package dns

import (
    "context"
    "net"
    "sync"
    "time"
    "github.com/miekg/dns"
)

type EnterpriseDNSServer struct {
    Config           *DNSConfig
    Cache            *DNSCache
    Resolver         *RecursiveResolver
    Authoritative    *AuthoritativeServer
    SecurityEngine   *DNSSecurityEngine
    LoadBalancer     *DNSLoadBalancer
    HealthChecker    *DNSHealthChecker
    MetricsCollector *DNSMetrics
    RateLimiter      *DNSRateLimiter
    mutex            sync.RWMutex
}

type DNSConfig struct {
    ListenAddress    string
    Port             int
    Protocol         string
    Zones            []*DNSZone
    Forwarders       []string
    CacheSize        int
    CacheTTL         time.Duration
    RateLimit        int
    EnableDNSSEC     bool
    EnableDoH        bool
    EnableDoT        bool
    TLSCertFile      string
    TLSKeyFile       string
}

type DNSZone struct {
    Name             string
    Type             ZoneType
    Records          map[string][]DNSRecord
    SOA              *SOARecord
    DNSSEC           *DNSSECConfig
    LastModified     time.Time
    SerialNumber     uint32
    mutex            sync.RWMutex
}

func NewEnterpriseDNSServer(config *DNSConfig) *EnterpriseDNSServer {
    return &EnterpriseDNSServer{
        Config:           config,
        Cache:            NewDNSCache(config.CacheSize, config.CacheTTL),
        Resolver:         NewRecursiveResolver(config.Forwarders),
        Authoritative:    NewAuthoritativeServer(config.Zones),
        SecurityEngine:   NewDNSSecurityEngine(),
        LoadBalancer:     NewDNSLoadBalancer(),
        HealthChecker:    NewDNSHealthChecker(),
        MetricsCollector: NewDNSMetrics(),
        RateLimiter:      NewDNSRateLimiter(config.RateLimit),
    }
}

func (eds *EnterpriseDNSServer) Start(ctx context.Context) error {
    // Start UDP listener
    udpAddr, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", eds.Config.ListenAddress, eds.Config.Port))
    if err != nil {
        return err
    }
    
    udpConn, err := net.ListenUDP("udp", udpAddr)
    if err != nil {
        return err
    }
    defer udpConn.Close()
    
    // Start TCP listener
    tcpAddr, err := net.ResolveTCPAddr("tcp", fmt.Sprintf("%s:%d", eds.Config.ListenAddress, eds.Config.Port))
    if err != nil {
        return err
    }
    
    tcpListener, err := net.ListenTCP("tcp", tcpAddr)
    if err != nil {
        return err
    }
    defer tcpListener.Close()
    
    // Start DNS over HTTPS if enabled
    if eds.Config.EnableDoH {
        go eds.startDoHServer(ctx)
    }
    
    // Start DNS over TLS if enabled
    if eds.Config.EnableDoT {
        go eds.startDoTServer(ctx)
    }
    
    // Start health checking
    go eds.HealthChecker.Start(ctx)
    
    // Start metrics collection
    go eds.MetricsCollector.Start(ctx)
    
    // Handle DNS queries
    go eds.handleUDPQueries(ctx, udpConn)
    go eds.handleTCPQueries(ctx, tcpListener)
    
    <-ctx.Done()
    return nil
}

func (eds *EnterpriseDNSServer) handleUDPQueries(ctx context.Context, conn *net.UDPConn) {
    buffer := make([]byte, 4096)
    
    for {
        select {
        case <-ctx.Done():
            return
        default:
            n, clientAddr, err := conn.ReadFromUDP(buffer)
            if err != nil {
                continue
            }
            
            go eds.processDNSQuery(buffer[:n], clientAddr, conn, "udp")
        }
    }
}

func (eds *EnterpriseDNSServer) processDNSQuery(data []byte, clientAddr net.Addr, 
                                               conn interface{}, protocol string) {
    startTime := time.Now()
    
    // Parse DNS message
    msg := new(dns.Msg)
    if err := msg.Unpack(data); err != nil {
        eds.MetricsCollector.IncrementParseErrors()
        return
    }
    
    // Security validation
    if !eds.SecurityEngine.ValidateQuery(msg, clientAddr) {
        eds.MetricsCollector.IncrementSecurityBlocks()
        return
    }
    
