# NestJS Backend Guidelines

## Overview

All backend services use NestJS with a consistent architecture. This guide covers controllers, services, DTOs, modules, and integration with the error handling system.

## Project Structure

```
apps/{project}/apps/backend/
├── src/
│   ├── main.ts                    # Bootstrap
│   ├── app.module.ts              # Root module
│   ├── db/
│   │   ├── schema/                # Drizzle schemas
│   │   ├── connection.ts          # DB singleton
│   │   ├── database.module.ts     # NestJS module
│   │   └── migrations/            # Migration files
│   ├── common/
│   │   ├── filters/               # Exception filters
│   │   ├── guards/                # Custom guards
│   │   └── decorators/            # Custom decorators
│   ├── health/
│   │   ├── health.controller.ts
│   │   └── health.module.ts
│   └── {feature}/
│       ├── {feature}.controller.ts
│       ├── {feature}.service.ts
│       ├── {feature}.module.ts
│       ├── {feature}.spec.ts
│       └── dto/
│           ├── create-{feature}.dto.ts
│           └── update-{feature}.dto.ts
├── test/
│   ├── jest-e2e.json
│   └── app.e2e-spec.ts
├── drizzle.config.ts
├── nest-cli.json
├── package.json
└── tsconfig.json
```

## Bootstrap (main.ts)

```typescript
// src/main.ts
import { NestFactory } from '@nestjs/core';
import { ValidationPipe, Logger } from '@nestjs/common';
import { AppModule } from './app.module';
import { AppExceptionFilter } from './common/filters/app-exception.filter';

async function bootstrap() {
	const app = await NestFactory.create(AppModule);
	const logger = new Logger('Bootstrap');

	// CORS
	const corsOrigins = process.env.CORS_ORIGINS?.split(',').map((o) => o.trim()) || [
		'http://localhost:3000',
		'http://localhost:5173',
		'http://localhost:8081',
	];

	app.enableCors({
		origin: corsOrigins,
		methods: ['GET', 'POST', 'PUT', 'PATCH', 'DELETE', 'OPTIONS'],
		credentials: true,
	});

	// Global validation pipe
	app.useGlobalPipes(
		new ValidationPipe({
			whitelist: true, // Strip unknown properties
			forbidNonWhitelisted: true, // Reject unknown properties
			transform: true, // Auto-transform types
			transformOptions: {
				enableImplicitConversion: true,
			},
		})
	);

	// Global exception filter
	app.useGlobalFilters(new AppExceptionFilter());

	// API prefix
	app.setGlobalPrefix('api/v1');

	const port = process.env.PORT || 3000;
	await app.listen(port);
	logger.log(`Application running on http://localhost:${port}`);
}

bootstrap();
```

## App Module

```typescript
// src/app.module.ts
import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';
import { DatabaseModule } from './db/database.module';
import { HealthModule } from './health/health.module';
import { FileModule } from './file/file.module';
import { FolderModule } from './folder/folder.module';

@Module({
	imports: [
		ConfigModule.forRoot({
			isGlobal: true,
			envFilePath: '.env',
		}),
		DatabaseModule,
		HealthModule,
		FileModule,
		FolderModule,
	],
})
export class AppModule {}
```

## Controllers

### Basic Pattern

```typescript
// src/file/file.controller.ts
import {
	Controller,
	Get,
	Post,
	Patch,
	Delete,
	Param,
	Body,
	Query,
	UseGuards,
	ParseUUIDPipe,
} from '@nestjs/common';
import { JwtAuthGuard, CurrentUser, CurrentUserData } from '@manacore/shared-nestjs-auth';
import { AppException } from '@manacore/shared-errors';
import { FileService } from './file.service';
import { CreateFileDto, UpdateFileDto, QueryFilesDto } from './dto';

@Controller('files')
@UseGuards(JwtAuthGuard) // Apply to all routes in controller
export class FileController {
	constructor(private readonly fileService: FileService) {}

	@Get()
	async list(@CurrentUser() user: CurrentUserData, @Query() query: QueryFilesDto) {
		const result = await this.fileService.findAll(user.userId, query);
		if (!result.ok) throw new AppException(result.error);
		return { files: result.data };
	}

	@Get(':id')
	async getById(@Param('id', ParseUUIDPipe) id: string, @CurrentUser() user: CurrentUserData) {
		const result = await this.fileService.findById(id, user.userId);
		if (!result.ok) throw new AppException(result.error);
		return { file: result.data };
	}

	@Post()
	async create(@Body() dto: CreateFileDto, @CurrentUser() user: CurrentUserData) {
		const result = await this.fileService.create(user.userId, dto);
		if (!result.ok) throw new AppException(result.error);
		return { file: result.data };
	}

	@Patch(':id')
	async update(
		@Param('id', ParseUUIDPipe) id: string,
		@Body() dto: UpdateFileDto,
		@CurrentUser() user: CurrentUserData
	) {
		const result = await this.fileService.update(id, user.userId, dto);
		if (!result.ok) throw new AppException(result.error);
		return { file: result.data };
	}

	@Delete(':id')
	async delete(@Param('id', ParseUUIDPipe) id: string, @CurrentUser() user: CurrentUserData) {
		const result = await this.fileService.delete(id, user.userId);
		if (!result.ok) throw new AppException(result.error);
		return { success: true };
	}
}
```

