/*
   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 (
	"bufio"
	"fmt"
	"io"
	"os"
	"path"
	"reflect"
	"sort"
	"strings"

	"github.com/coreos/coreos-cloudinit/config"
)

const (
	locksmithUnit    = "locksmithd.service"
	updateEngineUnit = "update-engine.service"
)

// Update is a top-level structure which contains its underlying configuration,
// config.Update, a function for reading the configuration (the default
// implementation reading from the filesystem), and provides the system-specific
// File() and Unit().
type Update struct {
	Config     config.Update
	ReadConfig func() (io.Reader, error)
}

func DefaultReadConfig() (io.Reader, error) {
	etcUpdate := path.Join("/etc", "coreos", "update.conf")
	usrUpdate := path.Join("/usr", "share", "coreos", "update.conf")

	f, err := os.Open(etcUpdate)
	if os.IsNotExist(err) {
		f, err = os.Open(usrUpdate)
	}
	return f, err
}

// File generates an `/etc/coreos/update.conf` file (if any update
// configuration options are set in cloud-config) by either rewriting the
// existing file on disk, or starting from `/usr/share/coreos/update.conf`
func (uc Update) File() (*File, error) {
	if config.IsZero(uc.Config) {
		return nil, nil
	}
	if err := config.AssertValid(uc.Config); err != nil {
		return nil, err
	}

	// Generate the list of possible substitutions to be performed based on the options that are configured
	subs := map[string]string{}
	uct := reflect.TypeOf(uc.Config)
	ucv := reflect.ValueOf(uc.Config)
	for i := 0; i < uct.NumField(); i++ {
		val := ucv.Field(i).String()
		if val == "" {
			continue
		}
		env := uct.Field(i).Tag.Get("env")
		subs[env] = fmt.Sprintf("%s=%s", env, val)
	}

	conf, err := uc.ReadConfig()
	if err != nil {
		return nil, err
	}
	scanner := bufio.NewScanner(conf)

	var out string
	for scanner.Scan() {
		line := scanner.Text()
		for env, value := range subs {
			if strings.HasPrefix(line, env) {
				line = value
				delete(subs, env)
				break
			}
		}
		out += line
		out += "\n"
		if err := scanner.Err(); err != nil {
			return nil, err
		}
	}

	for _, key := range sortedKeys(subs) {
		out += subs[key]
		out += "\n"
	}

	return &File{config.File{
		Path:               path.Join("etc", "coreos", "update.conf"),
		RawFilePermissions: "0644",
		Content:            out,
	}}, nil
}

// Units generates units for the cloud-init initializer to act on:
// - a locksmith Unit, if "reboot-strategy" was set in cloud-config
// - an update_engine Unit, if "group" or "server" was set in cloud-config
func (uc Update) Units() []Unit {
	var units []Unit
	if uc.Config.RebootStrategy != "" {
		ls := &Unit{config.Unit{
			Name:    locksmithUnit,
			Command: "restart",
			Mask:    false,
			Runtime: true,
		}}

		if uc.Config.RebootStrategy == "off" {
			ls.Command = "stop"
			ls.Mask = true
		}
		units = append(units, *ls)
	}

	if uc.Config.Group != "" || uc.Config.Server != "" {
		ue := Unit{config.Unit{
			Name:    updateEngineUnit,
			Command: "restart",
		}}
		units = append(units, ue)
	}

	return units
}

func sortedKeys(m map[string]string) (keys []string) {
	for key := range m {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	return
}