package mirko

import (
	"context"
	"flag"
	"fmt"
	"net"
	"net/http"
	"net/http/pprof"
	"os"
	"os/signal"
	"sort"
	"strings"
	"time"

	"github.com/golang/glog"
	"golang.org/x/net/trace"
	"google.golang.org/grpc"
	"google.golang.org/grpc/reflection"
	"k8s.io/client-go/kubernetes"

	"code.hackerspace.pl/hscloud/go/pki"
	"code.hackerspace.pl/hscloud/go/statusz"
)

var (
	flagListenAddress string
	flagDebugAddress  string
	flagDebugAllowAll bool
)

func init() {
	flag.StringVar(&flagListenAddress, "listen_address", "127.0.0.1:4200", "gRPC listen address")
	flag.StringVar(&flagDebugAddress, "debug_address", "127.0.0.1:4201", "HTTP debug/status listen address")
	flag.BoolVar(&flagDebugAllowAll, "debug_allow_all", false, "HTTP debug/status available to everyone")
	flag.Set("logtostderr", "true")
}

type Mirko struct {
	grpcListen net.Listener
	grpcServer *grpc.Server
	httpListen net.Listener
	httpServer *http.Server
	httpMux    *http.ServeMux

	kubernetesCS *kubernetes.Clientset

	ctx    context.Context
	cancel context.CancelFunc
}

func New() *Mirko {
	ctx, cancel := context.WithCancel(context.Background())
	return &Mirko{
		ctx:    ctx,
		cancel: cancel,
	}
}

func authRequest(req *http.Request) (any, sensitive bool) {
	host, _, err := net.SplitHostPort(req.RemoteAddr)
	if err != nil {
		host = req.RemoteAddr
	}

	if flagDebugAllowAll {
		return true, true
	}

	switch host {
	case "localhost", "127.0.0.1", "::1":
		return true, true
	default:
		return false, false
	}
}

func (m *Mirko) Listen() error {
	grpc.EnableTracing = true
	trace.AuthRequest = authRequest

	grpcLis, err := net.Listen("tcp", flagListenAddress)
	if err != nil {
		return fmt.Errorf("net.Listen: %v", err)
	}
	m.grpcListen = grpcLis
	m.grpcServer = grpc.NewServer(pki.WithServerHSPKI()...)
	reflection.Register(m.grpcServer)

	httpLis, err := net.Listen("tcp", flagDebugAddress)
	if err != nil {
		return fmt.Errorf("net.Listen: %v", err)
	}

	m.httpMux = http.NewServeMux()
	// Canonical URLs
	m.httpMux.HandleFunc("/debug/status", func(w http.ResponseWriter, r *http.Request) {
		any, _ := authRequest(r)
		if !any {
			http.Error(w, "not allowed", http.StatusUnauthorized)
			return
		}
		statusz.StatusHandler(w, r)
	})
	m.httpMux.HandleFunc("/debug/requests", trace.Traces)

	// pprof endpoints
	m.httpMux.HandleFunc("/debug/pprof/", pprof.Index)
	m.httpMux.HandleFunc("/debug/pprof/cmdline", pprof.Cmdline)
	m.httpMux.HandleFunc("/debug/pprof/profile", pprof.Profile)
	m.httpMux.HandleFunc("/debug/pprof/symbol", pprof.Symbol)
	m.httpMux.HandleFunc("/debug/pprof/trace", pprof.Trace)

	// -z legacy URLs
	m.httpMux.HandleFunc("/statusz", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/debug/status", http.StatusSeeOther)
	})
	m.httpMux.HandleFunc("/rpcz", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/debug/requests", http.StatusSeeOther)
	})
	m.httpMux.HandleFunc("/requestz", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/debug/requests", http.StatusSeeOther)
	})
	m.httpMux.HandleFunc("/profilez", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/debug/pprof", http.StatusSeeOther)
	})

	// root redirect
	m.httpMux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/debug/status", http.StatusSeeOther)
	})

	m.kubernetesCS = KubernetesClient()

	debugParts := strings.Split(flagDebugAddress, ":")
	debugPort := debugParts[len(debugParts)-1]
	statusz.PublicAddress = fmt.Sprintf("http://%s:%s/", m.Address().String(), debugPort)

	m.httpListen = httpLis
	m.httpServer = &http.Server{
		Addr:    flagDebugAddress,
		Handler: m.httpMux,
	}

	return nil
}

// Trace logs debug information to either a context trace (if present)
// or stderr (if not)
func Trace(ctx context.Context, f string, args ...interface{}) {
	tr, ok := trace.FromContext(ctx)
	if !ok {
		fmtd := fmt.Sprintf(f, args...)
		glog.Warningf("No trace in %v: %s", ctx, fmtd)
		return
	}
	tr.LazyPrintf(f, args...)
}

