package cgroups

import (
	"bufio"
	"bytes"
	"fmt"
	"io/ioutil"
	"math"
	"os"
	"path/filepath"
	"strconv"
	"strings"

	"github.com/containers/podman/v3/pkg/rootless"
	systemdDbus "github.com/coreos/go-systemd/v22/dbus"
	"github.com/godbus/dbus/v5"
	spec "github.com/opencontainers/runtime-spec/specs-go"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
)

var (
	// ErrCgroupDeleted means the cgroup was deleted
	ErrCgroupDeleted = errors.New("cgroup deleted")
	// ErrCgroupV1Rootless means the cgroup v1 were attempted to be used in rootless environment
	ErrCgroupV1Rootless = errors.New("no support for CGroups V1 in rootless environments")
	ErrStatCgroup       = errors.New("no cgroup available for gathering user statistics")
)

// CgroupControl controls a cgroup hierarchy
type CgroupControl struct {
	cgroup2 bool
	path    string
	systemd bool
	// List of additional cgroup subsystems joined that
	// do not have a custom handler.
	additionalControllers []controller
}

// CPUUsage keeps stats for the CPU usage (unit: nanoseconds)
type CPUUsage struct {
	Kernel uint64
	Total  uint64
	PerCPU []uint64
}

// MemoryUsage keeps stats for the memory usage
type MemoryUsage struct {
	Usage uint64
	Limit uint64
}

// CPUMetrics keeps stats for the CPU usage
type CPUMetrics struct {
	Usage CPUUsage
}

// BlkIOEntry describes an entry in the blkio stats
type BlkIOEntry struct {
	Op    string
	Major uint64
	Minor uint64
	Value uint64
}

// BlkioMetrics keeps usage stats for the blkio cgroup controller
type BlkioMetrics struct {
	IoServiceBytesRecursive []BlkIOEntry
}

// MemoryMetrics keeps usage stats for the memory cgroup controller
type MemoryMetrics struct {
	Usage MemoryUsage
}

// PidsMetrics keeps usage stats for the pids cgroup controller
type PidsMetrics struct {
	Current uint64
}

// Metrics keeps usage stats for the cgroup controllers
type Metrics struct {
	CPU    CPUMetrics
	Blkio  BlkioMetrics
	Memory MemoryMetrics
	Pids   PidsMetrics
}

type controller struct {
	name    string
	symlink bool
}

type controllerHandler interface {
	Create(*CgroupControl) (bool, error)
	Apply(*CgroupControl, *spec.LinuxResources) error
	Destroy(*CgroupControl) error
	Stat(*CgroupControl, *Metrics) error
}

const (
	cgroupRoot = "/sys/fs/cgroup"
	// CPU is the cpu controller
	CPU = "cpu"
	// CPUAcct is the cpuacct controller
	CPUAcct = "cpuacct"
	// CPUset is the cpuset controller
	CPUset = "cpuset"
	// Memory is the memory controller
	Memory = "memory"
	// Pids is the pids controller
	Pids = "pids"
	// Blkio is the blkio controller
	Blkio = "blkio"
)

var handlers map[string]controllerHandler

func init() {
	handlers = make(map[string]controllerHandler)
	handlers[CPU] = getCPUHandler()
	handlers[CPUset] = getCpusetHandler()
	handlers[Memory] = getMemoryHandler()
	handlers[Pids] = getPidsHandler()
	handlers[Blkio] = getBlkioHandler()
}

// getAvailableControllers get the available controllers
func getAvailableControllers(exclude map[string]controllerHandler, cgroup2 bool) ([]controller, error) {
	if cgroup2 {
		return nil, fmt.Errorf("getAvailableControllers not implemented yet for cgroup v2")
	}

	infos, err := ioutil.ReadDir(cgroupRoot)
	if err != nil {
		return nil, err
	}
	controllers := []controller{}
	for _, i := range infos {
		name := i.Name()
		if _, found := exclude[name]; found {
			continue
		}
		c := controller{
			name:    name,
			symlink: !i.IsDir(),
		}
		controllers = append(controllers, c)
	}
	return controllers, nil
}

