sub2api/backend/internal/repository/channel_cache.go

package repository

import (
	"context"
	"log/slog"

	"github.com/Wei-Shaw/sub2api/internal/service"
	"github.com/redis/go-redis/v9"
)

const channelCachePubSubKey = "channel_cache_updated"

type channelCache struct {
	rdb *redis.Client
}

// NewChannelCache creates the Redis-backed channel cache invalidation bus.
func NewChannelCache(rdb *redis.Client) service.ChannelCachePubSub {
	return &channelCache{rdb: rdb}
}

// NotifyUpdate notifies all instances to invalidate their local channel cache.
func (c *channelCache) NotifyUpdate(ctx context.Context) error {
	return c.rdb.Publish(ctx, channelCachePubSubKey, "refresh").Err()
}

// SubscribeUpdates subscribes to channel cache invalidation notifications.
func (c *channelCache) SubscribeUpdates(ctx context.Context, handler func()) {
	go func() {
		pubsub := c.rdb.Subscribe(ctx, channelCachePubSubKey)
		defer func() {
			if err := pubsub.Close(); err != nil {
				slog.Warn("failed to close channel cache subscriber", "error", err)
			}
		}()

		messages := pubsub.Channel()
		for {
			select {
			case <-ctx.Done():
				return
			case message, ok := <-messages:
				if !ok {
					slog.Warn("channel cache subscriber stopped", "reason", "channel_closed")
					return
				}
				if message != nil {
					handler()
				}
			}
		}
	}()
}