package monitor_daemon

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"os/signal"
	"path/filepath"
	"strings"
	"syscall"
	"time"

	"linkfog.com/public/lib/common"
	"linkfog.com/public/lib/file"
	"linkfog.com/public/lib/l"
)

const (
	defaultTimerInterval time.Duration = 60 * time.Second
	minTimerInterval     time.Duration = 10 * time.Second
)

type IsProcAbnormalCallback func() bool
type ForwardSignalType int

const (
	NoForwardSignal         ForwardSignalType = iota //不转发信号
	ForwardSignalChild                               //转发信号给子进程
	ForwardSignalChildGroup                          //转发信号给子进程所在进程组

	ForwardSignalInvalid //无效配置类型
)

type MonitorDaemon struct {
	signalSize        int
	forwardSignalType ForwardSignalType

	interval        time.Duration
	maxRetryTimes   int
	agentBackupPath string
	restartInterval *restartInterval
	cmdline         string
	childPid        int
	agentMd5        string
	cmdline0        string

	isProcAbnormalCallback IsProcAbnormalCallback
}

type MonitorDaemonOpt func(*MonitorDaemon)

func WithSignalSize(size int) MonitorDaemonOpt {
	return func(m *MonitorDaemon) {
		m.signalSize = size
	}
}

// WithMaxInterval 设置最大的重启间隔，设置后的重启时间间隔可以累增，防止频繁重启
func WithMaxInterval(maxInterval time.Duration) MonitorDaemonOpt {
	return func(m *MonitorDaemon) {
		if maxInterval > minTimerInterval {
			m.restartInterval.setMaxInterval(maxInterval)
		}
	}
}

// WithIncrInterval 设置每次累增的时间间隔
func WithIncrInterval(incrInterval time.Duration) MonitorDaemonOpt {
	return func(m *MonitorDaemon) {
		m.restartInterval.setIncr(incrInterval)
	}
}

func WithMaxRetryTimes(maxRetryTimes int) MonitorDaemonOpt {
	return func(m *MonitorDaemon) {
		m.maxRetryTimes = maxRetryTimes
	}
}

func WithAgentBackupPath(path string) MonitorDaemonOpt {
	return func(m *MonitorDaemon) {
		m.agentBackupPath = path
	}
}

func WithForwardSignalType(typeF ForwardSignalType) MonitorDaemonOpt {
	return func(m *MonitorDaemon) {
		if typeF < ForwardSignalInvalid && typeF > NoForwardSignal {
			m.forwardSignalType = typeF
		}
	}
}

func WithTimerInterval(interval time.Duration) MonitorDaemonOpt {
	return func(m *MonitorDaemon) {
		if interval >= minTimerInterval {
			m.interval = interval
		} else {
			m.interval = minTimerInterval
			l.Warnf("%v is less than minTimerInterval(%v), use %v", interval, minTimerInterval, minTimerInterval)
		}
	}
}

func WithIsProcAbnormalCallback(callback IsProcAbnormalCallback) MonitorDaemonOpt {
	return func(m *MonitorDaemon) {
		m.isProcAbnormalCallback = callback
	}
}

//实现容器内进程的监控与管理，上层调用前，需开启独立的日志功能
/*
* 1. 启动进程：
*	a. 新进程加入独立进程组，用于信号转发;
*	b. 新进程标准输入输出与当前进程一样，保证kubectl可以拿到日志
* 2. 进程监控：定时监控子进程，如果进程不存在负责启动进程。（监控子进程，最小间隔时间为1分钟）
* 3. 信号处理和转发（可配置两种转发模式）：
*	a. ForwardSignalChild: 转发信号到子进程
*	b. ForwardSignalChildGroup: 转发信号到子进程组
*	c. 目前不实现转发信号到容器内所有进程，风险过高。
* 4. 回收孙子进程，防止产生僵尸进程：
*	a. 当monitor是容器内1号进程，可回收容器内所有进程。
*	b. 非容器1号进程时，只处理子进程退出信号。
* 5. 杀死子进程或子进程组
*	a. 提供回调函数注册机制，monitor定时调用此函数，根据返回值判断是否杀死子进程
*	b. 若配置了ForwardSignalChildGroup，则杀死整个子进程组
 */
func New(cmdline string, opts ...MonitorDaemonOpt) (*MonitorDaemon, error) {
	if cmdline == "" || !filepath.IsAbs(cmdline) {
		return nil, fmt.Errorf("cmdline is invalid")
	}

