure_history] |> Enum.take(100)
      
      %{state | 
        monitored_components: new_monitored,
        failure_history: new_history
      }
    else
      # Increment failure count but don't mark as failed yet
      new_component_info = %{component_info | 
        failure_count: new_failure_count,
        last_check: DateTime.utc_now()
      }
      
      new_monitored = Map.put(state.monitored_components, component_id, new_component_info)
      %{state | monitored_components: new_monitored}
    end
  end
  
  defp trigger_failure_response(component_id, failure_classification) do
    response_strategy = Phoenix.FaultModel.determine_response(failure_classification)
    
    case response_strategy do
      :emergency_response -> 
        Phoenix.Emergency.trigger_emergency_response(component_id, failure_classification)
      :cluster_failover -> 
        Phoenix.Cluster.Failover.initiate_failover(component_id, failure_classification)
      :node_isolation -> 
        Phoenix.Node.Isolation.isolate_node(component_id, failure_classification)
      :local_restart -> 
        Phoenix.Local.Recovery.restart_component(component_id, failure_classification)
      :graceful_degradation -> 
        Phoenix.Degradation.enable_degraded_mode(component_id, failure_classification)
    end
  end
  
  defp start_heartbeat_monitoring() do
    # Start heartbeat monitoring process
    spawn_link(fn -> heartbeat_loop() end)
  end
  
  defp heartbeat_loop() do
    # Send heartbeats to all monitored components
    monitored_components = GenServer.call(__MODULE__, :get_monitored_components)
    
    Enum.each(monitored_components, fn {component_id, _spec} ->
      send_heartbeat(component_id)
    end)
    
    :timer.sleep(@heartbeat_interval)
    heartbeat_loop()
  end
end

defmodule Phoenix.CircuitBreaker do
  @moduledoc """
  Advanced circuit breaker implementation with multiple states and adaptive thresholds.
  
  States:
  - **Closed**: Normal operation, requests pass through
  - **Open**: Failure threshold exceeded, requests rejected immediately
  - **Half-Open**: Testing recovery, limited requests allowed
  - **Forced-Open**: Manual override, all requests rejected
  - **Forced-Closed**: Manual override, all requests allowed
  """
  
  use GenServer
  
  defstruct [
    :name,
    :state,
    :failure_count,
    :success_count,
    :failure_threshold,
    :success_threshold,
    :timeout,
    :last_failure_time,
    :request_count,
    :adaptive_threshold,
    :window_size,
    :metrics
  ]
  
  @type circuit_state :: :closed | :open | :half_open | :forced_open | :forced_closed
  @type circuit_config :: %{
    failure_threshold: pos_integer(),
    success_threshold: pos_integer(),
    timeout: pos_integer(),
    window_size: pos_integer(),
    adaptive: boolean()
  }
  
  @default_config %{
    failure_threshold: 5,
    success_threshold: 3,
    timeout: 30_000,
    window_size: 100,
    adaptive: true
  }
  
  def start_link(name, config \\ %{}) do
    merged_config = Map.merge(@default_config, config)
    
    GenServer.start_link(__MODULE__, {name, merged_config}, name: via_tuple(name))
  end
  
  def init({name, config}) do
    state = %__MODULE__{
      name: name,
      state: :closed,
      failure_count: 0,
      success_count: 0,
      failure_threshold: config.failure_threshold,
      success_threshold: config.success_threshold,
      timeout: config.timeout,
      last_failure_time: nil,
      request_count: 0,
      adaptive_threshold: config.adaptive,
      window_size: config.window_size,
      metrics: Phoenix.CircuitBreaker.Metrics.new()
    }
    
    {:ok, state}
  end
  
  @doc """
  Execute operation through circuit breaker with protection.
  """
  def call(circuit_name, operation, opts \\ []) do
    timeout = Keyword.get(opts, :timeout, 5000)
    fallback = Keyword.get(opts, :fallback)
    
    case GenServer.call(via_tuple(circuit_name), :check_state, timeout) do
      :allow ->
        execute_with_monitoring(circuit_name, operation, fallback)
        
      :reject ->
        case fallback do
          nil -> {:error, :circuit_open}
          fallback_fn when is_function(fallback_fn) -> 
            {:ok, fallback_fn.()}
          fallback_value -> 
            {:ok, fallback_value}
        end
    end
  end
  
  @doc """
  Force circuit breaker to specific state (for testing/emergency).
  """
  def force_state(circuit_name, forced_state) when forced_state in [:open, :closed, :reset] do
    GenServer.call(via_tuple(circuit_name), {:force_state, forced_state})
  end
  
  @doc """
  Get current circuit breaker state and metrics.
  """
  def state(circuit_name) do
    GenServer.call(via_tuple(circuit_name), :get_state)
  end
  
  def handle_call(:check_state, _from, state) do
    case state.state do
      :closed ->
        {:reply, :allow, increment_request_count(state)}
        
      :open ->
        if should_attempt_reset?(state) do
          new_state = %{state | state: :half_open}
          {:reply, :allow, increment_request_count(new_state)}
        else
          {:reply, :reject, state}
        end
        
      :half_open ->
        {:reply, :allow, increment_request_count(state)}
        
      :forced_open ->
        {:reply, :reject, state}
        
      :forced_closed ->
        {:reply, :allow, increment_request_count(state)}
    end
  end
  
  def handle_call({:force_state, forced_state}, _from, state) do
    new_state = case forced_state do
      :open -> %{state | state: :forced_open}
      :closed -> %{state | state: :forced_closed}
      :reset -> reset_circuit_breaker(state)
    end
    
    {:reply, :ok, new_state}
  end
  
  def handle_call(:get_state, _from, state) do
    state_info = %{
      state: state.state,
      failure_count: state.failure_count,
      success_count: state.success_count,
      request_count: state.request_count,
      failure_threshold: state.failure_threshold,
      last_failure_time: state.last_failure_time,
      metrics: Phoenix.CircuitBreaker.Metrics.summary(state.metrics)
    }
    
    {:reply, state_info, state}
  end
  
  def handle_cast({:record_success, execution_time}, state) do
    new_metrics = Phoenix.CircuitBreaker.Metrics.record_success(state.metrics, execution_time)
    new_state = %{state | 
      success_count: state.success_count + 1,
      metrics: new_metrics
    }
    
    # Check if circuit should close
    final_state = case state.state do
      :half_open ->
        if new_state.success_count >= state.success_threshold do
          reset_circuit_breaker(new_state)
        else
          new_state
        end
      _ ->
        new_state
    end
    
    # Update adaptive threshold if enabled
    final_state = if state.adaptive_threshold do
      update_adaptive_threshold(final_state)
    else
      final_state
    end
    
    {:noreply, final_state}
  end
  
  def handle_cast({:record_failure, error, execution_time}, state) do
    new_metrics = Phoenix.CircuitBreaker.Metrics.record_failure(state.metrics, error, execution_time)
    new_state = %{state | 
      failure_count: state.failure_count + 1,
      last_failure_time: System.monotonic_time(:millisecond),
      metrics: new_metrics
    }
    
    # Check if circuit should open
    final_state = case state.state do
      :closed ->
        if new_state.failure_count >= state.failure_threshold do
          %{new_state | state: :open}
        else
          new_state
        end
      :half_open ->
        # Failure during half-open immediately opens circuit
        %{new_state | state: :open}
      _ ->
        new_state
    end
    
    # Update adaptive threshold if enabled
    final_state = if state.adaptive_threshold do
      update_adaptive_threshold(final_state)
    else
      final_state
    end
    
    {:noreply, final_state}
  end
  
  defp execute_with_monitoring(circuit_name, operation, fallback) do
    start_time = System.monotonic_time(:microsecond)
    
    try do
      result = operation.()
      execution_time = System.monotonic_time(:microsecond) - start_time
      
