"""
Virtual Router Module

Implements packet routing between virtual clients and external internet:
- Maintain routing table for virtual network
- Forward packets based on destination IP
- Handle internal vs external routing decisions
- Support static route configuration
"""

import ipaddress
import time
import threading
from typing import Dict, List, Optional, Tuple, Set
from dataclasses import dataclass
from enum import Enum

from .ip_parser import ParsedPacket, IPv4Header


class RouteType(Enum):
    DIRECT = "DIRECT"      # Directly connected network
    STATIC = "STATIC"      # Static route
    DEFAULT = "DEFAULT"    # Default route


@dataclass
class RouteEntry:
    """Represents a routing table entry"""
    destination: str       # Network in CIDR notation (e.g., "10.0.0.0/24")
    gateway: Optional[str] # Next hop IP (None for direct routes)
    interface: str         # Interface name or identifier
    metric: int           # Route metric (lower is preferred)
    route_type: RouteType
    created_time: float
    last_used: Optional[float] = None
    use_count: int = 0
    
    def __post_init__(self):
        if self.created_time == 0:
            self.created_time = time.time()
    
    def record_use(self):
        """Record route usage"""
        self.use_count += 1
        self.last_used = time.time()
    
    def matches_destination(self, ip: str) -> bool:
        """Check if this route matches the destination IP"""
        try:
            network = ipaddress.ip_network(self.destination, strict=False)
            return ipaddress.ip_address(ip) in network
        except (ipaddress.AddressValueError, ValueError):
            return False
    
    def to_dict(self) -> Dict:
        """Convert route to dictionary"""
        return {
            'destination': self.destination,
            'gateway': self.gateway,
            'interface': self.interface,
            'metric': self.metric,
            'route_type': self.route_type.value,
            'created_time': self.created_time,
            'last_used': self.last_used,
            'use_count': self.use_count
        }


@dataclass
class Interface:
    """Represents a network interface"""
    name: str
    ip_address: str
    netmask: str
    network: str           # Network in CIDR notation
    enabled: bool = True
    mtu: int = 1500
    created_time: float = 0
    
    def __post_init__(self):
        if self.created_time == 0:
            self.created_time = time.time()
        
        # Calculate network if not provided
        if not self.network:
            try:
                interface_network = ipaddress.ip_interface(f"{self.ip_address}/{self.netmask}")
                self.network = str(interface_network.network)
            except (ipaddress.AddressValueError, ValueError):
                self.network = "0.0.0.0/0"
    
    def is_local_address(self, ip: str) -> bool:
        """Check if IP address belongs to this interface's network"""
        try:
            network = ipaddress.ip_network(self.network, strict=False)
            return ipaddress.ip_address(ip) in network
        except (ipaddress.AddressValueError, ValueError):
            return False
    
    def to_dict(self) -> Dict:
        """Convert interface to dictionary"""
        return {
            'name': self.name,
            'ip_address': self.ip_address,
            'netmask': self.netmask,
            'network': self.network,
            'enabled': self.enabled,
            'mtu': self.mtu,
            'created_time': self.created_time
        }


class VirtualRouter:
    """Virtual router implementation"""
    
    def __init__(self, config: Dict):
        self.config = config
        self.routing_table: List[RouteEntry] = []
        self.interfaces: Dict[str, Interface] = {}
        self.arp_table: Dict[str, str] = {}  # IP -> MAC mapping
        self.lock = threading.Lock()
        
        # Router configuration
        self.router_id = config.get('router_id', 'virtual-router-1')
        self.default_gateway = config.get('default_gateway')
        
        # Statistics
        self.stats = {
            'packets_routed': 0,
            'packets_dropped': 0,
            'route_lookups': 0,
            'arp_requests': 0,
            'arp_replies': 0,
            'routing_errors': 0
        }
        