	m := MonitorDaemon{
		signalSize:        10,
		forwardSignalType: NoForwardSignal,

		interval:        defaultTimerInterval,
		restartInterval: newRestartInterval(),
		cmdline:         cmdline,
		childPid:        0,

		isProcAbnormalCallback: nil,
	}

	for _, opt := range opts {
		opt(&m)
	}

	m.cmdline0 = strings.Split(m.cmdline, " ")[0]
	md5, err := file.GetFileMD5(m.cmdline0)
	if err != nil {
		l.Errorf("calculation of agent MD5(%s) failed err:%s", m.cmdline0, err)
	} else {
		m.agentMd5 = md5
	}

	//第一次启动进程
	err = m.startProcess()
	if err != nil {
		l.Errorf("start child process failed %s err:%v", cmdline, err)
		return nil, err
	}

	return &m, nil
}

// 此函数是阻塞的，默认不返回。支持以ä‹信号注册和转发：syscall.SIGINT, syscall.SIGTERM, syscall.SIGKILL
func (m *MonitorDaemon) Run(signals ...os.Signal) {
	sigs := []os.Signal{
		syscall.SIGCHLD,
	}

	supportSignal := map[syscall.Signal]bool{
		syscall.SIGINT:  true,
		syscall.SIGTERM: true,
		syscall.SIGKILL: true,
	}

	for _, sig := range signals {
		if support, ok := supportSignal[sig.(syscall.Signal)]; ok && support {
			sigs = append(sigs, sig)
		}
	}

	m.runWithSignal(sigs)
}

func (m *MonitorDaemon) runWithSignal(sigs []os.Signal) {
	l.Infof("tick: %+v", m.interval)
	tick := time.NewTimer(m.interval)
	defer tick.Stop()

	var notifications = make(chan os.Signal, m.signalSize)
	signal.Notify(notifications, sigs...)

	errRetryTimes := 0
	for {
		select {
		case sig := <-notifications:
			if sig == syscall.SIGCHLD {
				// 当子进程收到SIGSTOP和SIGCONT信号时，monitor会接收到SIGCHLD，因此使用debug日志记录
				l.Debug("monitor_daemon recv sig, sig:", sig)
				for {
					killPid, err := reapChildrenSig()
					if err != nil {
						l.Errorf("monitor_daemon reapChildrenSig error:%v", err)
						break
					} else if killPid <= 0 {
						//当子进程收到SIGSTOP和SIGCONT信号时，wait4获取到killPid为0,表示子进程状态未发生改变
						break
					}

					//如果wait的pid是子进程，并且开启了转发信号开关，则进行信号发送到子进程所在的进程组
					if killPid == m.childPid && ForwardSignalChildGroup == m.forwardSignalType {
						l.Infof("monitor_daemon forwarded signal SIGCHLD to children group %d", m.childPid)
						err := syscall.Kill(-m.childPid, syscall.SIGTERM)
						if err != nil {
							l.Errorf("monitor_daemon forwarded signal SIGCHLD, send syscall.SIGTERM to children group %d, err %v", m.childPid, err)
						}
					} else {
						l.Infof("monitor_daemon not forwarded signal SIGCHLD, killPid: %d, childPid: %d", killPid, m.childPid)
					}
				}
			} else {
				l.Info("monitor_daemon recv sig, sig:", sig)
				//TODO: signal check
				if ForwardSignalChild == m.forwardSignalType {
					l.Infof("forwarded signal %d to children %d", sig, m.childPid)
					err := syscall.Kill(m.childPid, sig.(syscall.Signal))
					if err != nil {
						l.Errorf("forwarded signal %d to children %d, err %v", sig, m.childPid, err)
					}
				} else if ForwardSignalChildGroup == m.forwardSignalType {
					l.Infof("forwarded signal %d to children group %d", sig, m.childPid)
					err := syscall.Kill(-m.childPid, sig.(syscall.Signal))
					if err != nil {
						l.Errorf("forwarded signal %d to children group %d, err %v", sig, m.childPid, err)
					}
				}

				l.Infof("exit monitor_daemon pid: %d, child pid: %d, signal: %d", os.Getpid(), m.childPid, sig)
				return
			}
		case <-tick.C:
			isAlive := m.monitorProcess()

