Backend Architecture¶

The backend is built with Django 5.1 and Django REST Framework.

Project Structure¶

backend/
├── apps/
│   ├── analytics/      # PostHog event tracking
│   ├── clipart/        # SVG clipart library
│   ├── core/           # Site settings, pages, audit, backups
│   ├── designs/        # Custom designs, templates, fonts
│   ├── invoices/       # Invoice generation, numbering
│   ├── orders/         # Orders and cart
│   ├── payments/       # Mollie payments, refunds, audit
│   ├── pricing/        # Discounts, volume, team, offers
│   ├── products/       # Product catalog, variants, images
│   └── users/          # User accounts, profiles, addresses
├── config/
│   ├── settings.py     # Django settings
│   ├── urls.py         # URL routing
│   └── celery.py       # Celery config + beat schedule
├── fixtures/seed/      # Git-tracked seed data
├── media/              # Uploaded files (dev only)
├── static/             # Static assets
└── templates/          # Django templates (emails, invoices)

App Responsibilities¶

Products App¶

Manages the product catalog including: - Product models with variants (color/size) - Categories with MPTT hierarchy - Multi-view print area configuration (front/back/left/right) - Product color images with WebP generation - Catalog import/export (seed data system)

Designs App¶

Handles custom design creation: - Multi-view design storage (Fabric.js JSON per view) - Design templates and fonts (uploaded + Google) - Text colors with price modifiers - Image upload handling

Orders App¶

Order processing workflow: - Shopping cart management - Order creation with pricing snapshots - Status tracking with email notifications - VAT calculation and order history

Payments App¶

Payment processing with Mollie: - Payment creation and webhook handling - Refund management - Payment audit logging with state snapshots

Invoices App¶

Invoice generation: - Sequential invoice numbering (INV-YYYY-NNNNN) - PDF generation with WeasyPrint - Idempotent generation (one invoice per order)

Pricing App¶

Complex discount system: - Discount codes (percentage/fixed) - Volume discounts with tiered pricing - Team order discounts - Special offers (time-limited) - Automated pricing rules

Core App¶

Platform infrastructure: - Singleton site settings (cached) - Static pages (Terms, Privacy, FAQ, etc.) - Admin audit logging (before/after state) - Database backup management (S3)

API Design¶

All APIs follow REST conventions:

GET /api/resources/ - List
POST /api/resources/ - Create
GET /api/resources/{id}/ - Retrieve
PUT /api/resources/{id}/ - Update
DELETE /api/resources/{id}/ - Delete

Serializers¶

class ProductSerializer(serializers.ModelSerializer):
    category = CategorySerializer()
    color_variants = ColorVariantSerializer(many=True)

    class Meta:
        model = Product
        fields = ['id', 'name', 'slug', 'category', ...]

ViewSets¶

class ProductViewSet(viewsets.ReadOnlyModelViewSet):
    queryset = Product.objects.filter(is_active=True)
    serializer_class = ProductSerializer
    filterset_class = ProductFilter

Background Tasks¶

Celery handles async operations via Redis broker:

Hourly database backups (S3 upload with checksums)
Email notifications (order confirmation, status changes via Resend)
Monitoring (disk space, payment anomaly detection)
Backup maintenance (retention cleanup, restore verification)

Celery Beat Schedule¶

Task	Schedule	Purpose
`backup.daily_backup`	Hourly (min=0)	Database backup to S3
`backup.cleanup_old_backups`	Daily 03:00	Retention enforcement
`backup.verify_latest_backup`	Daily 04:00	Backup integrity check
`backup.test_restore`	Monthly	Full restore test
`monitoring.check_disk_space`	Hourly (:30)	Disk usage alerts
`monitoring.check_payment_anomalies`	Every 15 min	Payment fraud detection