// getCgroupv1Path is a helper function to get the cgroup v1 path
func (c *CgroupControl) getCgroupv1Path(name string) string {
	return filepath.Join(cgroupRoot, name, c.path)
}

// createCgroupv2Path creates the cgroupv2 path and enables all the available controllers
func createCgroupv2Path(path string) (deferredError error) {
	if !strings.HasPrefix(path, cgroupRoot+"/") {
		return fmt.Errorf("invalid cgroup path %s", path)
	}
	content, err := ioutil.ReadFile(cgroupRoot + "/cgroup.controllers")
	if err != nil {
		return err
	}
	ctrs := bytes.Fields(content)
	res := append([]byte("+"), bytes.Join(ctrs, []byte(" +"))...)

	current := "/sys/fs"
	elements := strings.Split(path, "/")
	for i, e := range elements[3:] {
		current = filepath.Join(current, e)
		if i > 0 {
			if err := os.Mkdir(current, 0755); err != nil {
				if !os.IsExist(err) {
					return err
				}
			} else {
				// If the directory was created, be sure it is not left around on errors.
				defer func() {
					if deferredError != nil {
						os.Remove(current)
					}
				}()
			}
		}
		// We enable the controllers for all the path components except the last one.  It is not allowed to add
		// PIDs if there are already enabled controllers.
		if i < len(elements[3:])-1 {
			if err := ioutil.WriteFile(filepath.Join(current, "cgroup.subtree_control"), res, 0755); err != nil {
				return err
			}
		}
	}
	return nil
}

// initialize initializes the specified hierarchy
func (c *CgroupControl) initialize() (err error) {
	createdSoFar := map[string]controllerHandler{}
	defer func() {
		if err != nil {
			for name, ctr := range createdSoFar {
				if err := ctr.Destroy(c); err != nil {
					logrus.Warningf("error cleaning up controller %s for %s", name, c.path)
				}
			}
		}
	}()
	if c.cgroup2 {
		if err := createCgroupv2Path(filepath.Join(cgroupRoot, c.path)); err != nil {
			return errors.Wrapf(err, "error creating cgroup path %s", c.path)
		}
	}
	for name, handler := range handlers {
		created, err := handler.Create(c)
		if err != nil {
			return err
		}
		if created {
			createdSoFar[name] = handler
		}
	}

	if !c.cgroup2 {
		// We won't need to do this for cgroup v2
		for _, ctr := range c.additionalControllers {
			if ctr.symlink {
				continue
			}
			path := c.getCgroupv1Path(ctr.name)
			if err := os.MkdirAll(path, 0755); err != nil {
				return errors.Wrapf(err, "error creating cgroup path for %s", ctr.name)
			}
		}
	}

	return nil
}

func (c *CgroupControl) createCgroupDirectory(controller string) (bool, error) {
	cPath := c.getCgroupv1Path(controller)
	_, err := os.Stat(cPath)
	if err == nil {
		return false, nil
	}

	if !os.IsNotExist(err) {
		return false, err
	}

	if err := os.MkdirAll(cPath, 0755); err != nil {
		return false, errors.Wrapf(err, "error creating cgroup for %s", controller)
	}
	return true, nil
}

func readFileAsUint64(path string) (uint64, error) {
	data, err := ioutil.ReadFile(path)
	if err != nil {
		return 0, err
	}
	v := cleanString(string(data))
	if v == "max" {
		return math.MaxUint64, nil
	}
	ret, err := strconv.ParseUint(v, 10, 0)
	if err != nil {
		return ret, errors.Wrapf(err, "parse %s from %s", v, path)
	}
	return ret, nil
}

