package cgroup

import (
	"bufio"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"

	"linkfog.com/public/lib/cgroup/fs"
)

func GetContainerMemoryCgroupPath(pid int) (string, error) {
	if IsCgroup2() {
		return GetContainerCgroupPath(pid, "")
	}
	return GetContainerCgroupPath(pid, fs.MemorySubSystemName())
}

func GetContainerCPUCgroupPath(pid int) (string, error) {
	if IsCgroup2() {
		return GetContainerCgroupPath(pid, "")
	}
	return GetContainerCgroupPath(pid, fs.CPUSubSystemName())
}

func GetContainerIOCgroupPath(pid int) (string, error) {
	if IsCgroup2() {
		return GetContainerCgroupPath(pid, "")
	}
	return GetContainerCgroupPath(pid, fs.IOSubSystemName())
}

// 获取容器cgroup路径，当pid为-1时，代表进程自身，cgroup路径选择顺序如下：
// 1.主机视角，有hostPID权限：/proc/1/root/sys/fs/cgroup[/subsystem]/kubepods...
// 2.主机视角，挂载主机host：/host/sys/fs/cgroup[/subsystem]/kubepods...
// 3.容器视角，/proc/<pid>/root/sys/fs/cgroup[/subsystem]
func GetContainerCgroupPath(pid int, subsystem string) (string, error) {
	path, err := getContainerCgroupPathFromHost(pid, subsystem)
	if err == nil {
		return path, nil
	}

	path, err = getContainerCgroupPathFromContainer(pid, subsystem)
	if err == nil {
		return path, nil
	}

	return "", fmt.Errorf("unable to get container cgroup path")
}

// 主机视角，获取容器cgroup的特征
func GetContainerCgroupSpec(pid int, subsystem string) (string, error) {
	// 获取进程cgroup配置文件
	var pidCgroup string
	if pid == -1 {
		pidCgroup = "/proc/self/cgroup"
	} else {
		pidCgroup = filepath.Join("/proc", strconv.Itoa(pid), "cgroup")
	}

	// 解析进程cgroup配置文件，获取相对cgroup路径
	var relativeCgroupPath string
	var err error
	if IsCgroup2() {
		relativeCgroupPath, err = parseRelativeCgroupPathV2(pidCgroup)
	} else {
		relativeCgroupPath, err = parseRelativeCgroupPathV1(pidCgroup, subsystem)
	}
	return relativeCgroupPath, err
}

// 主机视角，获取容器cgroup路径
func getContainerCgroupPathFromHost(pid int, subsystem string) (string, error) {
	// 获取进程cgroup配置文件
	var pidCgroup string
	if pid == -1 {
		pidCgroup = "/proc/self/cgroup"
	} else {
		pidCgroup = filepath.Join("/proc", strconv.Itoa(pid), "cgroup")
	}

	// 解析进程cgroup配置文件，获取相对cgroup路径
	var relativeCgroupPath string
	var err error
	if IsCgroup2() {
		relativeCgroupPath, err = parseRelativeCgroupPathV2(pidCgroup)
	} else {
		relativeCgroupPath, err = parseRelativeCgroupPathV1(pidCgroup, subsystem)
	}
	if err != nil {
		return "", err
	}

	// 生成绝对cgroup路径
	cgroupPrefixs := []string{
		"/proc/1/root/sys/fs/cgroup",
		HostCgroup,
	}
	var absoluteCgroupPath string
	for _, prefix := range cgroupPrefixs {
		if IsCgroup2() {
			absoluteCgroupPath = filepath.Join(prefix, relativeCgroupPath)
		} else {
			absoluteCgroupPath = filepath.Join(prefix, subsystem, relativeCgroupPath)
		}

		if _, err := os.Stat(absoluteCgroupPath); err == nil {
			return absoluteCgroupPath, nil
		}
	}

	return "", fmt.Errorf("unable to get container cgroup path from host")
}

// 容器视角，获取容器cgroup路径
func getContainerCgroupPathFromContainer(pid int, subsystem string) (string, error) {
	var absoluteCgroupPath string
	if pid == -1 {
		absoluteCgroupPath = "/proc/self/root/sys/fs/cgroup"
	} else {
		absoluteCgroupPath = filepath.Join("/proc", strconv.Itoa(pid), "root/sys/fs/cgroup")
	}

	if !IsCgroup2() {
		absoluteCgroupPath = filepath.Join(absoluteCgroupPath, subsystem)
	}

	if _, err := os.Stat(absoluteCgroupPath); err == nil {
		return absoluteCgroupPath, nil
	}

	return "", fmt.Errorf("unable to get container cgroup path from container")
}

func parseRelativeCgroupPathV1(path string, subsystem string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()

	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		if strings.Contains(scanner.Text(), subsystem) {
			tokens := strings.SplitN(scanner.Text(), ":", 3)
			if len(tokens) == 3 {
				return tokens[2], nil
			}
			break
		}
	}
	return "", fmt.Errorf("unable to find subsystem(%s) relative cgroup path "+
		"in container cgroup file", subsystem)
}

func parseRelativeCgroupPathV2(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()

	reg := regexp.MustCompile("([0-9a-z]){64}")
	relativePath := ""
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		tokens := strings.SplitN(scanner.Text(), ":", 3)
		if len(tokens) == 3 {
			// example: "0::/kubepods/besteffort/podad1189b4-15b6-4ee5-b509-08..."
			if strings.HasPrefix(tokens[2], "/kubepods") {
				return tokens[2], nil
			}
			// 当找不到/kubepods时，用于兜底
			if relativePath == "" && reg.FindString(tokens[2]) != "" {
				relativePath = tokens[2]
			}
		}
	}

	if relativePath != "" {
		return relativePath, nil
	}

	return "", fmt.Errorf("unable to find relative cgroup path in container cgroup file")
}