			// 时间间隔未达到允许的时间间隔
			if !isAlive && !m.restartInterval.isNeedStart() {
				l.Infof("process will restart, curInterval=%s last=%s", m.restartInterval.GetCurInterval(),
					m.restartInterval.GetLastStart().Format("2006-01-02 15:04:05"))
			}

			if !isAlive && m.restartInterval.isNeedStart() {

				md5, err := file.GetFileMD5(m.cmdline0)
				if err != nil {
					l.Errorf("calculation of agent MD5(%s) failed err:%s", m.cmdline0, err)
				}
				err = m.startProcess()
				if err != nil {
					// 异常情况，直接无法启动，进行回滚操作
					errRetryTimes++
					l.Errorf("monitorProcess start child process failed %s, errRetryTimes:%d, err:%v", m.cmdline, errRetryTimes, err)
					if md5 != m.agentMd5 && errRetryTimes > m.maxRetryTimes {
						m.rollbackForAbnormalCase()
						errRetryTimes = 0
					}
				} else {
					if md5 == m.agentMd5 {
						errRetryTimes++
						// 异常情况，启动几秒后停止，进行回滚操作
						if errRetryTimes > m.maxRetryTimes {
							m.rollbackForAbnormalCase()
							errRetryTimes = 0
						}
					} else {
						m.agentMd5 = md5
					}
					l.Infof("monitorProcess start child process success pid: %d, errRetryTimes:%d", m.childPid, errRetryTimes)
				}
				m.restartInterval.setLastStart()
			}

			//当回调返回true时，进程异常，直接杀死子进程或子进程组
			if isAlive && m.isProcAbnormalCallback != nil {
				isAbnormal := m.isProcAbnormalCallback()
				if isAbnormal {
					m.killProcess()
				}
			}

			tick.Reset(m.interval)
		}
	}
}

func (m *MonitorDaemon) killProcess() {
	pid := m.childPid
	if pid != 0 {
		childExec := getProcExec(fmt.Sprintf("%d", pid))
		if strings.HasPrefix(m.cmdline, childExec) {
			killPid := m.childPid
			if ForwardSignalChildGroup == m.forwardSignalType {
				killPid = -m.childPid
				l.Infof("killProcess child process forwarded signal SIGTERM to group %d", m.childPid)
			}

			l.Infof("killProcess child process kill SIGTERM, pid: %d, exec:%s, cmdline: %s", m.childPid, childExec, m.cmdline)
			err := syscall.Kill(killPid, syscall.SIGTERM)
			if err != nil {
				l.Errorf("killProcess child process kill SIGTERM error: %v", err)
			}
		} else {
			l.Errorf("killProcess child process exec is not exist, pid: %d, exec:%s, cmdline: %s", m.childPid, childExec, m.cmdline)
		}
	} else {
		l.Errorf("killProcess child process pid is not exist, pid: %d, cmdline: %s", m.childPid, m.cmdline)
	}
}

func (m *MonitorDaemon) monitorProcess() bool {
	pid := m.childPid
	if pid != 0 {
		childExec := getProcExec(fmt.Sprintf("%d", pid))
		if strings.HasPrefix(m.cmdline, childExec) {
			err := syscall.Kill(pid, 0)
			if err != nil {
				l.Errorf("monitorProcess child process kill 0 error: %v, pid: %d, exec:%s, cmdline: %s", err, m.childPid, childExec, m.cmdline)
			} else {
				l.Infof("monitorProcess child process is alive, pid: %d, exec:%s, cmdline: %s", m.childPid, childExec, m.cmdline)
				return true
			}
		} else {
			l.Errorf("monitorProcess child process is not exist, pid: %d, exec:%s, cmdline: %s", m.childPid, childExec, m.cmdline)
		}
	}
	return false
}

