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/DebtCategoryController.ts

@@ -0,0 +1,89 @@
+import {FastifyRequest, FastifyReply} from 'fastify';
+import {DebtCategoryService} from '../services/DebtCategoryService';
+import {getUserId} from '../middleware/auth';
+import {z} from 'zod';
+
+const createCategorySchema = z.object({
+  name: z.string().min(1).max(255),
+  description: z.string().optional(),
+  color: z.string().regex(/^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$/).optional(),
+});
+
+const updateCategorySchema = z.object({
+  name: z.string().min(1).max(255).optional(),
+  description: z.string().optional(),
+  color: z.string().regex(/^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$/).optional(),
+});
+
+/**
+ * Controller for DebtCategory endpoints
+ * Implements Single Responsibility Principle - handles only HTTP layer
+ */
+export class DebtCategoryController {
+  constructor(private categoryService: DebtCategoryService) {}
+
+  /**
+   * Create a new debt category
+   */
+  async create(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const data = createCategorySchema.parse(request.body);
+
+    const category = await this.categoryService.create(userId, data);
+
+    return reply.status(201).send({category});
+  }
+
+  /**
+   * Get all debt categories
+   */
+  async getAll(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const {withStats} = request.query as {withStats?: string};
+
+    if (withStats === 'true') {
+      const categories = await this.categoryService.getWithStats(userId);
+      return reply.send({categories});
+    }
+
+    const categories = await this.categoryService.getAllByUser(userId);
+    return reply.send({categories});
+  }
+
+  /**
+   * Get a single debt category
+   */
+  async getOne(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const {id} = request.params as {id: string};
+
+    const category = await this.categoryService.getById(id, userId);
+
+    return reply.send({category});
+  }
+
+  /**
+   * Update a debt category
+   */
+  async update(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const {id} = request.params as {id: string};
+    const data = updateCategorySchema.parse(request.body);
+
+    const category = await this.categoryService.update(id, userId, data);
+
+    return reply.send({category});
+  }
+
+  /**
+   * Delete a debt category
+   */
+  async delete(request: FastifyRequest, reply: FastifyReply) {
+    const userId = getUserId(request);
+    const {id} = request.params as {id: string};
+
+    await this.categoryService.delete(id, userId);
+
+    return reply.status(204).send();
+  }
+}