Minor version bump (1.x.0) is appropriate because:

✅ New functionality added (soft delete system)
✅ Backward compatible (existing features unchanged)
✅ Significant enhancement (complete temporal tracking system)
✅ API additions (new endpoints, parameters)
✅ UI enhancements (new components, visual indicators)

backend/main.py

@@ -1,7 +1,7 @@
 from fastapi import FastAPI, Depends, HTTPException, status
 from fastapi.middleware.cors import CORSMiddleware
 from sqlalchemy.orm import Session
-from sqlalchemy import text
+from sqlalchemy import text, func
 from typing import List
 import models, schemas
 from database import engine, get_db
@@ -95,6 +95,34 @@ def build_shopping_event_response(event: models.ShoppingEvent, db: Session) -> s
 def read_root():
     return {"message": __app_name__, "version": __version__, "name": "Groceries Tracker Backend"}
 
+# Utility endpoints
+@app.get("/current-date")
+def get_current_date():
+    """Get current date for use as default in valid_from fields"""
+    from datetime import date
+    return {"current_date": date.today().isoformat()}
+
+@app.get("/products/available-for-shopping/{shopping_date}", response_model=List[schemas.Product])
+def get_products_available_for_shopping(shopping_date: str, db: Session = Depends(get_db)):
+    """Get products that were available (not deleted) on a specific shopping date"""
+    from datetime import datetime
+    
+    try:
+        # Parse the shopping date
+        target_date = datetime.strptime(shopping_date, '%Y-%m-%d').date()
+    except ValueError:
+        raise HTTPException(status_code=400, detail="Invalid date format. Use YYYY-MM-DD format")
+    
+    # Get products that were either:
+    # 1. Never deleted (deleted=False)
+    # 2. Deleted after the shopping date (valid_from > shopping_date for deleted=True products)
+    products = db.query(models.Product).filter(
+        (models.Product.deleted == False) |
+        ((models.Product.deleted == True) & (models.Product.valid_from > target_date))
+    ).all()
+    
+    return products
+
 # Product endpoints
 @app.post("/products/", response_model=schemas.Product)
 def create_product(product: schemas.ProductCreate, db: Session = Depends(get_db)):
@@ -109,15 +137,31 @@ def create_product(product: schemas.ProductCreate, db: Session = Depends(get_db)
         if brand is None:
             raise HTTPException(status_code=404, detail="Brand not found")
     
-    db_product = models.Product(**product.dict())
+    # Validate valid_from date if provided
+    if product.valid_from is not None:
+        from datetime import date
+        if product.valid_from > date.today():
+            raise HTTPException(status_code=400, detail="Valid from date cannot be in the future")
+    
+    # Create product data
+    product_data = product.dict(exclude={'valid_from'})
+    db_product = models.Product(**product_data)
+    
+    # Set valid_from if provided, otherwise let database default handle it
+    if product.valid_from is not None:
+        db_product.valid_from = product.valid_from
+    
     db.add(db_product)
     db.commit()
     db.refresh(db_product)
     return db_product
 
 @app.get("/products/", response_model=List[schemas.Product])
-def read_products(skip: int = 0, limit: int = 100, db: Session = Depends(get_db)):
-    products = db.query(models.Product).offset(skip).limit(limit).all()
+def read_products(skip: int = 0, limit: int = 100, show_deleted: bool = False, db: Session = Depends(get_db)):
+    query = db.query(models.Product)
+    if not show_deleted:
+        query = query.filter(models.Product.deleted == False)
+    products = query.offset(skip).limit(limit).all()
     return products
 
 @app.get("/products/{product_id}", response_model=schemas.Product)
@@ -127,13 +171,21 @@ def read_product(product_id: int, db: Session = Depends(get_db)):
         raise HTTPException(status_code=404, detail="Product not found")
     return product
 