func (m *MonitorDaemon) startProcess() error {
	cmd, err := startProc(m.cmdline)
	if err != nil {
		return err
	}

	if cmd.Process != nil {
		m.childPid = cmd.Process.Pid
	}

	return nil
}

func getProcExec(pid string) string {
	return common.ReadLink("/proc/" + pid + "/exe")
}

func startProc(cmdline string) (*exec.Cmd, error) {
	cmd := exec.Command("/bin/bash", "-c", cmdline)

	//设置子进程加入独立进程组，供父进程转发信号用
	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}

	// 设置子进程的标准输出为系统标准输出，保证kubectl可以拿到日志
	// 捕获子进程的标准错误，用日志库输出（既保存到持久化文件，又打印到标准输出），若捕获失败，则设置为系统标准错误
	cmd.Stdout = os.Stdout
	stderrReader, err := cmd.StderrPipe()
	if err != nil {
		l.Error("cmd create stderr pipe err:", err)
		cmd.Stderr = os.Stderr
	} else {
		go readStderr(stderrReader)
	}

	err = cmd.Start()
	if err != nil {
		return nil, err
	}

	return cmd, nil
}

// 容器1号进程时生效，用于回收儿子和孙子进程。
// 警告：
// 警告：
// 警告：不可与其他带wait操作的功能同时使用
func reapChildrenSig() (int, error) {
	pid := -1 //wait all sub process
	opts := syscall.WNOHANG
	var err error = nil

	var wstatus syscall.WaitStatus

	/*
	 *  Reap 'em, so that zombies don't accumulate.
	 *  Plants vs. Zombies!!
	 */
	pid, err = syscall.Wait4(pid, &wstatus, opts, nil)
	for syscall.EINTR == err {
		pid, err = syscall.Wait4(pid, &wstatus, opts, nil)
	}

	if pid > 0 {
		l.Infof("reaper cleanup: pid=%d, wstatus=%+v, msg=%v",
			pid, wstatus, waitStatusToError(wstatus))
	}

	return pid, err
} /*   End of function  reapChildren.  */

func waitStatusToError(wstatus syscall.WaitStatus) error {
	switch {
	case wstatus.Exited():
		es := wstatus.ExitStatus()
		if es == 0 {
			return nil
		}
		return errors.New(fmt.Sprint(es))
	case wstatus.Signaled():
		msg := fmt.Sprintf("signaled %v", wstatus.Signal())
		if wstatus.CoreDump() {
			msg += " (core dumped)"
		}
		return errors.New(msg)
	case wstatus.Stopped():
		msg := fmt.Sprintf("stopped %v", wstatus.StopSignal())
		trap := wstatus.TrapCause()
		if trap != -1 {
			msg += fmt.Sprintf(" (trapped %v)", trap)
		}
		return errors.New(msg)
	default:
		return fmt.Errorf("unknown WaitStatus %d", wstatus)
	}
}

func readStderr(stderrReader io.Reader) {
	scanner := bufio.NewScanner(stderrReader)
	for scanner.Scan() {
		stderrData := scanner.Text()
		if stderrData != "" {
			l.Error(stderrData)
		}
	}
	if err := scanner.Err(); err != nil {
		l.Error("read stderr err:", err)
	}
}

func (m *MonitorDaemon) rollbackForAbnormalCase() {
	if _, err := os.Stat(m.agentBackupPath); err == nil || !os.IsNotExist(err) {
		if m.cmdline0 != "" {
			err := os.Rename(m.agentBackupPath, m.cmdline0)
			if err != nil {
				l.Errorf("monitorProcess rollback agent process failed err:%v", err)
			} else {
				md5, err := file.GetFileMD5(m.cmdline0)
				if err != nil {
					l.Errorf("calculation of agent MD5(%s) failed err:%s", m.cmdline0, err)
				} else {
					m.agentMd5 = md5
				}
				l.Infof("monitorProcess rollback agent process successful md5:%s", md5)
			}
		}
	}
}