@auto-engineer/emmett-generator

@auto-engineer/emmett-generator

Code generation plugin for the Auto Engineer CLI that scaffolds event-driven backends using the Emmett event sourcing framework. This plugin takes FlowLang specifications and generates GraphQL servers with commands, events, projections, and queries.

Installation

This is a plugin for the Auto Engineer CLI. Install both the CLI and this plugin:

npm install -g @auto-engineer/cli
npm install @auto-engineer/emmett-generator

Configuration

Add this plugin to your auto.config.ts:

export default {
  plugins: [
    '@auto-engineer/emmett-generator',
    // ... other plugins
  ],
};

Commands

This plugin provides the following commands:

• generate:server - Generate a GraphQL server from flow specifications

What does this plugin do?

The Emmett Generator transforms high-level flow specifications into event-driven backends. It generates:

Command Handlers

• Command validation and business logic stubs
• Event emission patterns
• Error handling and domain validation
• Integration with the Emmett command bus

Event Sourcing Infrastructure

• Event store configuration
• Event versioning and migration support
• Projection builders for read models
• Event stream processing

GraphQL API Layer

• Type-safe GraphQL schema generation
• Mutation resolvers for commands
• Query resolvers for projections
• Subscription support for real-time updates

Testing Infrastructure

• Comprehensive test suites for all generated components
• Behavioral tests for command handlers
• Integration tests for the GraphQL API
• Test data factories and fixtures

Generated Project Structure

When you run auto generate:server, the plugin creates a complete backend project:

server/
├── src/
│   ├── domain/
│   │   ├── commands/           # Command handlers
│   │   ├── events/            # Event definitions
│   │   ├── projections/       # Read model projections
│   │   └── queries/           # Query handlers
│   ├── graphql/
│   │   ├── resolvers/         # GraphQL resolvers
│   │   └── schema.ts          # Generated schema
│   ├── infrastructure/
│   │   ├── eventStore.ts      # Event store setup
│   │   └── commandBus.ts      # Command bus configuration
│   └── server.ts              # Application entry point
├── tests/                     # Generated test suites
└── package.json

Features

Type-Safe Code Generation

All generated code is fully typed using TypeScript, ensuring compile-time safety and developer experience.

Event-Driven Architecture

Built on Emmett's event sourcing patterns:

• Commands represent intent to change state
• Events capture what actually happened
• Projections create read models from events
• Queries serve data to GraphQL clients

Infrastructure

Generated servers include:

• Error handling and logging
• Health checks and monitoring endpoints
• Environment-based configuration
• Database migration scripts

Templates

Uses EJS templating system for code generation:

• Command handler templates
• Event definition templates
• GraphQL resolver templates
• Test suite templates

Integration with FlowLang

This plugin is designed to work with @auto-engineer/flowlang specifications:

• Define your business flows using FlowLang DSL
• Export the flow schema using auto export:schema
• Generate the backend using auto generate:server
• The generator reads the schema and creates appropriate handlers

Example Workflow

# 1. Create a flow specification project
auto create:example

# 2. Define your business flows in flows/
# Edit flows/order-management.flow.ts

# 3. Generate the backend server
auto generate:server

# 4. The generated server is ready to run:
cd server
npm install
npm run start

Advanced Features

Custom Templates

Override default templates by providing your own EJS files:

• Place custom templates in .auto-engineer/templates/
• Templates follow the same structure as built-in ones
• Supports partial overrides for specific components

Plugin Integration

Works with other Auto Engineer plugins:

• @auto-engineer/server-implementer: AI-powered implementation of generated stubs
• @auto-engineer/backend-checks: Validation of generated code
• @auto-engineer/react-graphql-generator: Frontend generation from server schema

Configuration Options

Customize generation behavior through auto.config.ts:

export default {
  plugins: [
    [
      '@auto-engineer/emmett-generator',
      {
        outputDir: './backend',
        templateOverrides: './templates',
        generateMigrations: true,
      },
    ],
  ],
};

The Emmett Generator bridges the gap between high-level business requirements and backend infrastructure, enabling development of scalable, maintainable applications.