        # Initialize interfaces and routes
        self._initialize_interfaces()
        self._initialize_routes()
    
    def _initialize_interfaces(self):
        """Initialize network interfaces from configuration"""
        interfaces_config = self.config.get('interfaces', [])
        
        for iface_config in interfaces_config:
            interface = Interface(
                name=iface_config['name'],
                ip_address=iface_config['ip_address'],
                netmask=iface_config.get('netmask', '255.255.255.0'),
                network=iface_config.get('network'),
                enabled=iface_config.get('enabled', True),
                mtu=iface_config.get('mtu', 1500)
            )
            
            with self.lock:
                self.interfaces[interface.name] = interface
            
            # Add direct route for interface network
            self.add_route(
                destination=interface.network,
                gateway=None,
                interface=interface.name,
                metric=0,
                route_type=RouteType.DIRECT
            )
    
    def _initialize_routes(self):
        """Initialize static routes from configuration"""
        routes_config = self.config.get('static_routes', [])
        
        for route_config in routes_config:
            self.add_route(
                destination=route_config['destination'],
                gateway=route_config.get('gateway'),
                interface=route_config['interface'],
                metric=route_config.get('metric', 10),
                route_type=RouteType.STATIC
            )
        
        # Add default route if configured
        if self.default_gateway:
            # Find interface for default gateway
            default_interface = None
            for interface in self.interfaces.values():
                if interface.is_local_address(self.default_gateway):
                    default_interface = interface.name
                    break
            
            if default_interface:
                self.add_route(
                    destination="0.0.0.0/0",
                    gateway=self.default_gateway,
                    interface=default_interface,
                    metric=100,
                    route_type=RouteType.DEFAULT
                )
    
    def add_interface(self, name: str, ip_address: str, netmask: str = "255.255.255.0", 
                     network: Optional[str] = None, mtu: int = 1500) -> bool:
        """Add network interface"""
        with self.lock:
            if name in self.interfaces:
                return False
            
            interface = Interface(
                name=name,
                ip_address=ip_address,
                netmask=netmask,
                network=network,
                mtu=mtu
            )
            
            self.interfaces[name] = interface
        
        # Add direct route for interface network
        self.add_route(
            destination=interface.network,
            gateway=None,
            interface=name,
            metric=0,
            route_type=RouteType.DIRECT
        )
        
        return True
    
    def remove_interface(self, name: str) -> bool:
        """Remove network interface"""
        with self.lock:
            if name not in self.interfaces:
                return False
            
            # Remove interface
            del self.interfaces[name]
            
            # Remove routes associated with this interface
            self.routing_table = [
                route for route in self.routing_table 
                if route.interface != name
            ]
        
        return True
    
    def enable_interface(self, name: str) -> bool:
        """Enable network interface"""
        with self.lock:
            if name in self.interfaces:
                self.interfaces[name].enabled = True
                return True
        return False
    
    def disable_interface(self, name: str) -> bool:
        """Disable network interface"""
        with self.lock:
            if name in self.interfaces:
                self.interfaces[name].enabled = False
                return True
        return False
    
    def add_route(self, destination: str, gateway: Optional[str], interface: str, 
                  metric: int = 10, route_type: RouteType = RouteType.STATIC) -> bool:
        """Add route to routing table"""
        try:
            # Validate destination network
            ipaddress.ip_network(destination, strict=False)
            
            # Validate gateway if provided
            if gateway:
                ipaddress.ip_address(gateway)
            
            route = RouteEntry(
                destination=destination,
                gateway=gateway,
                interface=interface,
                metric=metric,
                route_type=route_type,
                created_time=time.time()
            )
            
            with self.lock:
                # Check if interface exists
                if interface not in self.interfaces:
                    return False
                
                # Remove existing route with same destination and interface
                self.routing_table = [
                    r for r in self.routing_table 
                    if not (r.destination == destination and r.interface == interface)
                ]
                
