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event_system.go
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event_system.go
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/*
* Copyright 2017 Huawei Technologies Co., Ltd
*
* 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.
*/
/*
* Created by on 2017/6/22.
*/
//Package event provides the different Listeners
package event
import (
"errors"
"regexp"
"strings"
"github.com/go-chassis/openlog"
)
//errors
var (
ErrNilListener = errors.New("nil listener")
)
// Event Constant
const (
Update = "UPDATE"
Delete = "DELETE"
Create = "CREATE"
InvalidAction = "INVALID-ACTION"
)
type PrefixIndex struct {
Prefix string
NextParts map[string]*PrefixIndex
}
func (pre *PrefixIndex) AddPrefix(prefix string) {
parts := strings.Split(prefix, ".")
cur := pre
for _, part := range parts {
if cur.NextParts == nil {
cur.NextParts = map[string]*PrefixIndex{}
}
next, ok := cur.NextParts[part]
if !ok {
next = &PrefixIndex{}
cur.NextParts[part] = next
}
cur = next
}
cur.Prefix = prefix
}
func (pre *PrefixIndex) RemovePrefix(prefix string) {
parts := strings.Split(prefix, ".")
cur := pre
var path []*PrefixIndex
path = append(path, cur)
for _, part := range parts {
if cur.NextParts == nil {
return
}
next, ok := cur.NextParts[part]
if !ok {
return
}
cur = next
path = append(path, cur)
}
cur.Prefix = ""
remove := ""
for i:=len(path); i>0; i-- {
cur = path[i-1]
if remove != "" {
delete(cur.NextParts, remove)
}
if len(cur.NextParts) > 0 {
break
}
if cur.Prefix != "" {
break
}
if i > 1 {
remove = parts[i-2]
} else {
cur.NextParts = nil
}
}
}
func (pre *PrefixIndex) FindPrefix(key string) string {
parts := strings.Split(key, ".")
cur := pre
for _, part := range parts {
if cur.Prefix != "" {
return cur.Prefix
}
next, ok := cur.NextParts[part]
if !ok {
return ""
}
cur = next
}
return cur.Prefix
}
// Event generated when any config changes
type Event struct {
EventSource string
EventType string
Key string
Value interface{}
HasUpdated bool
}
// Listener All Listener should implement this Interface
type Listener interface {
Event(event *Event)
}
// ModuleListener All moduleListener should implement this Interface
type ModuleListener interface {
Event(event []*Event)
}
//Dispatcher is the observer
type Dispatcher struct {
listeners map[string][]Listener
moduleListeners map[string][]ModuleListener
modulePrefixIndex PrefixIndex
}
// NewDispatcher is a new Dispatcher for listeners
func NewDispatcher() *Dispatcher {
dis := new(Dispatcher)
dis.listeners = make(map[string][]Listener)
dis.moduleListeners = make(map[string][]ModuleListener)
return dis
}
// RegisterListener registers listener for particular configuration
func (dis *Dispatcher) RegisterListener(listenerObj Listener, keys ...string) error {
if listenerObj == nil {
err := ErrNilListener
openlog.Error("nil listener supplied:" + err.Error())
return ErrNilListener
}
for _, key := range keys {
listenerList, ok := dis.listeners[key]
if !ok {
listenerList = make([]Listener, 0)
}
// for duplicate registration
for _, listener := range listenerList {
if listener == listenerObj {
return nil
}
}
// append new listener
listenerList = append(listenerList, listenerObj)
// assign latest listener list
dis.listeners[key] = listenerList
}
return nil
}
// UnRegisterListener un-register listener for a particular configuration
func (dis *Dispatcher) UnRegisterListener(listenerObj Listener, keys ...string) error {
if listenerObj == nil {
return ErrNilListener
}
for _, key := range keys {
listenerList, ok := dis.listeners[key]
if !ok {
continue
}
newListenerList := make([]Listener, 0)
// remove listener
for _, listener := range listenerList {
if listener == listenerObj {
continue
}
newListenerList = append(newListenerList, listener)
}
