package server

import (
	"context"
	"fmt"
	"log/slog"
	"net"
	"net/netip"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"git.wntrmute.dev/kyle/mc-proxy/internal/config"
	"git.wntrmute.dev/kyle/mc-proxy/internal/firewall"
	"git.wntrmute.dev/kyle/mc-proxy/internal/l7"
	"git.wntrmute.dev/kyle/mc-proxy/internal/proxy"
	"git.wntrmute.dev/kyle/mc-proxy/internal/proxyproto"
	"git.wntrmute.dev/kyle/mc-proxy/internal/sni"
)

// RouteInfo holds the full configuration for a single route.
type RouteInfo struct {
	Backend           string
	Mode              string // "l4" or "l7"
	TLSCert           string
	TLSKey            string
	BackendTLS        bool
	SendProxyProtocol bool
}

// ListenerState holds the mutable state for a single proxy listener.
type ListenerState struct {
	ID                int64 // database primary key
	Addr              string
	ProxyProtocol     bool
	MaxConnections    int64 // 0 = unlimited
	routes            map[string]RouteInfo // lowercase hostname → route info
	mu                sync.RWMutex
	ActiveConnections atomic.Int64
	activeConns       map[net.Conn]struct{} // tracked for forced shutdown
	connMu            sync.Mutex
}

// SetMaxConnections updates the connection limit at runtime.
func (ls *ListenerState) SetMaxConnections(n int64) {
	ls.mu.Lock()
	defer ls.mu.Unlock()
	ls.MaxConnections = n
}

// Routes returns a snapshot of the listener's route table.
func (ls *ListenerState) Routes() map[string]RouteInfo {
	ls.mu.RLock()
	defer ls.mu.RUnlock()

	m := make(map[string]RouteInfo, len(ls.routes))
	for k, v := range ls.routes {
		m[k] = v
	}
	return m
}

// AddRoute adds a route to the listener. Returns an error if the hostname
// already exists.
func (ls *ListenerState) AddRoute(hostname string, info RouteInfo) error {
	key := strings.ToLower(hostname)

	ls.mu.Lock()
	defer ls.mu.Unlock()

	if _, ok := ls.routes[key]; ok {
		return fmt.Errorf("route %q already exists", hostname)
	}
	ls.routes[key] = info
	return nil
}

// RemoveRoute removes a route from the listener. Returns an error if the
// hostname does not exist.
func (ls *ListenerState) RemoveRoute(hostname string) error {
	key := strings.ToLower(hostname)

	ls.mu.Lock()
	defer ls.mu.Unlock()

	if _, ok := ls.routes[key]; !ok {
		return fmt.Errorf("route %q not found", hostname)
	}
	delete(ls.routes, key)
	return nil
}

func (ls *ListenerState) lookupRoute(hostname string) (RouteInfo, bool) {
	ls.mu.RLock()
	defer ls.mu.RUnlock()

	info, ok := ls.routes[hostname]
	return info, ok
}

// ListenerData holds the data needed to construct a ListenerState.
type ListenerData struct {
	ID             int64
	Addr           string
	ProxyProtocol  bool
	MaxConnections int64
	Routes         map[string]RouteInfo // lowercase hostname → route info
}

// Server is the mc-proxy server. It manages listeners, firewall evaluation,
// SNI-based routing, and bidirectional proxying.
type Server struct {
	cfg       *config.Config
	fw        *firewall.Firewall
	listeners []*ListenerState
	logger    *slog.Logger
	wg        sync.WaitGroup
	startedAt time.Time
	version   string
}

// New creates a Server from pre-loaded data.
func New(cfg *config.Config, fw *firewall.Firewall, listenerData []ListenerData, logger *slog.Logger, version string) *Server {
	var listeners []*ListenerState
	for _, ld := range listenerData {
		listeners = append(listeners, &ListenerState{
			ID:             ld.ID,
			Addr:           ld.Addr,
			ProxyProtocol:  ld.ProxyProtocol,
			MaxConnections: ld.MaxConnections,
			routes:         ld.Routes,
			activeConns:    make(map[net.Conn]struct{}),
		})
	}

	return &Server{
		cfg:       cfg,
		fw:        fw,
		listeners: listeners,
		logger:    logger,
		version:   version,
	}
}

