package mpls

import (
    "net"
    "sync"
    "time"
    "context"
)

type MPLSController struct {
    RouterID        net.IP
    LabelSpace      *LabelSpace
    LDP             *LabelDistributionProtocol
    RSVP            *RSVPTEProtocol
    FIB             *ForwardingInformationBase
    TEDatabase      *TrafficEngineeringDatabase
    LSPManager      *LSPManager
    ConstraintSolver *ConstraintBasedSolver
    PolicyEngine    *TrafficPolicyEngine
    mutex           sync.RWMutex
}

type LabelSpace struct {
    LocalLabels     map[uint32]*LabelBinding
    RemoteLabels    map[uint32]*LabelBinding
    LabelPool       *LabelPool
    NextLabel       uint32
    ReservedLabels  map[uint32]bool
    mutex           sync.RWMutex
}

type LabelBinding struct {
    Label           uint32
    FEC             ForwardingEquivalenceClass
    NextHop         net.IP
    Interface       string
    Protocol        LabelProtocol
    CreatedTime     time.Time
    LastUsed        time.Time
    RefCount        int32
}

func NewMPLSController(config *MPLSConfig) *MPLSController {
    return &MPLSController{
        RouterID:        config.RouterID,
        LabelSpace:      NewLabelSpace(config.LabelSpaceConfig),
        LDP:             NewLDP(config.LDPConfig),
        RSVP:            NewRSVPTE(config.RSVPConfig),
        FIB:             NewForwardingInformationBase(),
        TEDatabase:      NewTrafficEngineeringDatabase(),
        LSPManager:      NewLSPManager(),
        ConstraintSolver: NewConstraintBasedSolver(),
        PolicyEngine:    NewTrafficPolicyEngine(),
    }
}

func (mc *MPLSController) Start(ctx context.Context) error {
    // Start Label Distribution Protocol
    if err := mc.LDP.Start(ctx); err != nil {
        return err
    }
    
    // Start RSVP-TE
    if err := mc.RSVP.Start(ctx); err != nil {
        return err
    }
    
    // Start LSP management
    go mc.LSPManager.ManageLSPs(ctx)
    
    // Start traffic engineering
    go mc.startTrafficEngineering(ctx)
    
    return nil
}

func (mc *MPLSController) CreateLSP(lspConfig *LSPConfig) (*LabelSwitchedPath, error) {
    // Validate LSP configuration
    if err := mc.validateLSPConfig(lspConfig); err != nil {
        return nil, err
    }
    
    // Calculate path using CSPF
    path, err := mc.ConstraintSolver.CalculatePath(
        lspConfig.Source,
        lspConfig.Destination,
        lspConfig.Constraints
    )
    if err != nil {
        return nil, err
    }
    
    // Reserve bandwidth along the path
    if err := mc.reserveBandwidth(path, lspConfig.Bandwidth); err != nil {
        return nil, err
    }
    
    // Create LSP
    lsp := &LabelSwitchedPath{
        ID:              generateLSPID(),
        Name:            lspConfig.Name,
        Source:          lspConfig.Source,
        Destination:     lspConfig.Destination,
        Path:            path,
        Bandwidth:       lspConfig.Bandwidth,
        Priority:        lspConfig.Priority,
        PreemptionLevel: lspConfig.PreemptionLevel,
        State:          LSPStateDown,
        CreatedTime:    time.Now(),
    }
    
    // Signal LSP using RSVP-TE
    if err := mc.RSVP.SignalLSP(lsp); err != nil {
        mc.releaseBandwidth(path, lspConfig.Bandwidth)
        return nil, err
    }
    
    // Install forwarding entries
    if err := mc.installLSPForwarding(lsp); err != nil {
        mc.RSVP.TeardownLSP(lsp.ID)
        mc.releaseBandwidth(path, lspConfig.Bandwidth)
        return nil, err
    }
    
    lsp.State = LSPStateUp
    mc.LSPManager.AddLSP(lsp)
    
    return lsp, nil
}

type LabelDistributionProtocol struct {
    LocalID         net.IP
    Peers           map[string]*LDPPeer
    LabelMappings   map[string]*LabelMapping
    FECDatabase     *FECDatabase
    MessageHandler  *LDPMessageHandler
    SessionManager  *LDPSessionManager
}

func (ldp *LabelDistributionProtocol) Start(ctx context.Context) error {
    // Start discovery process
    go ldp.startDiscovery(ctx)
    
