// +build linux

package systemd

import (
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"

	systemdDbus "github.com/coreos/go-systemd/dbus"
	systemdUtil "github.com/coreos/go-systemd/util"
	"github.com/godbus/dbus"
	"github.com/opencontainers/runc/libcontainer/cgroups"
	"github.com/opencontainers/runc/libcontainer/cgroups/fs"
	"github.com/opencontainers/runc/libcontainer/configs"
)

type Manager struct {
	mu      sync.Mutex
	Cgroups *configs.Cgroup
	Paths   map[string]string
}

type subsystem interface {
	// Returns the stats, as 'stats', corresponding to the cgroup under 'path'.
	GetStats(path string, stats *cgroups.Stats) error
	// Set the cgroup represented by cgroup.
	Set(path string, cgroup *configs.Cgroup) error
}

var subsystems = map[string]subsystem{
	"devices":      &fs.DevicesGroup{},
	"memory":       &fs.MemoryGroup{},
	"cpu":          &fs.CpuGroup{},
	"cpuset":       &fs.CpusetGroup{},
	"cpuacct":      &fs.CpuacctGroup{},
	"blkio":        &fs.BlkioGroup{},
	"hugetlb":      &fs.HugetlbGroup{},
	"perf_event":   &fs.PerfEventGroup{},
	"freezer":      &fs.FreezerGroup{},
	"net_prio":     &fs.NetPrioGroup{},
	"net_cls":      &fs.NetClsGroup{},
	"name=systemd": &fs.NameGroup{},
}

const (
	testScopeWait = 4
)

var (
	connLock                        sync.Mutex
	theConn                         *systemdDbus.Conn
	hasStartTransientUnit           bool
	hasTransientDefaultDependencies bool
)

func newProp(name string, units interface{}) systemdDbus.Property {
	return systemdDbus.Property{
		Name:  name,
		Value: dbus.MakeVariant(units),
	}
}

func UseSystemd() bool {
	if !systemdUtil.IsRunningSystemd() {
		return false
	}

	connLock.Lock()
	defer connLock.Unlock()

	if theConn == nil {
		var err error
		theConn, err = systemdDbus.New()
		if err != nil {
			return false
		}

		// Assume we have StartTransientUnit
		hasStartTransientUnit = true

		// But if we get UnknownMethod error we don't
		if _, err := theConn.StartTransientUnit("test.scope", "invalid", nil, nil); err != nil {
			if dbusError, ok := err.(dbus.Error); ok {
				if dbusError.Name == "org.freedesktop.DBus.Error.UnknownMethod" {
					hasStartTransientUnit = false
					return hasStartTransientUnit
				}
			}
		}

		// Ensure the scope name we use doesn't exist. Use the Pid to
		// avoid collisions between multiple libcontainer users on a
		// single host.
		scope := fmt.Sprintf("libcontainer-%d-systemd-test-default-dependencies.scope", os.Getpid())
		testScopeExists := true
		for i := 0; i <= testScopeWait; i++ {
			if _, err := theConn.StopUnit(scope, "replace", nil); err != nil {
				if dbusError, ok := err.(dbus.Error); ok {
					if strings.Contains(dbusError.Name, "org.freedesktop.systemd1.NoSuchUnit") {
						testScopeExists = false
						break
					}
				}
			}
			time.Sleep(time.Millisecond)
		}

		// Bail out if we can't kill this scope without testing for DefaultDependencies
		if testScopeExists {
			return hasStartTransientUnit
		}

		// Assume StartTransientUnit on a scope allows DefaultDependencies
		hasTransientDefaultDependencies = true
		ddf := newProp("DefaultDependencies", false)
		if _, err := theConn.StartTransientUnit(scope, "replace", []systemdDbus.Property{ddf}, nil); err != nil {
			if dbusError, ok := err.(dbus.Error); ok {
				if strings.Contains(dbusError.Name, "org.freedesktop.DBus.Error.PropertyReadOnly") {
					hasTransientDefaultDependencies = false
				}
			}
		}