// Firewall returns the server's firewall for use by the gRPC admin API.
func (s *Server) Firewall() *firewall.Firewall {
	return s.fw
}

// Listeners returns the server's listener states for use by the gRPC admin API.
func (s *Server) Listeners() []*ListenerState {
	return s.listeners
}

// StartedAt returns the time the server started.
func (s *Server) StartedAt() time.Time {
	return s.startedAt
}

// Version returns the server's version string.
func (s *Server) Version() string {
	return s.version
}

// TotalConnections returns the total number of active connections.
func (s *Server) TotalConnections() int64 {
	var total int64
	for _, ls := range s.listeners {
		total += ls.ActiveConnections.Load()
	}
	return total
}

// Run starts all listeners and blocks until ctx is cancelled.
func (s *Server) Run(ctx context.Context) error {
	s.startedAt = time.Now()

	var netListeners []net.Listener

	for _, ls := range s.listeners {
		ln, err := net.Listen("tcp", ls.Addr)
		if err != nil {
			for _, l := range netListeners {
				l.Close()
			}
			return fmt.Errorf("listening on %s: %w", ls.Addr, err)
		}
		s.logger.Info("listening", "addr", ln.Addr(), "routes", len(ls.routes))
		netListeners = append(netListeners, ln)
	}

	for i, ln := range netListeners {
		ln := ln
		ls := s.listeners[i]
		go s.serve(ctx, ln, ls)
	}

	<-ctx.Done()
	s.logger.Info("shutting down")

	for _, ln := range netListeners {
		ln.Close()
	}

	done := make(chan struct{})
	go func() {
		s.wg.Wait()
		close(done)
	}()

	select {
	case <-done:
		s.logger.Info("all connections drained")
	case <-time.After(s.cfg.Proxy.ShutdownTimeout.Duration):
		s.logger.Warn("shutdown timeout exceeded, forcing close")
		// Force-close all listener connections to unblock relay goroutines.
		s.forceCloseAll()
		<-done
	}

	s.fw.Close()
	return nil
}

// ReloadGeoIP reloads the GeoIP database from disk.
func (s *Server) ReloadGeoIP() error {
	return s.fw.ReloadGeoIP()
}

func (s *Server) serve(ctx context.Context, ln net.Listener, ls *ListenerState) {
	for {
		conn, err := ln.Accept()
		if err != nil {
			if ctx.Err() != nil {
				return
			}
			s.logger.Error("accept error", "error", err)
			continue
		}

		// Enforce per-listener connection limit.
		if ls.MaxConnections > 0 && ls.ActiveConnections.Load() >= ls.MaxConnections {
			conn.Close()
			s.logger.Debug("connection limit reached", "addr", ls.Addr, "limit", ls.MaxConnections)
			continue
		}

		s.wg.Add(1)
		ls.ActiveConnections.Add(1)
		go s.handleConn(ctx, conn, ls)
	}
}

// forceCloseAll closes all tracked connections across all listeners.
func (s *Server) forceCloseAll() {
	for _, ls := range s.listeners {
		ls.connMu.Lock()
		for conn := range ls.activeConns {
			conn.Close()
		}
		ls.connMu.Unlock()
	}
}

func (s *Server) handleConn(ctx context.Context, conn net.Conn, ls *ListenerState) {
	defer s.wg.Done()
	defer ls.ActiveConnections.Add(-1)
	defer conn.Close()

	ls.connMu.Lock()
	ls.activeConns[conn] = struct{}{}
	ls.connMu.Unlock()
	defer func() {
		ls.connMu.Lock()
		delete(ls.activeConns, conn)
		ls.connMu.Unlock()
	}()

	remoteAddr := conn.RemoteAddr().String()
	addrPort, err := netip.ParseAddrPort(remoteAddr)
	if err != nil {
		s.logger.Error("parsing remote address", "addr", remoteAddr, "error", err)
		return
	}
	addr := addrPort.Addr()

