1. Development Strategy

To build a robust stock management system that works both online and offline, we'll adopt a Progressive Web App (PWA) approach using Next.js with the App Router and TypeScript. Here's the proposed development strategy focusing on structure and architecture:

a. Overall Architecture:

• Frontend: Next.js (App Router) with TypeScript
• Backend: Supabase (PostgreSQL database, authentication, and storage)
• Offline Capability: Implement PWA features with service workers and IndexedDB/localStorage
• Deployment: Host on Vercel or another hosting provider that supports Next.js applications

b. Key Components:

• Authentication & Authorization:
  • Use Supabase Auth for managing user authentication.
  • Implement role-based access control (Admin and Cashier roles).
• State Management:
  • Use React Context API or a state management library like Zustand or Redux for managing global state.
• Data Synchronization:
  • Implement offline data storage using IndexedDB (e.g., utilizing libraries like Dexie.js).
  • Create a synchronization mechanism to sync local changes with the Supabase backend when the connection is re-established.
• Service Workers:
  • Use service workers to cache assets and API responses for offline use.
  • Implement strategies for cache invalidation and updating.
• PDF Generation:
  • Use a library like pdfmake or jspdf to generate invoices on the client side.
• File Storage:
  • Use Supabase Storage or a third-party service like Uploadthing for image uploads.
  • Ensure images are cached for offline viewing.

c. Project Structure:

• Pages and Routes:
  • Utilize Next.js App Router to create nested routes for different sections like /products, /orders, /reports, etc.
• Components:
  • Create reusable components for forms, tables, modals, etc.
• APIs:
  • Use Next.js API routes or Edge Functions (via Supabase) for server-side logic.
• Styles:
  • Use a CSS-in-JS solution like styled-components or Tailwind CSS for styling.
• TypeScript:
  • Define interfaces and types for all data models and API responses.

d. Offline Strategy:

• Caching:
  • Cache static assets (CSS, JS files) using service workers.
  • Cache API responses for read operations.
• Local Data Storage:
  • Store pending write operations (e.g., new orders) in IndexedDB.
  • Queue and sync these operations when back online.
• UI Indicators:
  • Show network status to the user.
  • Indicate when data is being saved locally vs. synced.

e. Synchronization Mechanism:

• Conflict Resolution:
  • Implement strategies for handling data conflicts (e.g., last-write-wins, manual merge).
• Background Sync:
  • Use the Background Sync API to sync data when the connection is restored.
• Notifications:
  • Notify users about the sync status and any errors that occur during synchronization.

2. API Endpoints

The application will require several API endpoints to manage products, categories, orders, clients, and more. Here are the key APIs:

a. Authentication APIs:

• POST /api/auth/login
  • Authenticate user and provide access token.
• POST /api/auth/logout
  • Invalidate the user session.
• GET /api/auth/me
  • Get current user information.

b. Product APIs:

• GET /api/products
  • Retrieve a list of products with optional filters (category, recent, etc.).
• GET /api/products/:id
  • Get details of a specific product.
• POST /api/products
  • Create a new product.
• PUT /api/products/:id
  • Update an existing product.
• DELETE /api/products/:id
  • Delete a product.

c. Category APIs:

• GET /api/categories
  • Retrieve a list of product categories.
• GET /api/categories/:id
  • Get details of a specific category.
• POST /api/categories
  • Create a new category.
• PUT /api/categories/:id
  • Update an existing category.
• DELETE /api/categories/:id
  • Delete a category.

d. Order APIs:

• GET /api/orders
  • Retrieve a list of orders with optional filters (date range, client, etc.).
• GET /api/orders/:id
  • Get details of a specific order.
• POST /api/orders
  • Create a new order (includes client info and order items).
• PUT /api/orders/:id
  • Update an existing order.
• DELETE /api/orders/:id
  • Delete an order.

e. Client APIs:

• GET /api/clients
  • Retrieve a list of clients.
• GET /api/clients/:id
  • Get details of a specific client.
• POST /api/clients
  • Create a new client.
• PUT /api/clients/:id
  • Update client information.
• DELETE /api/clients/:id
  • Delete a client.

f. Stock APIs:

• GET /api/stock
  • Retrieve stock levels for all products.
• GET /api/stock/:productId
  • Get stock level for a specific product.
• PUT /api/stock/:productId
  • Update stock level for a product.
• GET /api/stock/critical
  • Get products that have reached critical stock levels.

g. Report APIs:

• GET /api/reports/weekly
  • Generate and retrieve weekly reports.
• GET /api/reports/monthly
  • Generate and retrieve monthly reports.
• POST /api/reports/send
  • Send reports via email to designated recipients.

h. Image Upload APIs:

• POST /api/uploads
  • Upload product images to the bucket storage.

Note: Since you're using Supabase, you can leverage Supabase's Edge Functions for serverless functions or use Next.js API routes for custom API logic.