      GenServer.cast(via_tuple(circuit_name), {:record_success, execution_time})
      {:ok, result}
      
    rescue
      error ->
        execution_time = System.monotonic_time(:microsecond) - start_time
        GenServer.cast(via_tuple(circuit_name), {:record_failure, error, execution_time})
        
        case fallback do
          nil -> {:error, error}
          fallback_fn when is_function(fallback_fn) -> 
            {:ok, fallback_fn.()}
          fallback_value -> 
            {:ok, fallback_value}
        end
    end
  end
  
  defp should_attempt_reset?(state) do
    case state.last_failure_time do
      nil -> false
      last_failure ->
        current_time = System.monotonic_time(:millisecond)
        current_time - last_failure >= state.timeout
    end
  end
  
  defp reset_circuit_breaker(state) do
    %{state | 
      state: :closed,
      failure_count: 0,
      success_count: 0,
      last_failure_time: nil
    }
  end
  
  defp increment_request_count(state) do
    %{state | request_count: state.request_count + 1}
  end
  
  defp update_adaptive_threshold(state) do
    # Adjust threshold based on recent performance
    recent_failure_rate = calculate_recent_failure_rate(state.metrics)
    
    new_threshold = cond do
      recent_failure_rate > 0.3 -> 
        # High failure rate, lower threshold
        max(2, state.failure_threshold - 1)
      recent_failure_rate < 0.1 -> 
        # Low failure rate, raise threshold
        min(20, state.failure_threshold + 1)
      true -> 
        state.failure_threshold
    end
    
    %{state | failure_threshold: new_threshold}
  end
  
  defp calculate_recent_failure_rate(metrics) do
    Phoenix.CircuitBreaker.Metrics.failure_rate(metrics, window: :recent)
  end
  
  defp via_tuple(name) do
    {:via, Registry, {Phoenix.CircuitBreaker.Registry, name}}
  end
end

defmodule Phoenix.CircuitBreaker.Metrics do
  @moduledoc """
  Comprehensive metrics collection for circuit breaker performance analysis.
  """
  
  defstruct [
    :total_requests,
    :successful_requests,
    :failed_requests,
    :recent_window,
    :response_times,
    :error_types,
    :state_transitions
  ]
  
  @window_size 100
  
  def new() do
    %__MODULE__{
      total_requests: 0,
      successful_requests: 0,
      failed_requests: 0,
      recent_window: :queue.new(),
      response_times: [],
      error_types: %{},
      state_transitions: []
    }
  end
  
  def record_success(metrics, execution_time) do
    new_window = add_to_window(metrics.recent_window, {:success, execution_time})
    
    %{metrics |
      total_requests: metrics.total_requests + 1,
      successful_requests: metrics.successful_requests + 1,
      recent_window: new_window,
      response_times: [execution_time | metrics.response_times] |> Enum.take(1000)
    }
  end
  
  def record_failure(metrics, error, execution_time) do
    error_type = classify_error(error)
    new_window = add_to_window(metrics.recent_window, {:failure, error_type, execution_time})
    
    current_error_count = Map.get(metrics.error_types, error_type, 0)
    new_error_types = Map.put(metrics.error_types, error_type, current_error_count + 1)
    
    %{metrics |
      total_requests: metrics.total_requests + 1,
      failed_requests: metrics.failed_requests + 1,
      recent_window: new_window,
      error_types: new_error_types,
      response_times: [execution_time | metrics.response_times] |> Enum.take(1000)
    }
  end
  
  def failure_rate(metrics, opts \\ []) do
    window = Keyword.get(opts, :window, :total)
    
    case window do
      :total ->
        if metrics.total_requests > 0 do
          metrics.failed_requests / metrics.total_requests
        else
          0.0
        end
        
      :recent ->
        recent_items = :queue.to_list(metrics.recent_window)
        total_recent = length(recent_items)
        
        if total_recent > 0 do
          failures = Enum.count(recent_items, fn
            {:failure, _, _} -> true
            _ -> false
          end)
          failures / total_recent
        else
          0.0
        end
    end
  end
  
  def average_response_time(metrics) do
    if length(metrics.response_times) > 0 do
      Enum.sum(metrics.response_times) / length(metrics.response_times)
    else
      0.0
    end
  end
  
  def percentile_response_time(metrics, percentile) do
    if length(metrics.response_times) > 0 do
      sorted_times = Enum.sort(metrics.response_times)
      index = round(length(sorted_times) * percentile / 100) - 1
      index = max(0, min(index, length(sorted_times) - 1))
      Enum.at(sorted_times, index)
    else
      0.0
    end
  end
  
  def summary(metrics) do
    %{
      total_requests: metrics.total_requests,
      success_rate: success_rate(metrics),
      failure_rate: failure_rate(metrics),
      recent_failure_rate: failure_rate(metrics, window: :recent),
      average_response_time: average_response_time(metrics),
      p95_response_time: percentile_response_time(metrics, 95),
      p99_response_time: percentile_response_time(metrics, 99),
      error_distribution: metrics.error_types
    }
  end
  
  defp success_rate(metrics) do
    if metrics.total_requests > 0 do
      metrics.successful_requests / metrics.total_requests
    else
      0.0
    end
  end
  
  defp add_to_window(window, item) do
    new_window = :queue.in(item, window)
    
    if :queue.len(new_window) > @window_size do
      {_removed, trimmed_window} = :queue.out(new_window)
      trimmed_window
    else
      new_window
    end
  end
  
  defp classify_error(error) do
    case error do
      %{__exception__: true} -> error.__struct__
      {:timeout, _} -> :timeout
      {:error, reason} -> reason
      _ -> :unknown
    end
  end
end

defmodule Phoenix.Bulkhead.ResourcePool do
  @moduledoc """
  Resource pool implementation for bulkhead isolation.
  
  Features:
  - Configurable pool sizes per resource type
  - Queue management with timeouts
  - Resource health monitoring
  - Spillover to other pools when exhausted
  - Circuit breaker integration
  """
  
  use GenServer
  
  defstruct [
    :pool_name,
    :resource_type,
    :max_size,
    :current_size,
    :available_resources,
    :checked_out_resources,
    :waiting_queue,
    :health_monitor,
    :spillover_pools,
    :circuit_breaker
  ]
  
  @default_timeout 5_000
  @health_check_interval 10_000
  
  def start_link(opts) do
    pool_name = Keyword.fetch!(opts, :pool_name)
    
    GenServer.start_link(__MODULE__, opts, name: via_tuple(pool_name))
  end
  
  def init(opts) do
    pool_name = Keyword.fetch!(opts, :pool_name)
    resource_type = Keyword.fetch!(opts, :resource_type)
    max_size = Keyword.get(opts, :max_size, 10)
    
    state = %__MODULE__{
      pool_name: pool_name,
      resource_type: resource_type,
      max_size: max_size,
      current_size: 0,
      available_resources: :queue.new(),
      checked_out_resources: %{},
      waiting_queue: :queue.new(),
      health_monitor: Phoenix.ResourceHealthMonitor.new(),
      spillover_pools: Keyword.get(opts, :spillover_pools, []),
      circuit_breaker: Keyword.get(opts, :circuit_breaker)
    }
    
    # Pre-populate pool with initial resources
    initial_size = Keyword.get(opts, :initial_size, min(3, max_size))
    populated_state = populate_pool(state, initial_size)
    
    # Start health monitoring
    schedule_health_check()
    
    {:ok, populated_state}
  end
  
  @doc """
  Checkout resource from pool with timeout.
  """
  def checkout(pool_name, timeout \\ @default_timeout) do
    GenServer.call(via_tuple(pool_name), {:checkout, self()}, timeout)
  end
  
