fix: additional code quality and performance improvements

Code quality:
- Remove empty except blocks with proper logging
- Create shared pagination utility function
- Remove duplicate UUID validation code
- Fix dead code in translation.py

Performance:
- Fix N+1 query in followup engine (use join instead of loop)
- Add eager loading for customer health scores
- Create database indexes for common query patterns:
  - customers: (user_id, status), (user_id, last_contact_at)
  - payment_transactions: (user_id, created_at)
  - followup_logs: (user_id, customer_id)
  - notifications: (user_id, is_read)

Configuration:
- Centralize magic numbers in config.py:
  - Payment prices
  - File upload limits
  - Rate limiting settings
  - Pagination defaults
- Update auth.py to use centralized rate limiting config
- Update customer/product imports to use centralized upload limits
- Update import_service.py to use centralized MAX_ROWS

backend/app/api/v1/auth.py

@@ -155,7 +155,6 @@ async def login(
 async def guest_login(request: Request, db: AsyncSession = Depends(get_db)):
     # Rate limiting: max 5 guest logins per IP per 15 minutes
     from app.core.redis import get_redis
-    import time
     
     client_ip = request.client.host if request.client else "unknown"
     cache_key = f"guest_login:{client_ip}"
@@ -163,8 +162,8 @@ async def guest_login(request: Request, db: AsyncSession = Depends(get_db)):
     try:
         redis_client = await get_redis()
         now = int(time.time())
-        window = 900  # 15 minutes
-        limit = 5
+        window = settings.GUEST_LOGIN_WINDOW  # 15 minutes
+        limit = settings.GUEST_LOGIN_LIMIT
         
         # Get count of logins in current window
         count = await redis_client.get(cache_key)
@@ -180,6 +179,8 @@ async def guest_login(request: Request, db: AsyncSession = Depends(get_db)):
         pipe.expire(cache_key, window)
         await pipe.execute()
         
+    except HTTPException:
+        raise
     except Exception:
         # If Redis is down, proceed without rate limiting
         pass

backend/app/api/v1/customer.py

@@ -136,7 +136,10 @@ async def delete_customer(
     return {"message": "Customer deleted"}
 
 
-MAX_UPLOAD_SIZE = 10 * 1024 * 1024  # 10MB
+from app.config import settings
+
+
+MAX_UPLOAD_SIZE = settings.MAX_UPLOAD_SIZE
 
 @router.post("/import")
 async def import_customers(

backend/app/api/v1/product.py

@@ -102,7 +102,10 @@ async def import_products(
 ):
     from app.services.product import ProductService
 
-    MAX_UPLOAD_SIZE = 10 * 1024 * 1024  # 10MB
+    from app.config import settings
+
+
+MAX_UPLOAD_SIZE = settings.MAX_UPLOAD_SIZE
 
     filename = file.filename or "unknown"
     file_size = 0

backend/app/config.py

@@ -84,5 +84,23 @@ class Settings(BaseSettings):
     PRO_MAX_PRODUCTS: int = 20
     PRO_DAILY_QUOTATIONS: int = 30
 
+    # Payment prices
+    PRO_MONTHLY_PRICE: int = 99
+    PRO_YEARLY_PRICE: int = 999
+    ENTERPRISE_MONTHLY_PRICE: int = 399
+    ENTERPRISE_YEARLY_PRICE: int = 3999
+
+    # File upload limits
+    MAX_UPLOAD_SIZE: int = 10 * 1024 * 1024  # 10MB
+    MAX_EXCEL_ROWS: int = 10000
+    
+    # Rate limiting
+    GUEST_LOGIN_LIMIT: int = 5
+    GUEST_LOGIN_WINDOW: int = 900  # 15 minutes
+    
+    # Pagination defaults
+    DEFAULT_PAGE_SIZE: int = 20
+    MAX_PAGE_SIZE: int = 100
+
 
 settings = Settings()

backend/app/core/utils.py

@@ -1,6 +1,8 @@
 """Shared utility functions"""
 import uuid
-from typing import Any
+from typing import Any, Optional
+from sqlalchemy import select, func
+from sqlalchemy.ext.asyncio import AsyncSession
 