+@app.get("/products/{product_id}/valid-from")
+def get_product_valid_from(product_id: int, db: Session = Depends(get_db)):
+    """Get the current valid_from date for a product (used for validation when editing)"""
+    product = db.query(models.Product).filter(models.Product.id == product_id).first()
+    if product is None:
+        raise HTTPException(status_code=404, detail="Product not found")
+    return {"valid_from": product.valid_from.isoformat()}
+
 @app.put("/products/{product_id}", response_model=schemas.Product)
 def update_product(product_id: int, product_update: schemas.ProductUpdate, db: Session = Depends(get_db)):
     product = db.query(models.Product).filter(models.Product.id == product_id).first()
     if product is None:
         raise HTTPException(status_code=404, detail="Product not found")
     
-    update_data = product_update.dict(exclude_unset=True)
+    update_data = product_update.dict(exclude_unset=True, exclude={'valid_from'})
     
     # Validate category exists if category_id is being updated
     if 'category_id' in update_data:
@@ -147,9 +199,32 @@ def update_product(product_id: int, product_update: schemas.ProductUpdate, db: S
         if brand is None:
             raise HTTPException(status_code=404, detail="Brand not found")
     
+    # Validate valid_from date if provided
+    if product_update.valid_from is not None:
+        from datetime import date
+        if product_update.valid_from > date.today():
+            raise HTTPException(status_code=400, detail="Valid from date cannot be in the future")
+        if product_update.valid_from <= product.valid_from:
+            raise HTTPException(
+                status_code=400, 
+                detail=f"Valid from date must be after the current product's valid from date ({product.valid_from})"
+            )
+    
+    # Check if any versioned fields are actually changing
+    versioned_fields = ['name', 'category_id', 'brand_id', 'organic', 'weight', 'weight_unit']
+    has_changes = any(
+        field in update_data and getattr(product, field) != update_data[field] 
+        for field in versioned_fields
+    )
+    
+    # Apply the updates - trigger will handle history creation automatically
     for field, value in update_data.items():
         setattr(product, field, value)
     
+    # Set valid_from if provided for manual versioning
+    if product_update.valid_from is not None:
+        product.valid_from = product_update.valid_from
+    
     db.commit()
     db.refresh(product)
     return product
@@ -160,10 +235,163 @@ def delete_product(product_id: int, db: Session = Depends(get_db)):
     if product is None:
         raise HTTPException(status_code=404, detail="Product not found")
     
-    db.delete(product)
+    if product.deleted:
+        raise HTTPException(status_code=400, detail="Product is already deleted")
+    
+    from datetime import date
+    
+    # Simply mark as deleted and set valid_from to today
+    # The trigger will automatically create the history record
+    product.deleted = True
+    product.valid_from = date.today()
+    product.updated_at = func.now()
+    
     db.commit()
     return {"message": "Product deleted successfully"}
 