  @doc """
  Return resource to pool.
  """
  def checkin(pool_name, resource) do
    GenServer.cast(via_tuple(pool_name), {:checkin, resource})
  end
  
  @doc """
  Execute operation with automatic resource management.
  """
  def with_resource(pool_name, operation, opts \\ []) do
    timeout = Keyword.get(opts, :timeout, @default_timeout)
    
    case checkout(pool_name, timeout) do
      {:ok, resource} ->
        try do
          operation.(resource)
        after
          checkin(pool_name, resource)
        end
        
      {:error, :timeout} ->
        # Try spillover pools
        attempt_spillover(pool_name, operation, opts)
        
      error ->
        error
    end
  end
  
  @doc """
  Get pool statistics.
  """
  def stats(pool_name) do
    GenServer.call(via_tuple(pool_name), :stats)
  end
  
  def handle_call({:checkout, caller_pid}, from, state) do
    case :queue.out(state.available_resources) do
      {{:value, resource}, new_available} ->
        # Resource available immediately
        monitor_ref = Process.monitor(caller_pid)
        new_checked_out = Map.put(state.checked_out_resources, monitor_ref, {resource, caller_pid})
        
        new_state = %{state | 
          available_resources: new_available,
          checked_out_resources: new_checked_out
        }
        
        {:reply, {:ok, resource}, new_state}
        
      {:empty, _} ->
        # No resources available
        cond do
          state.current_size < state.max_size ->
            # Can create new resource
            case create_resource(state.resource_type) do
              {:ok, resource} ->
                monitor_ref = Process.monitor(caller_pid)
                new_checked_out = Map.put(state.checked_out_resources, monitor_ref, {resource, caller_pid})
                
                new_state = %{state | 
                  current_size: state.current_size + 1,
                  checked_out_resources: new_checked_out
                }
                
                {:reply, {:ok, resource}, new_state}
                
              {:error, _reason} ->
                # Queue the request
                new_waiting = :queue.in(from, state.waiting_queue)
                {:noreply, %{state | waiting_queue: new_waiting}}
            end
            
          true ->
            # Pool at capacity, queue the request
            new_waiting = :queue.in(from, state.waiting_queue)
            {:noreply, %{state | waiting_queue: new_waiting}}
        end
    end
  end
  
  def handle_call(:stats, _from, state) do
    stats = %{
      pool_name: state.pool_name,
      max_size: state.max_size,
      current_size: state.current_size,
      available: :queue.len(state.available_resources),
      checked_out: map_size(state.checked_out_resources),
      waiting: :queue.len(state.waiting_queue),
      utilization: map_size(state.checked_out_resources) / state.max_size
    }
    
    {:reply, stats, state}
  end
  
  def handle_cast({:checkin, resource}, state) do
    # Resource returned to pool
    case :queue.out(state.waiting_queue) do
      {{:value, waiting_caller}, new_waiting} ->
        # Someone is waiting, give resource directly
        GenServer.reply(waiting_caller, {:ok, resource})
        {:noreply, %{state | waiting_queue: new_waiting}}
        
      {:empty, _} ->
        # No one waiting, return to pool
        new_available = :queue.in(resource, state.available_resources)
        {:noreply, %{state | available_resources: new_available}}
    end
  end
  
  def handle_info({:DOWN, monitor_ref, :process, _pid, _reason}, state) do
    # Process that checked out resource died
    case Map.pop(state.checked_out_resources, monitor_ref) do
      {{resource, _pid}, new_checked_out} ->
        # Return resource to pool (may need cleanup)
        cleaned_resource = cleanup_resource(resource)
        new_available = :queue.in(cleaned_resource, state.available_resources)
        
        new_state = %{state | 
          available_resources: new_available,
          checked_out_resources: new_checked_out
        }
        
        {:noreply, new_state}
        
      {nil, _} ->
        # Unknown monitor reference
        {:noreply, state}
    end
  end
  
  def handle_info(:health_check, state) do
    # Perform health check on available resources
    {healthy_resources, unhealthy_count} = health_check_resources(state.available_resources)
    
    # Replace unhealthy resources
    new_state = if unhealthy_count > 0 do
      replace_unhealthy_resources(state, unhealthy_count, healthy_resources)
    else
      %{state | available_resources: healthy_resources}
    end
    
    schedule_health_check()
    {:noreply, new_state}
  end
  
  defp attempt_spillover(pool_name, operation, opts) do
    # Get spillover pools configuration
    spillover_pools = GenServer.call(via_tuple(pool_name), :get_spillover_pools)
    
    # Try each spillover pool
    Enum.find_value(spillover_pools, fn spillover_pool ->
      case with_resource(spillover_pool, operation, opts) do
        {:error, :timeout} -> nil
        result -> result
      end
    end) || {:error, :resource_unavailable}
  end
  
  defp populate_pool(state, count) do
    resources = for _ <- 1..count do
      case create_resource(state.resource_type) do
        {:ok, resource} -> resource
        {:error, _} -> nil
      end
    end
    |> Enum.filter(&(&1 != nil))
    
    new_available = Enum.reduce(resources, state.available_resources, fn resource, acc ->
      :queue.in(resource, acc)
    end)
    
    %{state | 
      available_resources: new_available,
      current_size: length(resources)
    }
  end
  
  defp create_resource(resource_type) do
    case resource_type do
      :database_connection -> create_database_connection()
      :http_client -> create_http_client()
      :worker_process -> create_worker_process()
      _ -> {:error, :unknown_resource_type}
    end
  end
  
  defp cleanup_resource(resource) do
    # Cleanup resource state before returning to pool
    # Implementation depends on resource type
    resource
  end
  
  defp health_check_resources(available_resources) do
    resources_list = :queue.to_list(available_resources)
    
    {healthy, unhealthy_count} = Enum.reduce(resources_list, {[], 0}, fn resource, {healthy_acc, unhealthy_count} ->
      if resource_healthy?(resource) do
        {[resource | healthy_acc], unhealthy_count}
      else
        {healthy_acc, unhealthy_count + 1}
      end
    end)
    
    healthy_queue = Enum.reduce(healthy, :queue.new(), fn resource, acc ->
      :queue.in(resource, acc)
    end)
    
    {healthy_queue, unhealthy_count}
  end
  
  defp schedule_health_check() do
    Process.send_after(self(), :health_check, @health_check_interval)
  end
  
  defp via_tuple(pool_name) do
    {:via, Registry, {Phoenix.Bulkhead.ResourcePool.Registry, pool_name}}
  end
  
  # Placeholder implementations
  defp create_database_connection(), do: {:ok, :db_connection}
  defp create_http_client(), do: {:ok, :http_client}
  defp create_worker_process(), do: {:ok, :worker_process}
  defp resource_healthy?(_resource), do: true
end

defmodule Phoenix.Bulkhead.IsolationBoundary do
  @moduledoc """
  Defines and enforces isolation boundaries between different system components.
  
