// Package routingtable provides a thread-safe in-memory representation of the DFZ routing table.
package routingtable

import (
	"compress/gzip"
	"encoding/json"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"git.eeqj.de/sneak/routewatch/internal/config"
	"github.com/google/uuid"
)

const (
	// routeStalenessThreshold is how old a route can be before we consider it stale
	// Using 30 minutes as a conservative value for snapshot loading
	routeStalenessThreshold = 30 * time.Minute

	// snapshotFilename is the name of the snapshot file
	snapshotFilename = "routingtable.json.gz"
)

// Route represents a single route entry in the routing table
type Route struct {
	PrefixID    uuid.UUID `json:"prefix_id"`
	Prefix      string    `json:"prefix"` // The actual prefix string (e.g., "10.0.0.0/8")
	OriginASNID uuid.UUID `json:"origin_asn_id"`
	OriginASN   int       `json:"origin_asn"` // The actual ASN number
	PeerASN     int       `json:"peer_asn"`
	ASPath      []int     `json:"as_path"` // Full AS path
	NextHop     string    `json:"next_hop"`
	AnnouncedAt time.Time `json:"announced_at"`
	AddedAt     time.Time `json:"added_at"` // When we added this route to our table
}

// RouteKey uniquely identifies a route in the table
type RouteKey struct {
	PrefixID    uuid.UUID
	OriginASNID uuid.UUID
	PeerASN     int
}

// RoutingTable is a thread-safe in-memory routing table
type RoutingTable struct {
	mu     sync.RWMutex
	routes map[RouteKey]*Route

	// Secondary indexes for efficient lookups
	byPrefix    map[uuid.UUID]map[RouteKey]*Route // Routes indexed by prefix ID
	byOriginASN map[uuid.UUID]map[RouteKey]*Route // Routes indexed by origin ASN ID
	byPeerASN   map[int]map[RouteKey]*Route       // Routes indexed by peer ASN

	// Metrics tracking
	ipv4Routes       int
	ipv6Routes       int
	ipv4Updates      uint64 // Updates counter for rate calculation
	ipv6Updates      uint64 // Updates counter for rate calculation
	lastMetricsReset time.Time

	// Configuration
	snapshotDir string
}

// New creates a new routing table, loading from snapshot if available
func New(cfg *config.Config, logger *slog.Logger) *RoutingTable {
	rt := &RoutingTable{
		routes:           make(map[RouteKey]*Route),
		byPrefix:         make(map[uuid.UUID]map[RouteKey]*Route),
		byOriginASN:      make(map[uuid.UUID]map[RouteKey]*Route),
		byPeerASN:        make(map[int]map[RouteKey]*Route),
		lastMetricsReset: time.Now(),
		snapshotDir:      cfg.GetStateDir(),
	}

	// Try to load from snapshot
	if err := rt.loadFromSnapshot(logger); err != nil {
		logger.Warn("Failed to load routing table from snapshot", "error", err)
	}

	return rt
}

// AddRoute adds or updates a route in the routing table
func (rt *RoutingTable) AddRoute(route *Route) {
	rt.mu.Lock()
	defer rt.mu.Unlock()

	key := RouteKey{
		PrefixID:    route.PrefixID,
		OriginASNID: route.OriginASNID,
		PeerASN:     route.PeerASN,
	}

	// If route already exists, remove it from indexes first
	if existingRoute, exists := rt.routes[key]; exists {
		rt.removeFromIndexes(key, existingRoute)
		// Decrement counter for existing route
		if isIPv6(existingRoute.Prefix) {
			rt.ipv6Routes--
		} else {
			rt.ipv4Routes--
		}
	}

	// Set AddedAt if not already set
	if route.AddedAt.IsZero() {
		route.AddedAt = time.Now().UTC()
	}

	// Add to main map
	rt.routes[key] = route

	// Update indexes
	rt.addToIndexes(key, route)

	// Update metrics
	if isIPv6(route.Prefix) {
		rt.ipv6Routes++
		atomic.AddUint64(&rt.ipv6Updates, 1)
	} else {
		rt.ipv4Routes++
		atomic.AddUint64(&rt.ipv4Updates, 1)
	}
}

