feat: implement audit trail system

backend/src/app.module.ts

@@ -14,7 +14,7 @@ import { cdnConfig } from './config/cdn.config';
 import { stellarConfig } from './config/stellar.config';
 import { smsConfig } from './config/sms.config';
 import { AuthModule } from './auth/auth.module';
-import { ObservabilityModule } from './modules/observability/observability.module';
+import { AuditModule } from './audit/audit.module';
 
 // Feature Modules
 import { UsersModule } from './modules/users/users.module';
@@ -114,6 +114,7 @@ ThrottlerModule.forRoot([{
     LostPetsModule,
     AllergiesModule,
     ConditionsModule,
+    AuditModule,
 
     VerificationModule,
     GdprModule,

backend/src/audit/audit.controller.spec.ts

@@ -0,0 +1,18 @@
+import { Test, TestingModule } from '@nestjs/testing';
+import { AuditController } from './audit.controller';
+
+describe('AuditController', () => {
+  let controller: AuditController;
+
+  beforeEach(async () => {
+    const module: TestingModule = await Test.createTestingModule({
+      controllers: [AuditController],
+    }).compile();
+
+    controller = module.get<AuditController>(AuditController);
+  });
+
+  it('should be defined', () => {
+    expect(controller).toBeDefined();
+  });
+});

backend/src/audit/audit.controller.ts

@@ -0,0 +1,12 @@
+import { Controller, Get } from '@nestjs/common';
+import { AuditService } from './audit.service';
+
+@Controller('audit')
+export class AuditController {
+  constructor(private readonly auditService: AuditService) {}
+
+  @Get()
+  getLogs() {
+    return this.auditService.findAll();
+  }
+}

backend/src/audit/audit.entity.ts

@@ -0,0 +1,31 @@
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn } from 'typeorm';
+
+@Entity('audit_logs')
+export class AuditLog {
+  @PrimaryGeneratedColumn('uuid')
+  id: string;
+
+  @Column()
+  action: string;
+
+  @Column({ nullable: true })
+  entity: string;
+
+  @Column({ nullable: true })
+  entityId: string;
+
+  @Column({ type: 'json', nullable: true })
+  oldData: any;
+
+  @Column({ type: 'json', nullable: true })
+  newData: any;
+
+  @Column()
+  userId: string;
+
+  @Column()
+  hash: string;
+
+  @CreateDateColumn()
+  createdAt: Date;
+}

backend/src/audit/audit.interceptor.ts

@@ -0,0 +1,34 @@
+import {
+  Injectable,
+  NestInterceptor,
+  ExecutionContext,
+  CallHandler,
+} from '@nestjs/common';
+import { tap } from 'rxjs';
+import { AuditService } from './audit.service';
+
+@Injectable()
+export class AuditInterceptor implements NestInterceptor {
+  constructor(private readonly auditService: AuditService) {}
+
+  intercept(context: ExecutionContext, next: CallHandler) {
+    const request = context.switchToHttp().getRequest();
+
+    const { method, url, body, user } = request;
+
+    return next.handle().pipe(
+      tap(async (responseData) => {
+        try {
+          await this.auditService.logAction({
+            action: method,
+            entity: url,
+            userId: user?.id || 'anonymous',
+            newData: body,
+          });
+        } catch (err) {
+          console.error('Audit log failed:', err);
+        }
+      }),
+    );
+  }
+}

backend/src/audit/audit.module.ts

@@ -0,0 +1,13 @@
+import { Module } from '@nestjs/common';
+import { TypeOrmModule } from '@nestjs/typeorm';
+import { AuditLog } from './audit.entity';
+import { AuditService } from './audit.service';
+import { AuditController } from './audit.controller';
+
+@Module({
+  imports: [TypeOrmModule.forFeature([AuditLog])],
+  controllers: [AuditController],
+  providers: [AuditService],
+  exports: [AuditService],
+})
+export class AuditModule {}

backend/src/audit/audit.service.spec.ts

@@ -0,0 +1,18 @@
+import { Test, TestingModule } from '@nestjs/testing';
+import { AuditService } from './audit.service';
+
+describe('AuditService', () => {
+  let service: AuditService;
+
+  beforeEach(async () => {
+    const module: TestingModule = await Test.createTestingModule({
+      providers: [AuditService],
+    }).compile();
+
+    service = module.get<AuditService>(AuditService);
+  });
+
+  it('should be defined', () => {
+    expect(service).toBeDefined();
+  });
+});

backend/src/audit/audit.service.ts

@@ -0,0 +1,37 @@
+import { Injectable } from '@nestjs/common';
+import { InjectRepository } from '@nestjs/typeorm';
+import { AuditLog } from './audit.entity';
+import { Repository } from 'typeorm';
+import * as crypto from 'crypto';
+
+@Injectable()
+export class AuditService {
+  constructor(
+    @InjectRepository(AuditLog)
+    private readonly auditRepo: Repository<AuditLog>,
+  ) {}
+
+  generateHash(data: any): string {
+    return crypto
+      .createHash('sha256')
+      .update(JSON.stringify(data))
+      .digest('hex');
+  }
+
+  async logAction(payload: Partial<AuditLog>) {
+    const hash = this.generateHash(payload);
+
+    const log = this.auditRepo.create({
+      ...payload,
+      hash,
+    });
+
+    return this.auditRepo.save(log);
+  }
+
+  async findAll() {
+    return this.auditRepo.find({
+      order: { createdAt: 'DESC' },
+    });
+  }
+}

backend/src/main.ts

@@ -4,10 +4,14 @@ import { ConfigService } from '@nestjs/config';
 import { NestExpressApplication } from '@nestjs/platform-express';
 import helmet from 'helmet';
 import { AppModule } from './app.module';
+import { AuditInterceptor } from './audit/audit.interceptor';
+import { AuditService } from './audit/audit.service';
 
 async function bootstrap() {
   const app = await NestFactory.create<NestExpressApplication>(AppModule);
   const configService = app.get(ConfigService);
+  const auditService = app.get(AuditService);
+  app.useGlobalInterceptors(new AuditInterceptor(auditService));
 
   // Trust proxy for correct IP address detection
   // eslint-disable-next-line @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-member-access