    // Rate limiting
    if !eds.RateLimiter.AllowQuery(clientAddr) {
        eds.sendRateLimitResponse(msg, clientAddr, conn, protocol)
        return
    }
    
    // Process query
    response := eds.processQuery(msg, clientAddr)
    
    // Send response
    eds.sendResponse(response, clientAddr, conn, protocol)
    
    // Update metrics
    processingTime := time.Since(startTime)
    eds.MetricsCollector.RecordQueryProcessing(msg.Question[0].Qtype, processingTime)
}

func (eds *EnterpriseDNSServer) processQuery(query *dns.Msg, clientAddr net.Addr) *dns.Msg {
    response := new(dns.Msg)
    response.SetReply(query)
    
    for _, question := range query.Question {
        // Check cache first
        if cachedResponse := eds.Cache.Get(question); cachedResponse != nil {
            response.Answer = append(response.Answer, cachedResponse...)
            eds.MetricsCollector.IncrementCacheHits()
            continue
        }
        
        // Check authoritative zones
        if eds.Authoritative.IsAuthoritative(question.Name) {
            authResponse := eds.Authoritative.Query(question)
            response.Answer = append(response.Answer, authResponse...)
            
            // Cache authoritative response
            eds.Cache.Set(question, authResponse)
            continue
        }
        
        // Recursive resolution
        recursiveResponse := eds.Resolver.Resolve(question)
        if recursiveResponse != nil {
            response.Answer = append(response.Answer, recursiveResponse...)
            
            // Cache recursive response
            eds.Cache.Set(question, recursiveResponse)
        } else {
            // NXDOMAIN response
            response.Rcode = dns.RcodeNameError
        }
    }
    
    // Apply DNSSEC if enabled
    if eds.Config.EnableDNSSEC {
        eds.SecurityEngine.SignResponse(response)
    }
    
    return response
}

type DNSCache struct {
    cache       map[string]*CacheEntry
    maxSize     int
    defaultTTL  time.Duration
    mutex       sync.RWMutex
}

type CacheEntry struct {
    Records     []dns.RR
    ExpiresAt   time.Time
    AccessCount int64
    LastAccess  time.Time
}

func NewDNSCache(maxSize int, defaultTTL time.Duration) *DNSCache {
    cache := &DNSCache{
        cache:      make(map[string]*CacheEntry),
        maxSize:    maxSize,
        defaultTTL: defaultTTL,
    }
    
    // Start cache cleanup goroutine
    go cache.cleanupExpired()
    
    return cache
}

func (dc *DNSCache) Get(question dns.Question) []dns.RR {
    dc.mutex.RLock()
    defer dc.mutex.RUnlock()
    
    key := dc.generateKey(question)
    entry, exists := dc.cache[key]
    
    if !exists || time.Now().After(entry.ExpiresAt) {
        return nil
    }
    
    // Update access statistics
    entry.AccessCount++
    entry.LastAccess = time.Now()
    
    return entry.Records
}

func (dc *DNSCache) Set(question dns.Question, records []dns.RR) {
    dc.mutex.Lock()
    defer dc.mutex.Unlock()
    
    // Check cache size limit
    if len(dc.cache) >= dc.maxSize {
        dc.evictLRU()
    }
    
    key := dc.generateKey(question)
    ttl := dc.calculateTTL(records)
    
    dc.cache[key] = &CacheEntry{
        Records:    records,
        ExpiresAt:  time.Now().Add(ttl),
        LastAccess: time.Now(),
    }
}

func (dc *DNSCache) evictLRU() {
    var oldestKey string
    var oldestTime time.Time = time.Now()
    
    for key, entry := range dc.cache {
        if entry.LastAccess.Before(oldestTime) {
            oldestTime = entry.LastAccess
            oldestKey = key
        }
    }
    
    if oldestKey != "" {
        delete(dc.cache, oldestKey)
    }
}

import hashlib
import base64
import time
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric import rsa, ec
from cryptography.hazmat.primitives.asymmetric.utils import encode_dss_signature
from dataclasses import dataclass
from typing import Dict, List, Optional, Tuple