  Features:
  - Resource quotas per isolation boundary
  - Traffic shaping and rate limiting
  - Priority-based resource allocation
  - Cascading failure prevention
  """
  
  defstruct [
    :boundary_name,
    :resource_quotas,
    :current_usage,
    :priority_levels,
    :rate_limiters,
    :circuit_breakers
  ]
  
  @doc """
  Define isolation boundary with resource constraints.
  """
  def define_boundary(boundary_name, config) do
    %__MODULE__{
      boundary_name: boundary_name,
      resource_quotas: Map.get(config, :quotas, %{}),
      current_usage: %{},
      priority_levels: Map.get(config, :priorities, %{}),
      rate_limiters: initialize_rate_limiters(config),
      circuit_breakers: initialize_circuit_breakers(config)
    }
  end
  
  @doc """
  Check if operation is allowed within isolation boundary.
  """
  def check_allowance(boundary, operation_spec) do
    with :ok <- check_resource_quota(boundary, operation_spec),
         :ok <- check_rate_limits(boundary, operation_spec),
         :ok <- check_circuit_breakers(boundary, operation_spec) do
      :ok
    else
      {:error, reason} -> {:error, reason}
    end
  end
  
  @doc """
  Execute operation within isolation boundary with resource tracking.
  """
  def execute_within_boundary(boundary, operation, operation_spec) do
    case check_allowance(boundary, operation_spec) do
      :ok ->
        # Reserve resources
        updated_boundary = reserve_resources(boundary, operation_spec)
        
        try do
          result = operation.()
          
          # Record successful execution
          record_execution_success(updated_boundary, operation_spec)
          {:ok, result}
          
        rescue
          error ->
            # Record failure and release resources
            record_execution_failure(updated_boundary, operation_spec, error)
            {:error, error}
        after
          # Always release resources
          release_resources(updated_boundary, operation_spec)
        end
        
      {:error, reason} ->
        {:error, reason}
    end
  end
  
  defp check_resource_quota(boundary, operation_spec) do
    required_resources = Map.get(operation_spec, :resources, %{})
    
    Enum.find_value(required_resources, :ok, fn {resource_type, required_amount} ->
      quota = Map.get(boundary.resource_quotas, resource_type, :unlimited)
      current = Map.get(boundary.current_usage, resource_type, 0)
      
      case quota do
        :unlimited -> nil
        quota_limit when current + required_amount <= quota_limit -> nil
        _exceeded -> {:error, {:quota_exceeded, resource_type}}
      end
    end)
  end
  
  defp check_rate_limits(boundary, operation_spec) do
    operation_type = Map.get(operation_spec, :type, :default)
    
    case Map.get(boundary.rate_limiters, operation_type) do
      nil -> :ok
      rate_limiter -> 
        Phoenix.RateLimiter.check_limit(rate_limiter, operation_spec)
    end
  end
  
  defp check_circuit_breakers(boundary, operation_spec) do
    operation_type = Map.get(operation_spec, :type, :default)
    
    case Map.get(boundary.circuit_breakers, operation_type) do
      nil -> :ok
      circuit_breaker -> 
        case Phoenix.CircuitBreaker.state(circuit_breaker) do
          %{state: :open} -> {:error, :circuit_open}
          _ -> :ok
        end
    end
  end
  
  defp reserve_resources(boundary, operation_spec) do
    required_resources = Map.get(operation_spec, :resources, %{})
    
    new_usage = Enum.reduce(required_resources, boundary.current_usage, fn {resource_type, amount}, acc ->
      current = Map.get(acc, resource_type, 0)
      Map.put(acc, resource_type, current + amount)
    end)
    
    %{boundary | current_usage: new_usage}
  end
  
  defp release_resources(boundary, operation_spec) do
    required_resources = Map.get(operation_spec, :resources, %{})
    
    new_usage = Enum.reduce(required_resources, boundary.current_usage, fn {resource_type, amount}, acc ->
      current = Map.get(acc, resource_type, 0)
      Map.put(acc, resource_type, max(0, current - amount))
    end)
    
    %{boundary | current_usage: new_usage}
  end
  
  defp initialize_rate_limiters(config) do
    rate_limits = Map.get(config, :rate_limits, %{})
    
    Enum.map(rate_limits, fn {operation_type, limit_config} ->
      {operation_type, Phoenix.RateLimiter.new(limit_config)}
    end)
    |> Enum.into(%{})
  end
  
  defp initialize_circuit_breakers(config) do
    circuit_configs = Map.get(config, :circuit_breakers, %{})
    
    Enum.map(circuit_configs, fn {operation_type, breaker_config} ->
      breaker_name = "#{config.boundary_name}_#{operation_type}"
      {:ok, _pid} = Phoenix.CircuitBreaker.start_link(breaker_name, breaker_config)
      {operation_type, breaker_name}
    end)
    |> Enum.into(%{})
  end
  
  defp record_execution_success(boundary, operation_spec) do
    # Record metrics for successful execution
    Phoenix.Metrics.increment("bulkhead.execution.success", %{
      boundary: boundary.boundary_name,
      operation_type: Map.get(operation_spec, :type, :default)
    })
  end
  
  defp record_execution_failure(boundary, operation_spec, error) do
    # Record metrics for failed execution
    Phoenix.Metrics.increment("bulkhead.execution.failure", %{
      boundary: boundary.boundary_name,
      operation_type: Map.get(operation_spec, :type, :default),
      error_type: classify_error(error)
    })
  end
  
  defp classify_error(error) do
    case error do
      %{__exception__: true} -> error.__struct__
      _ -> :unknown
    end
  end
end

defmodule Phoenix.PartitionDetector do
  @moduledoc """
  Network partition detection using multiple detection mechanisms.
  
  Detection Methods:
  1. **Heartbeat Monitoring**: Node-to-node heartbeats
  2. **Connectivity Probing**: Direct network connectivity tests
  3. **Consensus Participation**: Monitoring consensus protocol participation
  4. **External Witnesses**: Third-party partition detection services
  5. **Application-Level Indicators**: Business logic health checks
  """
  
  use GenServer
  
  defstruct [
    :node_id,
    :cluster_nodes,
    :heartbeat_intervals,
    :connectivity_map,
    :partition_history,
    :detection_thresholds,
    :external_witnesses
  ]
  
  @heartbeat_interval 2_000     # 2 seconds
  @partition_threshold 3        # Failed heartbeats before partition suspected
  @connectivity_timeout 1_000   # 1 second for connectivity probes
  
  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end
  
  def init(opts) do
    node_id = Keyword.get(opts, :node_id, node())
    cluster_nodes = Keyword.get(opts, :cluster_nodes, [node()])
    
    state = %__MODULE__{
      node_id: node_id,
      cluster_nodes: cluster_nodes,
      heartbeat_intervals: %{},
      connectivity_map: %{},
      partition_history: [],
      detection_thresholds: default_thresholds(),
      external_witnesses: Keyword.get(opts, :external_witnesses, [])
    }
    
    # Initialize connectivity monitoring
    initialize_monitoring(state)
    
    # Start heartbeat process
    schedule_heartbeat()
    
    {:ok, state}
  end
  
  @doc """
  Add node to partition monitoring.
  """
  def monitor_node(node) do
    GenServer.cast(__MODULE__, {:monitor_node, node})
  end
  
  @doc """
  Remove node from partition monitoring.
  """
  def stop_monitoring_node(node) do
    GenServer.cast(__MODULE__, {:stop_monitoring_node, node})
  end
  
  @doc """
  Get current partition status.
  """
  def partition_status() do
    GenServer.call(__MODULE__, :partition_status)
  end
  
  @doc """
  Trigger manual partition check.
  """
  def check_partitions() do
    GenServer.cast(__MODULE__, :check_partitions)
  end
  
  def handle_call(:partition_status, _from, state) do
    status = %{
      node_id: state.node_id,
      monitored_nodes: state.cluster_nodes,
      connectivity_map: state.connectivity_map,
      recent_partitions: Enum.take(state.partition_history, 10),
      detection_active: true
    }
    
    {:reply, status, state}
  end
  
  def handle_cast({:monitor_node, node}, state) do
    if node not in state.cluster_nodes do
      new_cluster_nodes = [node | state.cluster_nodes]
      new_connectivity_map = Map.put(state.connectivity_map, node, %{
        status: :unknown,
        last_heartbeat: nil,
        failed_heartbeats: 0,
        last_connectivity_check: nil
      })
      
      new_state = %{state | 
        cluster_nodes: new_cluster_nodes,
        connectivity_map: new_connectivity_map
      }
      