// New creates a new cgroup control
func New(path string, resources *spec.LinuxResources) (*CgroupControl, error) {
	cgroup2, err := IsCgroup2UnifiedMode()
	if err != nil {
		return nil, err
	}
	control := &CgroupControl{
		cgroup2: cgroup2,
		path:    path,
	}

	if !cgroup2 {
		controllers, err := getAvailableControllers(handlers, false)
		if err != nil {
			return nil, err
		}
		control.additionalControllers = controllers
	}

	if err := control.initialize(); err != nil {
		return nil, err
	}

	return control, nil
}

// NewSystemd creates a new cgroup control
func NewSystemd(path string) (*CgroupControl, error) {
	cgroup2, err := IsCgroup2UnifiedMode()
	if err != nil {
		return nil, err
	}
	control := &CgroupControl{
		cgroup2: cgroup2,
		path:    path,
		systemd: true,
	}
	return control, nil
}

// Load loads an existing cgroup control
func Load(path string) (*CgroupControl, error) {
	cgroup2, err := IsCgroup2UnifiedMode()
	if err != nil {
		return nil, err
	}
	control := &CgroupControl{
		cgroup2: cgroup2,
		path:    path,
		systemd: false,
	}
	if !cgroup2 {
		controllers, err := getAvailableControllers(handlers, false)
		if err != nil {
			return nil, err
		}
		control.additionalControllers = controllers
	}
	if !cgroup2 {
		for name := range handlers {
			p := control.getCgroupv1Path(name)
			if _, err := os.Stat(p); err != nil {
				if os.IsNotExist(err) {
					if rootless.IsRootless() {
						return nil, ErrCgroupV1Rootless
					}
					// compatible with the error code
					// used by containerd/cgroups
					return nil, ErrCgroupDeleted
				}
			}
		}
	}
	return control, nil
}

// CreateSystemdUnit creates the systemd cgroup
func (c *CgroupControl) CreateSystemdUnit(path string) error {
	if !c.systemd {
		return fmt.Errorf("the cgroup controller is not using systemd")
	}

	conn, err := systemdDbus.New()
	if err != nil {
		return err
	}
	defer conn.Close()

	return systemdCreate(path, conn)
}

// GetUserConnection returns an user connection to D-BUS
func GetUserConnection(uid int) (*systemdDbus.Conn, error) {
	return systemdDbus.NewConnection(func() (*dbus.Conn, error) {
		return dbusAuthConnection(uid, dbus.SessionBusPrivate)
	})
}

// CreateSystemdUserUnit creates the systemd cgroup for the specified user
func (c *CgroupControl) CreateSystemdUserUnit(path string, uid int) error {
	if !c.systemd {
		return fmt.Errorf("the cgroup controller is not using systemd")
	}

	conn, err := GetUserConnection(uid)
	if err != nil {
		return err
	}
	defer conn.Close()

	return systemdCreate(path, conn)
}

func dbusAuthConnection(uid int, createBus func(opts ...dbus.ConnOption) (*dbus.Conn, error)) (*dbus.Conn, error) {
	conn, err := createBus()
	if err != nil {
		return nil, err
	}

	methods := []dbus.Auth{dbus.AuthExternal(strconv.Itoa(uid))}

	err = conn.Auth(methods)
	if err != nil {
		conn.Close()
		return nil, err
	}
	if err := conn.Hello(); err != nil {
		return nil, err
	}

	return conn, nil
}

// Delete cleans a cgroup
func (c *CgroupControl) Delete() error {
	return c.DeleteByPath(c.path)
}

// rmDirRecursively delete recursively a cgroup directory.
// It differs from os.RemoveAll as it doesn't attempt to unlink files.
// On cgroupfs we are allowed only to rmdir empty directories.
func rmDirRecursively(path string) error {
	if err := os.Remove(path); err == nil || os.IsNotExist(err) {
		return nil
	}
	entries, err := ioutil.ReadDir(path)
	if err != nil {
		return err
	}
	for _, i := range entries {
		if i.IsDir() {
			if err := rmDirRecursively(filepath.Join(path, i.Name())); err != nil {
				return err
			}
		}
	}
	if err := os.Remove(path); err != nil {
		if !os.IsNotExist(err) {
			return errors.Wrapf(err, "remove %s", path)
		}
	}
	return nil
}

