package main

import (
    "fmt"
    "io/ioutil"
    "os"
    "os/exec"
)

type DaemonExec struct {
    cmd      *exec.Cmd
    lockFile string
    running  bool
}

func NewDaemonExec(cmd []string, lockFile string) *DaemonExec {
    if lockFile == "" {
        lockFile = ".tmp.daemon.lock"
    }
    return &DaemonExec{
        cmd:      exec.Command(cmd[0], cmd[1:]...),
        lockFile: lockFile,
    }
}

func (d *DaemonExec) Start() error {
    if d.cmd == nil {
        return fmt.Errorf("cmd is nil")
    }

    d.cmd.Stdout = os.Stdout
    d.cmd.Stderr = os.Stderr

    err := d.cmd.Start()

    if err != nil {
        return fmt.Errorf("start cmd failed: %v", err)
    }

    err = ioutil.WriteFile(d.lockFile, []byte(
        fmt.Sprintf("%d", d.cmd.Process.Pid)), 0644)
    if err != nil {
        return fmt.Errorf("write lock file failed: %v", err)
    }
    return nil
}

func (d *DaemonExec) Kill() error {
    if d.cmd == nil {
        return fmt.Errorf("cmd is nil")
    }
    err := d.cmd.Process.Kill()
    if err != nil {
        return fmt.Errorf("kill cmd failed: %v", err)
    }
    err = os.Remove(d.lockFile)
    if err != nil {
        return fmt.Errorf("remove lock file failed: %v", err)
    }
    return nil
}

func (d *DaemonExec) RunWithExec(cmd []string) error {
    if d.running {
        return fmt.Errorf("daemon is running")
    }

    d.cmd = exec.Command(cmd[0], cmd[1:]...)

    err := d.cmd.Start()
    if err != nil {
        return fmt.Errorf("start cmd failed: %v", err)
    }

    for {
        if d.cmd.ProcessState != nil {
            break
        }
    }

    return nil
}

func main() {
    if len(os.Args) < 2 {
        fmt.Printf("Usage: %s [command]\n", os.Args[0])
        os.Exit(1)
    }
    d := NewDaemonExec(os.Args[1:], "")
    err := d.Start()
    if err != nil {
        fmt.Printf("start daemon failed: %v\n", err)
        os.Exit(1)
    }
    fmt.Printf("start daemon success\n")

    fmt.Println("press any key to kill daemon")

    var s string
    _, err = fmt.Scanln(&s)
    if err != nil {
        fmt.Printf("scan input failed: %v\n", err)
    }

    err = d.Kill()
    if err != nil {
        fmt.Printf("kill daemon failed: %v\n", err)
        os.Exit(1)
    }
    fmt.Printf("kill daemon success\n")

}