// Copyright 2014 beego Author. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Description: http://grisha.org/blog/2014/06/03/graceful-restart-in-golang/
//
// Usage:
//
// import(
//   "log"
//	 "net/http"
//	 "os"
//
//   "github.com/astaxie/beego/grace"
// )
//
//  func handler(w http.ResponseWriter, r *http.Request) {
//	  w.Write([]byte("WORLD!"))
//  }
//
//  func main() {
//      mux := http.NewServeMux()
//      mux.HandleFunc("/hello", handler)
//
//	    err := grace.ListenAndServe("localhost:8080", mux1)
//      if err != nil {
//		   log.Println(err)
//	    }
//      log.Println("Server on 8080 stopped")
//	     os.Exit(0)
//    }
package grace

import (
	"crypto/tls"
	"flag"
	"fmt"
	"log"
	"net"
	"net/http"
	"os"
	"os/exec"
	"os/signal"
	"strings"
	"sync"
	"syscall"
	"time"
)

const (
	PRE_SIGNAL = iota
	POST_SIGNAL

	STATE_INIT
	STATE_RUNNING
	STATE_SHUTTING_DOWN
	STATE_TERMINATE
)

var (
	regLock              *sync.Mutex
	runningServers       map[string]*graceServer
	runningServersOrder  []string
	socketPtrOffsetMap   map[string]uint
	runningServersForked bool

	DefaultReadTimeOut    time.Duration
	DefaultWriteTimeOut   time.Duration
	DefaultMaxHeaderBytes int
	DefaultTimeout        time.Duration

	isChild     bool
	socketOrder string
)

func init() {
	regLock = &sync.Mutex{}
	flag.BoolVar(&isChild, "graceful", false, "listen on open fd (after forking)")
	flag.StringVar(&socketOrder, "socketorder", "", "previous initialization order - used when more than one listener was started")
	runningServers = make(map[string]*graceServer)
	runningServersOrder = []string{}
	socketPtrOffsetMap = make(map[string]uint)

	DefaultMaxHeaderBytes = 0

	// after a restart the parent will finish ongoing requests before
	// shutting down. set to a negative value to disable
	DefaultTimeout = 60 * time.Second
}

type graceServer struct {
	*http.Server
	GraceListener    net.Listener
	SignalHooks      map[int]map[os.Signal][]func()
	tlsInnerListener *graceListener
	wg               sync.WaitGroup
	sigChan          chan os.Signal
	isChild          bool
	state            uint8
	Network          string
}

// NewServer returns an intialized graceServer. Calling Serve on it will
// actually "start" the server.
func NewServer(addr string, handler http.Handler) (srv *graceServer) {
	regLock.Lock()
	defer regLock.Unlock()
	if !flag.Parsed() {
		flag.Parse()
	}
	if len(socketOrder) > 0 {
		for i, addr := range strings.Split(socketOrder, ",") {
			socketPtrOffsetMap[addr] = uint(i)
		}
	} else {
		socketPtrOffsetMap[addr] = uint(len(runningServersOrder))
	}

	srv = &graceServer{
		wg:      sync.WaitGroup{},
		sigChan: make(chan os.Signal),
		isChild: isChild,
		SignalHooks: map[int]map[os.Signal][]func(){
			PRE_SIGNAL: map[os.Signal][]func(){
				syscall.SIGHUP:  []func(){},
				syscall.SIGINT:  []func(){},
				syscall.SIGTERM: []func(){},
			},
			POST_SIGNAL: map[os.Signal][]func(){
				syscall.SIGHUP:  []func(){},
				syscall.SIGINT:  []func(){},
				syscall.SIGTERM: []func(){},
			},
		},
		state:   STATE_INIT,
		Network: "tcp",
	}
	srv.Server = &http.Server{}
	srv.Server.Addr = addr
	srv.Server.ReadTimeout = DefaultReadTimeOut
	srv.Server.WriteTimeout = DefaultWriteTimeOut
	srv.Server.MaxHeaderBytes = DefaultMaxHeaderBytes
	srv.Server.Handler = handler

	runningServersOrder = append(runningServersOrder, addr)
	runningServers[addr] = srv

	return
}

// ListenAndServe listens on the TCP network address addr
// and then calls Serve to handle requests on incoming connections.
func ListenAndServe(addr string, handler http.Handler) error {
	server := NewServer(addr, handler)
	return server.ListenAndServe()
}

// ListenAndServeTLS listens on the TCP network address addr and then calls
// Serve to handle requests on incoming TLS connections.
//
// Filenames containing a certificate and matching private key for the server must be provided.
// If the certificate is signed by a certificate authority,
// the certFile should be the concatenation of the server's certificate followed by the CA's certificate.
func ListenAndServeTLS(addr string, certFile string, keyFile string, handler http.Handler) error {
	server := NewServer(addr, handler)
	return server.ListenAndServeTLS(certFile, keyFile)
}