@dataclass
class DNSSECKey:
    key_id: int
    algorithm: int
    flags: int
    protocol: int
    public_key: bytes
    private_key: Optional[bytes] = None
    created_at: float = None
    
    def __post_init__(self):
        if self.created_at is None:
            self.created_at = time.time()

class DNSSECManager:
    def __init__(self):
        self.ksk_keys = {}  # Key Signing Keys
        self.zsk_keys = {}  # Zone Signing Keys
        self.signatures = {}
        self.key_rollover_manager = KeyRolloverManager()
        self.validation_engine = DNSSECValidationEngine()
        
    def generate_zone_keys(self, zone_name: str) -> Tuple[DNSSECKey, DNSSECKey]:
        """Generate KSK and ZSK for a zone"""
        # Generate Key Signing Key (KSK)
        ksk_private_key = rsa.generate_private_key(
            public_exponent=65537,
            key_size=2048
        )
        
        ksk_public_key = ksk_private_key.public_key()
        ksk_public_bytes = ksk_public_key.public_bytes(
            encoding=serialization.Encoding.DER,
            format=serialization.PublicFormat.SubjectPublicKeyInfo
        )
        
        ksk = DNSSECKey(
            key_id=self.calculate_key_id(ksk_public_bytes),
            algorithm=8,  # RSA/SHA-256
            flags=257,    # KSK flag
            protocol=3,
            public_key=ksk_public_bytes,
            private_key=ksk_private_key.private_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PrivateFormat.PKCS8,
                encryption_algorithm=serialization.NoEncryption()
            )
        )
        
        # Generate Zone Signing Key (ZSK)
        zsk_private_key = rsa.generate_private_key(
            public_exponent=65537,
            key_size=1024
        )
        
        zsk_public_key = zsk_private_key.public_key()
        zsk_public_bytes = zsk_public_key.public_bytes(
            encoding=serialization.Encoding.DER,
            format=serialization.PublicFormat.SubjectPublicKeyInfo
        )
        
        zsk = DNSSECKey(
            key_id=self.calculate_key_id(zsk_public_bytes),
            algorithm=8,  # RSA/SHA-256
            flags=256,    # ZSK flag
            protocol=3,
            public_key=zsk_public_bytes,
            private_key=zsk_private_key.private_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PrivateFormat.PKCS8,
                encryption_algorithm=serialization.NoEncryption()
            )
        )
        
        # Store keys
        self.ksk_keys[zone_name] = ksk
        self.zsk_keys[zone_name] = zsk
        
        return ksk, zsk
    
    def calculate_key_id(self, public_key: bytes) -> int:
        """Calculate DNSSEC key ID using RFC 4034 algorithm"""
        key_data = public_key
        ac = 0
        
        for i in range(len(key_data)):
            if i % 2 == 0:
                ac += (key_data[i] << 8)
            else:
                ac += key_data[i]
        
        ac += (ac >> 16) & 0xFFFF
        return ac & 0xFFFF
    
    def sign_rrset(self, zone_name: str, rrset: List[Dict], 
                   record_type: str) -> Dict:
        """Sign Resource Record Set with RRSIG"""
        if zone_name not in self.zsk_keys:
            raise ValueError(f"No ZSK found for zone {zone_name}")
        
        zsk = self.zsk_keys[zone_name]
        
        # Create RRSIG record
        rrsig = {
            'type': 'RRSIG',
            'type_covered': record_type,
            'algorithm': zsk.algorithm,
            'labels': len(rrset[0]['name'].split('.')),
            'original_ttl': rrset[0]['ttl'],
            'signature_expiration': int(time.time()) + (30 * 24 * 3600),  # 30 days
            'signature_inception': int(time.time()) - 3600,  # 1 hour ago
            'key_tag': zsk.key_id,
            'signer_name': zone_name,
            'signature': ''
        }
        
        # Create canonical representation for signing
        canonical_data = self.create_canonical_rrset(rrset, rrsig)
        
        # Sign the data
        private_key = serialization.load_pem_private_key(
            zsk.private_key,
            password=None
        )
        
        signature = private_key.sign(
            canonical_data,
            hashes.SHA256()
        )
        
        rrsig['signature'] = base64.b64encode(signature).decode('ascii')
        
        return rrsig
    
    def create_canonical_rrset(self, rrset: List[Dict], rrsig: Dict) -> bytes:
        """Create canonical representation of RRset for signing"""
        canonical_data = b''
        
        # Add RRSIG RDATA (without signature)
        rrsig_rdata = self.create_rrsig_rdata(rrsig, without_signature=True)
        canonical_data += rrsig_rdata
        
