package netns

// inspired from https://github.com/vishvananda/netns/blob/master/netns_linux.go#L95

import (
	"fmt"
	"github.com/docker/docker/pkg/namesgenerator"
	"golang.org/x/sys/unix"
	"os"
	"path"
)

// New create and persist a new namespace with random Name
func New() (handle NsHandle, error error) {
	origins, err := Get()
	if err != nil {
		return None(), err
	}
	defer deferClose(&origins, &error)

	if err := unix.Unshare(unix.CLONE_NEWNET); err != nil {
		return None(), err
	}

	newNs, err := Get()
	if err != nil {
		return None(), err
	}

	err = newNs.persist()
	if err != nil {
		defer deferClose(&newNs, &error)
		return newNs, err
	}

	err = Set(origins)
	if err != nil {
		return NsHandle{Fd: 0}, err
	}

	return newNs, nil
}

func deferClose(origins *NsHandle, e *error) {
	// return main error, or defer action error if occurred
	if err := origins.Close(); e == nil && err != nil {
		e = &err
	}
}

// Delete deletes a named network namespace
func Delete(ns NsHandle) error {
	namedPath := path.Join(bindMountPath, ns.Name)

	err := unix.Unmount(namedPath, unix.MNT_DETACH)
	if err != nil {
		return err
	}

	return os.Remove(namedPath)
}

// Get gets a handle to the current threads network namespace.
func Get() (NsHandle, error) {
	return GetFromPath(GetPath())
}

// GetPath gets path to the current threads network namespace.
func GetPath() string {
	tid := unix.Gettid()
	pid := os.Getpid()
	return fmt.Sprintf("/proc/%d/task/%d/ns/net", pid, tid)
}

// GetFromPath gets a handle to a network namespace
// identified by the path
func GetFromPath(path string) (NsHandle, error) {
	fd, err := unix.Open(path, unix.O_RDONLY|unix.O_CLOEXEC, 0)
	if err != nil {
		return None(), err
	}
	name := namesgenerator.GetRandomName(0)
	return NsHandle{fd, name}, nil
}

// Set sets the current network namespace to the namespace represented
// by NsHandle.
func Set(ns NsHandle) error {
	return unix.Setns(ns.Fd, unix.CLONE_NEWNET)
}