		// Not critical because of the stop unit logic above.
		theConn.StopUnit(scope, "replace", nil)
	}
	return hasStartTransientUnit
}

func getIfaceForUnit(unitName string) string {
	if strings.HasSuffix(unitName, ".scope") {
		return "Scope"
	}
	if strings.HasSuffix(unitName, ".service") {
		return "Service"
	}
	return "Unit"
}

func (m *Manager) Apply(pid int) error {
	var (
		c          = m.Cgroups
		unitName   = getUnitName(c)
		slice      = "system.slice"
		properties []systemdDbus.Property
	)

	if c.Parent != "" {
		slice = c.Parent
	}

	properties = append(properties,
		systemdDbus.PropSlice(slice),
		systemdDbus.PropDescription("docker container "+c.Name),
		newProp("PIDs", []uint32{uint32(pid)}),
		newProp("Delegate", true),
	)

	// Always enable accounting, this gets us the same behaviour as the fs implementation,
	// plus the kernel has some problems with joining the memory cgroup at a later time.
	properties = append(properties,
		newProp("MemoryAccounting", true),
		newProp("CPUAccounting", true),
		newProp("BlockIOAccounting", true))

	if hasTransientDefaultDependencies {
		properties = append(properties,
			newProp("DefaultDependencies", false))
	}

	if c.Memory != 0 {
		properties = append(properties,
			newProp("MemoryLimit", uint64(c.Memory)))
	}

	if c.CpuShares != 0 {
		properties = append(properties,
			newProp("CPUShares", uint64(c.CpuShares)))
	}

	if c.BlkioWeight != 0 {
		properties = append(properties,
			newProp("BlockIOWeight", uint64(c.BlkioWeight)))
	}

	// We need to set kernel memory before processes join cgroup because
	// kmem.limit_in_bytes can only be set when the cgroup is empty.
	// And swap memory limit needs to be set after memory limit, only
	// memory limit is handled by systemd, so it's kind of ugly here.
	if c.KernelMemory > 0 {
		if err := setKernelMemory(c); err != nil {
			return err
		}
	}

	if _, err := theConn.StartTransientUnit(unitName, "replace", properties, nil); err != nil {
		return err
	}

	if err := joinCgroups(c, pid); err != nil {
		return err
	}

	paths := make(map[string]string)
	for sysname := range subsystems {
		subsystemPath, err := getSubsystemPath(m.Cgroups, sysname)
		if err != nil {
			// Don't fail if a cgroup hierarchy was not found, just skip this subsystem
			if cgroups.IsNotFound(err) {
				continue
			}
			return err
		}
		paths[sysname] = subsystemPath
	}
	m.Paths = paths

	if paths["cpu"] != "" {
		if err := fs.CheckCpushares(paths["cpu"], c.CpuShares); err != nil {
			return err
		}
	}

	return nil
}

func (m *Manager) Destroy() error {
	m.mu.Lock()
	defer m.mu.Unlock()
	theConn.StopUnit(getUnitName(m.Cgroups), "replace", nil)
	if err := cgroups.RemovePaths(m.Paths); err != nil {
		return err
	}
	m.Paths = make(map[string]string)
	return nil
}

func (m *Manager) GetPaths() map[string]string {
	m.mu.Lock()
	paths := m.Paths
	m.mu.Unlock()
	return paths
}

func writeFile(dir, file, data string) error {
	// Normally dir should not be empty, one case is that cgroup subsystem
	// is not mounted, we will get empty dir, and we want it fail here.
	if dir == "" {
		return fmt.Errorf("no such directory for %s.", file)
	}
	return ioutil.WriteFile(filepath.Join(dir, file), []byte(data), 0700)
}

func join(c *configs.Cgroup, subsystem string, pid int) (string, error) {
	path, err := getSubsystemPath(c, subsystem)
	if err != nil {
		return "", err
	}
	if err := os.MkdirAll(path, 0755); err != nil {
		return "", err
	}
	if err := writeFile(path, "cgroup.procs", strconv.Itoa(pid)); err != nil {
		return "", err
	}

	return path, nil
}

// systemd represents slice heirarchy using `-`, so we need to follow suit when
// generating the path of slice. Essentially, test-a-b.slice becomes
// test.slice/test-a.slice/test-a-b.slice.
func expandSlice(slice string) (string, error) {
	suffix := ".slice"
	// Name has to end with ".slice", but can't be just ".slice".
	if len(slice) < len(suffix) || !strings.HasSuffix(slice, suffix) {
		return "", fmt.Errorf("invalid slice name: %s", slice)
	}

