# Traditional approach: local-first with distribution bolted on
agent = Agent.start_local(spec)
Agent.register_locally(agent)
# Later: add distribution layer

# Phoenix approach: distribution-native
agent = Phoenix.Agent.spawn(spec, placement: :optimal)
# ↑ Agent placement, registration, and operation are inherently distributed

# Default: eventual consistency for performance
Phoenix.Agent.update(agent_id, fn state -> new_state end)

# Explicit: strong consistency when required
Phoenix.Agent.update(agent_id, fn state -> new_state end, 
  consistency: :strong, 
  quorum: :majority
)

# Agent state composed of CRDT primitives
defmodule AgentState do
  use Phoenix.CRDT.Composite
  
  crdt_field :counters, Phoenix.CRDT.GCounter
  crdt_field :flags, Phoenix.CRDT.GSet
  crdt_field :config, Phoenix.CRDT.LWWMap
  crdt_field :logs, Phoenix.CRDT.OpBasedList
end

# Every operation produces structured telemetry
Phoenix.Agent.execute(agent_id, action, params)
# ↑ Automatically emits:
# - Distributed trace span
# - Performance metrics
# - State change events
# - Error correlation data

# Circuit breaker and bulkhead patterns built-in
Phoenix.Agent.call(agent_id, request, 
  timeout: 5000,
  circuit_breaker: :default,
  fallback: &fallback_handler/1
)

# Phoenix cluster topology
defmodule Phoenix.Cluster do
  @moduledoc """
  Multi-layer cluster architecture:
  
  Layer 1: Physical Nodes (BEAM VMs)
  Layer 2: Logical Regions (availability zones, data centers)  
  Layer 3: Agent Placement Groups (resource pools, isolation boundaries)
  Layer 4: Agent Instances (individual computational entities)
  """
  
  defstruct [
    :topology,      # Network topology graph
    :regions,       # Logical groupings for placement
    :placement_groups, # Resource and isolation boundaries
    :health_status, # Overall cluster health
    :consensus_state # Raft-based coordination state
  ]
end

# Control plane: Strong consistency via Raft
Phoenix.Consensus.propose_agent_placement(agent_spec)

# Data plane: Eventual consistency via CRDTs  
Phoenix.Agent.State.update_counter(agent_id, :requests, 1)

@type agent_identity :: {
  global_id :: binary(),     # Globally unique identifier
  placement_key :: term(),   # For consistent hashing
  instance_ref :: reference() # Local process reference
}

defmodule Phoenix.Transport do
  @moduledoc """
  Pluggable transport supporting multiple protocols:
  - Distributed Erlang (dev/test)
  - Partisan (production clusters)
  - HTTP/2 (cross-DC, hybrid clouds)
  - QUIC (low-latency, mobile)
  """
  
  @callback send_message(target, message, opts) :: :ok | {:error, term()}
  @callback broadcast_message(targets, message, opts) :: :ok | {:error, term()}
end

defmodule Phoenix.Agent do
  @moduledoc """
  Distributed agent implementation.
  
  An agent consists of:
  - Identity: Global unique identifier and placement metadata
  - State: CRDT-based replicated state across nodes
  - Behavior: Execution logic (actions, reactions, goals)
  - Lifecycle: Distributed supervision and migration
  - Communication: Message passing and coordination
  """
  
  defstruct [
    :identity,       # Global agent identity
    :state,         # CRDT-based distributed state
    :behavior_spec, # Behavior definition and capabilities
    :placement,     # Current placement in cluster
    :health,        # Health and performance metrics
    :comm_channels  # Communication endpoints
  ]
end

defmodule Phoenix.Agent.Lifecycle do
  @type state :: 
    :initializing    |  # Agent being created, state loading
    :active         |  # Normal operation
    :migrating      |  # Moving between nodes
    :degraded       |  # Operating with reduced capabilities
    :paused         |  # Temporarily suspended
    :terminating    |  # Shutting down gracefully
    :failed            # Unrecoverable error state
end

defmodule Phoenix.Agent.Behavior do
  @moduledoc """
  Agent behavior specification combining:
  - Actions: Capabilities the agent can execute
  - Reactions: Responses to events and messages
  - Goals: Long-term objectives and optimization targets
  - Constraints: Resource limits and operational boundaries
  """
  
