package worker

import (
	"bufio"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"syscall"
	"time"

	"golang.org/x/sys/unix"

	"github.com/codeskyblue/go-sh"
	"github.com/moby/moby/pkg/reexec"
)

type cgroupHook struct {
	emptyHook
	basePath  string
	baseGroup string
	created   bool
	subsystem string
	memLimit  MemBytes
}

func init () {
  reexec.Register("tunasync-exec", waitExec)
}

func waitExec () {
  binary, lookErr := exec.LookPath(os.Args[1])
  if lookErr != nil {
    panic(lookErr)
  }

  pipe := os.NewFile(3, "pipe")
  if pipe != nil {
    for {
      tmpBytes := make([]byte, 1)
      nRead, err := pipe.Read(tmpBytes)
      if err != nil {
        break
      }
      if nRead == 0 {
        break
      }
    }
    err := pipe.Close()
    if err != nil {
    }
  }

  args := os.Args[1:]
  env := os.Environ()
  execErr := syscall.Exec(binary, args, env)
  if execErr != nil {
    panic(execErr)
  }
  panic("Exec failed.")
}

func newCgroupHook(p mirrorProvider, basePath, baseGroup, subsystem string, memLimit MemBytes) *cgroupHook {
	if basePath == "" {
		basePath = "/sys/fs/cgroup"
	}
	if baseGroup == "" {
		baseGroup = "tunasync"
	}
	if subsystem == "" {
		subsystem = "cpu"
	}
	return &cgroupHook{
		emptyHook: emptyHook{
			provider: p,
		},
		basePath:  basePath,
		baseGroup: baseGroup,
		subsystem: subsystem,
	}
}

func (c *cgroupHook) preExec() error {
	c.created = true
	if err := sh.Command("cgcreate", "-g", c.Cgroup()).Run(); err != nil {
		return err
	}
	if c.subsystem != "memory" {
		return nil
	}
	if c.memLimit != 0 {
		gname := fmt.Sprintf("%s/%s", c.baseGroup, c.provider.Name())
		return sh.Command(
			"cgset", "-r",
			fmt.Sprintf("memory.limit_in_bytes=%d", c.memLimit.Value()),
			gname,
		).Run()
	}
	return nil
}

func (c *cgroupHook) postExec() error {
	err := c.killAll()
	if err != nil {
		logger.Errorf("Error killing tasks: %s", err.Error())
	}

	c.created = false
	return sh.Command("cgdelete", c.Cgroup()).Run()
}

func (c *cgroupHook) Cgroup() string {
	name := c.provider.Name()
	return fmt.Sprintf("%s:%s/%s", c.subsystem, c.baseGroup, name)
}

func (c *cgroupHook) killAll() error {
	if !c.created {
		return nil
	}
	name := c.provider.Name()

	readTaskList := func() ([]int, error) {
		taskList := []int{}
		taskFile, err := os.Open(filepath.Join(c.basePath, c.subsystem, c.baseGroup, name, "tasks"))
		if err != nil {
			return taskList, err
		}
		defer taskFile.Close()

		scanner := bufio.NewScanner(taskFile)
		for scanner.Scan() {
			pid, err := strconv.Atoi(scanner.Text())
			if err != nil {
				return taskList, err
			}
			taskList = append(taskList, pid)
		}
		return taskList, nil
	}

	for i := 0; i < 4; i++ {
		if i == 3 {
			return errors.New("Unable to kill all child tasks")
		}
		taskList, err := readTaskList()
		if err != nil {
			return err
		}
		if len(taskList) == 0 {
			return nil
		}
		for _, pid := range taskList {
			// TODO: deal with defunct processes
			logger.Debugf("Killing process: %d", pid)
			unix.Kill(pid, syscall.SIGKILL)
		}
		// sleep 10ms for the first round, and 1.01s, 2.01s, 3.01s for the rest
		time.Sleep(time.Duration(i)*time.Second + 10*time.Millisecond)
	}

	return nil
}