	// Path-separators are not allowed.
	if strings.Contains(slice, "/") {
		return "", fmt.Errorf("invalid slice name: %s", slice)
	}

	var path, prefix string
	sliceName := strings.TrimSuffix(slice, suffix)
	for _, component := range strings.Split(sliceName, "-") {
		// test--a.slice isn't permitted, nor is -test.slice.
		if component == "" {
			return "", fmt.Errorf("invalid slice name: %s", slice)
		}

		// Append the component to the path and to the prefix.
		path += prefix + component + suffix + "/"
		prefix += component + "-"
	}

	return path, nil
}

func getSubsystemPath(c *configs.Cgroup, subsystem string) (string, error) {
	mountpoint, err := cgroups.FindCgroupMountpoint(subsystem)
	if err != nil {
		return "", err
	}

	initPath, err := cgroups.GetInitCgroupDir(subsystem)
	if err != nil {
		return "", err
	}

	slice := "system.slice"
	if c.Parent != "" {
		slice = c.Parent
	}

	slice, err = expandSlice(slice)
	if err != nil {
		return "", err
	}

	return filepath.Join(mountpoint, initPath, slice, getUnitName(c)), nil
}

func (m *Manager) Freeze(state configs.FreezerState) error {
	path, err := getSubsystemPath(m.Cgroups, "freezer")
	if err != nil {
		return err
	}

	prevState := m.Cgroups.Freezer
	m.Cgroups.Freezer = state

	freezer := subsystems["freezer"]
	err = freezer.Set(path, m.Cgroups)
	if err != nil {
		m.Cgroups.Freezer = prevState
		return err
	}

	return nil
}

func (m *Manager) GetPids() ([]int, error) {
	path, err := getSubsystemPath(m.Cgroups, "devices")
	if err != nil {
		return nil, err
	}
	return cgroups.GetPids(path)
}

func (m *Manager) GetStats() (*cgroups.Stats, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	stats := cgroups.NewStats()
	for name, path := range m.Paths {
		sys, ok := subsystems[name]
		if !ok || !cgroups.PathExists(path) {
			continue
		}
		if err := sys.GetStats(path, stats); err != nil {
			return nil, err
		}
	}

	return stats, nil
}

func (m *Manager) Set(container *configs.Config) error {
	for name, path := range m.Paths {
		sys, ok := subsystems[name]
		if !ok || !cgroups.PathExists(path) {
			continue
		}
		if err := sys.Set(path, container.Cgroups); err != nil {
			return err
		}
	}

	return nil
}

func getUnitName(c *configs.Cgroup) string {
	return fmt.Sprintf("%s-%s.scope", c.ScopePrefix, c.Name)
}

func setKernelMemory(c *configs.Cgroup) error {
	path, err := getSubsystemPath(c, "memory")
	if err != nil && !cgroups.IsNotFound(err) {
		return err
	}

	if err := os.MkdirAll(path, 0755); err != nil {
		return err
	}

	if c.KernelMemory > 0 {
		err = writeFile(path, "memory.kmem.limit_in_bytes", strconv.FormatInt(c.KernelMemory, 10))
		if err != nil {
			return err
		}
	}

	return nil
}

func joinCgroups(c *configs.Cgroup, pid int) error {
	for name, sys := range subsystems {
		switch name {
		case "name=systemd":
			// let systemd handle this
			break
		case "cpuset":
			path, err := getSubsystemPath(c, name)
			if err != nil && !cgroups.IsNotFound(err) {
				return err
			}
			s := &fs.CpusetGroup{}
			if err := s.ApplyDir(path, c, pid); err != nil {
				return err
			}
			break
		default:
			_, err := join(c, name, pid)
			if err != nil {
				// Even if it's `not found` error, we'll return err
				// because devices cgroup is hard requirement for
				// container security.
				if name == "devices" {
					return err
				}
				// For other subsystems, omit the `not found` error
				// because they are optional.
				if !cgroups.IsNotFound(err) {
					return err
				}
			}
			path, err := getSubsystemPath(c, name)
			if err != nil && !cgroups.IsNotFound(err) {
				return err
			}

			if err := sys.Set(path, c); err != nil {
				return err
			}
		}
	}

	return nil
}
