// +build linux

package libcontainer

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"

	"github.com/docker/libcontainer/cgroups"
	"github.com/docker/libcontainer/cgroups/fs"
	"github.com/docker/libcontainer/cgroups/systemd"
	"github.com/docker/libcontainer/configs"
	"github.com/docker/libcontainer/configs/validate"
)

const (
	stateFilename = "state.json"
)

var (
	idRegex  = regexp.MustCompile(`^[\w_]+$`)
	maxIdLen = 1024
)

// InitArgs returns an options func to configure a LinuxFactory with the
// provided init arguments.
func InitArgs(args ...string) func(*LinuxFactory) error {
	return func(l *LinuxFactory) error {
		name := args[0]
		if filepath.Base(name) == name {
			if lp, err := exec.LookPath(name); err == nil {
				name = lp
			}
		}
		l.InitPath = name
		l.InitArgs = append([]string{name}, args[1:]...)
		return nil
	}
}

// InitPath returns an options func to configure a LinuxFactory with the
// provided absolute path to the init binary and arguements.
func InitPath(path string, args ...string) func(*LinuxFactory) error {
	return func(l *LinuxFactory) error {
		l.InitPath = path
		l.InitArgs = args
		return nil
	}
}

// SystemdCgroups is an options func to configure a LinuxFactory to return
// containers that use systemd to create and manage cgroups.
func SystemdCgroups(l *LinuxFactory) error {
	l.NewCgroupsManager = func(config *configs.Cgroup, paths map[string]string) cgroups.Manager {
		return &systemd.Manager{
			Cgroups: config,
			Paths:   paths,
		}
	}
	return nil
}

// Cgroupfs is an options func to configure a LinuxFactory to return
// containers that use the native cgroups filesystem implementation to
// create and manage cgroups.
func Cgroupfs(l *LinuxFactory) error {
	l.NewCgroupsManager = func(config *configs.Cgroup, paths map[string]string) cgroups.Manager {
		return &fs.Manager{
			Cgroups: config,
			Paths:   paths,
		}
	}
	return nil
}

// New returns a linux based container factory based in the root directory and
// configures the factory with the provided option funcs.
func New(root string, options ...func(*LinuxFactory) error) (Factory, error) {
	if root != "" {
		if err := os.MkdirAll(root, 0700); err != nil {
			return nil, newGenericError(err, SystemError)
		}
	}
	l := &LinuxFactory{
		Root:      root,
		Validator: validate.New(),
	}
	InitArgs(os.Args[0], "init")(l)
	Cgroupfs(l)
	for _, opt := range options {
		if err := opt(l); err != nil {
			return nil, err
		}
	}
	return l, nil
}

// LinuxFactory implements the default factory interface for linux based systems.
type LinuxFactory struct {
	// Root directory for the factory to store state.
	Root string

	// InitPath is the absolute path to the init binary.
	InitPath string

	// InitArgs are arguments for calling the init responsibilities for spawning
	// a container.
	InitArgs []string

	// Validator provides validation to container configurations.
	Validator validate.Validator

	// NewCgroupsManager returns an initialized cgroups manager for a single container.
	NewCgroupsManager func(config *configs.Cgroup, paths map[string]string) cgroups.Manager
}

func (l *LinuxFactory) Create(id string, config *configs.Config) (Container, error) {
	if l.Root == "" {
		return nil, newGenericError(fmt.Errorf("invalid root"), ConfigInvalid)
	}
	if err := l.validateID(id); err != nil {
		return nil, err
	}
	if err := l.Validator.Validate(config); err != nil {
		return nil, newGenericError(err, ConfigInvalid)
	}
	containerRoot := filepath.Join(l.Root, id)
	if _, err := os.Stat(containerRoot); err == nil {
		return nil, newGenericError(fmt.Errorf("Container with id exists: %v", id), IdInUse)
	} else if !os.IsNotExist(err) {
		return nil, newGenericError(err, SystemError)
	}
	if err := os.MkdirAll(containerRoot, 0700); err != nil {
		return nil, newGenericError(err, SystemError)
	}
	return &linuxContainer{
		id:            id,
		root:          containerRoot,
		config:        config,
		initPath:      l.InitPath,
		initArgs:      l.InitArgs,
		cgroupManager: l.NewCgroupsManager(config.Cgroups, nil),
	}, nil
}