    // Start session management
    go ldp.SessionManager.ManageSessions(ctx)
    
    // Start message processing
    go ldp.MessageHandler.ProcessMessages(ctx)
    
    return nil
}

func (ldp *LabelDistributionProtocol) EstablishSession(peerID net.IP) error {
    // Create LDP session
    session := &LDPSession{
        PeerID:     peerID,
        LocalID:    ldp.LocalID,
        State:      LDPSessionStateConnecting,
        KeepaliveInterval: 30 * time.Second,
        HoldTime:   90 * time.Second,
    }
    
    // TCP connection to peer
    conn, err := net.DialTimeout("tcp", 
        fmt.Sprintf("%s:646", peerID.String()), 
        10*time.Second)
    if err != nil {
        return err
    }
    
    session.Connection = conn
    
    // Send initialization message
    initMsg := &LDPInitializationMessage{
        Version:        1,
        KeepaliveTime:  30,
        LabelSpace:     0,
        LDPIdentifier:  ldp.LocalID,
        ProtocolData:   []byte{},
    }
    
    if err := ldp.sendMessage(session, initMsg); err != nil {
        conn.Close()
        return err
    }
    
    session.State = LDPSessionStateEstablished
    ldp.Peers[peerID.String()] = &LDPPeer{
        Session: session,
        Labels:  make(map[string]uint32),
    }
    
    // Start label exchange
    go ldp.exchangeLabels(session)
    
    return nil
}

// RSVP-TE Implementation
type RSVPTEProtocol struct {
    RouterID        net.IP
    Reservations    map[string]*Reservation
    PathStates      map[string]*PathState
    ReservationStates map[string]*ReservationState
    InterfaceManager *InterfaceManager
    BandwidthManager *BandwidthManager
}

func (rsvp *RSVPTEProtocol) SignalLSP(lsp *LabelSwitchedPath) error {
    // Create PATH message
    pathMsg := &RSVPPathMessage{
        SessionID:      lsp.ID,
        Source:         lsp.Source,
        Destination:    lsp.Destination,
        Bandwidth:      lsp.Bandwidth,
        ExplicitRoute:  lsp.Path.Hops,
        SessionAttr:    lsp.SessionAttributes,
        LabelRequest:   &LabelRequest{},
    }
    
    // Send PATH message downstream
    if err := rsvp.sendPathMessage(pathMsg, lsp.Path.NextHop); err != nil {
        return err
    }
    
    // Wait for RESV message
    resvChan := make(chan *RSVPReservationMessage, 1)
    timeout := time.After(30 * time.Second)
    
    select {
    case resvMsg := <-resvChan:
        return rsvp.processReservationMessage(resvMsg, lsp)
    case <-timeout:
        return fmt.Errorf("LSP signaling timeout")
    }
}

func (rsvp *RSVPTEProtocol) processPathMessage(pathMsg *RSVPPathMessage) error {
    // Validate bandwidth availability
    if !rsvp.BandwidthManager.HasAvailableBandwidth(
        pathMsg.IncomingInterface, 
        pathMsg.Bandwidth) {
        return rsvp.sendPathError(pathMsg, "Insufficient bandwidth")
    }
    
    // Store path state
    pathState := &PathState{
        SessionID:     pathMsg.SessionID,
        Source:        pathMsg.Source,
        Destination:   pathMsg.Destination,
        PreviousHop:   pathMsg.PreviousHop,
        NextHop:       pathMsg.getNextHop(),
        Bandwidth:     pathMsg.Bandwidth,
        ReceivedTime:  time.Now(),
    }
    
    rsvp.PathStates[pathMsg.SessionID] = pathState
    
    // If this is the destination, send RESV message
    if pathMsg.Destination.Equal(rsvp.RouterID) {
        return rsvp.sendReservationMessage(pathState)
    }
    