  defstruct [
    :actions,      # Map of action_name -> action_module
    :reactions,    # Event pattern -> reaction function
    :goals,        # List of goal specifications
    :constraints,  # Resource and operational limits
    :coordination  # Inter-agent coordination protocols
  ]
  
  defmacro __using__(opts) do
    quote do
      @behaviour Phoenix.Agent.Behavior
      
      # Define agent capabilities
      def actions, do: %{}
      def reactions, do: %{}
      def goals, do: []
      def constraints, do: %{}
      
      # Allow overriding
      defoverridable [actions: 0, reactions: 0, goals: 0, constraints: 0]
    end
  end
end

defmodule Phoenix.Registry do
  @moduledoc """
  Cluster-wide agent registry using consistent hashing and CRDT replication.
  
  Features:
  - O(1) agent lookup via consistent hashing
  - Automatic replication for fault tolerance
  - Dynamic rebalancing on topology changes
  - Conflict-free concurrent registration
  """
  
  use Phoenix.CRDT.Actor
  
  @crdt_state Phoenix.CRDT.LWWMap.new()
  
  def register_agent(agent_id, agent_spec) do
    # Determine optimal placement
    placement = Phoenix.Scheduler.determine_placement(agent_spec)
    
    # Register in CRDT registry
    registry_entry = %{
      agent_id: agent_id,
      placement: placement,
      capabilities: agent_spec.capabilities,
      registered_at: Phoenix.VectorClock.now(),
      health_status: :initializing
    }
    
    Phoenix.CRDT.LWWMap.put(@crdt_state, agent_id, registry_entry)
  end
  
  def locate_agent(agent_id) do
    case Phoenix.CRDT.LWWMap.get(@crdt_state, agent_id) do
      {:ok, entry} -> 
        case entry.placement do
          {:local, node} when node == node() -> 
            {:ok, :local, get_local_pid(agent_id)}
          {:remote, node} -> 
            {:ok, :remote, node, get_remote_ref(node, agent_id)}
          {:migrating, from_node, to_node} ->
            {:ok, :migrating, from_node, to_node}
        end
      :error -> {:error, :not_found}
    end
  end
end

defmodule Phoenix.HashRing do
  @moduledoc """
  Consistent hashing for deterministic agent placement.
  
  Features:
  - Configurable virtual nodes for load balancing
  - Minimal reshuffling on topology changes  
  - Resource-aware placement (CPU, memory, network)
  - Preference-based constraints (co-location, anti-affinity)
  """
  
  defstruct [
    :ring,           # Ordered map of hash -> node
    :virtual_nodes,  # Virtual nodes per physical node
    :node_weights,   # Resource-based weighting
    :constraints     # Placement constraints
  ]
  
  def place_agent(agent_spec, ring) do
    # Hash agent ID with placement preferences
    base_hash = :erlang.phash2(agent_spec.id)
    preference_hash = hash_preferences(agent_spec.placement_preferences)
    final_hash = combine_hashes(base_hash, preference_hash)
    
    # Find suitable nodes considering constraints
    candidate_nodes = find_candidate_nodes(ring, final_hash)
    
    # Select best node based on current load and constraints
    Phoenix.Scheduler.select_optimal_node(candidate_nodes, agent_spec)
  end
end

defmodule Phoenix.MessageRouter do
  @moduledoc """
  Intelligent message routing with delivery guarantees.
  
  Routing strategies:
  - Direct: Point-to-point delivery
  - Multicast: Efficient group communication
  - Gossip: Eventually consistent broadcast
  - Pipeline: Ordered processing chains
  """
  
  def route_message(target, message, opts \\ []) do
    strategy = Keyword.get(opts, :strategy, :direct)
    
    case strategy do
      :direct -> direct_route(target, message, opts)
      :multicast -> multicast_route(target, message, opts)
      :gossip -> gossip_route(target, message, opts)
      :pipeline -> pipeline_route(target, message, opts)
    end
  end
  