3. Database Implementation and Data Models

Designing an efficient database schema is crucial. Here's how you can implement your database using Supabase (PostgreSQL):

a. Tables and Schemas:

1. Users Table (users):

   • Columns:
     • id (UUID, primary key)
     • name (string)
     • email (string, unique)
     • password (hashed string)
     • role (enum: 'admin', 'cashier')
     • created_at (timestamp)
     • updated_at (timestamp)

2. Clients Table (clients):

   • Columns:
     • id (UUID, primary key)
     • name (string)
     • email (string)
     • phone (string)
     • address (string)
     • created_at (timestamp)
     • updated_at (timestamp)

3. Categories Table (categories):

   • Columns:
     • id (UUID, primary key)
     • name (string)
     • description (string)
     • created_at (timestamp)
     • updated_at (timestamp)

4. Products Table (products):

   • Columns:
     • id (UUID, primary key)
     • name (string)
     • description (string)
     • price (decimal)
     • category_id (foreign key to categories.id)
     • image_url (string)
     • created_at (timestamp)
     • updated_at (timestamp)

5. Stock Table (stock):

   • Columns:
     • id (UUID, primary key)
     • product_id (foreign key to products.id)
     • quantity (integer)
     • critical_level (integer) - threshold for critical stock notification
     • updated_at (timestamp)

6. Orders Table (orders):

   • Columns:
     • id (UUID, primary key)
     • client_id (foreign key to clients.id)
     • user_id (foreign key to users.id) - who created the order
     • total_amount (decimal)
     • status (enum: 'pending', 'completed', 'cancelled')
     • created_at (timestamp)
     • updated_at (timestamp)

7. Order Items Table (order_items):

   • Columns:
     • id (UUID, primary key)
     • order_id (foreign key to orders.id)
     • product_id (foreign key to products.id)
     • quantity (integer)
     • price (decimal) - price at the time of order
     • subtotal (decimal) - quantity * price

8. Reports Table (reports):

   • Columns:
     • id (UUID, primary key)
     • type (enum: 'weekly', 'monthly')
     • generated_at (timestamp)
     • data (JSONB) - summary data for the report
     • file_url (string) - link to the generated report file (if stored)

b. Relationships:

• Users and Orders:
  • One-to-many: One user can create many orders.
• Clients and Orders:
  • One-to-many: One client can have many orders.
• Orders and Order Items:
  • One-to-many: One order has many order items.
• Products and Order Items:
  • Many-to-many (through order_items): Products can be in many orders.
• Products and Categories:
  • Many-to-one: Many products belong to one category.
• Products and Stock:
  • One-to-one: Each product has one stock record.

c. Data Types and Constraints:

• Use appropriate data types (UUID for IDs, decimal for monetary values).
• Implement constraints (e.g., UNIQUE, NOT NULL, CHECK constraints for data validation).
• Use foreign keys to enforce referential integrity.

d. Indexing:

• Add indexes on frequently searched columns (e.g., product name, category_id, created_at).
• Use composite indexes for combined search queries.

e. Sample Data Models (TypeScript Interfaces):

// User
interface User {
  id: string;
  name: string;
  email: string;
  role: 'admin' | 'cashier';
  createdAt: string;
  updatedAt: string;
}

// Client
interface Client {
  id: string;
  name: string;
  email: string;
  phone: string;
  address: string;
  createdAt: string;
  updatedAt: string;
}

// Category
interface Category {
  id: string;
  name: string;
  description: string;
  createdAt: string;
  updatedAt: string;
}

// Product
interface Product {
  id: string;
  name: string;
  description: string;
  price: number;
  categoryId: string;
  imageUrl: string;
  createdAt: string;
  updatedAt: string;
}

// Stock
interface Stock {
  id: string;
  productId: string;
  quantity: number;
  criticalLevel: number;
  updatedAt: string;
}

// Order
interface Order {
  id: string;
  clientId: string;
  userId: string;
  totalAmount: number;
  status: 'pending' | 'completed' | 'cancelled';
  createdAt: string;
  updatedAt: string;
  orderItems: OrderItem[];
}

// Order Item
interface OrderItem {
  id: string;
  orderId: string;
  productId: string;
  quantity: number;
  price: number;
  subtotal: number;
}

// Report
interface Report {
  id: string;
  type: 'weekly' | 'monthly';
  generatedAt: string;
  data: any; // Define a more specific type based on report structure
  fileUrl: string;
}

f. Implementing in Supabase:

• Database Creation:
  • Use Supabase dashboard or SQL scripts to create tables and define relationships.
• Row-Level Security (RLS):
  • Implement RLS policies to secure data access based on user roles.
• Stored Procedures and Triggers:
  • Use triggers for actions like updating stock quantities when an order is placed.
  • Create stored procedures for complex queries or reports generation.

g. Data Synchronization Considerations:

• Conflict Handling:
  • Assign version numbers to records or use timestamps to detect and resolve conflicts.
• Sync Logs:
  • Keep a log of data changes to aid in synchronization and debugging.

Additional Notes:

• Testing:
  • Write unit tests for critical components and API endpoints.
  • Perform integration testing, especially for offline-online transitions.
• Security:
  • Secure APIs with authentication tokens.
  • Encrypt sensitive data both in transit (HTTPS) and at rest.
• Performance:
  • Optimize queries and API responses.
  • Lazy load data where appropriate.
• User Experience:
  • Design intuitive interfaces with clear navigation.
  • Provide feedback to users during operations (e.g., loading spinners, success messages).