      {:noreply, new_state}
    else
      {:noreply, state}
    end
  end
  
  def handle_cast({:stop_monitoring_node, node}, state) do
    new_cluster_nodes = List.delete(state.cluster_nodes, node)
    new_connectivity_map = Map.delete(state.connectivity_map, node)
    
    new_state = %{state | 
      cluster_nodes: new_cluster_nodes,
      connectivity_map: new_connectivity_map
    }
    
    {:noreply, new_state}
  end
  
  def handle_cast(:check_partitions, state) do
    new_state = perform_partition_detection(state)
    {:noreply, new_state}
  end
  
  def handle_info(:heartbeat, state) do
    # Send heartbeats to all monitored nodes
    new_state = send_heartbeats(state)
    
    schedule_heartbeat()
    {:noreply, new_state}
  end
  
  def handle_info({:heartbeat_response, from_node}, state) do
    # Received heartbeat response from node
    new_state = record_heartbeat_response(state, from_node)
    {:noreply, new_state}
  end
  
  def handle_info({:heartbeat_timeout, node}, state) do
    # Heartbeat timeout for specific node
    new_state = handle_heartbeat_timeout(state, node)
    {:noreply, new_state}
  end
  
  def handle_info(:connectivity_check, state) do
    # Perform direct connectivity checks
    new_state = perform_connectivity_checks(state)
    
    schedule_connectivity_check()
    {:noreply, new_state}
  end
  
  defp perform_partition_detection(state) do
    # Multi-method partition detection
    detection_results = %{
      heartbeat_detection: detect_partitions_by_heartbeat(state),
      connectivity_detection: detect_partitions_by_connectivity(state),
      consensus_detection: detect_partitions_by_consensus(state),
      witness_detection: detect_partitions_by_witnesses(state)
    }
    
    # Aggregate detection results
    partition_decision = aggregate_detection_results(detection_results, state.detection_thresholds)
    
    case partition_decision do
      {:partition_detected, partitioned_nodes} ->
        # Partition detected, trigger response
        partition_event = %{
          type: :partition_detected,
          timestamp: DateTime.utc_now(),
          partitioned_nodes: partitioned_nodes,
          detection_methods: detection_results,
          detector_node: state.node_id
        }
        
        # Record partition in history
        new_history = [partition_event | state.partition_history] |> Enum.take(100)
        
        # Trigger partition response
        Phoenix.PartitionHandler.handle_partition(partition_event)
        
        %{state | partition_history: new_history}
        
      {:partition_healed, healed_nodes} ->
        # Partition healed, trigger recovery
        heal_event = %{
          type: :partition_healed,
          timestamp: DateTime.utc_now(),
          healed_nodes: healed_nodes,
          detector_node: state.node_id
        }
        
        # Record heal in history
        new_history = [heal_event | state.partition_history] |> Enum.take(100)
        
        # Trigger heal response
        Phoenix.PartitionHandler.handle_partition_heal(heal_event)
        
        %{state | partition_history: new_history}
        
      :no_partition ->
        # No partition detected
        state
    end
  end
  
  defp detect_partitions_by_heartbeat(state) do
    # Check heartbeat failures
    partitioned_nodes = state.connectivity_map
    |> Enum.filter(fn {_node, info} ->
      info.failed_heartbeats >= @partition_threshold
    end)
    |> Enum.map(fn {node, _info} -> node end)
    
    if length(partitioned_nodes) > 0 do
      {:partition_detected, partitioned_nodes}
    else
      :no_partition
    end
  end
  
  defp detect_partitions_by_connectivity(state) do
    # Perform direct connectivity tests
    unreachable_nodes = state.cluster_nodes
    |> Enum.filter(fn node -> node != state.node_id end)
    |> Enum.filter(fn node -> not node_reachable?(node) end)
    
    if length(unreachable_nodes) > 0 do
      {:partition_detected, unreachable_nodes}
    else
      :no_partition
    end
  end
  
  defp detect_partitions_by_consensus(state) do
    # Check consensus protocol participation
    case Phoenix.Consensus.get_cluster_status() do
      {:ok, status} ->
        non_participating_nodes = status.cluster_nodes -- status.participating_nodes
        
        if length(non_participating_nodes) > 0 do
          {:partition_detected, non_participating_nodes}
        else
          :no_partition
        end
        
      {:error, _reason} ->
        # Consensus system unavailable
        :consensus_unavailable
    end
  end
  
  defp detect_partitions_by_witnesses(state) do
    # Query external witnesses
    witness_results = Enum.map(state.external_witnesses, fn witness ->
      query_witness(witness, state.cluster_nodes)
    end)
    
    # Aggregate witness responses
    aggregate_witness_results(witness_results)
  end
  
  defp aggregate_detection_results(results, thresholds) do
    # Combine results from different detection methods
    detections = results
    |> Enum.filter(fn {_method, result} -> 
      match?({:partition_detected, _}, result)
    end)
    |> Enum.map(fn {_method, {:partition_detected, nodes}} -> nodes end)
    
    if length(detections) >= Map.get(thresholds, :min_detection_methods, 2) do
      # Multiple methods agree on partition
      common_nodes = find_common_nodes(detections)
      
      if length(common_nodes) > 0 do
        {:partition_detected, common_nodes}
      else
        :no_partition
      end
    else
      :no_partition
    end
  end
  
  defp send_heartbeats(state) do
    # Send heartbeat to each monitored node
    Enum.each(state.cluster_nodes, fn node ->
      if node != state.node_id do
        send_heartbeat_to_node(node)
      end
    end)
    
    state
  end
  
  defp send_heartbeat_to_node(node) do
    # Send heartbeat message with timeout
    spawn(fn ->
      try do
        :rpc.call(node, Phoenix.PartitionDetector, :receive_heartbeat, [node()], @connectivity_timeout)
        send(Phoenix.PartitionDetector, {:heartbeat_response, node})
      catch
        _, _ ->
          send(Phoenix.PartitionDetector, {:heartbeat_timeout, node})
      end
    end)
  end
  
  def receive_heartbeat(from_node) do
    # Heartbeat receiver function (called by remote nodes)
    send(Phoenix.PartitionDetector, {:heartbeat_response, from_node})
    :ok
  end
  
  defp record_heartbeat_response(state, from_node) do
    # Update connectivity info for responding node
    case Map.get(state.connectivity_map, from_node) do
      nil -> state  # Node not monitored
      info ->
        updated_info = %{info | 
          status: :reachable,
          last_heartbeat: DateTime.utc_now(),
          failed_heartbeats: 0
        }
        
        new_connectivity_map = Map.put(state.connectivity_map, from_node, updated_info)
        %{state | connectivity_map: new_connectivity_map}
    end
  end
  
  defp handle_heartbeat_timeout(state, node) do
    # Handle heartbeat timeout for specific node
    case Map.get(state.connectivity_map, node) do
      nil -> state  # Node not monitored
      info ->
        updated_info = %{info | 
          failed_heartbeats: info.failed_heartbeats + 1
        }
        
        # Check if partition threshold reached
        if updated_info.failed_heartbeats >= @partition_threshold do
          updated_info = %{updated_info | status: :partitioned}
        end
        
        new_connectivity_map = Map.put(state.connectivity_map, node, updated_info)
        %{state | connectivity_map: new_connectivity_map}
    end
  end
  
  defp node_reachable?(node) do
    # Direct connectivity test
    try do
      :net_adm.ping(node) == :pong
    catch
      _, _ -> false
    end
  end
  
  defp schedule_heartbeat() do
    Process.send_after(self(), :heartbeat, @heartbeat_interval)
  end
  
  defp schedule_connectivity_check() do
    Process.send_after(self(), :connectivity_check, @heartbeat_interval * 2)
  end
  
  defp initialize_monitoring(state) do
    # Initialize connectivity map for all nodes
    initial_connectivity = Enum.reduce(state.cluster_nodes, %{}, fn node, acc ->
      if node != state.node_id do
        Map.put(acc, node, %{
          status: :unknown,
          last_heartbeat: nil,
          failed_heartbeats: 0,
          last_connectivity_check: nil
        })
      else
        acc
      end
    end)
    
    %{state | connectivity_map: initial_connectivity}
  end
  
  defp default_thresholds() do
    %{
      min_detection_methods: 2,
      heartbeat_threshold: @partition_threshold,
      connectivity_threshold: @connectivity_timeout
    }
  end
  
  # Placeholder implementations
  defp query_witness(_witness, _nodes), do: :no_partition
  defp aggregate_witness_results(_results), do: :no_partition
  defp find_common_nodes(node_lists) do
    case node_lists do
      [] -> []
      [first | rest] -> 
        Enum.reduce(rest, first, fn nodes, acc ->
          Enum.filter(acc, &(&1 in nodes))
        end)
    end
  end
end

defmodule Phoenix.PartitionHandler do
  @moduledoc """
  Comprehensive partition response strategies based on system configuration and partition characteristics.
  