  defp direct_route(target_agent_id, message, opts) do
    delivery_guarantee = Keyword.get(opts, :delivery, :at_most_once)
    
    with {:ok, location} <- Phoenix.Registry.locate_agent(target_agent_id),
         {:ok, route} <- determine_route(location, opts),
         {:ok, envelope} <- create_envelope(message, delivery_guarantee) do
      
      case delivery_guarantee do
        :at_most_once -> fire_and_forget(route, envelope)
        :at_least_once -> reliable_delivery(route, envelope, opts)
        :exactly_once -> exactly_once_delivery(route, envelope, opts)
      end
    end
  end
end

defmodule Phoenix.Transport.Manager do
  @moduledoc """
  Manages multiple transport protocols for different scenarios:
  
  - Distributed Erlang: Development and single-DC clusters
  - Partisan: Large-scale production clusters (>100 nodes)
  - HTTP/2: Cross-datacenter and hybrid cloud
  - QUIC: Low-latency and mobile connections
  """
  
  def send_message(target, message, opts \\ []) do
    transport = select_transport(target, opts)
    
    case transport do
      :distributed_erlang -> 
        DistributedErlang.send(target, message, opts)
      :partisan -> 
        Partisan.send(target, message, opts)
      :http2 -> 
        HTTP2Transport.send(target, message, opts)
      :quic -> 
        QUICTransport.send(target, message, opts)
    end
  end
  
  defp select_transport(target, opts) do
    cond do
      local_cluster?(target) -> :distributed_erlang
      large_cluster?() -> :partisan
      cross_dc?(target) -> :http2
      mobile_client?(target) -> :quic
      true -> Application.get_env(:phoenix, :default_transport)
    end
  end
end

defmodule Phoenix.Message do
  @moduledoc """
  Standard message format supporting multiple serialization protocols.
  
  Based on CloudEvents v1.0.2 with Phoenix extensions for:
  - Distributed tracing
  - Causal consistency
  - Delivery guarantees
  - Routing metadata
  """
  
  use TypedStruct
  
  typedstruct do
    # CloudEvents v1.0.2 fields
    field :specversion, String.t(), default: "1.0.2"
    field :id, String.t()
    field :source, String.t()
    field :type, String.t()
    field :subject, String.t()
    field :time, DateTime.t()
    field :datacontenttype, String.t(), default: "application/x-erlang-term"
    field :data, term()
    
    # Phoenix extensions
    field :phoenix_trace, Phoenix.Trace.Context.t()
    field :phoenix_causality, Phoenix.VectorClock.t()
    field :phoenix_delivery, Phoenix.Delivery.Guarantee.t()
    field :phoenix_routing, Phoenix.Routing.Metadata.t()
  end
  
  def serialize(message, format \\ :erlang_term) do
    case format do
      :erlang_term -> :erlang.term_to_binary(message)
      :json -> Jason.encode!(message)
      :msgpack -> Msgpax.pack!(message)
      :protobuf -> PhoenixProto.Message.encode(message)
    end
  end
end

defmodule Phoenix.Delivery do
  @moduledoc """
  Configurable delivery guarantees for different use cases.
  
  Guarantees:
  - at_most_once: Fire-and-forget (performance)
  - at_least_once: Retry until success (reliability)
  - exactly_once: Idempotent delivery (correctness)
  - causal_order: Respects causal dependencies
  """
  
  defmodule Guarantee do
    use TypedStruct
    
    typedstruct do
      field :delivery_mode, atom()
      field :timeout, pos_integer()
      field :retry_strategy, atom()
      field :ordering_requirement, atom()
      field :acknowledgment_required, boolean()
    end
  end
  
  def deliver_with_guarantee(target, message, guarantee) do
    case guarantee.delivery_mode do
      :at_most_once -> 
        fire_and_forget(target, message)
        
      :at_least_once -> 
        retry_until_success(target, message, guarantee)
        
      :exactly_once -> 
        idempotent_delivery(target, message, guarantee)
        
      :causal_order -> 
        causal_delivery(target, message, guarantee)
    end
  end
end

defmodule Phoenix.Agent.State do
  @moduledoc """
  Agent state management using conflict-free replicated data types.
  
