Add backend API for personal finance management application

- Introduced a comprehensive backend API using TypeScript, Fastify, and PostgreSQL.
- Added essential files including architecture documentation, environment configuration, and Docker setup.
- Implemented RESTful routes for managing assets, liabilities, clients, invoices, and cashflow.
- Established a robust database schema with Prisma for data management.
- Integrated middleware for authentication and error handling.
- Created service and repository layers to adhere to SOLID principles and clean architecture.
- Included example environment variables for development, staging, and production setups.

backend-api/src/controllers/InvoiceController.ts

@@ -0,0 +1,137 @@
+import {FastifyRequest, FastifyReply} from 'fastify';
+import {InvoiceService} from '../services/InvoiceService';
+import {getUserId} from '../middleware/auth';
+import {z} from 'zod';
+
+const lineItemSchema = z.object({
+  description: z.string().min(1),
+  quantity: z.number().min(1),
+  unitPrice: z.number().min(0),
+  amount: z.number().min(0),
+});
+
+const createInvoiceSchema = z.object({
+  clientId: z.string().uuid(),
+  issueDate: z.string().transform(str => new Date(str)),
+  dueDate: z.string().transform(str => new Date(str)),
+  lineItems: z.array(lineItemSchema).min(1),
+  notes: z.string().optional(),
+  terms: z.string().optional(),
+});
+
+const updateInvoiceSchema = z.object({
+  issueDate: z.string().transform(str => new Date(str)).optional(),
+  dueDate: z.string().transform(str => new Date(str)).optional(),
+  lineItems: z.array(lineItemSchema).min(1).optional(),
+  notes: z.string().optional(),
+  terms: z.string().optional(),
+});
+
+const updateStatusSchema = z.object({
+  status: z.enum(['DRAFT', 'SENT', 'PAID', 'OVERDUE', 'CANCELLED']),
+});
+
+/**
+ * Controller for Invoice endpoints
+ * Implements Single Responsibility Principle - handles only HTTP layer
+ */
+export class InvoiceController {
+  constructor(private invoiceService: InvoiceService) {}
+
+  /**
+   * Create a new invoice
+   */
+  async create(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const data = createInvoiceSchema.parse(request.body);
+
+    const invoice = await this.invoiceService.create(userId, data);
+
+    return reply.status(201).send({invoice});
+  }
+
+  /**
+   * Get all invoices for the authenticated user
+   */
+  async getAll(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const {clientId, status} = request.query as {clientId?: string; status?: string};
+
+    const invoices = await this.invoiceService.getAllByUser(userId, {
+      clientId,
+      status,
+    });
+
+    return reply.send({invoices});
+  }
+
+  /**
+   * Get a single invoice by ID
+   */
+  async getOne(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const {id} = request.params as {id: string};
+
+    const invoice = await this.invoiceService.getById(id, userId);
+
+    return reply.send({invoice});
+  }
+
+  /**
+   * Update an invoice
+   */
+  async update(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const {id} = request.params as {id: string};
+    const data = updateInvoiceSchema.parse(request.body);
+
+    const invoice = await this.invoiceService.update(id, userId, data);
+
+    return reply.send({invoice});
+  }
+
+  /**
+   * Update invoice status
+   */
+  async updateStatus(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const {id} = request.params as {id: string};
+    const {status} = updateStatusSchema.parse(request.body);
+
+    const invoice = await this.invoiceService.updateStatus(id, userId, status);
+
+    return reply.send({invoice});
+  }
+
+  /**
+   * Delete an invoice
+   */
+  async delete(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const {id} = request.params as {id: string};
+
+    await this.invoiceService.delete(id, userId);
+
+    return reply.status(204).send();
+  }
+
+  /**
+   * Get invoice statistics
+   */
+  async getStats(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const stats = await this.invoiceService.getStats(userId);
+
+    return reply.send({stats});
+  }
+
+  /**
+   * Get overdue invoices
+   */
+  async getOverdue(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const overdueInvoices = await this.invoiceService.getOverdueInvoices(userId);
+
+    return reply.send({invoices: overdueInvoices});
+  }
+}