### Public Endpoints (No Auth)

```typescript
@Controller('public')
export class PublicController {
	@Get('shares/:token') // No @UseGuards - public access
	async getSharedItem(@Param('token') token: string) {
		const result = await this.shareService.findByToken(token);
		if (!result.ok) throw new AppException(result.error);
		return { item: result.data };
	}
}
```

## Services

### Basic Pattern with Result Types

```typescript
// src/file/file.service.ts
import { Injectable, Inject, Logger } from '@nestjs/common';
import { Result, ok, err, ErrorCode } from '@manacore/shared-errors';
import { DATABASE_CONNECTION, Database } from '../db/database.module';
import { files, File, NewFile } from '../db/schema';
import { eq, and, desc } from 'drizzle-orm';
import { CreateFileDto, UpdateFileDto, QueryFilesDto } from './dto';

@Injectable()
export class FileService {
	private readonly logger = new Logger(FileService.name);

	constructor(@Inject(DATABASE_CONNECTION) private db: Database) {}

	async findAll(userId: string, query: QueryFilesDto): Promise<Result<File[]>> {
		try {
			const conditions = [eq(files.userId, userId), eq(files.isDeleted, false)];

			if (query.folderId) {
				conditions.push(eq(files.parentFolderId, query.folderId));
			}

			const result = await this.db
				.select()
				.from(files)
				.where(and(...conditions))
				.orderBy(desc(files.createdAt))
				.limit(query.limit ?? 50)
				.offset(query.offset ?? 0);

			return ok(result);
		} catch (error) {
			this.logger.error('Failed to fetch files', { userId, error: error.message });
			return err(ErrorCode.DATABASE_ERROR, 'Failed to fetch files');
		}
	}

	async findById(id: string, userId: string): Promise<Result<File>> {
		try {
			const [file] = await this.db
				.select()
				.from(files)
				.where(and(eq(files.id, id), eq(files.userId, userId), eq(files.isDeleted, false)));

			if (!file) {
				return err(ErrorCode.FILE_NOT_FOUND, `File ${id} not found`);
			}

			return ok(file);
		} catch (error) {
			this.logger.error('Failed to fetch file', { id, userId, error: error.message });
			return err(ErrorCode.DATABASE_ERROR, 'Failed to fetch file');
		}
	}

	async create(userId: string, dto: CreateFileDto): Promise<Result<File>> {
		// Validation
		if (!dto.name?.trim()) {
			return err(ErrorCode.MISSING_REQUIRED_FIELD, 'File name is required');
		}

		try {
			const newFile: NewFile = {
				userId,
				name: dto.name.trim(),
				originalName: dto.originalName,
				mimeType: dto.mimeType,
				size: dto.size,
				storagePath: dto.storagePath,
				storageKey: dto.storageKey,
				parentFolderId: dto.folderId ?? null,
			};

			const [created] = await this.db.insert(files).values(newFile).returning();
			return ok(created);
		} catch (error) {
			if (error.code === '23505') {
				return err(ErrorCode.DUPLICATE_ENTRY, 'A file with this name already exists');
			}
			this.logger.error('Failed to create file', { userId, error: error.message });
			return err(ErrorCode.DATABASE_ERROR, 'Failed to create file');
		}
	}

	async update(id: string, userId: string, dto: UpdateFileDto): Promise<Result<File>> {
		// Check ownership first
		const existingResult = await this.findById(id, userId);
		if (!existingResult.ok) return existingResult;

		try {
			const [updated] = await this.db
				.update(files)
				.set({
					...(dto.name && { name: dto.name.trim() }),
					...(dto.parentFolderId !== undefined && { parentFolderId: dto.parentFolderId }),
					updatedAt: new Date(),
				})
				.where(eq(files.id, id))
				.returning();

			return ok(updated);
		} catch (error) {
			this.logger.error('Failed to update file', { id, error: error.message });
			return err(ErrorCode.DATABASE_ERROR, 'Failed to update file');
		}
	}

	async delete(id: string, userId: string): Promise<Result<void>> {
		// Check ownership first
		const existingResult = await this.findById(id, userId);
		if (!existingResult.ok) return existingResult;

		try {
			await this.db
				.update(files)
				.set({ isDeleted: true, deletedAt: new Date() })
				.where(eq(files.id, id));

			return ok(undefined);
		} catch (error) {
			this.logger.error('Failed to delete file', { id, error: error.message });
			return err(ErrorCode.DATABASE_ERROR, 'Failed to delete file');
		}
	}
}
```

