Telegram Premium Features

┌─────────────────────────────────────────────────────────┐
│                    Feature Check Flow                    │
├─────────────────────────────────────────────────────────┤
│  1. User requests feature (e.g., send large file)       │
│  2. System checks user tier (free/premium)              │
│  3. If premium → allow                                  │
│  4. If free → check quota                               │
│  5. If quota exceeded → show upgrade prompt             │
└─────────────────────────────────────────────────────────┘

-- User subscription status
CREATE TABLE user_subscriptions (
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    user_id BIGINT NOT NULL,
    tier ENUM('free', 'basic', 'premium', 'business') DEFAULT 'free',
    status ENUM('active', 'expired', 'cancelled') DEFAULT 'active',
    started_at BIGINT DEFAULT 0,
    expires_at BIGINT DEFAULT 0,
    auto_renew BOOLEAN DEFAULT FALSE,
    payment_method VARCHAR(50),
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    UNIQUE KEY uk_user_id (user_id),
    INDEX idx_expires (expires_at),
    INDEX idx_status (status)
) ENGINE=InnoDB;

-- Subscription plans
CREATE TABLE subscription_plans (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50) NOT NULL,
    tier ENUM('basic', 'premium', 'business') NOT NULL,
    price_monthly DECIMAL(10,2) NOT NULL,
    price_yearly DECIMAL(10,2) NOT NULL,
    features JSON,
    is_active BOOLEAN DEFAULT TRUE,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB;

-- Insert default plans
INSERT INTO subscription_plans (name, tier, price_monthly, price_yearly, features) VALUES
('Basic', 'basic', 4.99, 49.99, '{"file_limit": 536870912, "history_months": 6, "ads": false}'),
('Premium', 'premium', 9.99, 99.99, '{"file_limit": 2147483648, "history_months": -1, "priority_support": true}'),
('Business', 'business', 19.99, 199.99, '{"file_limit": 4294967296, "history_months": -1, "custom_domain": true}');

-- User quotas (daily/monthly limits)
CREATE TABLE user_quotas (
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    user_id BIGINT NOT NULL,
    quota_type VARCHAR(50) NOT NULL,
    limit_value BIGINT DEFAULT 0,
    used_value BIGINT DEFAULT 0,
    reset_at BIGINT DEFAULT 0,
    UNIQUE KEY uk_user_type (user_id, quota_type)
) ENGINE=InnoDB;

-- Quota types: messages_daily, files_daily, storage_used

// subscription_manager.go

type SubscriptionManager struct {
    db    *sqlx.DB
    redis *redis.Client
}

// CheckUserTier 检查用户等级
func (m *SubscriptionManager) CheckUserTier(ctx context.Context, userID int64) (Tier, error) {
    // Try cache
    cacheKey := fmt.Sprintf("user:tier:%d", userID)
    cached, err := m.redis.Get(ctx, cacheKey).Result()
    if err == nil {
        return Tier(cached), nil
    }
    
    // Query database
    var sub UserSubscription
    err = m.db.GetContext(ctx, &sub, 
        "SELECT * FROM user_subscriptions WHERE user_id = ?", userID)
    if err == sql.ErrNoRows {
        return TierFree, nil
    }
    if err != nil {
        return TierFree, err
    }
    
    // Check expiration
    if sub.Status == "expired" || (sub.ExpiresAt > 0 && sub.ExpiresAt < time.Now().Unix()) {
        m.ExpireSubscription(ctx, userID)
        return TierFree, nil
    }
    
    // Cache result
    m.redis.Set(ctx, cacheKey, string(sub.Tier), 5*time.Minute)
    
    return Tier(sub.Tier), nil
}

// CheckFeatureAccess 检查功能访问权限
func (m *SubscriptionManager) CheckFeatureAccess(ctx context.Context, userID int64, feature string) (bool, error) {
    tier, err := m.CheckUserTier(ctx, userID)
    if err != nil {
        return false, err
    }
    
    // Feature requirement mapping
    requirements := map[string]Tier{
        "large_files":     TierBasic,
        "unlimited_history": TierPremium,
        "custom_domain":   TierBusiness,
        "priority_support": TierPremium,
    }
    
    requiredTier, exists := requirements[feature]
    if !exists {
        return true, nil // Feature doesn't require tier
    }
    
    return tier >= requiredTier, nil
}

// CheckQuota 检查配额
func (m *SubscriptionManager) CheckQuota(ctx context.Context, userID int64, quotaType string) (bool, int64, error) {
    tier, _ := m.CheckUserTier(ctx, userID)
    
    // Get tier limits
    limits := m.getTierLimits(tier)
    limit := limits[quotaType]
    
    if limit < 0 {
        return true, -1, nil // Unlimited
    }
    
    // Get current usage
    var quota UserQuota
    err := m.db.GetContext(ctx, &quota,
        "SELECT * FROM user_quotas WHERE user_id = ? AND quota_type = ?",
        userID, quotaType)
    
    if err == sql.ErrNoRows {
        // No record yet
        return true, limit, nil
    }
    if err != nil {
        return false, 0, err
    }
    