  Strategies:
  1. **Pause Minority**: Minority partition stops operations
  2. **Continue All**: All partitions continue with conflict resolution later  
  3. **Primary Partition**: Only primary partition continues operations
  4. **Quorum-Based**: Operations continue only with quorum
  5. **Application-Specific**: Custom business logic for partition handling
  """
  
  use GenServer
  
  defstruct [
    :node_id,
    :partition_strategy,
    :cluster_membership,
    :partition_state,
    :active_partitions,
    :strategy_config
  ]
  
  @type partition_strategy :: 
    :pause_minority |
    :continue_all |
    :primary_partition |
    :quorum_based |
    :application_specific
    
  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end
  
  def init(opts) do
    state = %__MODULE__{
      node_id: Keyword.get(opts, :node_id, node()),
      partition_strategy: Keyword.get(opts, :strategy, :quorum_based),
      cluster_membership: %{},
      partition_state: :normal,
      active_partitions: [],
      strategy_config: Keyword.get(opts, :strategy_config, %{})
    }
    
    {:ok, state}
  end
  
  @doc """
  Handle detected network partition.
  """
  def handle_partition(partition_event) do
    GenServer.cast(__MODULE__, {:handle_partition, partition_event})
  end
  
  @doc """
  Handle partition healing.
  """
  def handle_partition_heal(heal_event) do
    GenServer.cast(__MODULE__, {:handle_partition_heal, heal_event})
  end
  
  @doc """
  Get current partition status.
  """
  def partition_status() do
    GenServer.call(__MODULE__, :partition_status)
  end
  
  @doc """
  Override partition strategy temporarily.
  """
  def set_strategy(strategy, config \\ %{}) do
    GenServer.call(__MODULE__, {:set_strategy, strategy, config})
  end
  
  def handle_call(:partition_status, _from, state) do
    status = %{
      partition_state: state.partition_state,
      active_partitions: state.active_partitions,
      strategy: state.partition_strategy,
      node_id: state.node_id
    }
    
    {:reply, status, state}
  end
  
  def handle_call({:set_strategy, strategy, config}, _from, state) do
    new_state = %{state | 
      partition_strategy: strategy,
      strategy_config: Map.merge(state.strategy_config, config)
    }
    
    {:reply, :ok, new_state}
  end
  
  def handle_cast({:handle_partition, partition_event}, state) do
    # Determine partition response based on strategy
    response_plan = determine_response_plan(partition_event, state)
    
    # Execute response plan
    new_state = execute_partition_response(response_plan, partition_event, state)
    
    {:noreply, new_state}
  end
  
  def handle_cast({:handle_partition_heal, heal_event}, state) do
    # Handle partition healing
    new_state = execute_partition_heal(heal_event, state)
    
    {:noreply, new_state}
  end
  
  defp determine_response_plan(partition_event, state) do
    case state.partition_strategy do
      :pause_minority ->
        plan_pause_minority_response(partition_event, state)
        
      :continue_all ->
        plan_continue_all_response(partition_event, state)
        
      :primary_partition ->
        plan_primary_partition_response(partition_event, state)
        
      :quorum_based ->
        plan_quorum_based_response(partition_event, state)
        
      :application_specific ->
        plan_application_specific_response(partition_event, state)
    end
  end
  
  defp plan_pause_minority_response(partition_event, state) do
    all_nodes = get_all_cluster_nodes()
    reachable_nodes = all_nodes -- partition_event.partitioned_nodes
    
    if length(reachable_nodes) <= length(all_nodes) / 2 do
      # We're in minority, pause operations
      %{
        action: :pause_operations,
        reason: :minority_partition,
        affected_nodes: [state.node_id],
        recovery_condition: :partition_heal
      }
    else
      # We're in majority, continue operations
      %{
        action: :continue_operations,
        reason: :majority_partition,
        affected_nodes: partition_event.partitioned_nodes,
        pause_nodes: partition_event.partitioned_nodes
      }
    end
  end
  
  defp plan_continue_all_response(partition_event, state) do
    # All partitions continue, conflicts resolved later
    %{
      action: :continue_operations,
      reason: :conflict_resolution_strategy,
      affected_nodes: [],
      conflict_resolution: :enabled,
      reconciliation: :on_heal
    }
  end
  
  defp plan_primary_partition_response(partition_event, state) do
    primary_nodes = Map.get(state.strategy_config, :primary_nodes, [])
    
    if state.node_id in primary_nodes do
      # We're in primary partition, continue operations
      %{
        action: :continue_operations,
        reason: :primary_partition,
        affected_nodes: partition_event.partitioned_nodes,
        pause_nodes: partition_event.partitioned_nodes -- primary_nodes
      }
    else
      # We're not in primary partition, pause operations
      %{
        action: :pause_operations,
        reason: :non_primary_partition,
        affected_nodes: [state.node_id],
        recovery_condition: :primary_accessible
      }
    end
  end
  
  defp plan_quorum_based_response(partition_event, state) do
    all_nodes = get_all_cluster_nodes()
    reachable_nodes = all_nodes -- partition_event.partitioned_nodes
    quorum_size = Map.get(state.strategy_config, :quorum_size, div(length(all_nodes), 2) + 1)
    
    if length(reachable_nodes) >= quorum_size do
      # We have quorum, continue operations
      %{
        action: :continue_operations,
        reason: :quorum_maintained,
        affected_nodes: partition_event.partitioned_nodes,
        quorum_size: quorum_size,
        reachable_nodes: reachable_nodes
      }
    else
      # No quorum, pause operations
      %{
        action: :pause_operations,
        reason: :quorum_lost,
        affected_nodes: reachable_nodes,
        recovery_condition: :quorum_restored
      }
    end
  end
  
  defp plan_application_specific_response(partition_event, state) do
    # Custom application logic for partition handling
    handler_module = Map.get(state.strategy_config, :handler_module)
    
    if handler_module do
      handler_module.handle_partition(partition_event, state)
    else
      # Fall back to quorum-based strategy
      plan_quorum_based_response(partition_event, state)
    end
  end
  
  defp execute_partition_response(response_plan, partition_event, state) do
    case response_plan.action do
      :pause_operations ->
        execute_pause_operations(response_plan, state)
        
      :continue_operations ->
        execute_continue_operations(response_plan, state)
    end
    
    # Update partition state
    new_partition_state = case response_plan.action do
      :pause_operations -> :paused
      :continue_operations -> :degraded
    end
    
    new_active_partitions = [partition_event | state.active_partitions]
    
    %{state | 
      partition_state: new_partition_state,
      active_partitions: new_active_partitions
    }
  end
  
  defp execute_pause_operations(response_plan, state) do
    # Pause critical operations
    Phoenix.Agent.Supervisor.pause_all_agents()
    Phoenix.Signal.Bus.pause_signal_processing()
    Phoenix.Cluster.Registry.enter_readonly_mode()
    