    // Forward PATH message to next hop
    return rsvp.forwardPathMessage(pathMsg)
}

func (rsvp *RSVPTEProtocol) sendReservationMessage(pathState *PathState) error {
    // Allocate label
    label, err := rsvp.allocateLabel(pathState.SessionID)
    if err != nil {
        return err
    }
    
    // Create RESV message
    resvMsg := &RSVPReservationMessage{
        SessionID:      pathState.SessionID,
        Label:          label,
        Bandwidth:      pathState.Bandwidth,
        Style:         FixedFilter,
        FlowSpec:      &FlowSpec{
            ServiceType: GuaranteedService,
            Bandwidth:   pathState.Bandwidth,
        },
    }
    
    // Reserve bandwidth
    if err := rsvp.BandwidthManager.ReserveBandwidth(
        pathState.PreviousHop, 
        pathState.Bandwidth); err != nil {
        return err
    }
    
    // Send RESV message upstream
    return rsvp.sendMessage(pathState.PreviousHop, resvMsg)
}

class ConstraintBasedSolver:
    def __init__(self):
        self.topology_database = TopologyDatabase()
        self.bandwidth_tracker = BandwidthTracker()
        self.delay_calculator = DelayCalculator()
        self.reliability_calculator = ReliabilityCalculator()
        
    def calculate_path(self, source, destination, constraints):
        """Calculate optimal path considering multiple constraints"""
        # Get current network topology
        topology = self.topology_database.get_topology()
        
        # Apply constraints to create feasible topology
        feasible_topology = self.apply_constraints(topology, constraints)
        
        if not feasible_topology.has_path(source, destination):
            return None
        
        # Run modified Dijkstra with multiple metrics
        path = self.modified_dijkstra(
            feasible_topology, source, destination, constraints
        )
        
        return path
    
    def apply_constraints(self, topology, constraints):
        """Apply constraints to filter feasible links"""
        feasible_topology = topology.copy()
        
        for link in topology.links:
            if not self.link_satisfies_constraints(link, constraints):
                feasible_topology.remove_link(link)
        
        return feasible_topology
    
    def link_satisfies_constraints(self, link, constraints):
        """Check if link satisfies all constraints"""
        # Bandwidth constraint
        if constraints.bandwidth:
            available_bw = self.bandwidth_tracker.get_available_bandwidth(link)
            if available_bw < constraints.bandwidth:
                return False
        
        # Delay constraint
        if constraints.max_delay:
            link_delay = self.delay_calculator.get_link_delay(link)
            if link_delay > constraints.max_delay:
                return False
        
        # Administrative constraints
        if constraints.admin_groups:
            if not self.check_admin_groups(link, constraints.admin_groups):
                return False
        
        # Reliability constraint
        if constraints.min_reliability:
            link_reliability = self.reliability_calculator.get_reliability(link)
            if link_reliability < constraints.min_reliability:
                return False
        
        return True
    
    def modified_dijkstra(self, topology, source, destination, constraints):
        """Modified Dijkstra algorithm with multiple metrics"""
        # Initialize distances and predecessors
        distances = {node: float('inf') for node in topology.nodes}
        predecessors = {node: None for node in topology.nodes}
        distances[source] = 0
        
        # Priority queue with composite cost
        priority_queue = [(0, source)]
        visited = set()
        
        while priority_queue:
            current_cost, current_node = heapq.heappop(priority_queue)
            
            if current_node in visited:
                continue
            
            visited.add(current_node)
            
            if current_node == destination:
                break
            
            # Examine neighbors
            for neighbor, link in topology.get_neighbors(current_node):
                if neighbor in visited:
                    continue
                
                # Calculate composite cost
                composite_cost = self.calculate_composite_cost(
                    link, constraints, current_cost
                )
                
                new_distance = current_cost + composite_cost
                
                if new_distance < distances[neighbor]:
                    distances[neighbor] = new_distance
                    predecessors[neighbor] = current_node
                    heapq.heappush(priority_queue, (new_distance, neighbor))
        
        # Reconstruct path
        if distances[destination] == float('inf'):
            return None
        
        path = self.reconstruct_path(predecessors, source, destination)
        return path
    
    def calculate_composite_cost(self, link, constraints, current_cost):
        """Calculate composite cost considering multiple metrics"""
        weights = constraints.weights or {
            'bandwidth': 0.4,
            'delay': 0.3,
            'hop_count': 0.2,
            'utilization': 0.1
        }
        