// Serve accepts incoming connections on the Listener l,
// creating a new service goroutine for each.
// The service goroutines read requests and then call srv.Handler to reply to them.
func (srv *graceServer) Serve() (err error) {
	srv.state = STATE_RUNNING
	err = srv.Server.Serve(srv.GraceListener)
	log.Println(syscall.Getpid(), "Waiting for connections to finish...")
	srv.wg.Wait()
	srv.state = STATE_TERMINATE
	return
}

// ListenAndServe listens on the TCP network address srv.Addr and then calls Serve
// to handle requests on incoming connections. If srv.Addr is blank, ":http" is
// used.
func (srv *graceServer) ListenAndServe() (err error) {
	addr := srv.Addr
	if addr == "" {
		addr = ":http"
	}

	go srv.handleSignals()

	l, err := srv.getListener(addr)
	if err != nil {
		log.Println(err)
		return err
	}

	srv.GraceListener = newGraceListener(l, srv)

	if srv.isChild {
		process, err := os.FindProcess(os.Getppid())
		if err != nil {
			log.Println(err)
			return err
		}
		err = process.Kill()
		if err != nil {
			return err
		}
	}

	log.Println(os.Getpid(), srv.Addr)
	return srv.Serve()
}

// ListenAndServeTLS listens on the TCP network address srv.Addr and then calls
// Serve to handle requests on incoming TLS connections.
//
// Filenames containing a certificate and matching private key for the server must
// be provided. If the certificate is signed by a certificate authority, the
// certFile should be the concatenation of the server's certificate followed by the
// CA's certificate.
//
// If srv.Addr is blank, ":https" is used.
func (srv *graceServer) ListenAndServeTLS(certFile, keyFile string) (err error) {
	addr := srv.Addr
	if addr == "" {
		addr = ":https"
	}

	config := &tls.Config{}
	if srv.TLSConfig != nil {
		*config = *srv.TLSConfig
	}
	if config.NextProtos == nil {
		config.NextProtos = []string{"http/1.1"}
	}

	config.Certificates = make([]tls.Certificate, 1)
	config.Certificates[0], err = tls.LoadX509KeyPair(certFile, keyFile)
	if err != nil {
		return
	}

	go srv.handleSignals()

	l, err := srv.getListener(addr)
	if err != nil {
		log.Println(err)
		return err
	}

	srv.tlsInnerListener = newGraceListener(l, srv)
	srv.GraceListener = tls.NewListener(srv.tlsInnerListener, config)

	if srv.isChild {
		process, err := os.FindProcess(os.Getppid())
		if err != nil {
			log.Println(err)
			return err
		}
		err = process.Kill()
		if err != nil {
			return err
		}
	}
	log.Println(os.Getpid(), srv.Addr)
	return srv.Serve()
}

// getListener either opens a new socket to listen on, or takes the acceptor socket
// it got passed when restarted.
func (srv *graceServer) getListener(laddr string) (l net.Listener, err error) {
	if srv.isChild {
		var ptrOffset uint = 0
		if len(socketPtrOffsetMap) > 0 {
			ptrOffset = socketPtrOffsetMap[laddr]
			log.Println("laddr", laddr, "ptr offset", socketPtrOffsetMap[laddr])
		}

		f := os.NewFile(uintptr(3+ptrOffset), "")
		l, err = net.FileListener(f)
		if err != nil {
			err = fmt.Errorf("net.FileListener error: %v", err)
			return
		}
	} else {
		l, err = net.Listen(srv.Network, laddr)
		if err != nil {
			err = fmt.Errorf("net.Listen error: %v", err)
			return
		}
	}
	return
}

// handleSignals listens for os Signals and calls any hooked in function that the
// user had registered with the signal.
func (srv *graceServer) handleSignals() {
	var sig os.Signal

	signal.Notify(
		srv.sigChan,
		syscall.SIGHUP,
		syscall.SIGINT,
		syscall.SIGTERM,
	)

	pid := syscall.Getpid()
	for {
		sig = <-srv.sigChan
		srv.signalHooks(PRE_SIGNAL, sig)
		switch sig {
		case syscall.SIGHUP:
			log.Println(pid, "Received SIGHUP. forking.")
			err := srv.fork()
			if err != nil {
				log.Println("Fork err:", err)
			}
		case syscall.SIGINT:
			log.Println(pid, "Received SIGINT.")
			srv.shutdown()
		case syscall.SIGTERM:
			log.Println(pid, "Received SIGTERM.")
			srv.shutdown()
		default:
			log.Printf("Received %v: nothing i care about...\n", sig)
		}
		srv.signalHooks(POST_SIGNAL, sig)
	}
}

func (srv *graceServer) signalHooks(ppFlag int, sig os.Signal) {
	if _, notSet := srv.SignalHooks[ppFlag][sig]; !notSet {
		return
	}
	for _, f := range srv.SignalHooks[ppFlag][sig] {
		f()
	}
	return
}