// DeleteByPathConn deletes the specified cgroup path using the specified
// dbus connection if needed.
func (c *CgroupControl) DeleteByPathConn(path string, conn *systemdDbus.Conn) error {
	if c.systemd {
		return systemdDestroyConn(path, conn)
	}
	if c.cgroup2 {
		return rmDirRecursively(filepath.Join(cgroupRoot, c.path))
	}
	var lastError error
	for _, h := range handlers {
		if err := h.Destroy(c); err != nil {
			lastError = err
		}
	}

	for _, ctr := range c.additionalControllers {
		if ctr.symlink {
			continue
		}
		p := c.getCgroupv1Path(ctr.name)
		if err := rmDirRecursively(p); err != nil {
			lastError = errors.Wrapf(err, "remove %s", p)
		}
	}
	return lastError
}

// DeleteByPath deletes the specified cgroup path
func (c *CgroupControl) DeleteByPath(path string) error {
	if c.systemd {
		conn, err := systemdDbus.New()
		if err != nil {
			return err
		}
		defer conn.Close()
		return c.DeleteByPathConn(path, conn)
	}
	return c.DeleteByPathConn(path, nil)
}

// Update updates the cgroups
func (c *CgroupControl) Update(resources *spec.LinuxResources) error {
	for _, h := range handlers {
		if err := h.Apply(c, resources); err != nil {
			return err
		}
	}
	return nil
}

// AddPid moves the specified pid to the cgroup
func (c *CgroupControl) AddPid(pid int) error {
	pidString := []byte(fmt.Sprintf("%d\n", pid))

	if c.cgroup2 {
		p := filepath.Join(cgroupRoot, c.path, "cgroup.procs")
		if err := ioutil.WriteFile(p, pidString, 0644); err != nil {
			return errors.Wrapf(err, "write %s", p)
		}
		return nil
	}

	names := make([]string, 0, len(handlers))
	for n := range handlers {
		names = append(names, n)
	}

	for _, c := range c.additionalControllers {
		if !c.symlink {
			names = append(names, c.name)
		}
	}

	for _, n := range names {
		// If we aren't using cgroup2, we won't write correctly to unified hierarchy
		if !c.cgroup2 && n == "unified" {
			continue
		}
		p := filepath.Join(c.getCgroupv1Path(n), "tasks")
		if err := ioutil.WriteFile(p, pidString, 0644); err != nil {
			return errors.Wrapf(err, "write %s", p)
		}
	}
	return nil
}

// Stat returns usage statistics for the cgroup
func (c *CgroupControl) Stat() (*Metrics, error) {
	m := Metrics{}
	found := false
	for _, h := range handlers {
		if err := h.Stat(c, &m); err != nil {
			if !os.IsNotExist(errors.Cause(err)) {
				return nil, err
			}
			logrus.Warningf("Failed to retrieve cgroup stats: %v", err)
			continue
		}
		found = true
	}
	if !found {
		return nil, ErrStatCgroup
	}
	return &m, nil
}

func readCgroup2MapPath(path string) (map[string][]string, error) {
	ret := map[string][]string{}
	f, err := os.Open(path)
	if err != nil {
		if os.IsNotExist(err) {
			return ret, nil
		}
		return nil, errors.Wrapf(err, "open file %s", path)
	}
	defer f.Close()
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := scanner.Text()
		parts := strings.Fields(line)
		if len(parts) < 2 {
			continue
		}
		ret[parts[0]] = parts[1:]
	}
	if err := scanner.Err(); err != nil {
		return nil, errors.Wrapf(err, "parsing file %s", path)
	}
	return ret, nil
}

func readCgroup2MapFile(ctr *CgroupControl, name string) (map[string][]string, error) {
	p := filepath.Join(cgroupRoot, ctr.path, name)

	return readCgroup2MapPath(p)
}
