# Product Discounts - Implementation Summary

## Files Created/Modified

### ✅ NEW FILES CREATED

```
shop/
├── discount_views.py                                    # Core discount logic & AJAX handlers
├── migrations/
│   └── 0016_discount_model.py                          # Database migration
├── management/
│   ├── __init__.py
│   └── commands/
│       ├── __init__.py
│       └── discount_manager.py                         # CLI management tool

DOCUMENTATION/
├── DISCOUNT_QUICKSTART.md                              # Quick start guide
├── DISCOUNT_SYSTEM.md                                  # Complete documentation
└── DISCOUNT_TEMPLATES.md                               # Template snippets
```

### 📝 MODIFIED FILES

1. **shop/models.py**
   - Added `Discount` model (lines ~460+)
   - Updated `Order` model: added discount tracking fields
   - Updated `CartItem` model: added discount calculation methods
   - Updated `Product` model: added `get_active_discount()` method

2. **shop/admin.py**
   - Imported `Discount` model
   - Added `DiscountAdmin` class with full management interface
   - Badge/status indicators
   - Usage tracking display

3. **shop/forms.py**
   - Added `DiscountCodeForm` for checkout
   - Added `DiscountForm` for admin creation
   - Full validation logic

4. **shop/urls.py**
   - Imported discount views
   - Added `/discount/apply/` endpoint (POST)
   - Added `/discount/remove/` endpoint (POST)

## Feature Summary

### Discount Model Features

| Feature | Type | Details |
|---------|------|---------|
| **Discount Types** | percentage, fixed | 0-100% or fixed amount in $ |
| **Applicability** | Product, Category | All, specific products, specific categories |
| **Availability** | Date Range | Start/end date control |
| **Activation** | Active Toggle | Turn on/off |
| **Usage Tracking** | Global Limit | Max total uses |
| **User Limits** | Per-user Limit | Max uses per customer |
| **Minimum Purchase** | Amount Threshold | Min cart value to qualify |
| **Promo Codes** | Optional Code | e.g., SAVE20, WELCOME500 |

### Methods Available

```python
# Discount model methods
discount.is_valid()                      # Check if active & within date range
discount.can_user_use(user)              # Check user limit
discount.is_applicable_to_product(prod)  # Check product eligibility
discount.calculate_discount_amount(amt)  # Calculate savings
discount.calculate_discounted_price(p)   # Get final price
discount.apply()                         # Record usage

# Product model methods
product.get_active_discount()            # Get best active discount

# CartItem model methods
item.get_discounted_price()              # Price with discount
item.get_total_with_discount()           # Line total with discount

# Utility functions (discount_views.py)
calculate_cart_totals(cart, discount)    # Full cost breakdown
get_applied_discount(request)            # Get from session
get_product_discount_info(product)       # Display info
apply_discount_code(request)             # AJAX apply endpoint
remove_discount_code(request)            # AJAX remove endpoint
```

## Database Changes

### New Table: shop_discount
```sql
CREATE TABLE shop_discount (
    id BIGINT PRIMARY KEY,
    name VARCHAR(200),
    description TEXT,
    code VARCHAR(50) UNIQUE,
    discount_type VARCHAR(20),  -- 'percentage' or 'fixed'
    discount_value DECIMAL(10, 2),
    min_purchase DECIMAL(10, 2) DEFAULT 0,
    is_active BOOLEAN DEFAULT TRUE,
    start_date DATETIME,
    end_date DATETIME,
    usage_limit INT,
    usage_count INT DEFAULT 0,
    usage_limit_per_user INT,
    created_at DATETIME AUTO_NOW_ADD,
    updated_at DATETIME AUTO_NOW,
    created_by_id INT FK users.user
);

-- ManyToMany tables
shop_discount_products (discount_id, product_id)
shop_discount_categories (discount_id, category_id)
```

### Updated: shop_order
```sql
ALTER TABLE shop_order ADD COLUMN discount_id INT FK shop_discount;
ALTER TABLE shop_order ADD COLUMN subtotal DECIMAL(10, 2) DEFAULT 0;
ALTER TABLE shop_order ADD COLUMN discount_amount DECIMAL(10, 2) DEFAULT 0;
```

## URL Endpoints

### Apply Discount Code
```
POST /discount/apply/
Parameters: code (text)
Response: JSON {success, message, discount, totals}
```