        # Bandwidth cost (inverse of available bandwidth)
        available_bw = self.bandwidth_tracker.get_available_bandwidth(link)
        bandwidth_cost = 1.0 / max(available_bw, 1)
        
        # Delay cost
        delay_cost = self.delay_calculator.get_link_delay(link)
        
        # Hop count cost
        hop_cost = 1
        
        # Utilization cost
        utilization = self.bandwidth_tracker.get_utilization(link)
        utilization_cost = utilization ** 2  # Exponential penalty
        
        # Composite cost
        composite_cost = (
            weights['bandwidth'] * bandwidth_cost +
            weights['delay'] * delay_cost +
            weights['hop_count'] * hop_cost +
            weights['utilization'] * utilization_cost
        )
        
        return composite_cost

class TrafficEngineeringOptimizer:
    def __init__(self):
        self.demand_matrix = DemandMatrix()
        self.path_computer = ConstraintBasedSolver()
        self.load_balancer = TELoadBalancer()
        self.optimization_engine = OptimizationEngine()
        
    def optimize_traffic_distribution(self, network_topology, traffic_demands):
        """Optimize traffic distribution across the network"""
        # Calculate initial paths for all demands
        initial_paths = self.calculate_initial_paths(traffic_demands)
        
        # Analyze network utilization
        utilization_analysis = self.analyze_utilization(
            network_topology, initial_paths
        )
        
        # Identify optimization opportunities
        optimization_opportunities = self.identify_optimization_opportunities(
            utilization_analysis
        )
        
        # Apply optimization strategies
        optimized_paths = self.apply_optimization_strategies(
            initial_paths, optimization_opportunities
        )
        
        return optimized_paths
    
    def calculate_initial_paths(self, traffic_demands):
        """Calculate initial paths for all traffic demands"""
        paths = {}
        
        for demand in traffic_demands:
            constraints = Constraints(
                bandwidth=demand.bandwidth,
                max_delay=demand.max_delay,
                reliability=demand.reliability_requirement
            )
            
            path = self.path_computer.calculate_path(
                demand.source, demand.destination, constraints
            )
            
            if path:
                paths[demand.id] = path
            else:
                # Handle infeasible demands
                self.handle_infeasible_demand(demand)
        
        return paths
    
    def analyze_utilization(self, topology, paths):
        """Analyze network utilization with current path assignment"""
        link_utilization = {}
        
        for link in topology.links:
            total_demand = 0
            demands_on_link = []
            
            for demand_id, path in paths.items():
                if link in path.links:
                    demand = self.demand_matrix.get_demand(demand_id)
                    total_demand += demand.bandwidth
                    demands_on_link.append(demand_id)
            
            utilization = total_demand / link.capacity
            
            link_utilization[link.id] = {
                'utilization': utilization,
                'total_demand': total_demand,
                'capacity': link.capacity,
                'demands': demands_on_link
            }
        
        return link_utilization
    
    def identify_optimization_opportunities(self, utilization_analysis):
        """Identify opportunities for traffic optimization"""
        opportunities = []
        
        # Find heavily utilized links
        for link_id, stats in utilization_analysis.items():
            if stats['utilization'] > 0.8:  # 80% threshold
                opportunities.append({
                    'type': 'congestion',
                    'link_id': link_id,
                    'utilization': stats['utilization'],
                    'affected_demands': stats['demands'],
                    'priority': 'high' if stats['utilization'] > 0.9 else 'medium'
                })
        
        # Find underutilized parallel paths
        parallel_paths = self.find_parallel_paths(utilization_analysis)
        for parallel in parallel_paths:
            if parallel['utilization_difference'] > 0.3:
                opportunities.append({
                    'type': 'load_balancing',
                    'primary_path': parallel['primary'],
                    'alternative_path': parallel['alternative'],
                    'utilization_difference': parallel['utilization_difference'],
                    'priority': 'medium'
                })
        
        return opportunities
    
    def apply_optimization_strategies(self, initial_paths, opportunities):
        """Apply optimization strategies to improve network performance"""
        optimized_paths = initial_paths.copy()
        
