defmodule Object.CoordinationService do
  @moduledoc """
  Distributed coordination service for multi-object operations.
  Uses consensus algorithms and conflict resolution for large-scale coordination.
  """
  
  use GenServer
  require Logger
  
  alias Object.MessageRouter
  
  defstruct [
    :node_id,
    :coordination_sessions,
    :conflict_resolution_queue,
    :consensus_state,
    :performance_metrics,
    :worker_pool
  ]
  
  # Client API
  
  @doc """
  Starts the coordination service GenServer.
  
  ## Returns
  `{:ok, pid}` on successful startup
  """
  def start_link(_) do
    GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
  end
  
  @doc """
  Coordinates a task across multiple objects using consensus algorithms.
  
  ## Parameters
  - `object_ids`: List of object IDs to coordinate
  - `coordination_task`: Task specification with type, objectives, and constraints
  
  ## Returns
  `{:ok, session_id}` with the coordination session identifier
  
  ## Examples
      iex> Object.CoordinationService.coordinate_objects(["obj1", "obj2"], %{type: :optimization})
      {:ok, "session_abc123"}
  """
  def coordinate_objects(object_ids, coordination_task) do
    GenServer.call(__MODULE__, {:coordinate_objects, object_ids, coordination_task}, 30_000)
  end
  
  @doc """
  Resolves conflicts between objects using configured resolution strategies.
  
  ## Parameters
  - `conflict_context`: Context describing the conflict and involved parties
  
  ## Returns
  Resolution result with method and outcome
  """
  def resolve_conflict(conflict_context) do
    GenServer.call(__MODULE__, {:resolve_conflict, conflict_context}, 15_000)
  end
  
  @doc """
  Gets the current status of a coordination session.
  
  ## Parameters
  - `session_id`: ID of the coordination session
  
  ## Returns
  `{:ok, status}` where status is `:voting`, `:in_progress`, `:completed`, or `:failed`
  """
  def get_coordination_status(session_id) do
    GenServer.call(__MODULE__, {:get_status, session_id})
  end
  
  @doc """
  Adds an object to an existing coordination session.
  
  ## Parameters
  - `session_id`: ID of the coordination session
  - `object_id`: ID of the object to add
  
  ## Returns
  `:ok` on success, `{:error, reason}` on failure
  """
  def join_coordination(session_id, object_id) do
    GenServer.call(__MODULE__, {:join_coordination, session_id, object_id})
  end
  
  @doc """
  Removes an object from a coordination session.
  
  ## Parameters
  - `session_id`: ID of the coordination session
  - `object_id`: ID of the object to remove
  
  ## Returns
  `:ok` on success, `{:ok, :session_cancelled}` if last participant left
  """
  def leave_coordination(session_id, object_id) do
    GenServer.call(__MODULE__, {:leave_coordination, session_id, object_id})
  end
  
  @doc """
  Gets performance metrics for the coordination service.
  
  ## Returns
  Map with metrics including active sessions, completed sessions, and uptime
  """
  def get_metrics() do
    GenServer.call(__MODULE__, :get_metrics)
  end
  
  # Server callbacks
  
  @impl true
  def init(:ok) do
    node_id = Node.self()
    
    # Initialize worker pool for coordination tasks
    pool_size = System.schedulers_online()
    worker_pool = for _i <- 1..pool_size, do: spawn_link(fn -> coordination_worker() end)
    
    state = %__MODULE__{
      node_id: node_id,
      coordination_sessions: %{},
      conflict_resolution_queue: :queue.new(),
      consensus_state: %{},
      performance_metrics: init_metrics(),
      worker_pool: worker_pool
    }
    
    # Start periodic cleanup
    schedule_cleanup()
    
    Logger.info("Coordination Service started on node #{node_id} with #{pool_size} workers")
    {:ok, state}
  end
  
  @impl true
  def handle_call({:coordinate_objects, object_ids, coordination_task}, from, state) do
    session_id = generate_session_id()
    
    coordination_session = %{
      id: session_id,
      participants: object_ids,
      task: coordination_task,
      status: :initializing,
      coordinator: from,
      started_at: DateTime.utc_now(),
      phases: init_coordination_phases(coordination_task),
      current_phase: 0,
      results: %{}
    }
    
    # Use worker pool instead of spawning new process
    assign_to_worker_pool(state.worker_pool, {:coordinate, coordination_session})
    
    updated_sessions = Map.put(state.coordination_sessions, session_id, coordination_session)
    updated_state = %{state | coordination_sessions: updated_sessions}
    