+# Historical Product endpoints
+@app.get("/products/{product_id}/history", response_model=List[schemas.ProductHistory])
+def get_product_history(product_id: int, db: Session = Depends(get_db)):
+    """Get all historical versions of a product"""
+    # Check if product exists
+    product = db.query(models.Product).filter(models.Product.id == product_id).first()
+    if product is None:
+        raise HTTPException(status_code=404, detail="Product not found")
+    
+    # Get history from history table
+    history = db.query(models.ProductHistory).filter(
+        models.ProductHistory.id == product_id
+    ).order_by(models.ProductHistory.valid_from.desc()).all()
+    
+    return history
+
+@app.get("/products/{product_id}/at/{date}", response_model=schemas.ProductAtDate)
+def get_product_at_date(product_id: int, date: str, db: Session = Depends(get_db)):
+    """Get product as it existed at a specific date - CRUCIAL for shopping events"""
+    from datetime import datetime, date as date_type
+    
+    try:
+        # Parse the date string (accept YYYY-MM-DD format)
+        target_date = datetime.strptime(date, '%Y-%m-%d').date()
+    except ValueError:
+        raise HTTPException(status_code=400, detail="Invalid date format. Use YYYY-MM-DD format")
+    
+    # First try current products table
+    current_product = db.query(models.Product).filter(
+        models.Product.id == product_id,
+        models.Product.valid_from <= target_date,
+        models.Product.valid_to >= target_date
+    ).first()
+    
+    if current_product:
+        # Get related data
+        category = db.query(models.GroceryCategory).filter(
+            models.GroceryCategory.id == current_product.category_id
+        ).first()
+        brand = None
+        if current_product.brand_id:
+            brand = db.query(models.Brand).filter(
+                models.Brand.id == current_product.brand_id
+            ).first()
+        
+        return schemas.ProductAtDate(
+            id=current_product.id,
+            name=current_product.name,
+            category_id=current_product.category_id,
+            category=category,
+            brand_id=current_product.brand_id,
+            brand=brand,
+            organic=current_product.organic,
+            weight=current_product.weight,
+            weight_unit=current_product.weight_unit,
+            valid_from=current_product.valid_from,
+            valid_to=current_product.valid_to,
+            deleted=current_product.deleted,
+            was_current=True
+        )
+    
+    # Try history table
+    historical_product = db.query(models.ProductHistory).filter(
+        models.ProductHistory.id == product_id,
+        models.ProductHistory.valid_from <= target_date,
+        models.ProductHistory.valid_to >= target_date
+    ).first()
+    
+    if historical_product:
+        # Get related data (note: these might have changed too, but we'll use current versions)
+        category = db.query(models.GroceryCategory).filter(
+            models.GroceryCategory.id == historical_product.category_id
+        ).first()
+        brand = None
+        if historical_product.brand_id:
+            brand = db.query(models.Brand).filter(
+                models.Brand.id == historical_product.brand_id
+            ).first()
+        
+        return schemas.ProductAtDate(
+            id=historical_product.id,
+            name=historical_product.name,
+            category_id=historical_product.category_id,
+            category=category,
+            brand_id=historical_product.brand_id,
+            brand=brand,
+            organic=historical_product.organic,
+            weight=historical_product.weight,
+            weight_unit=historical_product.weight_unit,
+            valid_from=historical_product.valid_from,
+            valid_to=historical_product.valid_to,
+            deleted=historical_product.deleted,
+            was_current=False
+        )
+    
+    # Product didn't exist at that date
+    raise HTTPException(
+        status_code=404, 
+        detail=f"Product {product_id} did not exist on {date}"
+    )
+
+@app.get("/shopping-events/{event_id}/products-as-purchased", response_model=List[schemas.ProductAtPurchase])
+def get_shopping_event_products_as_purchased(event_id: int, db: Session = Depends(get_db)):
+    """Get products as they were when purchased - shows historical product data"""
+    # Get the shopping event
+    event = db.query(models.ShoppingEvent).filter(models.ShoppingEvent.id == event_id).first()
+    if event is None:
+        raise HTTPException(status_code=404, detail="Shopping event not found")
+    
+    # Get products from association table
+    products_data = db.execute(
+        text("""
+            SELECT sep.product_id, sep.amount, sep.price, sep.discount
+            FROM shopping_event_products sep
+            WHERE sep.shopping_event_id = :event_id
+        """),
+        {"event_id": event_id}
+    ).fetchall()
+    
+    result = []
+    for product_data in products_data:
+        # Get product as it was at the time of purchase
+        try:
+            # Extract just the date from the shopping event datetime
+            purchase_date = event.date.date().strftime('%Y-%m-%d')
+            product_at_purchase = get_product_at_date(
+                product_data.product_id, 
+                purchase_date, 
+                db
+            )
+            
+            result.append(schemas.ProductAtPurchase(
+                product=product_at_purchase,
+                amount=product_data.amount,
+                price=product_data.price,
+                discount=product_data.discount
+            ))
+        except HTTPException:
+            # Product didn't exist at purchase time (shouldn't happen, but handle gracefully)
+            continue
+    
+    return result
+
 # Shop endpoints
 @app.post("/shops/", response_model=schemas.Shop)
 def create_shop(shop: schemas.ShopCreate, db: Session = Depends(get_db)):