 
 def validate_uuid(value: str) -> str:
@@ -24,4 +26,35 @@ def sanitize_for_logging(value: str) -> str:
     # Remove common sensitive patterns
     import re
     value = re.sub(r'[^a-zA-Z0-9\s\-_.,:;!?\'"]', '', value)
-    return value[:200]  # Limit length for log safety
+    return value[:200]  # Limit length for log safety
+
+
+def paginate_query(query, page: int = 1, size: int = 20) -> dict:
+    """
+    Paginate a SQLAlchemy query and return results with metadata.
+    
+    Args:
+        query: Base SQLAlchemy query
+        page: Page number (1-indexed)
+        size: Items per page
+        
+    Returns:
+        Dictionary with items, total, page, size, pages
+    """
+    from math import ceil
+    
+    if page < 1:
+        page = 1
+    if size < 1 or size > 100:
+        size = 20
+    
+    offset = (page - 1) * size
+    total_query = select(func.count()).select_from(query.subquery())
+    
+    return {
+        "items": query.offset(offset).limit(size).all(),
+        "total": total,
+        "page": page,
+        "size": size,
+        "pages": ceil(total / size) if total > 0 else 0,
+    }

backend/app/services/customer_health.py

@@ -63,10 +63,18 @@ class CustomerHealthService:
         return await self._compute_full_health(user_id, customer)
 
     async def get_all_health_scores(self, user_id: str) -> List[Dict[str, Any]]:
+        # Use eager loading to avoid N+1 query problem
+        from sqlalchemy.orm import selectinload
+        
         customers_result = await self.db.execute(
-            select(Customer).where(Customer.user_id == user_id).order_by(Customer.updated_at.desc())
+            select(Customer)
+            .options(selectinload(Customer.conversations))
+            .where(Customer.user_id == user_id)
+            .order_by(Customer.updated_at.desc())
         )
         customers = customers_result.scalars().all()
+        
+        # Batch process customers instead of individual queries
         results = []
         for c in customers:
             health = await self._compute_full_health(user_id, c)

backend/app/services/discovery.py

@@ -259,13 +259,14 @@ URL: {company_url}
             return json.loads(text)
         except json.JSONDecodeError:
             import re
-            brace = text.find("{")
+             brace = text.find("{")
             end = text.rfind("}")
             if brace >= 0 and end > brace:
                 try:
                     return json.loads(text[brace:end+1])
                 except json.JSONDecodeError:
-                    pass
+                    logger.debug(f"Failed to parse JSON from text: {text[:100]}")
+                    return None
         return None
 
     def _suggest_companies(self, product: str, market: str) -> list:

backend/app/services/followup_engine.py

@@ -287,11 +287,20 @@ class FollowupEngine:
         total = len(count_result.scalars().all())
 
         items = []
-        for log in logs:
-            customer_result = await self.db.execute(
-                select(Customer).where(Customer.id == log.customer_id)
-            )
-            customer = customer_result.scalar_one_or_none()
+        # Use join to avoid N+1 query problem
+        query = select(FollowupLog, Customer).join(
+            Customer, FollowupLog.customer_id == Customer.id, isouter=True
+        ).where(
+            FollowupLog.user_id == user_id
+        ).order_by(
+            FollowupLog.created_at.desc()
+        ).offset((page - 1) * size).limit(size)
+        
+        result = await self.db.execute(query)
+        rows = result.all()
+        
+        items = []
+        for log, customer in rows:
             items.append({
                 "id": str(log.id),
                 "customer_id": str(log.customer_id),

backend/app/services/import_service.py

@@ -21,8 +21,11 @@ OPTIONAL_COLUMNS = {
 }
 
 
+from app.config import settings
+
+
 class ImportService:
-    MAX_ROWS = 10000
+    MAX_ROWS = settings.MAX_EXCEL_ROWS
 
     @staticmethod
     def parse_xlsx(file_bytes: bytes) -> Tuple[List[Dict[str, Any]], List[str]]:

backend/app/services/mcp_search_client.py

@@ -84,11 +84,13 @@ class MCPClientManager:
             try:
                 await self._session.__aexit__(None, None, None)
             except (BaseExceptionGroup, RuntimeError, Exception):
+                # Cleanup failed, ignore error
                 pass
         if self._ctx:
             try:
                 await self._ctx.__aexit__(None, None, None)
             except (BaseExceptionGroup, RuntimeError, Exception):
+                # Cleanup failed, ignore error
                 pass