    {:reply, {:ok, session_id}, updated_state}
  end
  
  @impl true
  def handle_call({:resolve_conflict, conflict_context}, _from, state) do
    conflict_id = generate_conflict_id()
    
    resolution_task = %{
      id: conflict_id,
      context: conflict_context,
      strategy: determine_resolution_strategy(conflict_context),
      created_at: DateTime.utc_now()
    }
    
    # Add to conflict resolution queue
    updated_queue = :queue.in(resolution_task, state.conflict_resolution_queue)
    
    # Process conflict immediately if queue was empty
    resolution_result = if :queue.len(state.conflict_resolution_queue) == 0 do
      process_conflict_resolution(resolution_task)
    else
      {:queued, conflict_id}
    end
    
    updated_state = %{state | conflict_resolution_queue: updated_queue}
    
    {:reply, resolution_result, updated_state}
  end
  
  @impl true
  def handle_call({:get_status, session_id}, _from, state) do
    case Map.get(state.coordination_sessions, session_id) do
      nil -> {:reply, {:error, :session_not_found}, state}
      session -> {:reply, {:ok, session.status}, state}
    end
  end
  
  @impl true
  def handle_call({:join_coordination, session_id, object_id}, _from, state) do
    case Map.get(state.coordination_sessions, session_id) do
      nil ->
        {:reply, {:error, :session_not_found}, state}
      
      session ->
        if object_id in session.participants do
          {:reply, {:error, :already_participant}, state}
        else
          updated_participants = [object_id | session.participants]
          updated_session = %{session | participants: updated_participants}
          updated_sessions = Map.put(state.coordination_sessions, session_id, updated_session)
          
          {:reply, :ok, %{state | coordination_sessions: updated_sessions}}
        end
    end
  end
  
  @impl true
  def handle_call({:leave_coordination, session_id, object_id}, _from, state) do
    case Map.get(state.coordination_sessions, session_id) do
      nil ->
        {:reply, {:error, :session_not_found}, state}
      
      session ->
        updated_participants = List.delete(session.participants, object_id)
        
        if length(updated_participants) == 0 do
          # Cancel session if no participants left
          updated_sessions = Map.delete(state.coordination_sessions, session_id)
          {:reply, {:ok, :session_cancelled}, %{state | coordination_sessions: updated_sessions}}
        else
          updated_session = %{session | participants: updated_participants}
          updated_sessions = Map.put(state.coordination_sessions, session_id, updated_session)
          
          {:reply, :ok, %{state | coordination_sessions: updated_sessions}}
        end
    end
  end
  
  @impl true
  def handle_call(:get_metrics, _from, state) do
    current_metrics = calculate_current_metrics(state)
    {:reply, current_metrics, state}
  end
  
  @impl true
  def handle_cast({:coordination_phase_complete, session_id, phase_result}, state) do
    case Map.get(state.coordination_sessions, session_id) do
      nil ->
        Logger.warning("Received phase completion for unknown session: #{session_id}")
        {:noreply, state}
      
      session ->
        updated_session = advance_coordination_phase(session, phase_result)
        updated_sessions = Map.put(state.coordination_sessions, session_id, updated_session)
        
        # Check if coordination is complete
        if updated_session.status == :completed do
          GenServer.reply(updated_session.coordinator, {:ok, updated_session.results})
        end
        
        {:noreply, %{state | coordination_sessions: updated_sessions}}
    end
  end
  
  @impl true
  def handle_info(:cleanup, state) do
    # Clean up old sessions and process conflict queue
    current_time = DateTime.utc_now()
    
    # Remove sessions older than 1 hour
    cleaned_sessions = state.coordination_sessions
                      |> Enum.reject(fn {_id, session} ->
                        DateTime.diff(current_time, session.started_at, :second) > 3600
                      end)
                      |> Enum.into(%{})
    
    # Process next conflict in queue
    {updated_queue, _processed} = process_conflict_queue(state.conflict_resolution_queue)
    
    updated_state = %{state |
      coordination_sessions: cleaned_sessions,
      conflict_resolution_queue: updated_queue
    }
    
    schedule_cleanup()
    {:noreply, updated_state}
  end
  
  # Private functions
  
  defp generate_session_id do
    :crypto.strong_rand_bytes(8) |> Base.encode16() |> String.downcase()
  end
  
  defp generate_conflict_id do
    :crypto.strong_rand_bytes(6) |> Base.encode16() |> String.downcase()
  end
  
  defp init_coordination_phases(coordination_task) do
    case coordination_task.type do
      :system_optimization ->
        [:analysis, :planning, :execution, :validation]
      
      :resource_allocation ->
        [:discovery, :negotiation, :allocation, :monitoring]
      
      :task_distribution ->
        [:decomposition, :assignment, :execution, :aggregation]
      
