package routewatch

import (
	"net"
	"strings"
	"sync"
	"time"

	"git.eeqj.de/sneak/routewatch/internal/database"
	"git.eeqj.de/sneak/routewatch/internal/logger"
	"git.eeqj.de/sneak/routewatch/internal/metrics"
	"git.eeqj.de/sneak/routewatch/internal/ristypes"
	"github.com/google/uuid"
)

const (
	// prefixHandlerQueueSize is the queue capacity for prefix tracking
	// operations, about 4 seconds of feed at peak. The streamer drops rather
	// than blocks when a queue is full, so this bounds memory. Batches still
	// flush on a timer (prefixBatchTimeout).
	prefixHandlerQueueSize = 20000

	// prefixBatchSize is the number of prefix updates to batch together
	prefixBatchSize = 25000

	// prefixBatchTimeout is the maximum time to wait before flushing a batch
	// DO NOT reduce this timeout - larger batches are more efficient
	prefixBatchTimeout = 1 * time.Second

	// IP version constants
	ipv4Version = 4
	ipv6Version = 6
)

// PrefixHandler tracks BGP prefixes and maintains a live routing table in the database.
// Routes are added on announcement and deleted on withdrawal.
type PrefixHandler struct {
	db      database.Store
	logger  *logger.Logger
	metrics *metrics.Tracker

	// Batching
	mu        sync.Mutex
	batch     []prefixUpdate
	lastFlush time.Time
	stopCh    chan struct{}
	wg        sync.WaitGroup
}

type prefixUpdate struct {
	prefix      string
	originASN   int
	peer        string
	messageType string
	timestamp   time.Time
	path        []int
}

// NewPrefixHandler creates a new batched prefix tracking handler
func NewPrefixHandler(db database.Store, logger *logger.Logger) *PrefixHandler {
	h := &PrefixHandler{
		db:        db,
		logger:    logger,
		batch:     make([]prefixUpdate, 0, prefixBatchSize),
		lastFlush: time.Now(),
		stopCh:    make(chan struct{}),
	}

	// Start the flush timer goroutine
	h.wg.Add(1)
	go h.flushLoop()

	return h
}

// SetMetricsTracker sets the metrics tracker for recording route updates
func (h *PrefixHandler) SetMetricsTracker(metrics *metrics.Tracker) {
	h.metrics = metrics
}

// WantsMessage returns true if this handler wants to process messages of the given type
func (h *PrefixHandler) WantsMessage(messageType string) bool {
	// We only care about UPDATE messages for the routing table
	return messageType == "UPDATE"
}

// QueueCapacity returns the desired queue capacity for this handler
func (h *PrefixHandler) QueueCapacity() int {
	// Batching allows us to use a larger queue
	return prefixHandlerQueueSize
}

// HandleMessage processes a message to track prefix information
func (h *PrefixHandler) HandleMessage(msg *ristypes.RISMessage) {
	// Use the pre-parsed timestamp
	timestamp := msg.ParsedTimestamp

	// Get origin ASN from path (last element)
	var originASN int
	if len(msg.Path) > 0 {
		originASN = msg.Path[len(msg.Path)-1]
	}

	h.mu.Lock()
	defer h.mu.Unlock()

	// Process announcements
	for _, announcement := range msg.Announcements {
		for _, prefix := range announcement.Prefixes {
			h.batch = append(h.batch, prefixUpdate{
				prefix:      prefix,
				originASN:   originASN,
				peer:        msg.Peer,
				messageType: "announcement",
				timestamp:   timestamp,
				path:        msg.Path,
			})
			// Record announcement in metrics
			if h.metrics != nil {
				h.metrics.RecordAnnouncement()
			}
		}
	}

	// Process withdrawals
	for _, prefix := range msg.Withdrawals {
		h.batch = append(h.batch, prefixUpdate{
			prefix:      prefix,
			originASN:   originASN, // Use the originASN from path if available
			peer:        msg.Peer,
			messageType: "withdrawal",
			timestamp:   timestamp,
			path:        msg.Path,
		})
		// Record withdrawal in metrics
		if h.metrics != nil {
			h.metrics.RecordWithdrawal()
		}
	}

	// Check if we need to flush
	if len(h.batch) >= prefixBatchSize {
		h.flushBatchLocked()
	}
}

// flushLoop runs in a goroutine and periodically flushes batches
func (h *PrefixHandler) flushLoop() {
	defer h.wg.Done()
	ticker := time.NewTicker(prefixBatchTimeout)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			h.mu.Lock()
			if time.Since(h.lastFlush) >= prefixBatchTimeout {
				h.flushBatchLocked()
			}
			h.mu.Unlock()
		case <-h.stopCh:
			// Final flush
			h.mu.Lock()
			h.flushBatchLocked()
			h.mu.Unlock()

			return
		}
	}
}

// flushBatchLocked flushes the prefix batch to the database (must be called with mutex held)
func (h *PrefixHandler) flushBatchLocked() {
	if len(h.batch) == 0 {
		return
	}

	startTime := time.Now()
	batchSize := len(h.batch)