// GRPC returns the microservice's grpc.Server object
func (m *Mirko) GRPC() *grpc.Server {
	if m.grpcServer == nil {
		panic("GRPC() called before Listen()")
	}
	return m.grpcServer
}

// HTTPMux returns the microservice's debug HTTP mux
func (m *Mirko) HTTPMux() *http.ServeMux {
	if m.httpMux == nil {
		panic("HTTPMux() called before Listen()")
	}
	return m.httpMux
}

// Context returns a background microservice context that will be canceled
// when the service is shut down
func (m *Mirko) Context() context.Context {
	return m.ctx
}

// Done() returns a channel that will emit a value when the service is
// shut down. This should be used in the main() function instead of a select{}
// call, to allow the background context to be canceled fully.
func (m *Mirko) Done() <-chan struct{} {
	return m.Context().Done()
}

// Serve starts serving HTTP and gRPC requests
func (m *Mirko) Serve() error {
	errs := make(chan error, 1)
	go func() {
		if err := m.grpcServer.Serve(m.grpcListen); err != nil {
			errs <- err
		}
	}()
	go func() {
		if err := m.httpServer.Serve(m.httpListen); err != nil {
			errs <- err
		}
	}()

	signalCh := make(chan os.Signal, 1)
	signal.Notify(signalCh, os.Interrupt)
	go func() {
		select {
		case <-signalCh:
			m.cancel()
		}
	}()

	ticker := time.NewTicker(1 * time.Second)
	select {
	case <-ticker.C:
		glog.Infof("gRPC listening on %s", flagListenAddress)
		glog.Infof("HTTP listening on %s", flagDebugAddress)
		return nil
	case err := <-errs:
		return err
	}
}

// Address returns a linkable address where this service is running, sans port.
// If running within kubernetes, this will return the pod IP.
// Otherwise, this will guess the main, 'external' IP address of the machine it's running on.
// On failures, returns loopback address.
func (m *Mirko) Address() net.IP {
	// If we're not running in Kubernetes and binding to 127.0.0.1, return loopback.
	if m.kubernetesCS == nil && strings.HasPrefix(flagListenAddress, "127.0.0.1:") {
		return net.ParseIP("127.0.0.1")
	}

	ifaces, err := net.Interfaces()
	if err != nil {
		glog.Errorf("net.Interface(): %v", err)
		return net.ParseIP("127.0.0.1")
	}

	addrmap := make(map[string]net.IP)

	for _, iface := range ifaces {
		addrs, err := iface.Addrs()
		if err != nil {
			glog.Errorf("iface(%q).Addrs(): %v", iface.Name, err)
			continue
		}

		for _, addr := range addrs {
			var ip net.IP
			switch v := addr.(type) {
			case *net.IPNet:
				ip = v.IP
			case *net.IPAddr:
				ip = v.IP
			default:
				continue
			}

			if strings.HasPrefix(ip.String(), "fe80:") {
				continue
			}
			addrmap[iface.Name] = ip
		}
	}

	if m.kubernetesCS != nil {
		addr, ok := addrmap["eth0"]
		if !ok {
			glog.Errorf("Running on Kubernetes but no eth0! Available interfaces: %v", addrmap)
			return net.ParseIP("127.0.0.1")
		}

		return addr
	}

	if len(addrmap) == 0 {
		glog.Errorf("No interfaces found!")
		return net.ParseIP("127.0.0.1")
	}

	// Heuristics ahoy!
	prioritized := []*ifaceWithPriority{}
	for iface, addr := range addrmap {
		prio := &ifaceWithPriority{
			iface: iface,
			addr:  addr,
		}
		switch {
		case strings.HasPrefix(iface, "lo"):
			prio.priority = -10
		case strings.HasPrefix(iface, "tap"):
			prio.priority = -5
		case strings.HasPrefix(iface, "tun"):
			prio.priority = -5
		case strings.HasPrefix(iface, "veth"):
			prio.priority = 5
		case strings.HasPrefix(iface, "wl"):
			prio.priority = 5
		case strings.HasPrefix(iface, "enp"):
			prio.priority = 10
		case strings.HasPrefix(iface, "eth"):
			prio.priority = 10
		}

		prioritized = append(prioritized, prio)
	}

	sort.Slice(prioritized, func(i, j int) bool { return prioritized[i].priority > prioritized[j].priority })
	return prioritized[0].addr
}

type ifaceWithPriority struct {
	iface    string
	addr     net.IP
	priority int
}