  State composition:
  - Core State: Critical data requiring strong consistency
  - Operational State: Metrics and logs with eventual consistency
  - Cache State: Performance optimization with TTL
  - Derived State: Computed from other state components
  """
  
  use Phoenix.CRDT.Composite
  
  # Core state with strong consistency requirements
  crdt_field :identity, Phoenix.CRDT.LWWRegister
  crdt_field :capabilities, Phoenix.CRDT.GSet
  crdt_field :configuration, Phoenix.CRDT.LWWMap
  
  # Operational state with eventual consistency
  crdt_field :counters, Phoenix.CRDT.PNCounter
  crdt_field :flags, Phoenix.CRDT.TwoPhaseSet
  crdt_field :logs, Phoenix.CRDT.OpBasedList
  
  # Cache state with TTL
  crdt_field :cache, Phoenix.CRDT.TTLMap
  
  def update_state(agent_id, update_fn, opts \\ []) do
    consistency = Keyword.get(opts, :consistency, :eventual)
    
    case consistency do
      :eventual -> 
        # Local update + async replication
        update_local_state(agent_id, update_fn)
        async_replicate_to_cluster(agent_id)
        
      :strong ->
        # Coordinate with replicas before committing
        coordinate_strong_update(agent_id, update_fn, opts)
        
      :causal ->
        # Ensure causal consistency
        update_with_causal_order(agent_id, update_fn, opts)
    end
  end
end

defmodule Phoenix.VectorClock do
  @moduledoc """
  Vector clock implementation for tracking causal relationships.
  
  Features:
  - Efficient encoding for network transmission
  - Automatic pruning of old entries
  - Integration with CRDT operations
  - Conflict detection and resolution
  """
  
  defstruct [
    :clocks,     # Map of node_id -> logical_time
    :node_id,    # This node's identifier
    :version     # Schema version for compatibility
  ]
  
  def new(node_id), do: %__MODULE__{
    clocks: %{node_id => 0},
    node_id: node_id,
    version: 1
  }
  
  def tick(vector_clock) do
    %{vector_clock | 
      clocks: Map.update!(vector_clock.clocks, vector_clock.node_id, &(&1 + 1))
    }
  end
  
  def compare(clock_a, clock_b) do
    all_nodes = MapSet.union(
      MapSet.new(Map.keys(clock_a.clocks)),
      MapSet.new(Map.keys(clock_b.clocks))
    )
    
    comparisons = Enum.map(all_nodes, fn node ->
      time_a = Map.get(clock_a.clocks, node, 0)
      time_b = Map.get(clock_b.clocks, node, 0)
      
      cond do
        time_a < time_b -> :less
        time_a > time_b -> :greater
        true -> :equal
      end
    end)
    
    determine_relationship(comparisons)
  end
end

defmodule Phoenix.Conflict do
  @moduledoc """
  Conflict resolution strategies for distributed state management.
  
  Strategies:
  - Last Writer Wins: Simple, may lose data
  - Vector Clock: Preserves causality
  - Semantic Merge: Domain-specific resolution
  - Manual Resolution: Human intervention required
  """
  
  def resolve_conflict(conflicting_states, strategy, context \\ %{}) do
    case strategy do
      :last_writer_wins -> 
        Enum.max_by(conflicting_states, & &1.last_modified)
        
      :vector_clock ->
        resolve_with_vector_clocks(conflicting_states)
        
      :semantic_merge ->
        semantic_merge_states(conflicting_states, context)
        
      :manual_resolution ->
        queue_for_manual_resolution(conflicting_states, context)
        
      custom_resolver when is_function(custom_resolver) ->
        custom_resolver.(conflicting_states, context)
    end
  end
  
  defp semantic_merge_states(states, context) do
    case context.data_type do
      :counter -> 
        # Sum all counter values
        Enum.reduce(states, 0, fn state, acc -> 
          acc + get_counter_value(state) 
        end)
        
      :set ->
        # Union of all sets
        Enum.reduce(states, MapSet.new(), fn state, acc ->
          MapSet.union(acc, get_set_value(state))
        end)
        
      :map ->
        # Merge maps with conflict resolution per key
        merge_maps_with_resolution(states, context)
    end
  end
end

defmodule Phoenix.CircuitBreaker do
  @moduledoc """
  Circuit breaker implementation for preventing cascade failures.
  