	// Group updates by prefix to deduplicate
	// For each prefix, keep the latest update
	prefixMap := make(map[string]prefixUpdate)
	for _, update := range h.batch {
		key := update.prefix
		if existing, ok := prefixMap[key]; !ok || update.timestamp.After(existing.timestamp) {
			prefixMap[key] = update
		}
	}

	// Collect routes to upsert and delete
	var routesToUpsert []*database.LiveRoute
	var routesToDelete []database.LiveRouteDeletion

	// Collect unique prefixes to update
	prefixesToUpdate := make(map[string]time.Time)

	for _, update := range prefixMap {
		// Track prefix for both announcements and withdrawals
		if _, exists := prefixesToUpdate[update.prefix]; !exists || update.timestamp.After(prefixesToUpdate[update.prefix]) {
			prefixesToUpdate[update.prefix] = update.timestamp
		}

		if update.messageType == "announcement" && update.originASN > 0 {
			// Create live route for batch upsert
			route := h.createLiveRoute(update)
			if route != nil {
				routesToUpsert = append(routesToUpsert, route)
			}
		} else if update.messageType == "withdrawal" {
			// Parse CIDR to get IP version
			_, ipVersion, err := parseCIDR(update.prefix)
			if err != nil {
				h.logger.Error("Failed to parse CIDR for withdrawal", "prefix", update.prefix, "error", err)

				continue
			}

			// Create deletion record for batch delete
			routesToDelete = append(routesToDelete, database.LiveRouteDeletion{
				Prefix:    update.prefix,
				OriginASN: update.originASN,
				PeerIP:    update.peer,
				IPVersion: ipVersion,
			})
		}
	}

	// Process batch operations
	successCount := 0
	if len(routesToUpsert) > 0 {
		if err := h.db.UpsertLiveRouteBatch(routesToUpsert); err != nil {
			h.logger.Error("Failed to upsert route batch", "error", err, "count", len(routesToUpsert))
		} else {
			successCount += len(routesToUpsert)
		}
	}

	if len(routesToDelete) > 0 {
		if err := h.db.DeleteLiveRouteBatch(routesToDelete); err != nil {
			h.logger.Error("Failed to delete route batch", "error", err, "count", len(routesToDelete))
		} else {
			successCount += len(routesToDelete)
		}
	}

	// Update prefix tables
	if len(prefixesToUpdate) > 0 {
		if err := h.db.UpdatePrefixesBatch(prefixesToUpdate); err != nil {
			h.logger.Error("Failed to update prefix batch", "error", err, "count", len(prefixesToUpdate))
		}
	}

	elapsed := time.Since(startTime)
	h.logger.Debug("Flushed prefix batch",
		"batch_size", batchSize,
		"unique_prefixes", len(prefixMap),
		"success", successCount,
		"duration_ms", elapsed.Milliseconds(),
	)

	// Clear batch
	h.batch = h.batch[:0]
	h.lastFlush = time.Now()
}

// parseCIDR extracts the mask length and IP version from a prefix string
func parseCIDR(prefix string) (maskLength int, ipVersion int, err error) {
	_, ipNet, err := net.ParseCIDR(prefix)
	if err != nil {
		return 0, 0, err
	}

	ones, _ := ipNet.Mask.Size()
	if strings.Contains(prefix, ":") {
		return ones, ipv6Version, nil
	}

	return ones, ipv4Version, nil
}

// processAnnouncement handles storing an announcement in the database
// nolint:unused // kept for potential future use
func (h *PrefixHandler) processAnnouncement(_ *database.Prefix, update prefixUpdate) {
	// Parse CIDR to get mask length
	maskLength, ipVersion, err := parseCIDR(update.prefix)
	if err != nil {
		h.logger.Error("Failed to parse CIDR",
			"prefix", update.prefix,
			"error", err,
		)

		return
	}

	// Track route update metrics
	if h.metrics != nil {
		if ipVersion == ipv4Version {
			h.metrics.RecordIPv4Update()
		} else {
			h.metrics.RecordIPv6Update()
		}
	}

	// Create live route record
	liveRoute := &database.LiveRoute{
		ID:          uuid.New(),
		Prefix:      update.prefix,
		MaskLength:  maskLength,
		IPVersion:   ipVersion,
		OriginASN:   update.originASN,
		PeerIP:      update.peer,
		ASPath:      update.path,
		NextHop:     update.peer, // Using peer as next hop
		LastUpdated: update.timestamp,
	}

	// For IPv4, calculate the IP range
	if ipVersion == ipv4Version {
		start, end, err := database.CalculateIPv4Range(update.prefix)
		if err == nil {
			liveRoute.V4IPStart = &start
			liveRoute.V4IPEnd = &end
		} else {
			h.logger.Error("Failed to calculate IPv4 range",
				"prefix", update.prefix,
				"error", err,
			)
		}
	}

	if err := h.db.UpsertLiveRoute(liveRoute); err != nil {
		h.logger.Error("Failed to upsert live route",
			"prefix", update.prefix,
			"error", err,
		)
	}
}

