/*
   Copyright The containerd Authors.

   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.
*/

package runc

import (
	"os/exec"
	"syscall"
	"time"
)

var Monitor ProcessMonitor = &defaultMonitor{}

type Exit struct {
	Timestamp time.Time
	Pid       int
	Status    int
}

// ProcessMonitor is an interface for process monitoring
//
// It allows daemons using go-runc to have a SIGCHLD handler
// to handle exits without introducing races between the handler
// and go's exec.Cmd
// These methods should match the methods exposed by exec.Cmd to provide
// a consistent experience for the caller
type ProcessMonitor interface {
	Start(*exec.Cmd) (chan Exit, error)
	Wait(*exec.Cmd, chan Exit) (int, error)
}

type defaultMonitor struct {
}

func (m *defaultMonitor) Start(c *exec.Cmd) (chan Exit, error) {
	if err := c.Start(); err != nil {
		return nil, err
	}
	ec := make(chan Exit, 1)
	go func() {
		var status int
		if err := c.Wait(); err != nil {
			status = 255
			if exitErr, ok := err.(*exec.ExitError); ok {
				if ws, ok := exitErr.Sys().(syscall.WaitStatus); ok {
					status = ws.ExitStatus()
				}
			}
		}
		ec <- Exit{
			Timestamp: time.Now(),
			Pid:       c.Process.Pid,
			Status:    status,
		}
		close(ec)
	}()
	return ec, nil
}

func (m *defaultMonitor) Wait(c *exec.Cmd, ec chan Exit) (int, error) {
	e := <-ec
	return e.Status, nil
}