veza/veza-backend-api/internal/websocket/chat/presence_service.go

package chat

import (
	"context"
	"encoding/json"
	"fmt"
	"time"

	"veza-backend-api/internal/metrics"

	"github.com/google/uuid"
	"github.com/redis/go-redis/v9"
	"go.uber.org/zap"
)

const (
	presenceTTL       = 2 * time.Minute
	presenceKeyPrefix = "chat:presence:"
)

type PresenceInfo struct {
	UserID   uuid.UUID `json:"user_id"`
	Online   bool      `json:"online"`
	LastSeen time.Time `json:"last_seen"`
}

type ChatPresenceService struct {
	redis  *redis.Client
	logger *zap.Logger
}

func NewChatPresenceService(redisClient *redis.Client, logger *zap.Logger) *ChatPresenceService {
	if logger == nil {
		logger = zap.NewNop()
	}
	return &ChatPresenceService{
		redis:  redisClient,
		logger: logger,
	}
}

func (s *ChatPresenceService) presenceKey(userID uuid.UUID) string {
	return fmt.Sprintf("%s%s", presenceKeyPrefix, userID.String())
}

func (s *ChatPresenceService) SetOnline(ctx context.Context, userID uuid.UUID) error {
	if s.redis == nil {
		return nil
	}

	info := PresenceInfo{
		UserID:   userID,
		Online:   true,
		LastSeen: time.Now(),
	}

	data, err := json.Marshal(info)
	if err != nil {
		return fmt.Errorf("marshal presence: %w", err)
	}

	if err := s.redis.Set(ctx, s.presenceKey(userID), data, presenceTTL).Err(); err != nil {
		metrics.RecordCacheMiss("presence")
		s.logger.Warn("Failed to set online presence", zap.Error(err), zap.String("user_id", userID.String()))
		return fmt.Errorf("set presence: %w", err)
	}
	metrics.RecordCacheHit("presence")
	return nil
}

func (s *ChatPresenceService) SetOffline(ctx context.Context, userID uuid.UUID) error {
	if s.redis == nil {
		return nil
	}

	if err := s.redis.Del(ctx, s.presenceKey(userID)).Err(); err != nil {
		metrics.RecordCacheMiss("presence")
		s.logger.Warn("Failed to delete presence", zap.Error(err), zap.String("user_id", userID.String()))
		return fmt.Errorf("delete presence: %w", err)
	}
	metrics.RecordCacheHit("presence")
	return nil
}

func (s *ChatPresenceService) Heartbeat(ctx context.Context, userID uuid.UUID) error {
	if s.redis == nil {
		return nil
	}

	info := PresenceInfo{
		UserID:   userID,
		Online:   true,
		LastSeen: time.Now(),
	}

	data, err := json.Marshal(info)
	if err != nil {
		return fmt.Errorf("marshal presence: %w", err)
	}

	if err := s.redis.Set(ctx, s.presenceKey(userID), data, presenceTTL).Err(); err != nil {
		metrics.RecordCacheMiss("presence")
		s.logger.Warn("Failed to heartbeat presence", zap.Error(err), zap.String("user_id", userID.String()))
		return fmt.Errorf("heartbeat presence: %w", err)
	}
	metrics.RecordCacheHit("presence")
	return nil
}

func (s *ChatPresenceService) GetPresence(ctx context.Context, userID uuid.UUID) (*PresenceInfo, error) {
	if s.redis == nil {
		return &PresenceInfo{UserID: userID, Online: false}, nil
	}

	data, err := s.redis.Get(ctx, s.presenceKey(userID)).Bytes()
	if err == redis.Nil {
		// "redis.Nil" = key doesn't exist = user is offline. That's a
		// legitimate read result, not an error — count as a hit so the
		// hit-rate metric reflects "Redis answered correctly".
		metrics.RecordCacheHit("presence")
		return &PresenceInfo{UserID: userID, Online: false}, nil
	}
	if err != nil {
		metrics.RecordCacheMiss("presence")
		return nil, fmt.Errorf("get presence: %w", err)
	}
	metrics.RecordCacheHit("presence")

	var info PresenceInfo
	if err := json.Unmarshal(data, &info); err != nil {
		return nil, fmt.Errorf("unmarshal presence: %w", err)
	}

	return &info, nil
}