      _ ->
        [:preparation, :execution, :completion]
    end
  end
  
  defp execute_coordination(session) do
    Logger.info("Starting coordination session #{session.id} with #{length(session.participants)} participants")
    
    try do
      # Execute each phase sequentially
      final_session = Enum.reduce(session.phases, session, fn phase, acc_session ->
        execute_coordination_phase(acc_session, phase)
      end)
      
      # Mark as completed
      _completed_session = %{final_session | status: :completed}
      GenServer.cast(__MODULE__, {:coordination_phase_complete, session.id, :final})
      
    rescue
      error ->
        Logger.error("Coordination session #{session.id} failed: #{inspect(error)}")
        _failed_session = %{session | status: :failed, results: %{error: error}}
        GenServer.reply(session.coordinator, {:error, error})
    end
  end
  
  defp execute_coordination_phase(session, phase) do
    Logger.debug("Executing phase #{phase} for session #{session.id}")
    
    # Send coordination message to all participants
    coordination_message = %{
      session_id: session.id,
      phase: phase,
      task: session.task,
      participants: session.participants
    }
    
    # Collect responses from all participants
    phase_results = collect_phase_responses(session.participants, coordination_message)
    
    # Update session with phase results
    updated_results = Map.put(session.results, phase, phase_results)
    %{session | 
      results: updated_results,
      current_phase: session.current_phase + 1
    }
  end
  
  defp collect_phase_responses(participants, coordination_message) do
    # Send messages to all participants
    Enum.each(participants, fn object_id ->
      message = %{
        id: generate_session_id(),
        from: "coordination_service",
        to: object_id,
        type: :coordination,
        content: coordination_message,
        timestamp: DateTime.utc_now(),
        priority: :high,
        requires_ack: true,
        ttl: 300  # 5 minutes
      }
      
      MessageRouter.route_message(message)
    end)
    
    # Collect responses (simplified - in real implementation would use proper synchronization)
    %{
      phase_completed: true,
      participant_responses: length(participants),
      timestamp: DateTime.utc_now()
    }
  end
  
  defp advance_coordination_phase(session, _phase_result) do
    if session.current_phase >= length(session.phases) do
      %{session | status: :completed}
    else
      %{session | status: :in_progress}
    end
  end
  
  defp determine_resolution_strategy(conflict_context) do
    case conflict_context.priority do
      :critical -> :immediate_arbitration
      :high -> :fast_negotiation
      _ -> :consensus_building
    end
  end
  
  defp process_conflict_resolution(resolution_task) do
    Logger.info("Processing conflict resolution: #{resolution_task.id}")
    
    case resolution_task.strategy do
      :immediate_arbitration ->
        %{
          resolution: :arbitrated,
          decision: :priority_override,
          timestamp: DateTime.utc_now()
        }
      
      :fast_negotiation ->
        %{
          resolution: :negotiated,
          decision: :compromise,
          timestamp: DateTime.utc_now()
        }
      
      :consensus_building ->
        %{
          resolution: :consensus,
          decision: :majority_vote,
          timestamp: DateTime.utc_now()
        }
    end
  end
  
  defp process_conflict_queue(queue) do
    case :queue.out(queue) do
      {{:value, conflict_task}, new_queue} ->
        _result = process_conflict_resolution(conflict_task)
        {new_queue, 1}
      
      {:empty, queue} ->
        {queue, 0}
    end
  end
  
  defp schedule_cleanup do
    Process.send_after(self(), :cleanup, 60_000)  # 1 minute
  end
  
  defp init_metrics do
    %{
      sessions_created: 0,
      sessions_completed: 0,
      sessions_failed: 0,
      conflicts_resolved: 0,
      average_coordination_time: 0.0,
      started_at: DateTime.utc_now()
    }
  end
  
  defp calculate_current_metrics(state) do
    active_sessions = map_size(state.coordination_sessions)
    pending_conflicts = :queue.len(state.conflict_resolution_queue)
    uptime = DateTime.diff(DateTime.utc_now(), state.performance_metrics.started_at, :second)
    
    Map.merge(state.performance_metrics, %{
      active_sessions: active_sessions,
      pending_conflicts: pending_conflicts,
      uptime_seconds: uptime
    })
  end

  defp assign_to_worker_pool(worker_pool, task) do
    # Simple round-robin assignment to available worker
    worker = Enum.random(worker_pool)
    send(worker, task)
  end

  defp coordination_worker do
    receive do
      {:coordinate, session} ->
        execute_coordination(session)
        coordination_worker()
      
      :stop ->
        :ok
      
      _ ->
        coordination_worker()
    end
  end
end