package server

import (
	"context"
	"fmt"
	"log/slog"
	"net"
	"net/http"
	"sync"
	"time"

	"linum/internal/blocklist"
	"linum/internal/cache"
	"linum/internal/config"
	"linum/internal/resolver"

	"codeberg.org/miekg/dns"
)

type Server struct {
	resolver    *resolver.Resolver
	cache       *cache.Cache
	blocklist   *blocklist.Blocklist
	logger      *slog.Logger
	cfg         config.ServerConfig
	baseCtx     context.Context
	udp         *dns.Server
	tcp         *dns.Server
	doh         *http.Server
	admin       *Admin
	aclNets     []*net.IPNet
	rateLimiter *rateLimiter

	mu    sync.RWMutex
	upUDP bool
	upTCP bool
	upDoH bool

	cancel context.CancelFunc
}

func (s *Server) Ready() bool {
	s.mu.RLock()
	defer s.mu.RUnlock()
	wantUDP := s.cfg.ListenUDP != ""
	wantTCP := s.cfg.ListenTCP != ""
	wantDoH := s.cfg.ListenDOH != ""
	return (!wantUDP || s.upUDP) && (!wantTCP || s.upTCP) && (!wantDoH || s.upDoH)

}
func New(udpAddr, tcpAddr, dohAddr string, logger *slog.Logger, r *resolver.Resolver, c *cache.Cache, bl *blocklist.Blocklist, cfg config.Config) (*Server, error) {
	baseCtx, cancel := context.WithCancel(context.Background())
	s := &Server{
		logger:      logger,
		resolver:    r,
		cache:       c,
		blocklist:   bl,
		cfg:         cfg.Server,
		baseCtx:     baseCtx,
		cancel:      cancel,
		aclNets:     make([]*net.IPNet, 0, len(cfg.ACL.Allow)),
		rateLimiter: newRateLimiter(cfg.ACL.RateLimitQPS, cfg.ACL.RateLimitBurst),
	}

	for _, cidr := range cfg.ACL.Allow {
		_, ipnet, err := net.ParseCIDR(cidr)
		if err != nil {
			cancel()
			return nil, fmt.Errorf("invalid acl CIDR %q: %w", cidr, err)
		}
		s.aclNets = append(s.aclNets, ipnet)
	}

	mux := dns.NewServeMux()
	mux.HandleFunc(".", s.handleQuery)

	if udpAddr != "" {
		s.udp = &dns.Server{
			Addr:        udpAddr,
			Net:         "udp",
			Handler:     mux,
			UDPSize:     4096,
			ReadTimeout: 5 * time.Second,
			ReusePort:   true,
		}
	}

	if tcpAddr != "" {
		s.tcp = &dns.Server{
			Addr:        tcpAddr,
			Net:         "tcp",
			Handler:     mux,
			ReadTimeout: 5 * time.Second,
		}
	}

	if dohAddr != "" {
		dohMux := http.NewServeMux()
		dohMux.HandleFunc("/dns-query", s.dohHandler)
		s.doh = &http.Server{
			Addr:         dohAddr,
			Handler:      dohMux,
			ReadTimeout:  5 * time.Second,
			WriteTimeout: 5 * time.Second,
		}
	}

	if cfg.Admin.Listen != "" {
		s.admin = NewAdmin(cfg.Admin.Listen, s)
	}

	return s, nil
}
func (s *Server) Run(ctx context.Context) error {
	s.mu.Lock()
	if s.udp != nil {
		s.upUDP = true
	}
	if s.tcp != nil {
		s.upTCP = true
	}
	if s.doh != nil {
		s.upDoH = true
	}
	s.mu.Unlock()

	if s.admin != nil {
		s.admin.Start()
	}

	errCh := make(chan error, 3)
	if s.udp != nil {
		go func() {
			s.logger.Info("udp listener active", "addr", s.udp.Addr)
			errCh <- s.udp.ListenAndServe()
		}()
	}

	if s.tcp != nil {
		go func() {
			s.logger.Info("tcp listener active", "addr", s.tcp.Addr)
			errCh <- s.tcp.ListenAndServe()
		}()
	}

	if s.doh != nil {
		go func() {
			s.logger.Info("doh listener active", "addr", s.doh.Addr)
			errCh <- s.doh.ListenAndServe()
		}()
	}

	select {
	case <-ctx.Done():
		shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()

		if s.udp != nil {
			s.udp.Shutdown(shutdownCtx)
		}
		if s.tcp != nil {
			s.tcp.Shutdown(shutdownCtx)
		}
		if s.doh != nil {
			s.doh.Shutdown(shutdownCtx)
		}
		return ctx.Err()
	case err := <-errCh:
		return err
	}
}

func (s *Server) Close() error {
	if s.admin != nil {
		s.admin.Close()
	}
	if s.udp != nil {
		s.udp.Shutdown(context.Background())
	}
	if s.tcp != nil {
		s.tcp.Shutdown(context.Background())
	}
	if s.doh != nil {
		s.doh.Close()
	}
	return nil
}

type rateLimiter struct {
	mu      sync.Mutex
	rate    float64
	burst   float64
	buckets map[string]*rateBucket
}

type rateBucket struct {
	tokens float64
	last   time.Time
}

func newRateLimiter(qps, burst int) *rateLimiter {
	if qps <= 0 && burst <= 0 {
		return nil
	}
	if burst <= 0 {
		burst = qps
	}
	return &rateLimiter{
		rate:    float64(qps),
		burst:   float64(burst),
		buckets: make(map[string]*rateBucket),
	}
}

func (rl *rateLimiter) allow(ip string) bool {
	now := time.Now()
	rl.mu.Lock()
	defer rl.mu.Unlock()

	b, ok := rl.buckets[ip]
	if !ok {
		b = &rateBucket{tokens: rl.burst, last: now}
		rl.buckets[ip] = b
	}

	elapsed := now.Sub(b.last).Seconds()
	b.tokens += elapsed * rl.rate
	if b.tokens > rl.burst {
		b.tokens = rl.burst
	}
	b.last = now

	if b.tokens < 1 {
		return false
	}
	b.tokens--
	return true
}