    // Check if need reset
    if quota.ResetAt < time.Now().Unix() {
        m.resetQuota(ctx, userID, quotaType)
        return true, limit, nil
    }
    
    remaining := limit - quota.UsedValue
    return remaining > 0, remaining, nil
}

// UseQuota 使用配额
func (m *SubscriptionManager) UseQuota(ctx context.Context, userID int64, quotaType string, amount int64) error {
    _, err := m.db.ExecContext(ctx,
        `INSERT INTO user_quotas (user_id, quota_type, used_value, reset_at) 
         VALUES (?, ?, ?, ?)
         ON DUPLICATE KEY UPDATE used_value = used_value + VALUES(used_value)`,
        userID, quotaType, amount, getNextResetTime())
    return err
}

func (m *SubscriptionManager) getTierLimits(tier Tier) map[string]int64 {
    limits := map[Tier]map[string]int64{
        TierFree: {
            "messages_daily": 1000,
            "files_daily":    50,
            "file_size":      100 * 1024 * 1024, // 100MB
            "storage":        1024 * 1024 * 1024, // 1GB
        },
        TierBasic: {
            "messages_daily": 10000,
            "files_daily":    500,
            "file_size":      500 * 1024 * 1024, // 500MB
            "storage":        10 * 1024 * 1024 * 1024, // 10GB
        },
        TierPremium: {
            "messages_daily": -1, // Unlimited
            "files_daily":    -1,
            "file_size":      2 * 1024 * 1024 * 1024, // 2GB
            "storage":        100 * 1024 * 1024 * 1024, // 100GB
        },
    }
    return limits[tier]
}

// stripe_payment.go

import "github.com/stripe/stripe-go/v74"

type StripePayment struct {
    client *stripe.Client
}

func (p *StripePayment) CreateCheckoutSession(ctx context.Context, userID int64, planID int) (string, error) {
    // Get plan details
    plan, err := p.getPlan(ctx, planID)
    if err != nil {
        return "", err
    }
    
    params := &stripe.CheckoutSessionParams{
        CustomerEmail: stripe.String(getUserEmail(userID)),
        LineItems: []*stripe.CheckoutSessionLineItemParams{
            {
                PriceData: &stripe.CheckoutSessionLineItemPriceDataParams{
                    Currency: stripe.String("usd"),
                    ProductData: &stripe.CheckoutSessionLineItemPriceDataProductDataParams{
                        Name: stripe.String(plan.Name),
                    },
                    UnitAmount: stripe.Int64(int64(plan.Price * 100)), // cents
                },
                Quantity: stripe.Int64(1),
            },
        },
        Mode:       stripe.String(string(stripe.CheckoutSessionModeSubscription)),
        SuccessURL: stripe.String(fmt.Sprintf("https://yourapp.com/success?user=%d", userID)),
        CancelURL:  stripe.String("https://yourapp.com/cancel"),
        Metadata: map[string]string{
            "user_id": fmt.Sprintf("%d", userID),
            "plan_id": fmt.Sprintf("%d", planID),
        },
    }
    
    session, err := stripe.CheckoutSession(params)
    if err != nil {
        return "", err
    }
    
    return session.URL, nil
}

func (p *StripePayment) HandleWebhook(payload []byte, sig string) error {
    event, err := stripe.Webhook(payload, sig, webhookSecret)
    if err != nil {
        return err
    }
    
    switch event.Type {
    case "checkout.session.completed":
        var session stripe.CheckoutSession
        err := json.Unmarshal(event.Data.Raw, &session)
        if err != nil {
            return err
        }
        
        userID, _ := strconv.ParseInt(session.Metadata["user_id"], 10, 64)
        planID, _ := strconv.Atoi(session.Metadata["plan_id"])
        
        // Activate subscription
        p.activateSubscription(userID, planID, session.Subscription.ID)
        
    case "invoice.payment_failed":
        // Handle failed payment
        p.handlePaymentFailure(event)
    }
    
    return nil
}

// payment_webhook.go

func (s *Server) PaymentWebhook(ctx context.Context, req *PaymentWebhookReq) (*Bool, error) {
    switch req.Provider {
    case "stripe":
        err := s.stripePayment.HandleWebhook(req.Payload, req.Signature)
        if err != nil {
            return BoolFalse, err
        }
    case "alipay":
        err := s.alipayPayment.HandleNotify(req.Payload)
        if err != nil {
            return BoolFalse, err
        }
    }
    
    return BoolTrue, nil
}

// middleware/premium_middleware.go

func PremiumMiddleware(next HandlerFunc) HandlerFunc {
    return func(ctx context.Context, req Request) (Response, error) {
        userID := getUserIDFromContext(ctx)
        feature := getFeatureFromRequest(req)
        
        // Check access
        hasAccess, err := subscriptionManager.CheckFeatureAccess(ctx, userID, feature)
        if err != nil {
            return nil, err
        }
        
        if !hasAccess {
            return nil, status.Error(codes.PermissionDenied, 
                "This feature requires premium subscription")
        }
        
