136 lines
2.8 KiB
Go
136 lines
2.8 KiB
Go
// ©AngelaMos | 2026
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// bus.go
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package bus
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import (
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"context"
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"encoding/json"
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"log/slog"
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"sync"
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"sync/atomic"
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"github.com/carterperez-dev/monitor-the-situation/backend/internal/events"
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)
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const (
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defaultBufferSize = 512
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defaultSubscriberSize = 256
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)
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type Config struct {
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BufferSize int
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Persister Persister
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Broadcaster Broadcaster
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Logger *slog.Logger
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}
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type Bus struct {
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ch chan events.Event
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persister Persister
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broadcaster Broadcaster
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logger *slog.Logger
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dropped atomic.Uint64
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subsMu sync.RWMutex
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subscribers []chan events.Event
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subDropped atomic.Uint64
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}
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func New(cfg Config) *Bus {
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if cfg.BufferSize <= 0 {
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cfg.BufferSize = defaultBufferSize
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}
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logger := cfg.Logger
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if logger == nil {
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logger = slog.Default()
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}
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return &Bus{
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ch: make(chan events.Event, cfg.BufferSize),
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persister: cfg.Persister,
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broadcaster: cfg.Broadcaster,
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logger: logger,
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}
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}
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func (b *Bus) Emit(ev events.Event) {
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select {
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case b.ch <- ev:
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default:
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b.dropped.Add(1)
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b.logger.Warn("event bus full, dropped",
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"topic", ev.Topic, "source", ev.Source)
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}
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}
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func (b *Bus) DroppedCount() uint64 {
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return b.dropped.Load()
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}
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// SubscriberDroppedCount counts events dropped to channel subscribers
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// (separate from the main bus drop counter).
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func (b *Bus) SubscriberDroppedCount() uint64 {
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return b.subDropped.Load()
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}
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// Subscribe returns a buffered channel that receives every event the bus
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// sees. Slow subscribers drop events rather than block the persist+
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// broadcast hot path; SubscriberDroppedCount reports total drops. Wire
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// subscribers at startup before Run() begins.
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func (b *Bus) Subscribe() <-chan events.Event {
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b.subsMu.Lock()
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defer b.subsMu.Unlock()
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ch := make(chan events.Event, defaultSubscriberSize)
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b.subscribers = append(b.subscribers, ch)
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return ch
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}
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func (b *Bus) Run(ctx context.Context) error {
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defer b.closeSubscribers()
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for {
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select {
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case <-ctx.Done():
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return ctx.Err()
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case ev := <-b.ch:
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if b.persister != nil {
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if err := b.persister.Save(ctx, ev); err != nil {
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b.logger.Error("persist event failed",
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"err", err, "topic", ev.Topic)
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}
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}
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if b.broadcaster != nil {
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payload, err := json.Marshal(ev.Payload)
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if err != nil {
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b.logger.Error("marshal payload failed",
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"err", err, "topic", ev.Topic)
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continue
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}
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b.broadcaster.Broadcast(string(ev.Topic), payload)
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}
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b.fanout(ev)
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}
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}
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}
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func (b *Bus) fanout(ev events.Event) {
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b.subsMu.RLock()
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subs := b.subscribers
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b.subsMu.RUnlock()
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for _, ch := range subs {
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select {
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case ch <- ev:
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default:
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b.subDropped.Add(1)
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}
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}
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}
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func (b *Bus) closeSubscribers() {
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b.subsMu.Lock()
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defer b.subsMu.Unlock()
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for _, ch := range b.subscribers {
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close(ch)
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}
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b.subscribers = nil
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}
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