    # Emit partition event
    :telemetry.execute([:phoenix, :partition, :operations_paused], %{}, %{
      node: state.node_id,
      reason: response_plan.reason
    })
    
    Logger.warn("Phoenix operations paused due to partition: #{inspect(response_plan.reason)}")
  end
  
  defp execute_continue_operations(response_plan, state) do
    # Continue operations with degraded mode
    Phoenix.Agent.Supervisor.enable_degraded_mode()
    Phoenix.Signal.Bus.enable_partition_mode()
    Phoenix.Cluster.Registry.enable_partition_tolerance()
    
    # Emit partition event
    :telemetry.execute([:phoenix, :partition, :degraded_mode], %{}, %{
      node: state.node_id,
      reason: response_plan.reason
    })
    
    Logger.info("Phoenix entering degraded mode due to partition: #{inspect(response_plan.reason)}")
  end
  
  defp execute_partition_heal(heal_event, state) do
    # Resume normal operations
    Phoenix.Agent.Supervisor.resume_normal_mode()
    Phoenix.Signal.Bus.resume_normal_mode()
    Phoenix.Cluster.Registry.exit_readonly_mode()
    
    # Trigger reconciliation if needed
    if requires_reconciliation?(state) do
      Phoenix.StateReconciliation.trigger_reconciliation(heal_event)
    end
    
    # Clear active partitions
    %{state | 
      partition_state: :normal,
      active_partitions: []
    }
  end
  
  defp get_all_cluster_nodes() do
    [node() | Node.list()]
  end
  
  defp requires_reconciliation?(state) do
    # Check if state reconciliation is needed after partition heal
    state.partition_state in [:degraded, :paused] and 
    length(state.active_partitions) > 0
  end
end

defmodule Phoenix.StateReconciliation do
  @moduledoc """
  Comprehensive state reconciliation after partition healing.
  
  Features:
  - CRDT-based automatic reconciliation
  - Vector clock conflict detection
  - Manual conflict resolution for critical data
  - Incremental reconciliation for large datasets
  - Rollback capabilities for failed reconciliation
  """
  
  use GenServer
  
  defstruct [
    :reconciliation_id,
    :participating_nodes,
    :reconciliation_state,
    :conflict_registry,
    :resolution_strategies,
    :progress_tracker
  ]
  
  @type reconciliation_state :: :idle | :collecting | :analyzing | :resolving | :applying | :complete | :failed
  
  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end
  
  def init(opts) do
    state = %__MODULE__{
      reconciliation_id: nil,
      participating_nodes: [],
      reconciliation_state: :idle,
      conflict_registry: %{},
      resolution_strategies: default_resolution_strategies(),
      progress_tracker: %{}
    }
    
    {:ok, state}
  end
  
  @doc """
  Trigger state reconciliation after partition heal.
  """
  def trigger_reconciliation(heal_event) do
    GenServer.call(__MODULE__, {:trigger_reconciliation, heal_event})
  end
  
  @doc """
  Get reconciliation status.
  """
  def reconciliation_status() do
    GenServer.call(__MODULE__, :reconciliation_status)
  end
  
  @doc """
  Register custom conflict resolution strategy.
  """
  def register_resolution_strategy(data_type, strategy_fn) do
    GenServer.call(__MODULE__, {:register_strategy, data_type, strategy_fn})
  end
  
  def handle_call({:trigger_reconciliation, heal_event}, _from, state) do
    if state.reconciliation_state == :idle do
      # Start new reconciliation process
      reconciliation_id = generate_reconciliation_id()
      participating_nodes = determine_participating_nodes(heal_event)
      
      new_state = %{state | 
        reconciliation_id: reconciliation_id,
        participating_nodes: participating_nodes,
        reconciliation_state: :collecting,
        conflict_registry: %{},
        progress_tracker: initialize_progress_tracker(participating_nodes)
      }
      
      # Start reconciliation process
      spawn_link(fn -> execute_reconciliation(new_state) end)
      
      {:reply, {:ok, reconciliation_id}, new_state}
    else
      {:reply, {:error, :reconciliation_in_progress}, state}
    end
  end
  
  def handle_call(:reconciliation_status, _from, state) do
    status = %{
      reconciliation_id: state.reconciliation_id,
      state: state.reconciliation_state,
      participating_nodes: state.participating_nodes,
      conflicts_detected: map_size(state.conflict_registry),
      progress: calculate_progress(state.progress_tracker)
    }
    
    {:reply, status, state}
  end
  
  def handle_call({:register_strategy, data_type, strategy_fn}, _from, state) do
    new_strategies = Map.put(state.resolution_strategies, data_type, strategy_fn)
    {:reply, :ok, %{state | resolution_strategies: new_strategies}}
  end
  
  def handle_cast({:reconciliation_progress, phase, node, status}, state) do
    # Update progress tracking
    new_progress = update_progress(state.progress_tracker, phase, node, status)
    
    new_state = %{state | progress_tracker: new_progress}
    
    # Check if phase is complete
    if phase_complete?(new_progress, phase, state.participating_nodes) do
      advance_to_next_phase(state.reconciliation_state, state)
    end
    
    {:noreply, new_state}
  end
  
  def handle_cast({:reconciliation_complete, result}, state) do
    case result do
      :success ->
        Logger.info("State reconciliation completed successfully: #{state.reconciliation_id}")
        :telemetry.execute([:phoenix, :reconciliation, :success], %{}, %{
          reconciliation_id: state.reconciliation_id,
          participating_nodes: length(state.participating_nodes),
          conflicts_resolved: map_size(state.conflict_registry)
        })
        
      {:failure, reason} ->
        Logger.error("State reconciliation failed: #{state.reconciliation_id}, reason: #{inspect(reason)}")
        :telemetry.execute([:phoenix, :reconciliation, :failure], %{}, %{
          reconciliation_id: state.reconciliation_id,
          reason: reason
        })
    end
    
    # Reset state
    reset_state = %{state | 
      reconciliation_id: nil,
      participating_nodes: [],
      reconciliation_state: :idle,
      conflict_registry: %{},
      progress_tracker: %{}
    }
    
    {:noreply, reset_state}
  end
  
  defp execute_reconciliation(state) do
    try do
      # Phase 1: Collect states from all nodes
      collected_states = collect_states_from_nodes(state.participating_nodes)
      update_reconciliation_state(:analyzing)
      
      # Phase 2: Analyze for conflicts
      conflicts = analyze_state_conflicts(collected_states)
      update_conflict_registry(conflicts)
      update_reconciliation_state(:resolving)
      
      # Phase 3: Resolve conflicts
      resolutions = resolve_conflicts(conflicts, state.resolution_strategies)
      update_reconciliation_state(:applying)
      
      # Phase 4: Apply resolutions
      apply_resolutions(resolutions, state.participating_nodes)
      update_reconciliation_state(:complete)
      
      # Notify completion
      GenServer.cast(__MODULE__, {:reconciliation_complete, :success})
      
    rescue
      error ->
        Logger.error("Reconciliation error: #{inspect(error)}")
        update_reconciliation_state(:failed)
        GenServer.cast(__MODULE__, {:reconciliation_complete, {:failure, error}})
    end
  end
  
  defp collect_states_from_nodes(nodes) do
    # Collect state snapshots from all participating nodes
    collection_tasks = Enum.map(nodes, fn node ->
      Task.async(fn ->
        case :rpc.call(node, Phoenix.StateSnapshot, :create_snapshot, [], 30_000) do
          {:badrpc, reason} -> {:error, {node, reason}}
          snapshot -> {:ok, {node, snapshot}}
        end
      end)
    end)
    