        # Sort opportunities by priority
        sorted_opportunities = sorted(
            opportunities, 
            key=lambda x: {'high': 3, 'medium': 2, 'low': 1}[x['priority']], 
            reverse=True
        )
        
        for opportunity in sorted_opportunities:
            if opportunity['type'] == 'congestion':
                optimized_paths = self.apply_congestion_relief(
                    optimized_paths, opportunity
                )
            elif opportunity['type'] == 'load_balancing':
                optimized_paths = self.apply_load_balancing(
                    optimized_paths, opportunity
                )
        
        return optimized_paths
    
    def apply_congestion_relief(self, paths, congestion_opportunity):
        """Apply congestion relief strategies"""
        affected_demands = congestion_opportunity['affected_demands']
        
        # Try to reroute some demands to alternative paths
        for demand_id in affected_demands:
            current_path = paths[demand_id]
            demand = self.demand_matrix.get_demand(demand_id)
            
            # Calculate alternative path avoiding congested link
            alternative_constraints = Constraints(
                bandwidth=demand.bandwidth,
                excluded_links=[congestion_opportunity['link_id']]
            )
            
            alternative_path = self.path_computer.calculate_path(
                demand.source, 
                demand.destination, 
                alternative_constraints
            )
            
            if alternative_path and self.is_better_path(alternative_path, current_path):
                paths[demand_id] = alternative_path
                break  # Reroute one demand at a time
        
        return paths

class LSPManager:
    def __init__(self):
        self.lsps = {}
        self.protection_manager = ProtectionManager()
        self.preemption_manager = PreemptionManager()
        self.restoration_manager = RestorationManager()
        
    def manage_lsps(self, ctx):
        """Main LSP management loop"""
        ticker = time.NewTicker(30 * time.Second)
        defer ticker.Stop()
        
        for {
            select {
            case <-ctx.Done():
                return
            case <-ticker.C:
                self.periodic_lsp_maintenance()
            }
        }
    
    def periodic_lsp_maintenance(self):
        """Perform periodic LSP maintenance tasks"""
        # Check LSP health
        self.check_lsp_health()
        
        # Optimize LSP paths
        self.optimize_lsp_paths()
        
        # Handle protection switching
        self.handle_protection_switching()
        
        # Clean up stale LSPs
        self.cleanup_stale_lsps()
    
    def check_lsp_health(self):
        """Check health of all LSPs"""
        for lsp_id, lsp in self.lsps.items():
            if lsp.state == LSPStateUp:
                # Send BFD or ICMP ping
                if not self.ping_lsp(lsp):
                    self.handle_lsp_failure(lsp)
    
    def handle_lsp_failure(self, failed_lsp):
        """Handle LSP failure"""
        # Check for protection LSP
        protection_lsp = self.protection_manager.get_protection_lsp(failed_lsp.id)
        
        if protection_lsp:
            # Fast reroute to protection LSP
            self.protection_manager.switch_to_protection(failed_lsp, protection_lsp)
        else:
            # Attempt restoration
            self.restoration_manager.restore_lsp(failed_lsp)
    
    def create_protection_lsp(self, primary_lsp):
        """Create protection LSP for primary LSP"""
        # Calculate diverse path
        diverse_constraints = Constraints(
            bandwidth=primary_lsp.bandwidth,
            excluded_links=primary_lsp.path.links,
            excluded_nodes=primary_lsp.path.nodes[1:-1]  # Exclude intermediate nodes
        )
        
        protection_path = self.path_computer.calculate_path(
            primary_lsp.source,
            primary_lsp.destination,
            diverse_constraints
        )
        
        if protection_path:
            protection_lsp = self.create_lsp({
                'name': f"{primary_lsp.name}_protection",
                'source': primary_lsp.source,
                'destination': primary_lsp.destination,
                'bandwidth': primary_lsp.bandwidth,
                'priority': primary_lsp.priority,
                'protection_type': 'facility_backup'
            })
            
            self.protection_manager.associate_protection(
                primary_lsp.id, protection_lsp.id
            )
            
            return protection_lsp
        
        return None