// createLiveRoute creates a LiveRoute from a prefix update
func (h *PrefixHandler) createLiveRoute(update prefixUpdate) *database.LiveRoute {
	// Parse CIDR to get mask length
	maskLength, ipVersion, err := parseCIDR(update.prefix)
	if err != nil {
		h.logger.Error("Failed to parse CIDR",
			"prefix", update.prefix,
			"error", err,
		)

		return nil
	}

	// Track route update metrics
	if h.metrics != nil {
		if ipVersion == ipv4Version {
			h.metrics.RecordIPv4Update()
		} else {
			h.metrics.RecordIPv6Update()
		}
	}

	// Create live route record
	liveRoute := &database.LiveRoute{
		ID:          uuid.New(),
		Prefix:      update.prefix,
		MaskLength:  maskLength,
		IPVersion:   ipVersion,
		OriginASN:   update.originASN,
		PeerIP:      update.peer,
		ASPath:      update.path,
		NextHop:     update.peer, // Using peer as next hop
		LastUpdated: update.timestamp,
	}

	// For IPv4, calculate the IP range
	if ipVersion == ipv4Version {
		start, end, err := database.CalculateIPv4Range(update.prefix)
		if err == nil {
			liveRoute.V4IPStart = &start
			liveRoute.V4IPEnd = &end
		} else {
			h.logger.Error("Failed to calculate IPv4 range",
				"prefix", update.prefix,
				"error", err,
			)
		}
	}

	return liveRoute
}

// processAnnouncementDirect handles storing an announcement directly without prefix table
// nolint:unused // kept for potential future use
func (h *PrefixHandler) processAnnouncementDirect(update prefixUpdate) {
	// Parse CIDR to get mask length
	maskLength, ipVersion, err := parseCIDR(update.prefix)
	if err != nil {
		h.logger.Error("Failed to parse CIDR",
			"prefix", update.prefix,
			"error", err,
		)

		return
	}

	// Track route update metrics
	if h.metrics != nil {
		if ipVersion == ipv4Version {
			h.metrics.RecordIPv4Update()
		} else {
			h.metrics.RecordIPv6Update()
		}
	}

	// Create live route record
	liveRoute := &database.LiveRoute{
		ID:          uuid.New(),
		Prefix:      update.prefix,
		MaskLength:  maskLength,
		IPVersion:   ipVersion,
		OriginASN:   update.originASN,
		PeerIP:      update.peer,
		ASPath:      update.path,
		NextHop:     update.peer, // Using peer as next hop
		LastUpdated: update.timestamp,
	}

	// For IPv4, calculate the IP range
	if ipVersion == ipv4Version {
		start, end, err := database.CalculateIPv4Range(update.prefix)
		if err == nil {
			liveRoute.V4IPStart = &start
			liveRoute.V4IPEnd = &end
		} else {
			h.logger.Error("Failed to calculate IPv4 range",
				"prefix", update.prefix,
				"error", err,
			)
		}
	}

	if err := h.db.UpsertLiveRoute(liveRoute); err != nil {
		h.logger.Error("Failed to upsert live route",
			"prefix", update.prefix,
			"error", err,
		)
	}
}

// processWithdrawalDirect handles removing a route directly without prefix table
// nolint:unused // kept for potential future use
func (h *PrefixHandler) processWithdrawalDirect(update prefixUpdate) {
	// For withdrawals, we need to delete the route from live_routes
	if update.originASN > 0 {
		if err := h.db.DeleteLiveRoute(update.prefix, update.originASN, update.peer); err != nil {
			h.logger.Error("Failed to delete live route",
				"prefix", update.prefix,
				"origin_asn", update.originASN,
				"peer", update.peer,
				"error", err,
			)
		}
	} else {
		// If no origin ASN, just delete all routes for this prefix from this peer
		if err := h.db.DeleteLiveRoute(update.prefix, 0, update.peer); err != nil {
			h.logger.Error("Failed to delete live route (no origin ASN)",
				"prefix", update.prefix,
				"peer", update.peer,
				"error", err,
			)
		}
	}
}

// processWithdrawal handles removing a route from the live routing table
// nolint:unused // kept for potential future use
func (h *PrefixHandler) processWithdrawal(_ *database.Prefix, update prefixUpdate) {
	// For withdrawals, we need to delete the route from live_routes
	// Since we have the origin ASN from the update, we can delete the specific route
	if update.originASN > 0 {
		if err := h.db.DeleteLiveRoute(update.prefix, update.originASN, update.peer); err != nil {
			h.logger.Error("Failed to delete live route",
				"prefix", update.prefix,
				"origin_asn", update.originASN,
				"peer", update.peer,
				"error", err,
			)
		}
	} else {
		// If no origin ASN, just delete all routes for this prefix from this peer
		if err := h.db.DeleteLiveRoute(update.prefix, 0, update.peer); err != nil {
			h.logger.Error("Failed to delete live route (no origin ASN)",
				"prefix", update.prefix,
				"peer", update.peer,
				"error", err,
			)
		}
	}
}

// Stop gracefully stops the handler and flushes remaining batches
func (h *PrefixHandler) Stop() {
	close(h.stopCh)
	h.wg.Wait()
}