	// Parse PROXY protocol header if enabled on this listener.
	if ls.ProxyProtocol {
		hdr, err := proxyproto.Parse(conn, time.Now().Add(5*time.Second))
		if err != nil {
			s.logger.Debug("PROXY protocol parse failed", "addr", addr, "error", err)
			return
		}
		if hdr.Command == proxyproto.CommandProxy {
			addr = hdr.SrcAddr.Addr()
			addrPort = hdr.SrcAddr
			s.logger.Debug("PROXY protocol", "real_addr", addr, "peer_addr", remoteAddr)
		}
	}

	if s.fw.Blocked(addr) {
		s.logger.Debug("blocked by firewall", "addr", addr)
		return
	}

	hostname, peeked, err := sni.Extract(conn, time.Now().Add(10*time.Second))
	if err != nil {
		s.logger.Debug("SNI extraction failed", "addr", addr, "error", err)
		return
	}

	route, ok := ls.lookupRoute(hostname)
	if !ok {
		s.logger.Debug("no route for hostname", "addr", addr, "hostname", hostname)
		return
	}

	// Dispatch based on route mode.
	switch route.Mode {
	case "l7":
		s.handleL7(ctx, conn, addr, addrPort, hostname, route, peeked)
	default:
		s.handleL4(ctx, conn, addr, addrPort, hostname, route, peeked)
	}
}

// handleL4 handles an L4 (passthrough) connection.
func (s *Server) handleL4(ctx context.Context, conn net.Conn, addr netip.Addr, clientAddrPort netip.AddrPort, hostname string, route RouteInfo, peeked []byte) {
	backendConn, err := net.DialTimeout("tcp", route.Backend, s.cfg.Proxy.ConnectTimeout.Duration)
	if err != nil {
		s.logger.Error("backend dial failed", "hostname", hostname, "backend", route.Backend, "error", err)
		return
	}
	defer backendConn.Close()

	// Send PROXY protocol v2 header to backend if configured.
	if route.SendProxyProtocol {
		backendAddrPort, _ := netip.ParseAddrPort(backendConn.RemoteAddr().String())
		if err := proxyproto.WriteV2(backendConn, clientAddrPort, backendAddrPort); err != nil {
			s.logger.Error("writing PROXY protocol header", "hostname", hostname, "error", err)
			return
		}
	}

	s.logger.Debug("proxying", "addr", addr, "hostname", hostname, "backend", route.Backend)

	result, err := proxy.Relay(ctx, conn, backendConn, peeked, s.cfg.Proxy.IdleTimeout.Duration)
	if err != nil && ctx.Err() == nil {
		s.logger.Debug("relay ended", "hostname", hostname, "error", err)
	}

	s.logger.Info("connection closed",
		"addr", addr,
		"hostname", hostname,
		"client_bytes", result.ClientBytes,
		"backend_bytes", result.BackendBytes,
	)
}

// handleL7 handles an L7 (TLS-terminating) connection.
func (s *Server) handleL7(ctx context.Context, conn net.Conn, addr netip.Addr, clientAddrPort netip.AddrPort, hostname string, route RouteInfo, peeked []byte) {
	s.logger.Debug("L7 proxying", "addr", addr, "hostname", hostname, "backend", route.Backend)

	rc := l7.RouteConfig{
		Backend:           route.Backend,
		TLSCert:           route.TLSCert,
		TLSKey:            route.TLSKey,
		BackendTLS:        route.BackendTLS,
		SendProxyProtocol: route.SendProxyProtocol,
		ConnectTimeout:    s.cfg.Proxy.ConnectTimeout.Duration,
	}

	if err := l7.Serve(ctx, conn, peeked, rc, clientAddrPort, s.logger); err != nil {
		if ctx.Err() == nil {
			s.logger.Debug("L7 serve ended", "hostname", hostname, "error", err)
		}
	}

	s.logger.Info("L7 connection closed", "addr", addr, "hostname", hostname)
}