                # Add new route
                self.routing_table.append(route)
                
                # Sort by metric (lower metric = higher priority)
                self.routing_table.sort(key=lambda r: (r.metric, r.created_time))
            
            return True
            
        except (ipaddress.AddressValueError, ValueError):
            return False
    
    def remove_route(self, destination: str, interface: str) -> bool:
        """Remove route from routing table"""
        with self.lock:
            original_count = len(self.routing_table)
            self.routing_table = [
                route for route in self.routing_table
                if not (route.destination == destination and route.interface == interface)
            ]
            return len(self.routing_table) < original_count
    
    def lookup_route(self, destination_ip: str) -> Optional[RouteEntry]:
        """Look up route for destination IP"""
        self.stats['route_lookups'] += 1
        
        with self.lock:
            # Find all matching routes
            matching_routes = []
            for route in self.routing_table:
                # Skip disabled interfaces
                interface = self.interfaces.get(route.interface)
                if not interface or not interface.enabled:
                    continue
                
                if route.matches_destination(destination_ip):
                    matching_routes.append(route)
            
            if not matching_routes:
                self.stats['routing_errors'] += 1
                return None
            
            # Sort by specificity (longest prefix match) and then by metric
            def route_priority(route):
                try:
                    network = ipaddress.ip_network(route.destination, strict=False)
                    return (-network.prefixlen, route.metric, route.created_time)
                except:
                    return (0, route.metric, route.created_time)
            
            matching_routes.sort(key=route_priority)
            best_route = matching_routes[0]
            best_route.record_use()
            
            return best_route
    
    def route_packet(self, packet: ParsedPacket) -> Optional[Tuple[str, str]]:
        """Route packet and return (next_hop_ip, interface)"""
        self.stats['packets_routed'] += 1
        
        destination_ip = packet.ip_header.dest_ip
        
        # Look up route
        route = self.lookup_route(destination_ip)
        if not route:
            self.stats['packets_dropped'] += 1
            return None
        
        # Determine next hop
        if route.gateway:
            next_hop = route.gateway
        else:
            # Direct route - destination is next hop
            next_hop = destination_ip
        
        return (next_hop, route.interface)
    
    def is_local_destination(self, ip: str) -> bool:
        """Check if IP is a local destination (belongs to router interfaces)"""
        with self.lock:
            for interface in self.interfaces.values():
                if interface.ip_address == ip:
                    return True
        return False
    
    def is_local_network(self, ip: str) -> bool:
        """Check if IP belongs to any local network"""
        with self.lock:
            for interface in self.interfaces.values():
                if interface.is_local_address(ip):
                    return True
        return False
    
    def get_interface_for_ip(self, ip: str) -> Optional[Interface]:
        """Get interface that can reach the given IP"""
        with self.lock:
            for interface in self.interfaces.values():
                if interface.enabled and interface.is_local_address(ip):
                    return interface
        return None
    
    def add_arp_entry(self, ip: str, mac: str):
        """Add ARP table entry"""
        with self.lock:
            self.arp_table[ip] = mac
    
    def get_arp_entry(self, ip: str) -> Optional[str]:
        """Get MAC address from ARP table"""
        with self.lock:
            return self.arp_table.get(ip)
    
    def remove_arp_entry(self, ip: str) -> bool:
        """Remove ARP table entry"""
        with self.lock:
            if ip in self.arp_table:
                del self.arp_table[ip]
                return True
        return False
    
    def clear_arp_table(self):
        """Clear ARP table"""
        with self.lock:
            self.arp_table.clear()
    
    def get_routing_table(self) -> List[Dict]:
        """Get routing table"""
        with self.lock:
            return [route.to_dict() for route in self.routing_table]
    
    def get_interfaces(self) -> Dict[str, Dict]:
        """Get network interfaces"""
        with self.lock:
            return {
                name: interface.to_dict()
                for name, interface in self.interfaces.items()
            }
    
    def get_arp_table(self) -> Dict[str, str]:
        """Get ARP table"""
        with self.lock:
            return self.arp_table.copy()
    
