package dnstt

import (
	"net/netip"
	"sort"
	"strings"
	"sync"
	"time"
)

// ClientTimeout is how long since the last query before a session is considered inactive.
const ClientTimeout = 30 * time.Second

// Collector accumulates observed DNSTT DNS traffic.
type Collector struct {
	mu      sync.Mutex
	domains []string
	tunnels map[string]*tunnelState
	now     func() time.Time
	geo     GeoResolver
}

type tunnelState struct {
	series  map[geoKey]*seriesState
	clients map[string]*clientState
}

type seriesState struct {
	queries     uint64
	bytesIn     uint64
	bytesOut    uint64
	peakClients int
}

type clientState struct {
	firstSeen time.Time
	lastSeen  time.Time
	queries   uint64
	bytesIn   uint64
	firstKey  geoKey
	lastKey   geoKey
}

type geoKey struct {
	country string
	asn     string
}

// Snapshot is a point-in-time copy of observed traffic.
type Snapshot struct {
	Tunnels map[string]TunnelSnapshot
}

// TunnelSnapshot is a point-in-time copy of one DNSTT domain.
type TunnelSnapshot struct {
	Domain        string
	ActiveClients int
	PeakClients   int
	TotalSessions int
	TotalQueries  uint64
	BytesIn       uint64
	BytesOut      uint64
	Series        []SeriesSnapshot
}

// SeriesSnapshot is a per-label metric series for a tunnel.
type SeriesSnapshot struct {
	Domain        string
	Country       string
	ASN           string
	ActiveClients int
	PeakClients   int
	TotalSessions int
	TotalQueries  uint64
	BytesIn       uint64
	BytesOut      uint64
}

// CollectorOption configures a Collector.
type CollectorOption func(*Collector)

// WithNow overrides the clock. It is intended for deterministic tests.
func WithNow(now func() time.Time) CollectorOption {
	return func(c *Collector) {
		c.now = now
	}
}

// WithGeoResolver enables optional GeoIP labels for resolver IP addresses.
func WithGeoResolver(resolver GeoResolver) CollectorOption {
	return func(c *Collector) {
		c.geo = resolver
	}
}

// NewCollector creates a collector for the provided DNSTT domains.
func NewCollector(domains []string, opts ...CollectorOption) *Collector {
	c := &Collector{
		tunnels: make(map[string]*tunnelState),
		now:     time.Now,
	}

	for _, domain := range domains {
		domain = normalizeDomain(domain)
		if domain == "" {
			continue
		}
		if _, exists := c.tunnels[domain]; exists {
			continue
		}
		c.domains = append(c.domains, domain)
		c.tunnels[domain] = &tunnelState{
			series:  make(map[geoKey]*seriesState),
			clients: make(map[string]*clientState),
		}
	}

	for _, opt := range opts {
		opt(c)
	}

	return c
}

// GeoLabelNames returns the optional GeoIP label names used by this collector.
func (c *Collector) GeoLabelNames() []string {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.geoLabelNamesLocked()
}

// Domains returns the normalized DNSTT domains this collector recognizes.
func (c *Collector) Domains() []string {
	c.mu.Lock()
	defer c.mu.Unlock()

	domains := make([]string, len(c.domains))
	copy(domains, c.domains)
	return domains
}

// RecordQuery records an observed DNSTT DNS query.
func (c *Collector) RecordQuery(domain string, clientID string, size int) {
	c.RecordQueryFrom(domain, clientID, netip.Addr{}, size)
}

// RecordQueryFrom records an observed DNSTT DNS query from a resolver address.
func (c *Collector) RecordQueryFrom(domain string, clientID string, resolverIP netip.Addr, size int) {
	c.mu.Lock()
	defer c.mu.Unlock()

	tunnel, ok := c.findTunnelLocked(domain)
	if !ok {
		return
	}

	key := c.geoKeyLocked(resolverIP)
	series := ensureSeries(tunnel, key)
	series.queries++
	if size > 0 {
		series.bytesIn += uint64(size)
	}

	if clientID == "" {
		return
	}

	now := c.now()
	client, exists := tunnel.clients[clientID]
	if !exists {
		client = &clientState{firstSeen: now, firstKey: key}
		tunnel.clients[clientID] = client
	}
	client.lastSeen = now
	client.lastKey = key
	client.queries++
	if size > 0 {
		client.bytesIn += uint64(size)
	}

	updatePeaks(tunnel, now)
}

// RecordResponse records an observed DNSTT DNS response.
func (c *Collector) RecordResponse(domain string, size int) {
	c.RecordResponseFrom(domain, netip.Addr{}, size)
}