  States:
  - Closed: Normal operation, requests pass through
  - Open: Failures exceeded threshold, requests rejected
  - Half-Open: Testing if service recovered
  """
  
  use GenServer
  
  defstruct [
    :name,
    :state,           # :closed | :open | :half_open
    :failure_count,
    :failure_threshold,
    :recovery_timeout,
    :last_failure_time,
    :request_count,
    :success_count
  ]
  
  def call(circuit_name, operation, opts \\ []) do
    case get_circuit_state(circuit_name) do
      :closed -> 
        execute_with_monitoring(circuit_name, operation)
        
      :open -> 
        case should_attempt_recovery?(circuit_name) do
          true -> transition_to_half_open(circuit_name, operation)
          false -> {:error, :circuit_open}
        end
        
      :half_open -> 
        test_recovery(circuit_name, operation)
    end
  end
  
  defp execute_with_monitoring(circuit_name, operation) do
    start_time = System.monotonic_time()
    
    try do
      result = operation.()
      execution_time = System.monotonic_time() - start_time
      
      record_success(circuit_name, execution_time)
      {:ok, result}
      
    rescue
      error ->
        record_failure(circuit_name, error)
        evaluate_circuit_state(circuit_name)
        {:error, error}
    end
  end
end

defmodule Phoenix.Bulkhead do
  @moduledoc """
  Resource isolation using bulkhead pattern.
  
  Isolates different types of operations to prevent
  resource exhaustion in one area from affecting others.
  """
  
  defstruct [
    :pools,          # Map of pool_name -> pool_config
    :total_capacity,
    :allocations     # Current resource allocations
  ]
  
  def execute_in_pool(pool_name, operation, opts \\ []) do
    timeout = Keyword.get(opts, :timeout, 5000)
    
    case checkout_resource(pool_name, timeout) do
      {:ok, resource} ->
        try do
          operation.(resource)
        after
          checkin_resource(pool_name, resource)
        end
        
      {:error, :pool_exhausted} ->
        handle_pool_exhaustion(pool_name, operation, opts)
        
      {:error, :timeout} ->
        {:error, :resource_timeout}
    end
  end
  
  defp handle_pool_exhaustion(pool_name, operation, opts) do
    strategy = get_exhaustion_strategy(pool_name)
    
    case strategy do
      :reject -> {:error, :resource_unavailable}
      :queue -> queue_operation(pool_name, operation, opts)
      :spillover -> find_spillover_pool(pool_name, operation, opts)
      :adaptive -> adapt_pool_size(pool_name, operation, opts)
    end
  end
end

defmodule Phoenix.Supervision do
  @moduledoc """
  Distributed supervision for agent processes.
  
  Features:
  - Cross-node supervision relationships
  - Automatic failover and recovery
  - Coordinated shutdown procedures
  - Resource cleanup on failures
  """
  
  def supervise_agent(agent_spec, supervision_opts \\ []) do
    # Determine supervision strategy
    strategy = Keyword.get(supervision_opts, :strategy, :one_for_one)
    replicas = Keyword.get(supervision_opts, :replicas, 3)
    
    # Select supervisor nodes
    supervisor_nodes = select_supervisor_nodes(replicas)
    
    # Start supervision on selected nodes
    supervision_refs = Enum.map(supervisor_nodes, fn node ->
      start_remote_supervisor(node, agent_spec, strategy)
    end)
    
    # Register supervision group
    Phoenix.SupervisionRegistry.register_group(
      agent_spec.id, 
      supervision_refs
    )
  end
  
  def handle_agent_failure(agent_id, failure_reason) do
    case get_supervision_strategy(agent_id) do
      :restart -> 
        restart_agent_with_backoff(agent_id)
        
      :migrate -> 
        migrate_agent_to_healthy_node(agent_id)
        
      :replicate -> 
        activate_backup_replica(agent_id)
        
      :fail_fast -> 
        propagate_failure_to_dependents(agent_id, failure_reason)
    end
  end
end

defmodule Phoenix.LoadBalancer do
  @moduledoc """
  Adaptive load balancing considering multiple factors:
  