// RemoveRoute removes a route from the routing table
func (rt *RoutingTable) RemoveRoute(prefixID, originASNID uuid.UUID, peerASN int) bool {
	rt.mu.Lock()
	defer rt.mu.Unlock()

	key := RouteKey{
		PrefixID:    prefixID,
		OriginASNID: originASNID,
		PeerASN:     peerASN,
	}

	route, exists := rt.routes[key]
	if !exists {
		return false
	}

	// Remove from indexes
	rt.removeFromIndexes(key, route)

	// Remove from main map
	delete(rt.routes, key)

	// Update metrics
	if isIPv6(route.Prefix) {
		rt.ipv6Routes--
		atomic.AddUint64(&rt.ipv6Updates, 1)
	} else {
		rt.ipv4Routes--
		atomic.AddUint64(&rt.ipv4Updates, 1)
	}

	return true
}

// WithdrawRoutesByPrefixAndPeer removes all routes for a specific prefix from a specific peer
func (rt *RoutingTable) WithdrawRoutesByPrefixAndPeer(prefixID uuid.UUID, peerASN int) int {
	rt.mu.Lock()
	defer rt.mu.Unlock()

	prefixRoutes, exists := rt.byPrefix[prefixID]
	if !exists {
		return 0
	}

	// Collect keys to delete (can't delete while iterating)
	var keysToDelete []RouteKey
	for key, route := range prefixRoutes {
		if route.PeerASN == peerASN {
			keysToDelete = append(keysToDelete, key)
		}
	}

	// Delete the routes
	count := 0
	for _, key := range keysToDelete {
		route, exists := rt.routes[key]
		if !exists {
			continue
		}

		rt.removeFromIndexes(key, route)
		delete(rt.routes, key)
		count++

		// Update metrics
		if isIPv6(route.Prefix) {
			rt.ipv6Routes--
			atomic.AddUint64(&rt.ipv6Updates, 1)
		} else {
			rt.ipv4Routes--
			atomic.AddUint64(&rt.ipv4Updates, 1)
		}
	}

	return count
}

// GetRoute retrieves a specific route
func (rt *RoutingTable) GetRoute(prefixID, originASNID uuid.UUID, peerASN int) (*Route, bool) {
	rt.mu.RLock()
	defer rt.mu.RUnlock()

	key := RouteKey{
		PrefixID:    prefixID,
		OriginASNID: originASNID,
		PeerASN:     peerASN,
	}

	route, exists := rt.routes[key]
	if !exists {
		return nil, false
	}

	// Return a copy to prevent external modification
	routeCopy := *route

	return &routeCopy, true
}

// GetRoutesByPrefix returns all routes for a specific prefix
func (rt *RoutingTable) GetRoutesByPrefix(prefixID uuid.UUID) []*Route {
	rt.mu.RLock()
	defer rt.mu.RUnlock()

	routes := make([]*Route, 0)
	if prefixRoutes, exists := rt.byPrefix[prefixID]; exists {
		for _, route := range prefixRoutes {
			routeCopy := *route
			routes = append(routes, &routeCopy)
		}
	}

	return routes
}

// GetRoutesByOriginASN returns all routes originated by a specific ASN
func (rt *RoutingTable) GetRoutesByOriginASN(originASNID uuid.UUID) []*Route {
	rt.mu.RLock()
	defer rt.mu.RUnlock()

	routes := make([]*Route, 0)
	if asnRoutes, exists := rt.byOriginASN[originASNID]; exists {
		for _, route := range asnRoutes {
			routeCopy := *route
			routes = append(routes, &routeCopy)
		}
	}

	return routes
}

// GetRoutesByPeerASN returns all routes received from a specific peer ASN
func (rt *RoutingTable) GetRoutesByPeerASN(peerASN int) []*Route {
	rt.mu.RLock()
	defer rt.mu.RUnlock()

	routes := make([]*Route, 0)
	if peerRoutes, exists := rt.byPeerASN[peerASN]; exists {
		for _, route := range peerRoutes {
			routeCopy := *route
			routes = append(routes, &routeCopy)
		}
	}

