package tunneldns

import (
	"net"
	"strconv"
	"sync"
	"os"

	"github.com/coredns/coredns/core/dnsserver"
	"github.com/coredns/coredns/plugin"
	"github.com/coredns/coredns/plugin/cache"
	"github.com/pkg/errors"
	"github.com/rs/zerolog"
)

const (
	LogFieldAddress         = "address"
	LogFieldURL             = "url"
	MaxUpstreamConnsDefault = 5
)

// Listener is an adapter between CoreDNS server and Warp runnable
type Listener struct {
	server *dnsserver.Server
	wg     sync.WaitGroup
	log    *zerolog.Logger
}

// Create a CoreDNS server plugin from configuration
func createConfig(address string, port uint16, p plugin.Handler) *dnsserver.Config {
	c := &dnsserver.Config{
		Zone:        ".",
		Transport:   "dns",
		ListenHosts: []string{address},
		Port:        strconv.FormatUint(uint64(port), 10),
	}

	c.AddPlugin(func(next plugin.Handler) plugin.Handler { return p })
	return c
}

// Start blocks for serving requests
func (l *Listener) Start(readySignal chan struct{}) error {
	defer close(readySignal)
	l.log.Info().Str(LogFieldAddress, l.server.Address()).Msg("Starting DNS over HTTPS proxy server")

	// Start UDP listener
	if udp, err := l.server.ListenPacket(); err == nil {
		l.wg.Add(1)
		go func() {
			_ = l.server.ServePacket(udp)
			l.wg.Done()
		}()
	} else {
		return errors.Wrap(err, "failed to create a UDP listener")
	}

	// Start TCP listener
	tcp, err := l.server.Listen()
	if err == nil {
		l.wg.Add(1)
		go func() {
			_ = l.server.Serve(tcp)
			l.wg.Done()
		}()
	}

	return errors.Wrap(err, "failed to create a TCP listener")
}

// Stop signals server shutdown and blocks until completed
func (l *Listener) Stop() error {
	if err := l.server.Stop(); err != nil {
		return err
	}

	l.wg.Wait()
	return nil
}

// CreateListener configures the server and bound sockets
func CreateListener(address string, port uint16, upstreams []string, bootstraps []string, maxUpstreamConnections int, log *zerolog.Logger) (*Listener, error) {
	// Build the list of upstreams
	upstreamList := make([]Upstream, 0)
	for _, url := range upstreams {
		log.Info().Str(LogFieldURL, url).Msg("Adding DNS upstream")
		upstream, err := NewUpstreamHTTPS(url, bootstraps, maxUpstreamConnections, log)
		if err != nil {
			return nil, errors.Wrap(err, "failed to create HTTPS upstream")
		}
		upstreamList = append(upstreamList, upstream)
	}

	// Format an endpoint
	endpoint := "dns://" + net.JoinHostPort(address, strconv.FormatUint(uint64(port), 10))

	// get middlewares for DNS Server
	middlewares := getMiddlewares(upstreamList)
	chain := NewMetricsPlugin(middlewares)

	// Create the actual middleware server
	server, err := dnsserver.NewServer(endpoint, []*dnsserver.Config{createConfig(address, port, chain)})
	if err != nil {
		return nil, err
	}
	

	return &Listener{server: server, log: log}, nil
}

// getMiddlewares() returns the middleware chain for DNS Server
// 
// Middleware includes features like...
// * Response Cache
// * HTTP Proxy Settings
func getMiddlewares(upstreamList []Upstream) plugin.Handler { 
	proxyPlugin := ProxyPlugin{
		Upstreams: upstreamList,
	}
	cachePlugin := cache.New()
	cachePlugin.Next = proxyPlugin

	if os.Getenv("DISABLE_TUNNELDNS_CACHE") == "true" { 
		return cachePlugin 
	} 
	return proxyPlugin
}