  - Node resource utilization (CPU, memory, network)
  - Agent-specific requirements and preferences
  - Network topology and latency
  - Historical performance data
  """
  
  def select_placement_node(agent_spec, available_nodes) do
    # Score each node based on multiple criteria
    scored_nodes = Enum.map(available_nodes, fn node ->
      score = calculate_placement_score(node, agent_spec)
      {node, score}
    end)
    
    # Select best node with some randomization for load spreading
    select_with_weighted_randomization(scored_nodes)
  end
  
  defp calculate_placement_score(node, agent_spec) do
    resource_score = calculate_resource_score(node, agent_spec)
    affinity_score = calculate_affinity_score(node, agent_spec)
    latency_score = calculate_latency_score(node, agent_spec)
    historical_score = calculate_historical_score(node, agent_spec)
    
    # Weighted combination of factors
    resource_score * 0.4 + 
    affinity_score * 0.3 + 
    latency_score * 0.2 + 
    historical_score * 0.1
  end
end

defmodule Phoenix.Performance do
  @moduledoc """
  Real-time performance monitoring and automatic optimization.
  
  Monitors:
  - Message latency and throughput
  - Agent execution times
  - Resource utilization patterns
  - Network congestion indicators
  """
  
  def monitor_agent_performance(agent_id) do
    # Collect performance metrics
    metrics = %{
      message_latency: measure_message_latency(agent_id),
      execution_time: measure_execution_time(agent_id),
      memory_usage: measure_memory_usage(agent_id),
      cpu_utilization: measure_cpu_utilization(agent_id),
      network_io: measure_network_io(agent_id)
    }
    
    # Detect performance anomalies
    anomalies = detect_anomalies(agent_id, metrics)
    
    # Trigger optimization if needed
    if not Enum.empty?(anomalies) do
      optimize_agent_performance(agent_id, anomalies, metrics)
    end
    
    # Record metrics for historical analysis
    Phoenix.Metrics.record(agent_id, metrics)
  end
  
  defp optimize_agent_performance(agent_id, anomalies, metrics) do
    Enum.each(anomalies, fn anomaly ->
      case anomaly do
        :high_latency -> 
          consider_agent_migration(agent_id, :latency_optimization)
          
        :memory_pressure -> 
          trigger_garbage_collection(agent_id)
          consider_state_compaction(agent_id)
          
        :cpu_saturation -> 
          implement_request_throttling(agent_id)
          consider_load_shedding(agent_id)
          
        :network_congestion -> 
          enable_message_compression(agent_id)
          batch_outgoing_messages(agent_id)
      end
    end)
  end
end

defmodule Phoenix.Scaling do
  @moduledoc """
  Horizontal scaling strategies for the Phoenix cluster.
  
  Scaling triggers:
  - Resource utilization thresholds
  - Performance degradation detection
  - Predictive scaling based on patterns
  - Manual scaling requests
  """
  
  def evaluate_scaling_need() do
    cluster_metrics = collect_cluster_metrics()
    
    scaling_decision = cond do
      cpu_utilization_high?(cluster_metrics) -> 
        {:scale_out, :cpu_pressure}
        
      memory_utilization_high?(cluster_metrics) -> 
        {:scale_out, :memory_pressure}
        
      message_queue_backlog?(cluster_metrics) -> 
        {:scale_out, :throughput_pressure}
        
      underutilized_cluster?(cluster_metrics) -> 
        {:scale_in, :resource_optimization}
        
      true -> 
        {:no_action, :stable}
    end
    
    execute_scaling_decision(scaling_decision)
  end
  
  defp execute_scaling_decision({action, reason}) do
    case action do
      :scale_out -> 
        new_nodes = provision_additional_nodes(reason)
        integrate_nodes_into_cluster(new_nodes)
        rebalance_agents_across_cluster()
        
      :scale_in -> 
        candidate_nodes = select_nodes_for_removal()
        drain_agents_from_nodes(candidate_nodes)
        remove_nodes_from_cluster(candidate_nodes)
        
      :no_action -> 
        :ok
    end
  end
end