// shutdown closes the listener so that no new connections are accepted. it also
// starts a goroutine that will hammer (stop all running requests) the server
// after DefaultTimeout.
func (srv *graceServer) shutdown() {
	if srv.state != STATE_RUNNING {
		return
	}

	srv.state = STATE_SHUTTING_DOWN
	if DefaultTimeout >= 0 {
		go srv.serverTimeout(DefaultTimeout)
	}
	err := srv.GraceListener.Close()
	if err != nil {
		log.Println(syscall.Getpid(), "Listener.Close() error:", err)
	} else {
		log.Println(syscall.Getpid(), srv.GraceListener.Addr(), "Listener closed.")
	}
}

// hammerTime forces the server to shutdown in a given timeout - whether it
// finished outstanding requests or not. if Read/WriteTimeout are not set or the
// max header size is very big a connection could hang...
//
// srv.Serve() will not return until all connections are served. this will
// unblock the srv.wg.Wait() in Serve() thus causing ListenAndServe(TLS) to
// return.
func (srv *graceServer) serverTimeout(d time.Duration) {
	defer func() {
		// we are calling srv.wg.Done() until it panics which means we called
		// Done() when the counter was already at 0 and we're done.
		// (and thus Serve() will return and the parent will exit)
		if r := recover(); r != nil {
			log.Println("WaitGroup at 0", r)
		}
	}()
	if srv.state != STATE_SHUTTING_DOWN {
		return
	}
	time.Sleep(d)
	log.Println("[STOP - Hammer Time] Forcefully shutting down parent")
	for {
		if srv.state == STATE_TERMINATE {
			break
		}
		srv.wg.Done()
	}
}

func (srv *graceServer) fork() (err error) {
	// only one server isntance should fork!
	regLock.Lock()
	defer regLock.Unlock()
	if runningServersForked {
		return
	}
	runningServersForked = true

	var files = make([]*os.File, len(runningServers))
	var orderArgs = make([]string, len(runningServers))
	// get the accessor socket fds for _all_ server instances
	for _, srvPtr := range runningServers {
		// introspect.PrintTypeDump(srvPtr.EndlessListener)
		switch srvPtr.GraceListener.(type) {
		case *graceListener:
			// normal listener
			files[socketPtrOffsetMap[srvPtr.Server.Addr]] = srvPtr.GraceListener.(*graceListener).File()
		default:
			// tls listener
			files[socketPtrOffsetMap[srvPtr.Server.Addr]] = srvPtr.tlsInnerListener.File()
		}
		orderArgs[socketPtrOffsetMap[srvPtr.Server.Addr]] = srvPtr.Server.Addr
	}

	log.Println(files)
	path := os.Args[0]
	var args []string
	if len(os.Args) > 1 {
		for _, arg := range os.Args[1:] {
			if arg == "-graceful" {
				break
			}
			args = append(args, arg)
		}
	}
	args = append(args, "-graceful")
	if len(runningServers) > 1 {
		args = append(args, fmt.Sprintf(`-socketorder=%s`, strings.Join(orderArgs, ",")))
		log.Println(args)
	}
	cmd := exec.Command(path, args...)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	cmd.ExtraFiles = files
	err = cmd.Start()
	if err != nil {
		log.Fatalf("Restart: Failed to launch, error: %v", err)
	}

	return
}

type graceListener struct {
	net.Listener
	stop    chan error
	stopped bool
	server  *graceServer
}

func (gl *graceListener) Accept() (c net.Conn, err error) {
	tc, err := gl.Listener.(*net.TCPListener).AcceptTCP()
	if err != nil {
		return
	}

	tc.SetKeepAlive(true)                  // see http.tcpKeepAliveListener
	tc.SetKeepAlivePeriod(3 * time.Minute) // see http.tcpKeepAliveListener

	c = graceConn{
		Conn:   tc,
		server: gl.server,
	}

	gl.server.wg.Add(1)
	return
}

func newGraceListener(l net.Listener, srv *graceServer) (el *graceListener) {
	el = &graceListener{
		Listener: l,
		stop:     make(chan error),
		server:   srv,
	}

	// Starting the listener for the stop signal here because Accept blocks on
	// el.Listener.(*net.TCPListener).AcceptTCP()
	// The goroutine will unblock it by closing the listeners fd
	go func() {
		_ = <-el.stop
		el.stopped = true
		el.stop <- el.Listener.Close()
	}()
	return
}

func (el *graceListener) Close() error {
	if el.stopped {
		return syscall.EINVAL
	}
	el.stop <- nil
	return <-el.stop
}

func (el *graceListener) File() *os.File {
	// returns a dup(2) - FD_CLOEXEC flag *not* set
	tl := el.Listener.(*net.TCPListener)
	fl, _ := tl.File()
	return fl
}

type graceConn struct {
	net.Conn
	server *graceServer
}

func (c graceConn) Close() error {
	c.server.wg.Done()
	return c.Conn.Close()
}