    # Wait for all collections to complete
    results = Task.await_many(collection_tasks, 60_000)
    
    # Separate successful and failed collections
    {successful, failed} = Enum.split_with(results, fn
      {:ok, _} -> true
      {:error, _} -> false
    end)
    
    if length(failed) > 0 do
      Logger.warn("Failed to collect states from nodes: #{inspect(failed)}")
    end
    
    successful
    |> Enum.map(fn {:ok, {node, snapshot}} -> {node, snapshot} end)
    |> Enum.into(%{})
  end
  
  defp analyze_state_conflicts(collected_states) do
    # Compare states to identify conflicts
    all_data_keys = collected_states
    |> Map.values()
    |> Enum.flat_map(&Map.keys/1)
    |> Enum.uniq()
    
    conflicts = Enum.reduce(all_data_keys, %{}, fn data_key, acc ->
      values_by_node = collected_states
      |> Enum.map(fn {node, state} -> {node, Map.get(state, data_key)} end)
      |> Enum.filter(fn {_node, value} -> value != nil end)
      |> Enum.into(%{})
      
      if conflicting_values?(values_by_node) do
        Map.put(acc, data_key, values_by_node)
      else
        acc
      end
    end)
    
    conflicts
  end
  
  defp conflicting_values?(values_by_node) when map_size(values_by_node) <= 1, do: false
  defp conflicting_values?(values_by_node) do
    # Check if values are different across nodes
    unique_values = values_by_node
    |> Map.values()
    |> Enum.uniq()
    
    length(unique_values) > 1
  end
  
  defp resolve_conflicts(conflicts, resolution_strategies) do
    # Resolve each conflict using appropriate strategy
    Enum.map(conflicts, fn {data_key, conflicting_values} ->
      data_type = determine_data_type(data_key)
      strategy = Map.get(resolution_strategies, data_type, :last_writer_wins)
      
      resolution = case strategy do
        :last_writer_wins -> resolve_lww(conflicting_values)
        :vector_clock -> resolve_vector_clock(conflicting_values)
        :crdt_merge -> resolve_crdt_merge(conflicting_values)
        :manual -> queue_for_manual_resolution(data_key, conflicting_values)
        custom_fn when is_function(custom_fn) -> custom_fn.(conflicting_values)
      end
      
      {data_key, resolution}
    end)
  end
  
  defp apply_resolutions(resolutions, nodes) do
    # Apply resolved values to all nodes
    application_tasks = Enum.map(nodes, fn node ->
      Task.async(fn ->
        case :rpc.call(node, Phoenix.StateSnapshot, :apply_resolutions, [resolutions], 30_000) do
          {:badrpc, reason} -> {:error, {node, reason}}
          :ok -> {:ok, node}
        end
      end)
    end)
    
    # Wait for all applications to complete
    results = Task.await_many(application_tasks, 60_000)
    
    # Check for failures
    failed_applications = Enum.filter(results, fn
      {:error, _} -> true
      _ -> false
    end)
    
    if length(failed_applications) > 0 do
      raise "Failed to apply resolutions to nodes: #{inspect(failed_applications)}"
    end
    
    :ok
  end
  
  defp resolve_lww(conflicting_values) do
    # Last-writer-wins resolution based on timestamps
    conflicting_values
    |> Enum.max_by(fn {_node, value} -> get_timestamp(value) end)
    |> elem(1)
  end
  
  defp resolve_vector_clock(conflicting_values) do
    # Vector clock based resolution
    vector_clocks = Enum.map(conflicting_values, fn {node, value} ->
      {node, get_vector_clock(value)}
    end)
    
    # Find causally latest value
    find_causally_latest(vector_clocks, conflicting_values)
  end
  
  defp resolve_crdt_merge(conflicting_values) do
    # CRDT merge resolution
    values = Map.values(conflicting_values)
    
    case values do
      [] -> nil
      [single_value] -> single_value
      [first | rest] -> 
        Enum.reduce(rest, first, &Phoenix.CRDT.merge/2)
    end
  end
  
  defp queue_for_manual_resolution(data_key, conflicting_values) do
    # Queue conflict for manual resolution
    Phoenix.ConflictResolution.queue_manual_conflict(%{
      data_key: data_key,
      conflicting_values: conflicting_values,
      timestamp: DateTime.utc_now()
    })
    
    # Return placeholder resolution
    {:manual_resolution_pending, data_key}
  end
  
  # Helper functions
  defp generate_reconciliation_id() do
    "reconciliation_#{System.system_time(:microsecond)}_#{node()}"
  end
  
  defp determine_participating_nodes(heal_event) do
    # Determine which nodes should participate in reconciliation
    all_nodes = [node() | Node.list()]
    healed_nodes = Map.get(heal_event, :healed_nodes, [])
    
    [node() | healed_nodes] |> Enum.uniq() |> Enum.filter(&(&1 in all_nodes))
  end
  
  defp default_resolution_strategies() do
    %{
      agent_state: :crdt_merge,
      configuration: :last_writer_wins,
      metrics: :crdt_merge,
      logs: :vector_clock
    }
  end
  
  defp update_reconciliation_state(new_state) do
    GenServer.cast(__MODULE__, {:update_state, new_state})
  end
  
  defp update_conflict_registry(conflicts) do
    GenServer.cast(__MODULE__, {:update_conflicts, conflicts})
  end
  
  defp determine_data_type(data_key) do
    # Determine data type from key pattern
    cond do
      String.contains?(to_string(data_key), "agent") -> :agent_state
      String.contains?(to_string(data_key), "config") -> :configuration
      String.contains?(to_string(data_key), "metric") -> :metrics
      String.contains?(to_string(data_key), "log") -> :logs
      true -> :unknown
    end
  end
  
  defp get_timestamp(value) do
    # Extract timestamp from value metadata
    case value do
      %{metadata: %{timestamp: ts}} -> ts
      %{timestamp: ts} -> ts
      _ -> 0
    end
  end
  
  defp get_vector_clock(value) do
    # Extract vector clock from value metadata
    case value do
      %{metadata: %{vector_clock: vc}} -> vc
      %{vector_clock: vc} -> vc
      _ -> Phoenix.VectorClock.new(node())
    end
  end
  
  defp find_causally_latest(vector_clocks, conflicting_values) do
    # Find the value with the causally latest vector clock
    # This is a simplified implementation
    {_node, latest_clock} = Enum.max_by(vector_clocks, fn {_node, clock} ->
      Phoenix.VectorClock.sum(clock)
    end)
    
    # Return the value associated with the latest clock
    Enum.find_value(conflicting_values, fn {node, value} ->
      if Map.get(vector_clocks, node) == latest_clock do
        value
      end
    end)
  end
  
  defp initialize_progress_tracker(nodes) do
    phases = [:collecting, :analyzing, :resolving, :applying]
    
    for phase <- phases, node <- nodes, into: %{} do
      {{phase, node}, :pending}
    end
  end
  
  defp update_progress(tracker, phase, node, status) do
    Map.put(tracker, {phase, node}, status)
  end
  
  defp calculate_progress(tracker) do
    completed = tracker |> Map.values() |> Enum.count(&(&1 == :completed))
    total = map_size(tracker)
    
    if total > 0 do
      completed / total
    else
      0.0
    end
  end
  
  defp phase_complete?(tracker, phase, nodes) do
    Enum.all?(nodes, fn node ->
      Map.get(tracker, {phase, node}) == :completed
    end)
  end
  
  defp advance_to_next_phase(current_phase, state) do
    next_phase = case current_phase do
      :collecting -> :analyzing
      :analyzing -> :resolving
      :resolving -> :applying
      :applying -> :complete
      _ -> current_phase
    end
    
    GenServer.cast(__MODULE__, {:update_state, next_phase})
  end
end