### Service with External Dependencies

```typescript
@Injectable()
export class UploadService {
	private readonly logger = new Logger(UploadService.name);

	constructor(
		@Inject(DATABASE_CONNECTION) private db: Database,
		private readonly storageService: StorageService,
		private readonly fileService: FileService
	) {}

	async uploadFile(
		userId: string,
		file: Express.Multer.File,
		folderId?: string
	): Promise<Result<File>> {
		// 1. Upload to storage
		const storageResult = await this.storageService.upload(
			generateStorageKey(userId, file.originalname),
			file.buffer,
			{ contentType: file.mimetype }
		);

		if (!storageResult.ok) {
			return err(ErrorCode.UPLOAD_FAILED, 'Failed to upload file to storage');
		}

		// 2. Create database record
		const createResult = await this.fileService.create(userId, {
			name: file.originalname,
			originalName: file.originalname,
			mimeType: file.mimetype,
			size: file.size,
			storagePath: storageResult.data.path,
			storageKey: storageResult.data.key,
			folderId,
		});

		if (!createResult.ok) {
			// Cleanup on failure
			await this.storageService.delete(storageResult.data.key);
			return createResult;
		}

		return createResult;
	}
}
```

## DTOs

### Create DTO

```typescript
// src/file/dto/create-file.dto.ts
import { IsString, IsOptional, IsNumber, IsUUID, MaxLength, Min } from 'class-validator';

export class CreateFileDto {
	@IsString()
	@MaxLength(500)
	name: string;

	@IsOptional()
	@IsString()
	@MaxLength(500)
	originalName?: string;

	@IsString()
	@MaxLength(255)
	mimeType: string;

	@IsNumber()
	@Min(0)
	size: number;

	@IsString()
	@MaxLength(1000)
	storagePath: string;

	@IsString()
	@MaxLength(500)
	storageKey: string;

	@IsOptional()
	@IsUUID()
	folderId?: string;
}
```

### Update DTO (Partial)

```typescript
// src/file/dto/update-file.dto.ts
import { IsString, IsOptional, IsUUID, MaxLength } from 'class-validator';

export class UpdateFileDto {
	@IsOptional()
	@IsString()
	@MaxLength(500)
	name?: string;

	@IsOptional()
	@IsUUID()
	parentFolderId?: string | null;
}
```

### Query DTO

```typescript
// src/file/dto/query-files.dto.ts
import { IsOptional, IsUUID, IsNumber, Min, Max } from 'class-validator';
import { Transform } from 'class-transformer';

export class QueryFilesDto {
	@IsOptional()
	@IsUUID()
	folderId?: string;

	@IsOptional()
	@Transform(({ value }) => parseInt(value, 10))
	@IsNumber()
	@Min(1)
	@Max(100)
	limit?: number = 50;

	@IsOptional()
	@Transform(({ value }) => parseInt(value, 10))
	@IsNumber()
	@Min(0)
	offset?: number = 0;
}
```

### DTO Index

```typescript
// src/file/dto/index.ts
export * from './create-file.dto';
export * from './update-file.dto';
export * from './query-files.dto';
```