// assign latest listener list
dis.listeners[key] = newListenerList
}
return nil
}
// DispatchEvent sends the action trigger for a particular event on a configuration
func (dis *Dispatcher) DispatchEvent(event *Event) error {
if event == nil {
return errors.New("empty event provided")
}
for regKey, listeners := range dis.listeners {
matched, err := regexp.MatchString(regKey, event.Key)
if err != nil {
openlog.Error("regular expression for key " + regKey + " failed:" + err.Error())
continue
}
if matched {
for _, listener := range listeners {
openlog.Info("event generated for " + regKey)
go listener.Event(event)
}
}
}
return nil
}
// RegisterModuleListener registers moduleListener for particular configuration
func (dis *Dispatcher) RegisterModuleListener(listenerObj ModuleListener, modulePrefixes ...string) error {
if listenerObj == nil {
err := ErrNilListener
openlog.Error("nil moduleListener supplied:" + err.Error())
return ErrNilListener
}
for _, prefix := range modulePrefixes {
moduleListeners, ok := dis.moduleListeners[prefix]
if !ok {
moduleListeners = make([]ModuleListener, 0)
dis.modulePrefixIndex.AddPrefix(prefix)
}
// for duplicate registration
for _, listener := range moduleListeners {
if listener == listenerObj {
return nil
}
}
// append new moduleListener
moduleListeners = append(moduleListeners, listenerObj)
// assign latest moduleListener list
dis.moduleListeners[prefix] = moduleListeners
}
return nil
}
// UnRegisterModuleListener un-register moduleListener for a particular configuration
func (dis *Dispatcher) UnRegisterModuleListener(listenerObj ModuleListener, modulePrefixes ...string) error {
if listenerObj == nil {
return ErrNilListener
}
for _, prefix := range modulePrefixes {
listenerList, ok := dis.moduleListeners[prefix]
if !ok {
continue
}
newListenerList := make([]ModuleListener, 0)
// remove moduleListener
for _, listener := range listenerList {
if listener == listenerObj {
continue
}
newListenerList = append(newListenerList, listener)
}
// assign latest moduleListener list
dis.moduleListeners[prefix] = newListenerList
if len(newListenerList) == 0 {
dis.modulePrefixIndex.RemovePrefix(prefix)
}
}
return nil
}
// DispatchModuleEvent finds the registered function for callback according to the prefix of key in events
func (dis *Dispatcher) DispatchModuleEvent(events []*Event) error {
if events == nil || len(events) == 0 {
return errors.New("empty events provided")
}
// 1. According to the key in the event, events with the same prefix are placed in the same slice
eventsList := dis.parseEvents(events)
// 2. Events with the same prefix will only be callback once.
for key, events := range eventsList {
if listeners, ok := dis.moduleListeners[key]; ok {
for _, listener := range listeners {
openlog.Info("events generated for " + key)
go listener.Event(events)
}
}
}
return nil
}
// Event key with the same subscription prefix is placed in the same slice
func (dis *Dispatcher) parseEvents(events []*Event) map[string][]*Event {
var eventList = make(map[string][]*Event)
for _, event := range events {
// find first prefix from event.key
//registerKey := dis.findFirstRegisterPrefix(event.Key)
prefix := dis.modulePrefixIndex.FindPrefix(event.Key)
if prefix == "" {
continue
}
if module, ok := eventList[prefix]; ok {
events := module
events = append(events, event)
eventList[prefix] = events
} else {
newModule := append([]*Event{}, event)
eventList[prefix] = newModule
}
}
return eventList
}
// Find first prefix from event.key
// Ignore the case where namespace and module key(prefix) have the same name
func (dis *Dispatcher) findFirstRegisterPrefix(eventKey string) string {
keyArr := strings.Split(eventKey, ".")
for _, key := range keyArr {
if _, ok := dis.moduleListeners[key]; ok {
return key
}
}
return ""
}