	return routes
}

// GetAllRoutes returns all active routes in the routing table
func (rt *RoutingTable) GetAllRoutes() []*Route {
	rt.mu.RLock()
	defer rt.mu.RUnlock()

	routes := make([]*Route, 0, len(rt.routes))
	for _, route := range rt.routes {
		routeCopy := *route
		routes = append(routes, &routeCopy)
	}

	return routes
}

// Size returns the total number of routes in the table
func (rt *RoutingTable) Size() int {
	rt.mu.RLock()
	defer rt.mu.RUnlock()

	return len(rt.routes)
}

// Stats returns statistics about the routing table
func (rt *RoutingTable) Stats() map[string]int {
	rt.mu.RLock()
	defer rt.mu.RUnlock()

	stats := map[string]int{
		"total_routes":    len(rt.routes),
		"unique_prefixes": len(rt.byPrefix),
		"unique_origins":  len(rt.byOriginASN),
		"unique_peers":    len(rt.byPeerASN),
	}

	return stats
}

// DetailedStats contains detailed routing table statistics
type DetailedStats struct {
	IPv4Routes      int
	IPv6Routes      int
	IPv4UpdatesRate float64
	IPv6UpdatesRate float64
	TotalRoutes     int
	UniquePrefixes  int
	UniqueOrigins   int
	UniquePeers     int
}

// GetDetailedStats returns detailed statistics including IPv4/IPv6 breakdown and update rates
func (rt *RoutingTable) GetDetailedStats() DetailedStats {
	rt.mu.Lock()
	defer rt.mu.Unlock()

	// Calculate update rates
	elapsed := time.Since(rt.lastMetricsReset).Seconds()
	ipv4Updates := atomic.LoadUint64(&rt.ipv4Updates)
	ipv6Updates := atomic.LoadUint64(&rt.ipv6Updates)

	stats := DetailedStats{
		IPv4Routes:      rt.ipv4Routes,
		IPv6Routes:      rt.ipv6Routes,
		IPv4UpdatesRate: float64(ipv4Updates) / elapsed,
		IPv6UpdatesRate: float64(ipv6Updates) / elapsed,
		TotalRoutes:     len(rt.routes),
		UniquePrefixes:  len(rt.byPrefix),
		UniqueOrigins:   len(rt.byOriginASN),
		UniquePeers:     len(rt.byPeerASN),
	}

	// Reset counters for next period
	atomic.StoreUint64(&rt.ipv4Updates, 0)
	atomic.StoreUint64(&rt.ipv6Updates, 0)
	rt.lastMetricsReset = time.Now()

	return stats
}

// Clear removes all routes from the routing table
func (rt *RoutingTable) Clear() {
	rt.mu.Lock()
	defer rt.mu.Unlock()

	rt.routes = make(map[RouteKey]*Route)
	rt.byPrefix = make(map[uuid.UUID]map[RouteKey]*Route)
	rt.byOriginASN = make(map[uuid.UUID]map[RouteKey]*Route)
	rt.byPeerASN = make(map[int]map[RouteKey]*Route)
	rt.ipv4Routes = 0
	rt.ipv6Routes = 0
	atomic.StoreUint64(&rt.ipv4Updates, 0)
	atomic.StoreUint64(&rt.ipv6Updates, 0)
	rt.lastMetricsReset = time.Now()
}

// RLock acquires a read lock on the routing table
// This is exposed for the snapshotter to use
func (rt *RoutingTable) RLock() {
	rt.mu.RLock()
}

// RUnlock releases a read lock on the routing table
// This is exposed for the snapshotter to use
func (rt *RoutingTable) RUnlock() {
	rt.mu.RUnlock()
}

// GetAllRoutesUnsafe returns all routes without copying
// IMPORTANT: Caller must hold RLock before calling this method
func (rt *RoutingTable) GetAllRoutesUnsafe() []*Route {
	routes := make([]*Route, 0, len(rt.routes))
	for _, route := range rt.routes {
		routes = append(routes, route)
	}

	return routes
}

// Helper methods for index management

func (rt *RoutingTable) addToIndexes(key RouteKey, route *Route) {
	// Add to prefix index
	if rt.byPrefix[route.PrefixID] == nil {
		rt.byPrefix[route.PrefixID] = make(map[RouteKey]*Route)
	}
	rt.byPrefix[route.PrefixID][key] = route