func (l *LinuxFactory) Load(id string) (Container, error) {
	if l.Root == "" {
		return nil, newGenericError(fmt.Errorf("invalid root"), ConfigInvalid)
	}
	containerRoot := filepath.Join(l.Root, id)
	state, err := l.loadState(containerRoot)
	if err != nil {
		return nil, err
	}
	r := &restoredProcess{
		processPid:       state.InitProcessPid,
		processStartTime: state.InitProcessStartTime,
	}
	return &linuxContainer{
		initProcess:   r,
		id:            id,
		config:        &state.Config,
		initPath:      l.InitPath,
		initArgs:      l.InitArgs,
		cgroupManager: l.NewCgroupsManager(state.Config.Cgroups, state.CgroupPaths),
		root:          containerRoot,
	}, nil
}

// StartInitialization loads a container by opening the pipe fd from the parent to read the configuration and state
// This is a low level implementation detail of the reexec and should not be consumed externally
func (l *LinuxFactory) StartInitialization(pipefd uintptr) (err error) {
	var (
		pipe = os.NewFile(uintptr(pipefd), "pipe")
		it   = initType(os.Getenv("_LIBCONTAINER_INITTYPE"))
	)
	// clear the current process's environment to clean any libcontainer
	// specific env vars.
	os.Clearenv()
	defer func() {
		// if we have an error during the initialization of the container's init then send it back to the
		// parent process in the form of an initError.
		if err != nil {
			// ensure that any data sent from the parent is consumed so it doesn't
			// receive ECONNRESET when the child writes to the pipe.
			ioutil.ReadAll(pipe)
			if err := json.NewEncoder(pipe).Encode(newSystemError(err)); err != nil {
				panic(err)
			}
		}
		// ensure that this pipe is always closed
		pipe.Close()
	}()
	i, err := newContainerInit(it, pipe)
	if err != nil {
		return err
	}
	return i.Init()
}

func (l *LinuxFactory) loadState(root string) (*State, error) {
	f, err := os.Open(filepath.Join(root, stateFilename))
	if err != nil {
		if os.IsNotExist(err) {
			return nil, newGenericError(err, ContainerNotExists)
		}
		return nil, newGenericError(err, SystemError)
	}
	defer f.Close()
	var state *State
	if err := json.NewDecoder(f).Decode(&state); err != nil {
		return nil, newGenericError(err, SystemError)
	}
	return state, nil
}

func (l *LinuxFactory) validateID(id string) error {
	if !idRegex.MatchString(id) {
		return newGenericError(fmt.Errorf("Invalid id format: %v", id), InvalidIdFormat)
	}
	if len(id) > maxIdLen {
		return newGenericError(fmt.Errorf("Invalid id format: %v", id), InvalidIdFormat)
	}
	return nil
}

// restoredProcess represents a process where the calling process may or may not be
// the parent process.  This process is created when a factory loads a container from
// a persisted state.
type restoredProcess struct {
	processPid       int
	processStartTime string
}

func (p *restoredProcess) start() error {
	return newGenericError(fmt.Errorf("restored process cannot be started"), SystemError)
}

func (p *restoredProcess) pid() int {
	return p.processPid
}

func (p *restoredProcess) terminate() error {
	return newGenericError(fmt.Errorf("restored process cannot be terminated"), SystemError)
}

func (p *restoredProcess) wait() (*os.ProcessState, error) {
	return nil, newGenericError(fmt.Errorf("restored process cannot be waited on"), SystemError)
}

func (p *restoredProcess) startTime() (string, error) {
	return p.processStartTime, nil
}

func (p *restoredProcess) signal(s os.Signal) error {
	return newGenericError(fmt.Errorf("restored process cannot be signaled"), SystemError)
}