        // Check quota for usage-based features
        if isQuotaBased(feature) {
            allowed, remaining, err := subscriptionManager.CheckQuota(ctx, userID, feature)
            if err != nil {
                return nil, err
            }
            if !allowed {
                return nil, status.Errorf(codes.ResourceExhausted,
                    "Quota exceeded. Upgrade to get more.")
            }
            // Update context with remaining quota
            ctx = context.WithValue(ctx, "remaining_quota", remaining)
        }
        
        return next(ctx, req)
    }
}

func (s *Server) MessagesSendDocument(ctx context.Context, req *SendDocumentReq) (*Message, error) {
    userID := getUserIDFromContext(ctx)
    fileSize := req.File.Size
    
    // Check file size limit
    tier, _ := s.subManager.CheckUserTier(ctx, userID)
    limits := s.subManager.getTierLimits(tier)
    
    if fileSize > limits["file_size"] {
        return nil, status.Errorf(codes.FailedPrecondition,
            "File too large. Max size for your tier: %d MB", 
            limits["file_size"]/(1024*1024))
    }
    
    // Check and use quota
    allowed, _, err := s.subManager.CheckQuota(ctx, userID, "files_daily")
    if err != nil {
        return nil, err
    }
    if !allowed {
        return nil, status.Errorf(codes.ResourceExhausted,
            "Daily file upload limit reached. Upgrade for unlimited uploads.")
    }
    
    // Use quota
    s.subManager.UseQuota(ctx, userID, "files_daily", 1)
    
    // Process document...
}

// admin/analytics.go

type RevenueAnalytics struct {
    db *sqlx.DB
}

func (a *RevenueAnalytics) GetRevenueReport(ctx context.Context, start, end time.Time) (*RevenueReport, error) {
    query := `
        SELECT 
            DATE(created_at) as date,
            SUM(amount) as revenue,
            COUNT(*) as transactions,
            tier,
            payment_method
        FROM premium_transactions
        WHERE status = 1 
          AND created_at BETWEEN ? AND ?
        GROUP BY DATE(created_at), tier, payment_method
        ORDER BY date DESC
    `
    
    var rows []RevenueRow
    err := a.db.SelectContext(ctx, &rows, query, start, end)
    if err != nil {
        return nil, err
    }
    
    return &RevenueReport{
        Rows:       rows,
        Total:      sumRevenue(rows),
        StartDate:  start,
        EndDate:    end,
    }, nil
}

func (a *RevenueAnalytics) GetUserRetention(ctx context.Context) (*RetentionReport, error) {
    query := `
        SELECT 
            tier,
            COUNT(*) as total_users,
            SUM(CASE WHEN expires_at > NOW() THEN 1 ELSE 0 END) as active_users,
            SUM(CASE WHEN auto_renew = 1 THEN 1 ELSE 0 END) as auto_renew_users
        FROM user_subscriptions
        GROUP BY tier
    `
    
    var rows []RetentionRow
    err := a.db.SelectContext(ctx, &rows, query)
    return &RetentionReport{Rows: rows}, err
}

// Client receives error and shows upgrade dialog
func handleSendFileError(err error) {
    if status.Code(err) == codes.FailedPrecondition {
        // Show upgrade dialog
        showUpgradeDialog(
            title: "File Too Large",
            message: "Upgrade to Premium to send files up to 2GB",
            plans: getAvailablePlans()
        )
    } else if status.Code(err) == codes.ResourceExhausted {
        // Show quota exceeded dialog
        showUpgradeDialog(
            title: "Daily Limit Reached",
            message: "You've reached your daily upload limit. Upgrade for unlimited uploads.",
            plans: getAvailablePlans()
        )
    }
}

func TestSubscriptionManager(t *testing.T) {
    ctx := context.Background()
    manager := NewSubscriptionManager(testDB, testRedis)
    
    t.Run("CheckUserTier", func(t *testing.T) {
        // Free user
        tier, err := manager.CheckUserTier(ctx, 1)
        assert.NoError(t, err)
        assert.Equal(t, TierFree, tier)
        
        // Premium user
        tier, err = manager.CheckUserTier(ctx, 2)
        assert.NoError(t, err)
        assert.Equal(t, TierPremium, tier)
    })
    
    t.Run("CheckFeatureAccess", func(t *testing.T) {
        // Free user can't access premium feature
        hasAccess, err := manager.CheckFeatureAccess(ctx, 1, "large_files")
        assert.NoError(t, err)
        assert.False(t, hasAccess)
        
        // Premium user can access
        hasAccess, err = manager.CheckFeatureAccess(ctx, 2, "large_files")
        assert.NoError(t, err)
        assert.True(t, hasAccess)
    })
    
    t.Run("CheckQuota", func(t *testing.T) {
        // Free user has limited quota
        allowed, remaining, err := manager.CheckQuota(ctx, 1, "files_daily")
        assert.NoError(t, err)
        assert.True(t, allowed)
        assert.Equal(t, int64(50), remaining)
        
        // Premium user has unlimited
        allowed, remaining, err = manager.CheckQuota(ctx, 2, "files_daily")
        assert.NoError(t, err)
        assert.True(t, allowed)
        assert.Equal(t, int64(-1), remaining) // Unlimited
    })
}