Backend Complete: Interface Refactoring & Service Container Enhancements

Repository Interface Optimization:
- Created IBaseRepository.ts and IPaginatedRepository.ts
- Refactored all 7 repository interfaces to extend base interfaces
- Eliminated ~200 lines of redundant code (70% reduction)
- Improved type safety and maintainability

 Dependency Injection Improvements:
- Added EmailService and GameTokenService to DIContainer
- Updated CreateUserCommandHandler constructor for DI
- Updated RequestPasswordResetCommandHandler constructor for DI
- Enhanced testability and service consistency

 Environment Configuration:
- Created comprehensive .env.example with 40+ variables
- Organized into 12 logical sections (Database, Security, Email, etc.)
- Added security guidelines and best practices
- Documented all backend environment requirements

 Documentation:
- Added comprehensive codebase review
- Created refactoring summary report
- Added frontend implementation guide

Impact: Improved code quality, reduced maintenance overhead, enhanced developer experience

SerpentRace_Backend/src/Application/User/commands/CreateUserCommandHandler.ts

@@ -0,0 +1,91 @@
+import { IUserRepository } from '../../../Domain/IRepository/IUserRepository';
+import { CreateUserCommand } from './CreateUserCommand';
+import { ShortUserDto } from '../../DTOs/UserDto';
+import { UserAggregate, UserState } from '../../../Domain/User/UserAggregate';
+import { UserMapper } from '../../DTOs/Mappers/UserMapper';
+import { PasswordService } from '../../Services/PasswordService';
+import { EmailService } from '../../Services/EmailService';
+import { TokenService } from '../../Services/TokenService';
+import { logDatabase, logError, logAuth, logWarning } from '../../Services/Logger';
+
+export class CreateUserCommandHandler {
+  constructor(
+    private readonly userRepo: IUserRepository,
+    private readonly emailService: EmailService
+  ) {}
+
+  async execute(cmd: CreateUserCommand): Promise<ShortUserDto> {
+    try {
+      // Validate password strength
+      const passwordValidation = PasswordService.validatePasswordStrength(cmd.password);
+      if (!passwordValidation.isValid) {
+        throw new Error(`Password validation failed: ${passwordValidation.errors.join(', ')}`);
+      }
+
+      const user = new UserAggregate();
+      user.username = cmd.username;
+      
+      // Hash the password before storing
+      user.password = await PasswordService.hashPassword(cmd.password);
+      
+      // Generate verification token
+      const verificationTokenData = TokenService.generateVerificationToken();
+      user.token = await TokenService.hashToken(verificationTokenData.token);
+      user.TokenExpires = verificationTokenData.expiresAt;
+      
+      user.email = cmd.email;
+      user.fname = cmd.fname;
+      user.lname = cmd.lname;
+      user.orgid = cmd.orgid || null;
+      user.phone = cmd.phone || null;
+      user.state = UserState.REGISTERED_NOT_VERIFIED;
+      
+      const created = await this.userRepo.create(user);
+      
+      // Send verification email (non-blocking)
+      this.sendVerificationEmailAsync(created, verificationTokenData.token);
+      
+      return UserMapper.toShortDto(created);
+    } catch (error) {
+      // Only log the error once here, don't log again in router
+      const errorMessage = (error as Error).message;
+      
+      // Re-throw validation errors as-is (don't log as these are user input errors)
+      if (errorMessage.includes('Password validation failed')) {
+        throw error;
+      }
+      
+      // Handle database constraint errors
+      if (errorMessage.includes('duplicate') || errorMessage.includes('unique') || 
+          errorMessage.includes('UNIQUE constraint') || errorMessage.includes('already exists')) {
+        throw new Error('User with this username or email already exists');
+      }
+      
+      // Log database/system errors but throw user-friendly message
+      logError('CreateUserCommandHandler error', error as Error);
+      throw new Error('Failed to create user');
+    }
+  }
+
+  private async sendVerificationEmailAsync(user: UserAggregate, token: string): Promise<void> {
+    try {
+      const baseUrl = process.env.APP_BASE_URL || 'http://localhost:3000';
+      const verificationUrl = TokenService.generateVerificationUrl(baseUrl, token);
+      
+      const emailSent = await this.emailService.sendVerificationEmail(
+        user.email,
+        `${user.fname} ${user.lname}`,
+        token,
+        verificationUrl
+      );
+      
+      if (!emailSent) {
+        logWarning('Failed to send verification email', { email: user.email, userId: user.id });
+      } else {
+        logAuth('Verification email sent successfully', user.id, { email: user.email });
+      }
+    } catch (emailError) {
+      logError('Error sending verification email', emailError as Error);
+    }
+  }
+}