        # Sort RRset in canonical order
        sorted_rrset = sorted(rrset, key=lambda x: x['rdata'])
        
        # Add each RR in canonical form
        for rr in sorted_rrset:
            canonical_rr = self.create_canonical_rr(rr)
            canonical_data += canonical_rr
        
        return canonical_data
    
    def validate_signature(self, rrset: List[Dict], rrsig: Dict, 
                          zone_name: str) -> bool:
        """Validate DNSSEC signature"""
        if zone_name not in self.zsk_keys:
            return False
        
        zsk = self.zsk_keys[zone_name]
        
        # Recreate canonical data
        canonical_data = self.create_canonical_rrset(rrset, rrsig)
        
        # Verify signature
        public_key = serialization.load_der_public_key(zsk.public_key)
        signature = base64.b64decode(rrsig['signature'])
        
        try:
            public_key.verify(
                signature,
                canonical_data,
                hashes.SHA256()
            )
            return True
        except Exception:
            return False

class KeyRolloverManager:
    """Automated DNSSEC key rollover management"""
    
    def __init__(self):
        self.rollover_schedule = {}
        self.rollover_policies = {}
        
    def schedule_key_rollover(self, zone_name: str, key_type: str, 
                            rollover_date: float):
        """Schedule automated key rollover"""
        if zone_name not in self.rollover_schedule:
            self.rollover_schedule[zone_name] = {}
        
        self.rollover_schedule[zone_name][key_type] = rollover_date
    
    def perform_zsk_rollover(self, zone_name: str, dnssec_manager: DNSSECManager):
        """Perform ZSK rollover using pre-publish method"""
        # Phase 1: Pre-publish new ZSK
        new_zsk_private_key = rsa.generate_private_key(
            public_exponent=65537,
            key_size=1024
        )
        
        new_zsk_public_key = new_zsk_private_key.public_key()
        new_zsk_public_bytes = new_zsk_public_key.public_bytes(
            encoding=serialization.Encoding.DER,
            format=serialization.PublicFormat.SubjectPublicKeyInfo
        )
        
        new_zsk = DNSSECKey(
            key_id=dnssec_manager.calculate_key_id(new_zsk_public_bytes),
            algorithm=8,
            flags=256,
            protocol=3,
            public_key=new_zsk_public_bytes,
            private_key=new_zsk_private_key.private_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PrivateFormat.PKCS8,
                encryption_algorithm=serialization.NoEncryption()
            )
        )
        
        # Publish new DNSKEY record (but don't sign with it yet)
        # Wait for TTL period...
        
        # Phase 2: Start signing with new key
        old_zsk = dnssec_manager.zsk_keys[zone_name]
        dnssec_manager.zsk_keys[zone_name] = new_zsk
        
        # Re-sign zone with new ZSK
        # Wait for TTL period...
        
        # Phase 3: Remove old DNSKEY record
        # Old key can now be safely removed
        
        return new_zsk
    
    def perform_ksk_rollover(self, zone_name: str, dnssec_manager: DNSSECManager):
        """Perform KSK rollover using double-signature method"""
        # Generate new KSK
        new_ksk_private_key = rsa.generate_private_key(
            public_exponent=65537,
            key_size=2048
        )
        
        new_ksk_public_key = new_ksk_private_key.public_key()
        new_ksk_public_bytes = new_ksk_public_key.public_bytes(
            encoding=serialization.Encoding.DER,
            format=serialization.PublicFormat.SubjectPublicKeyInfo
        )
        
        new_ksk = DNSSECKey(
            key_id=dnssec_manager.calculate_key_id(new_ksk_public_bytes),
            algorithm=8,
            flags=257,
            protocol=3,
            public_key=new_ksk_public_bytes,
            private_key=new_ksk_private_key.private_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PrivateFormat.PKCS8,
                encryption_algorithm=serialization.NoEncryption()
            )
        )
        
        # Double-signature period: sign DNSKEY RRset with both old and new KSK
        old_ksk = dnssec_manager.ksk_keys[zone_name]
        