    def get_stats(self) -> Dict:
        """Get router statistics"""
        with self.lock:
            stats = self.stats.copy()
            stats['total_routes'] = len(self.routing_table)
            stats['total_interfaces'] = len(self.interfaces)
            stats['enabled_interfaces'] = sum(1 for iface in self.interfaces.values() if iface.enabled)
            stats['arp_entries'] = len(self.arp_table)
        
        return stats
    
    def reset_stats(self):
        """Reset router statistics"""
        self.stats = {
            'packets_routed': 0,
            'packets_dropped': 0,
            'route_lookups': 0,
            'arp_requests': 0,
            'arp_replies': 0,
            'routing_errors': 0
        }
        
        # Reset route usage statistics
        with self.lock:
            for route in self.routing_table:
                route.use_count = 0
                route.last_used = None
    
    def flush_routes(self, route_type: Optional[RouteType] = None):
        """Flush routes of specified type (or all if None)"""
        with self.lock:
            if route_type:
                self.routing_table = [
                    route for route in self.routing_table
                    if route.route_type != route_type
                ]
            else:
                self.routing_table.clear()
    
    def export_config(self) -> Dict:
        """Export router configuration"""
        return {
            'router_id': self.router_id,
            'default_gateway': self.default_gateway,
            'interfaces': [
                {
                    'name': iface.name,
                    'ip_address': iface.ip_address,
                    'netmask': iface.netmask,
                    'network': iface.network,
                    'enabled': iface.enabled,
                    'mtu': iface.mtu
                }
                for iface in self.interfaces.values()
            ],
            'static_routes': [
                {
                    'destination': route.destination,
                    'gateway': route.gateway,
                    'interface': route.interface,
                    'metric': route.metric
                }
                for route in self.routing_table
                if route.route_type == RouteType.STATIC
            ]
        }
    
    def import_config(self, config: Dict):
        """Import router configuration"""
        # Clear existing configuration
        with self.lock:
            self.interfaces.clear()
            self.routing_table.clear()
            self.arp_table.clear()
        
        # Update router settings
        self.router_id = config.get('router_id', self.router_id)
        self.default_gateway = config.get('default_gateway', self.default_gateway)
        
        # Reinitialize from new config
        self.config.update(config)
        self._initialize_interfaces()
        self._initialize_routes()


class RouterUtils:
    """Utility functions for router operations"""
    
    @staticmethod
    def ip_to_int(ip: str) -> int:
        """Convert IP address to integer"""
        return int(ipaddress.ip_address(ip))
    
    @staticmethod
    def int_to_ip(ip_int: int) -> str:
        """Convert integer to IP address"""
        return str(ipaddress.ip_address(ip_int))
    
    @staticmethod
    def calculate_network(ip: str, netmask: str) -> str:
        """Calculate network address from IP and netmask"""
        try:
            interface = ipaddress.ip_interface(f"{ip}/{netmask}")
            return str(interface.network)
        except (ipaddress.AddressValueError, ValueError):
            return "0.0.0.0/0"
    
    @staticmethod
    def is_private_ip(ip: str) -> bool:
        """Check if IP address is private"""
        try:
            ip_obj = ipaddress.ip_address(ip)
            return ip_obj.is_private
        except (ipaddress.AddressValueError, ValueError):
            return False
    
    @staticmethod
    def is_multicast_ip(ip: str) -> bool:
        """Check if IP address is multicast"""
        try:
            ip_obj = ipaddress.ip_address(ip)
            return ip_obj.is_multicast
        except (ipaddress.AddressValueError, ValueError):
            return False
    
    @staticmethod
    def validate_cidr(cidr: str) -> bool:
        """Validate CIDR notation"""
        try:
            ipaddress.ip_network(cidr, strict=False)
            return True
        except (ipaddress.AddressValueError, ValueError):
            return False