	// Add to origin ASN index
	if rt.byOriginASN[route.OriginASNID] == nil {
		rt.byOriginASN[route.OriginASNID] = make(map[RouteKey]*Route)
	}
	rt.byOriginASN[route.OriginASNID][key] = route

	// Add to peer ASN index
	if rt.byPeerASN[route.PeerASN] == nil {
		rt.byPeerASN[route.PeerASN] = make(map[RouteKey]*Route)
	}
	rt.byPeerASN[route.PeerASN][key] = route
}

func (rt *RoutingTable) removeFromIndexes(key RouteKey, route *Route) {
	// Remove from prefix index
	if prefixRoutes, exists := rt.byPrefix[route.PrefixID]; exists {
		delete(prefixRoutes, key)
		if len(prefixRoutes) == 0 {
			delete(rt.byPrefix, route.PrefixID)
		}
	}

	// Remove from origin ASN index
	if asnRoutes, exists := rt.byOriginASN[route.OriginASNID]; exists {
		delete(asnRoutes, key)
		if len(asnRoutes) == 0 {
			delete(rt.byOriginASN, route.OriginASNID)
		}
	}

	// Remove from peer ASN index
	if peerRoutes, exists := rt.byPeerASN[route.PeerASN]; exists {
		delete(peerRoutes, key)
		if len(peerRoutes) == 0 {
			delete(rt.byPeerASN, route.PeerASN)
		}
	}
}

// String returns a string representation of the route key
func (k RouteKey) String() string {
	return fmt.Sprintf("%s/%s/%d", k.PrefixID, k.OriginASNID, k.PeerASN)
}

// isIPv6 returns true if the prefix is an IPv6 address
func isIPv6(prefix string) bool {
	return strings.Contains(prefix, ":")
}

// loadFromSnapshot attempts to load the routing table from a snapshot file
func (rt *RoutingTable) loadFromSnapshot(logger *slog.Logger) error {
	// If no snapshot directory specified, nothing to load
	if rt.snapshotDir == "" {
		return nil
	}

	snapshotPath := filepath.Join(rt.snapshotDir, snapshotFilename)

	// Check if snapshot file exists
	if _, err := os.Stat(snapshotPath); os.IsNotExist(err) {
		// No snapshot file exists, this is normal - start with empty routing table
		return nil
	}

	// Open the snapshot file
	file, err := os.Open(filepath.Clean(snapshotPath))
	if err != nil {
		return fmt.Errorf("failed to open snapshot file: %w", err)
	}
	defer func() { _ = file.Close() }()

	// Create gzip reader
	gzReader, err := gzip.NewReader(file)
	if err != nil {
		return fmt.Errorf("failed to create gzip reader: %w", err)
	}
	defer func() { _ = gzReader.Close() }()

	// Decode the snapshot
	var snapshot struct {
		Timestamp time.Time     `json:"timestamp"`
		Stats     DetailedStats `json:"stats"`
		Routes    []*Route      `json:"routes"`
	}

	decoder := json.NewDecoder(gzReader)
	if err := decoder.Decode(&snapshot); err != nil {
		return fmt.Errorf("failed to decode snapshot: %w", err)
	}

	// Calculate staleness cutoff time
	now := time.Now().UTC()
	cutoffTime := now.Add(-routeStalenessThreshold)

	// Load non-stale routes
	loadedCount := 0
	staleCount := 0

	for _, route := range snapshot.Routes {
		// Check if route is stale based on AddedAt time
		if route.AddedAt.Before(cutoffTime) {
			staleCount++

			continue
		}

		// Add the route (this will update counters and indexes)
		rt.AddRoute(route)
		loadedCount++
	}

	logger.Info("Loaded routing table from snapshot",
		"snapshot_time", snapshot.Timestamp,
		"loaded_routes", loadedCount,
		"stale_routes", staleCount,
		"total_routes_in_snapshot", len(snapshot.Routes),
	)

	return nil
}