# GraphBrainz Overview

## Project Identity

| Property | Value |
|----------|-------|
| Name | GraphBrainz |
| Version | 9.0.0 |
| Repository | https://github.com/exogen/graphbrainz |
| License | MIT (2016 Brian Beck) |
| Language | JavaScript (ESM) |
| Runtime | Node.js >=12.18.0 |
| Core Stack | Express + GraphQL |
| NPM Package | graphbrainz |
| Binary Command | graphbrainz |

## Purpose

GraphBrainz provides a GraphQL schema and Express server/middleware for querying the MusicBrainz API. It transforms the REST-based MusicBrainz web service into a modern GraphQL interface with extensible integrations for additional metadata sources.

The project serves three primary use cases:

1. **Standalone GraphQL Server** - Run as a dedicated service with built-in Express server
2. **Express Middleware** - Embed GraphQL endpoint into existing Express applications
3. **Direct GraphQL Client** - Import schema and context for programmatic queries

## Core Dependencies

| Package | Version | Purpose |
|---------|---------|---------|
| graphql | 15.5.0 | GraphQL implementation |
| express-graphql | 0.12.0 | Express middleware for GraphQL |
| @graphql-tools/schema | 7.1.3 | Schema composition utilities |
| dataloader | 2.0.0 | Request batching and deduplication |
| lru-cache | 6.0.0 | Shared response caching |
| got | 11.8.2 | HTTP client for API requests |
| graphql-relay | 0.6.0 | Relay specification helpers |
| debug | * | Namespace-based logging |
| es6-error | * | Custom error classes |
| dotenv | * | Environment configuration |

## Entry Points

The application flow starts at `cli.js` which delegates to `src/index.js` and its `start()` function. This entry point handles:

- Environment variable loading via dotenv
- Extension discovery and loading
- Schema construction and extension
- Server initialization (standalone mode)
- Middleware export (embedded mode)

## Extension System

GraphBrainz includes 4 built-in extensions and supports 3 external extensions via separate npm packages.

### Built-in Extensions

| Extension | Source | Purpose |
|-----------|--------|---------|
| Cover Art Archive | http://coverartarchive.org/ | Album artwork and thumbnails |
| fanart.tv | http://webservice.fanart.tv/v3/ | Artist backgrounds, logos, banners |
| MediaWiki | MusicBrainz Wiki | Image URLs and metadata |
| TheAudioDB | http://www.theaudiodb.com/ | Artist biographies and logos |

### External Extensions

| Extension | NPM Package | Purpose |
|-----------|-------------|---------|
| Last.fm | graphbrainz-extension-lastfm | Scrobbling data and statistics |
| Discogs | graphbrainz-extension-discogs | Release marketplace data |
| Spotify | graphbrainz-extension-spotify | Streaming platform metadata |

Extensions are loaded via the `GRAPHBRAINZ_EXTENSIONS` environment variable or programmatic options. Each extension receives its own HTTP client, DataLoader instance, and LRU cache.

## Deployment Modes

### Standalone Server

```bash
npm start
# or
graphbrainz
```

Starts Express server on port 3000 (configurable via `PORT` env var) with GraphQL endpoint at `/` (configurable via `GRAPHBRAINZ_PATH`).

### Express Middleware

```javascript
import { middleware } from 'graphbrainz';

app.use('/graphql', middleware());
```

Embeds GraphQL endpoint into existing Express application.

### Direct GraphQL Client

```javascript
import { schema, context } from 'graphbrainz';
import { graphql } from 'graphql';

const result = await graphql({
  schema,
  source: query,
  contextValue: context
});
```

Programmatic access to schema and context for custom integrations.

## Architecture Highlights

### Schema Construction

GraphBrainz uses programmatic schema construction via GraphQL.js constructors rather than SDL (Schema Definition Language) for the core schema. This approach provides:

- Type-safe schema building
- Dynamic field generation
- Runtime schema introspection
- Programmatic extension points

Extensions use SDL strings merged via `extendSchema()` from `@graphql-tools/schema`.

### Performance Optimization

Two-tier caching strategy:

1. **DataLoader** - Per-request batching and deduplication
2. **LRU Cache** - Shared cache across requests (8192 items, 1 day TTL)

Custom rate limiter with priority queue ensures compliance with MusicBrainz API limits (5 requests per 5.5 seconds) and extension limits (10 requests per second).

### Resolver Intelligence

Resolvers inspect the GraphQL AST to determine which MusicBrainz `inc` parameters are needed. This eliminates over-fetching and under-fetching by requesting exactly the data required for the query.

## Package Distribution

The NPM package exports:

- Main module with `start()`, `middleware()`, `schema`, `context`
- Built-in extensions as separate modules
- `schema.json` for tooling and introspection
- Binary command for CLI usage

## Version Requirements

| Component | Minimum Version | Notes |
|-----------|----------------|-------|
| Node.js | 12.18.0 | ESM support required |
| GraphQL | 15.5.0 | Not latest (v16+ available) |
| Express | 4.x | Via express-graphql |

## Configuration Surface

GraphBrainz exposes 10+ environment variables for configuration:

- `MUSICBRAINZ_BASE_URL` - MusicBrainz API endpoint
- `GRAPHBRAINZ_PATH` - GraphQL endpoint path
- `GRAPHBRAINZ_CORS_ORIGIN` - CORS configuration
- `GRAPHBRAINZ_CACHE_SIZE` - LRU cache size
- `GRAPHBRAINZ_CACHE_TTL` - Cache TTL in milliseconds
- `GRAPHBRAINZ_GRAPHIQL` - Enable GraphiQL interface
- `GRAPHBRAINZ_EXTENSIONS` - Extension loading
- `PORT` - Server port
- `NODE_ENV` - Environment mode
- Per-extension variables (API keys, cache settings)

## Development Tooling

| Tool | Purpose |
|------|---------|
| AVA | Test framework |
| ava-nock | HTTP mocking (play/record/cache) |
| c8 | Code coverage |
| Travis CI | Continuous integration (Node 12/14/15) |
| Codecov + Coveralls | Coverage reporting |
| debug | Namespace-based logging |

## Project Maturity

GraphBrainz v9.0.0 represents a mature, stable project with:

- Comprehensive test suite (1475+ lines)
- Production-proven caching and rate limiting
- Relay-compliant GraphQL implementation
- Extensible architecture for metadata aggregation
- 5+ years of development history

The project has not seen major updates in recent years, indicating stability but potential technical debt in dependencies (Node.js 12 baseline, GraphQL v15).