        # Update parent zone DS records
        new_ds_record = self.generate_ds_record(new_ksk, zone_name)
        
        # After parent zone propagation, remove old KSK
        dnssec_manager.ksk_keys[zone_name] = new_ksk
        
        return new_ksk, new_ds_record

class DNSSecurityEngine:
    """Advanced DNS security engine"""
    
    def __init__(self):
        self.threat_intelligence = ThreatIntelligence()
        self.rate_limiter = DNSRateLimiter()
        self.anomaly_detector = DNSAnomalyDetector()
        self.response_policy_zones = ResponsePolicyZones()
        
    def validate_query(self, query, client_addr) -> bool:
        """Comprehensive query validation"""
        # Rate limiting
        if not self.rate_limiter.allow_query(client_addr):
            return False
        
        # Threat intelligence check
        if self.threat_intelligence.is_malicious_domain(query.question[0].name):
            return False
        
        # Anomaly detection
        if self.anomaly_detector.detect_anomaly(query, client_addr):
            return False
        
        # Response Policy Zone filtering
        if self.response_policy_zones.should_block(query.question[0].name):
            return False
        
        return True
    
    def apply_dns_filtering(self, query) -> Optional[dict]:
        """Apply DNS filtering policies"""
        domain = query.question[0].name.lower()
        
        # Category-based filtering
        category = self.categorize_domain(domain)
        if category in ['malware', 'phishing', 'botnet']:
            return self.generate_block_response(query, category)
        
        # Custom policy filtering
        policy_action = self.check_custom_policies(domain)
        if policy_action:
            return policy_action
        
        return None
    
    def generate_block_response(self, query, reason: str) -> dict:
        """Generate blocked response"""
        return {
            'blocked': True,
            'reason': reason,
            'redirect_ip': '192.0.2.1',  # RFC5737 test IP
            'log_event': True
        }

class DNSOverHTTPS:
    """DNS over HTTPS (DoH) implementation"""
    
    def __init__(self, dns_server, cert_file: str, key_file: str):
        self.dns_server = dns_server
        self.cert_file = cert_file
        self.key_file = key_file
        
    async def handle_doh_request(self, request):
        """Handle DoH request"""
        if request.method == 'GET':
            # GET request with dns parameter
            dns_param = request.query.get('dns')
            if not dns_param:
                return web.Response(status=400, text='Missing dns parameter')
            
            dns_query = base64.urlsafe_b64decode(dns_param + '==')
        
        elif request.method == 'POST':
            # POST request with DNS message in body
            dns_query = await request.read()
        
        else:
            return web.Response(status=405, text='Method not allowed')
        
        # Process DNS query
        response = await self.process_dns_query(dns_query)
        
        # Return HTTP response
        return web.Response(
            body=response,
            content_type='application/dns-message',
            headers={'Cache-Control': 'max-age=300'}
        )
    
    async def process_dns_query(self, dns_query: bytes) -> bytes:
        """Process DNS query and return response"""
        # Parse DNS message
        query_msg = dns.message.from_wire(dns_query)
        
        # Process through DNS server
        response_msg = await self.dns_server.process_query_async(query_msg)
        
        # Convert to wire format
        return response_msg.to_wire()

class DNSAnalytics:
    """Advanced DNS analytics and monitoring"""
    
    def __init__(self):
        self.query_analyzer = QueryAnalyzer()
        self.performance_monitor = PerformanceMonitor()
        self.security_monitor = SecurityMonitor()
        
    def analyze_query_patterns(self, time_window: int = 3600):
        """Analyze DNS query patterns"""
        analysis = {
            'top_domains': self.query_analyzer.get_top_domains(time_window),
            'query_types': self.query_analyzer.get_query_type_distribution(time_window),
            'client_patterns': self.query_analyzer.get_client_patterns(time_window),
            'geographic_distribution': self.query_analyzer.get_geo_distribution(time_window),
            'performance_metrics': self.performance_monitor.get_metrics(time_window),
            'security_events': self.security_monitor.get_events(time_window)
        }
        
        return analysis
    
    def generate_insights(self, analysis: dict) -> List[str]:
        """Generate actionable insights from analysis"""
        insights = []
        
        # Performance insights
        if analysis['performance_metrics']['avg_response_time'] > 100:
            insights.append("High average response time detected - consider cache optimization")
        
        # Security insights
        if analysis['security_events']['blocked_queries'] > 1000:
            insights.append("High number of blocked queries - potential security threat")
        
        # Capacity insights
        if analysis['performance_metrics']['query_rate'] > 10000:
            insights.append("High query rate - consider scaling DNS infrastructure")
        
        return insights