/*
   Copyright 2014 CoreOS, Inc.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package system

import (
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"path"
	"strings"

	"github.com/coreos/coreos-cloudinit/Godeps/_workspace/src/github.com/coreos/go-systemd/dbus"
	"github.com/coreos/coreos-cloudinit/config"
)

func NewUnitManager(root string) UnitManager {
	return &systemd{root}
}

type systemd struct {
	root string
}

// fakeMachineID is placed on non-usr CoreOS images and should
// never be used as a true MachineID
const fakeMachineID = "42000000000000000000000000000042"

// PlaceUnit writes a unit file at its desired destination, creating parent
// directories as necessary.
func (s *systemd) PlaceUnit(u Unit) error {
	file := File{config.File{
		Path:               u.Destination(s.root),
		Content:            u.Content,
		RawFilePermissions: "0644",
	}}

	_, err := WriteFile(&file, "/")
	return err
}

// PlaceUnitDropIn writes a unit drop-in file at its desired destination,
// creating parent directories as necessary.
func (s *systemd) PlaceUnitDropIn(u Unit, d config.UnitDropIn) error {
	file := File{config.File{
		Path:               u.DropInDestination(s.root, d),
		Content:            d.Content,
		RawFilePermissions: "0644",
	}}

	_, err := WriteFile(&file, "/")
	return err
}

func (s *systemd) EnableUnitFile(u Unit) error {
	conn, err := dbus.New()
	if err != nil {
		return err
	}

	units := []string{u.Name}
	_, _, err = conn.EnableUnitFiles(units, u.Runtime, true)
	return err
}

func (s *systemd) RunUnitCommand(u Unit, c string) (string, error) {
	conn, err := dbus.New()
	if err != nil {
		return "", err
	}

	var fn func(string, string) (string, error)
	switch c {
	case "start":
		fn = conn.StartUnit
	case "stop":
		fn = conn.StopUnit
	case "restart":
		fn = conn.RestartUnit
	case "reload":
		fn = conn.ReloadUnit
	case "try-restart":
		fn = conn.TryRestartUnit
	case "reload-or-restart":
		fn = conn.ReloadOrRestartUnit
	case "reload-or-try-restart":
		fn = conn.ReloadOrTryRestartUnit
	default:
		return "", fmt.Errorf("Unsupported systemd command %q", c)
	}

	return fn(u.Name, "replace")
}

func (s *systemd) DaemonReload() error {
	conn, err := dbus.New()
	if err != nil {
		return err
	}

	return conn.Reload()
}

// MaskUnit masks the given Unit by symlinking its unit file to
// /dev/null, analogous to `systemctl mask`.
// N.B.: Unlike `systemctl mask`, this function will *remove any existing unit
// file at the location*, to ensure that the mask will succeed.
func (s *systemd) MaskUnit(u Unit) error {
	masked := u.Destination(s.root)
	if _, err := os.Stat(masked); os.IsNotExist(err) {
		if err := os.MkdirAll(path.Dir(masked), os.FileMode(0755)); err != nil {
			return err
		}
	} else if err := os.Remove(masked); err != nil {
		return err
	}
	return os.Symlink("/dev/null", masked)
}

// UnmaskUnit is analogous to systemd's unit_file_unmask. If the file
// associated with the given Unit is empty or appears to be a symlink to
// /dev/null, it is removed.
func (s *systemd) UnmaskUnit(u Unit) error {
	masked := u.Destination(s.root)
	ne, err := nullOrEmpty(masked)
	if os.IsNotExist(err) {
		return nil
	} else if err != nil {
		return err
	}
	if !ne {
		log.Printf("%s is not null or empty, refusing to unmask", masked)
		return nil
	}
	return os.Remove(masked)
}

// nullOrEmpty checks whether a given path appears to be an empty regular file
// or a symlink to /dev/null
func nullOrEmpty(path string) (bool, error) {
	fi, err := os.Stat(path)
	if err != nil {
		return false, err
	}
	m := fi.Mode()
	if m.IsRegular() && fi.Size() <= 0 {
		return true, nil
	}
	if m&os.ModeCharDevice > 0 {
		return true, nil
	}
	return false, nil
}

func ExecuteScript(scriptPath string) (string, error) {
	props := []dbus.Property{
		dbus.PropDescription("Unit generated and executed by coreos-cloudinit on behalf of user"),
		dbus.PropExecStart([]string{"/bin/bash", scriptPath}, false),
	}

	base := path.Base(scriptPath)
	name := fmt.Sprintf("coreos-cloudinit-%s.service", base)

	log.Printf("Creating transient systemd unit '%s'", name)

	conn, err := dbus.New()
	if err != nil {
		return "", err
	}

	_, err = conn.StartTransientUnit(name, "replace", props...)
	return name, err
}

func SetHostname(hostname string) error {
	return exec.Command("hostnamectl", "set-hostname", hostname).Run()
}

func Hostname() (string, error) {
	return os.Hostname()
}

func MachineID(root string) string {
	contents, _ := ioutil.ReadFile(path.Join(root, "etc", "machine-id"))
	id := strings.TrimSpace(string(contents))

	if id == fakeMachineID {
		id = ""
	}

	return id
}