## Modules

```typescript
// src/file/file.module.ts
import { Module } from '@nestjs/common';
import { FileController } from './file.controller';
import { FileService } from './file.service';
import { UploadService } from './upload.service';
import { StorageModule } from '../storage/storage.module';

@Module({
	imports: [StorageModule],
	controllers: [FileController],
	providers: [FileService, UploadService],
	exports: [FileService], // Export for use in other modules
})
export class FileModule {}
```

## Exception Filter

```typescript
// src/common/filters/app-exception.filter.ts
import { ExceptionFilter, Catch, ArgumentsHost, HttpStatus, Logger } from '@nestjs/common';
import { Response } from 'express';
import { AppException, ERROR_STATUS_MAP, ErrorCode } from '@manacore/shared-errors';

@Catch(AppException)
export class AppExceptionFilter implements ExceptionFilter {
	private readonly logger = new Logger(AppExceptionFilter.name);

	catch(exception: AppException, host: ArgumentsHost) {
		const ctx = host.switchToHttp();
		const response = ctx.getResponse<Response>();

		const status = ERROR_STATUS_MAP[exception.error.code] ?? HttpStatus.INTERNAL_SERVER_ERROR;

		// Log server errors
		if (status >= 500) {
			this.logger.error('Server error', {
				code: exception.error.code,
				message: exception.error.message,
				details: exception.error.details,
			});
		}

		response.status(status).json({
			ok: false,
			error: {
				code: exception.error.code,
				message: exception.error.message,
				...(process.env.NODE_ENV === 'development' && {
					details: exception.error.details,
				}),
			},
		});
	}
}
```

## File Upload

```typescript
// src/file/file.controller.ts
import { UseInterceptors, UploadedFile, ParseFilePipe, MaxFileSizeValidator } from '@nestjs/common';
import { FileInterceptor } from '@nestjs/platform-express';

@Controller('files')
@UseGuards(JwtAuthGuard)
export class FileController {
	@Post('upload')
	@UseInterceptors(FileInterceptor('file'))
	async uploadFile(
		@UploadedFile(
			new ParseFilePipe({
				validators: [
					new MaxFileSizeValidator({ maxSize: 100 * 1024 * 1024 }), // 100MB
				],
			})
		)
		file: Express.Multer.File,
		@Query('folderId') folderId: string | undefined,
		@CurrentUser() user: CurrentUserData
	) {
		const result = await this.uploadService.uploadFile(user.userId, file, folderId);
		if (!result.ok) throw new AppException(result.error);
		return { file: result.data };
	}
}
```

## Health Check

```typescript
// src/health/health.controller.ts
import { Controller, Get } from '@nestjs/common';
import { Inject } from '@nestjs/common';
import { DATABASE_CONNECTION, Database } from '../db/database.module';
import { sql } from 'drizzle-orm';

@Controller('health')
export class HealthController {
	constructor(@Inject(DATABASE_CONNECTION) private db: Database) {}

	@Get()
	async check() {
		try {
			await this.db.execute(sql`SELECT 1`);
			return {
				status: 'ok',
				timestamp: new Date().toISOString(),
				database: 'connected',
			};
		} catch (error) {
			return {
				status: 'error',
				timestamp: new Date().toISOString(),
				database: 'disconnected',
			};
		}
	}
}
```

## API Response Format

### Success Responses

```typescript
// Single resource
{ file: { id: '...', name: '...', ... } }

// Multiple resources
{ files: [...] }

// With pagination
{ files: [...], total: 100, page: 1, limit: 20 }

// Action success
{ success: true }

// Action with data
{ success: true, message: 'File moved', file: {...} }
```

### Error Responses

```typescript
{
  ok: false,
  error: {
    code: 'ERR_4003',
    message: 'File not found'
  }
}
```

## Environment Variables

```env
# Required
NODE_ENV=development
PORT=3016
DATABASE_URL=postgresql://user:pass@localhost:5432/db
MANA_CORE_AUTH_URL=http://localhost:3001

# CORS
CORS_ORIGINS=http://localhost:5173,http://localhost:3000

# Storage
S3_ENDPOINT=http://localhost:9000
S3_REGION=us-east-1
S3_ACCESS_KEY=minioadmin
S3_SECRET_KEY=minioadmin

# Optional - Development bypass
DEV_BYPASS_AUTH=true
DEV_USER_ID=dev-user-123
```