// RecordResponseFrom records an observed DNSTT DNS response to a resolver address.
func (c *Collector) RecordResponseFrom(domain string, resolverIP netip.Addr, size int) {
	c.mu.Lock()
	defer c.mu.Unlock()

	tunnel, ok := c.findTunnelLocked(domain)
	if !ok {
		return
	}
	key := c.geoKeyLocked(resolverIP)
	series := ensureSeries(tunnel, key)
	if size > 0 {
		series.bytesOut += uint64(size)
	}
}

// Snapshot returns a stable copy of all current metrics.
func (c *Collector) Snapshot() Snapshot {
	c.mu.Lock()
	defer c.mu.Unlock()

	now := c.now()
	snapshot := Snapshot{Tunnels: make(map[string]TunnelSnapshot, len(c.tunnels))}
	for _, domain := range c.domains {
		tunnel := c.tunnels[domain]
		updatePeaks(tunnel, now)
		series := c.seriesSnapshotsLocked(domain, tunnel, now)

		tunnelSnapshot := TunnelSnapshot{Domain: domain, Series: series}
		for _, s := range series {
			tunnelSnapshot.ActiveClients += s.ActiveClients
			tunnelSnapshot.TotalSessions += s.TotalSessions
			tunnelSnapshot.TotalQueries += s.TotalQueries
			tunnelSnapshot.BytesIn += s.BytesIn
			tunnelSnapshot.BytesOut += s.BytesOut
			if s.PeakClients > tunnelSnapshot.PeakClients {
				tunnelSnapshot.PeakClients = s.PeakClients
			}
		}
		snapshot.Tunnels[domain] = tunnelSnapshot
	}

	return snapshot
}

func (c *Collector) findTunnelLocked(queryDomain string) (*tunnelState, bool) {
	queryDomain = normalizeDomain(queryDomain)
	if tunnel, ok := c.tunnels[queryDomain]; ok {
		return tunnel, true
	}
	for _, domain := range c.domains {
		if strings.HasSuffix(queryDomain, "."+domain) {
			return c.tunnels[domain], true
		}
	}
	return nil, false
}

func ensureSeries(tunnel *tunnelState, key geoKey) *seriesState {
	series, ok := tunnel.series[key]
	if !ok {
		series = &seriesState{}
		tunnel.series[key] = series
	}
	return series
}

func updatePeaks(tunnel *tunnelState, now time.Time) {
	activeByKey := make(map[geoKey]int)
	for _, client := range tunnel.clients {
		if now.Sub(client.lastSeen) < ClientTimeout {
			activeByKey[client.lastKey]++
		}
	}
	for key, active := range activeByKey {
		series := ensureSeries(tunnel, key)
		if active > series.peakClients {
			series.peakClients = active
		}
	}
}

func (c *Collector) seriesSnapshotsLocked(domain string, tunnel *tunnelState, now time.Time) []SeriesSnapshot {
	activeByKey := make(map[geoKey]int)
	sessionsByKey := make(map[geoKey]int)
	for _, client := range tunnel.clients {
		sessionsByKey[client.firstKey]++
		if now.Sub(client.lastSeen) < ClientTimeout {
			activeByKey[client.lastKey]++
		}
	}

	keys := make([]geoKey, 0, len(tunnel.series))
	for key := range tunnel.series {
		keys = append(keys, key)
	}
	sort.Slice(keys, func(i, j int) bool {
		if keys[i].country != keys[j].country {
			return keys[i].country < keys[j].country
		}
		return keys[i].asn < keys[j].asn
	})

	series := make([]SeriesSnapshot, 0, len(keys))
	for _, key := range keys {
		state := tunnel.series[key]
		series = append(series, SeriesSnapshot{
			Domain:        domain,
			Country:       key.country,
			ASN:           key.asn,
			ActiveClients: activeByKey[key],
			PeakClients:   state.peakClients,
			TotalSessions: sessionsByKey[key],
			TotalQueries:  state.queries,
			BytesIn:       state.bytesIn,
			BytesOut:      state.bytesOut,
		})
	}
	return series
}

func (c *Collector) geoLabelNamesLocked() []string {
	if c.geo == nil {
		return nil
	}
	names := c.geo.LabelNames()
	out := make([]string, 0, len(names))
	for _, name := range names {
		if name == "country" || name == "asn" {
			out = append(out, name)
		}
	}
	return out
}

func (c *Collector) geoKeyLocked(addr netip.Addr) geoKey {
	var key geoKey
	if c.geo == nil {
		return key
	}

	labels := c.geo.Lookup(addr)
	for _, name := range c.geoLabelNamesLocked() {
		switch name {
		case "country":
			key.country = labels.Country
			if key.country == "" {
				key.country = UnknownCountry
			}
		case "asn":
			key.asn = labels.ASN
			if key.asn == "" {
				key.asn = UnknownASN
			}
		}
	}
	return key
}