first commit

bus/bus.go

@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2023 mysubarumq
+// SPDX-FileContributor: alex-savin
+
+package bus
+
+import (
+	"fmt"
+	"sync"
+
+	"log/slog"
+)
+
+// Event is used to transport user data over bus.
+type Event struct {
+	Data        interface{}
+	ChannelName string
+}
+
+// eventChannel stores subscriptions for channels.
+type eventChannel struct {
+	subscribers map[string]chan Event
+}
+
+// newEventChannel creates new eventChannel.
+func newEventChannel() *eventChannel {
+	return &eventChannel{
+		subscribers: make(map[string]chan Event),
+	}
+}
+
+// addSubscriber adds new subscriber.
+func (ch *eventChannel) addSubscriber(subName string, size int) error {
+	if _, ok := ch.subscribers[subName]; ok {
+		return fmt.Errorf("subscriber %s already exists", subName)
+	}
+
+	ch.subscribers[subName] = make(chan Event, size)
+
+	return nil
+}
+
+// delSubscriber removes subscriber.
+func (ch *eventChannel) delSubscriber(subName string) {
+	delete(ch.subscribers, subName)
+}
+
+// Bus should be created by New().
+type Bus struct {
+	mu       sync.Mutex
+	channels map[string]*eventChannel
+}
+
+// New creates new Bus instance.
+func New() *Bus {
+	b := &Bus{
+		channels: make(map[string]*eventChannel),
+	}
+
+	return b
+}
+
+// Subscribe adds new subscriber to channel.
+func (b *Bus) Subscribe(channelName, subName string, size int) (chan Event, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	if _, ok := b.channels[channelName]; !ok {
+		b.channels[channelName] = newEventChannel()
+	}
+
+	ch := b.channels[channelName]
+
+	if err := ch.addSubscriber(subName, size); err != nil {
+		return nil, err
+	}
+
+	return ch.subscribers[subName], nil
+
+}
+
+// Unsubscribe removes subscriber from channel.
+// If this is last subscriber channel will be removed.
+func (b *Bus) Unsubscribe(channelName, subName string) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	channel, ok := b.channels[channelName]
+	if !ok {
+		return
+	}
+	channel.delSubscriber(subName)
+
+	if len(channel.subscribers) == 0 {
+		delete(b.channels, channelName)
+	}
+}
+
+// Publish data to channel.
+func (b *Bus) Publish(channelName string, data interface{}) error {
+	channel, ok := b.channels[channelName]
+	if !ok {
+		return fmt.Errorf("channel %s don't exists", channelName)
+	}
+	e := Event{
+		ChannelName: channelName,
+		Data:        data,
+	}
+
+	for subName, subscriber := range channel.subscribers {
+		if cap(subscriber) > 0 && len(subscriber) >= cap(subscriber) {
+			slog.Info("channel %s for subscriber %s is full, not publishing new messages", channelName, subName)
+			continue
+		}
+		subscriber <- e
+	}
+	return nil
+}