### Remove Discount
```
POST /discount/remove/
Response: JSON {success, message}
```

## Admin Interface

**Location:** Django Admin → Shop → Discounts

**Features:**
- Create/edit/delete discounts
- Status badges (Active/Inactive)
- Usage tracking (X / Y)
- Fieldset organization
- Filter by active/type/date
- Search by name/code/description
- Multi-select products/categories
- Automatic created_by assignment

## Session Storage

Applied discounts stored in Django session:
```python
request.session['applied_discount_id'] = discount_id
```

Session cleared when:
- User removes discount
- Discount becomes invalid
- User logs out

## Integration Points

### In Cart Template
- Display applied discount
- Show "You Save" amount
- Form to enter discount code
- Button to remove discount

### In Product Templates
- Show discount badge
- Display original/sale price
- Show percentage/amount saved
- Display discount name

### In Checkout
- Confirm discount is applied
- Show discount breakdown
- Final total with discount

### In Order Confirmation
- Email shows discount applied
- Display amount saved
- Thank you message

## Admin Actions

### View All Discounts
Django Admin → Discounts → Table view

### Create New Discount
```
Click "Add Discount"
Fill in fields:
- Name, Code, Description
- Type, Value, Min Purchase
- Select Products/Categories
- Set Date Range
- Set Usage Limits
- Save
```

### Quick Create via CLI
```bash
python manage.py discount_manager --action=create \
    --name="Sale Name" \
    --code="CODENAME" \
    --type=percentage \
    --value=20
```

### View Report
```bash
python manage.py discount_manager --action=report
```

Shows all active discounts with status and usage.

## Testing the System

### Test 1: Apply Valid Discount
1. Create discount in admin
2. Add items to cart
3. Enter discount code
4. Verify totals update
5. Proceed to checkout

### Test 2: Check User Limits
1. Create discount with `usage_limit_per_user=1`
2. Apply discount to order
3. Try applying same discount again
4. Should be denied

### Test 3: Check Date Ranges
1. Create discount with start_date in future
2. Try to apply
3. Should be denied (not yet valid)
4. Check code - works

### Test 4: Check Min Purchase
1. Create discount with `min_purchase=50000`
2. Add items totaling $40,000
3. Apply discount
4. Should be denied
5. Add more items to $50,000+
6. Apply discount - should work

## Performance Considerations

- Discounts cached via `get_active_discount()`
- Database queries optimized with `select_related()`
- Session-based storage (no additional queries per request)
- Usage tracking increments atomically
- Admin list optimized for filters

## Security Considerations

✓ Django CSRF protection on form submissions
✓ Login required for discount endpoints
✓ User limit enforcement
✓ Usage tracking prevents fraud
✓ Date validation server-side
✓ Admin permissions required for management

## Migration Instructions

```bash
# 1. Copy all files (already done)
# 2. Run migration
python manage.py migrate shop

# 3. Test in admin
python manage.py runserver
# Visit: http://localhost:8000/admin/shop/discount/

# 4. Create test discount
# 5. Test in frontend

# 6. Deploy to production
python manage.py collectstatic
```

## Rollback (if needed)

```bash
python manage.py migrate shop 0015_product_barcode_product_qr_code
```

This removes the Discount model (but keeps migration history).

## Monitoring

Check in admin:
- Active discounts count
- Usage vs limits
- Code popularity
- Savings total per discount
- Customer usage patterns

## Future Enhancements

- [ ] Bulk discount creation
- [ ] Discount analytics dashboard
- [ ] A/B testing discounts
- [ ] Dynamic pricing
- [ ] Volume/tiered discounts
- [ ] Referral discounts
- [ ] Seasonal automation
- [ ] Personalized discounts
- [ ] Discount recommendations
- [ ] Integration with email marketing

## Support & Documentation

Comprehensive docs included:
- **DISCOUNT_QUICKSTART.md** - Get started in 5 minutes
- **DISCOUNT_SYSTEM.md** - Complete technical reference
- **DISCOUNT_TEMPLATES.md** - Frontend integration examples
- **Code comments** - Inline documentation

## Summary

✅ **New Discount Model** - Flexible, feature-rich
✅ **Admin Interface** - Easy management
✅ **AJAX Endpoints** - Seamless application
✅ **Validation** - Comprehensive checks
✅ **Session Storage** - Performance optimized
✅ **CLI Tools** - Batch operations
✅ **Documentation** - Complete guides
✅ **Ready to Deploy** - Production ready

The discount system is fully integrated, documented, and ready to use!
