> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cow.bleu.builders/llms.txt
> Use this file to discover all available pages before exploring further.

# Services

> Business logic services for the CoW Protocol BFF, implementing clean architecture patterns with dependency injection

# Services

The services library implements business logic through clean architecture patterns. Services follow dependency injection principles using InversifyJS with Symbol-based identifiers. They orchestrate repositories while maintaining single responsibility and full TypeScript type safety.

## Architecture Principles

Services follow clean architecture patterns with:

* **Single responsibility** - Each service handles one domain
* **Dependency injection** - Using InversifyJS with Symbol-based identifiers
* **Repository composition** - Services orchestrate multiple repositories
* **Full type safety** - Complete TypeScript typing throughout

## Core Services

### USD Service

Retrieves token pricing across chains. Delegates to the `UsdRepository`, which implements fallback strategies across multiple data sources like CoinGecko.

### Slippage Service

Calculates dynamic slippage tolerance based on volatility and market conditions, accepting optional order context for precision. The service returns recommended slippage in basis points plus detailed volatility metrics.

### Simulation Service

Uses Tenderly to simulate transaction bundles before execution, providing gas usage and balance change analysis.

### Token Holder Service

Retrieves top token holders for analytics purposes.

### Token Balances Service

Fetches multiple token balances in a single call.

### Balance Tracking Service

Offers real-time monitoring through Server-Sent Events, emitting balance change and allowance change events.

### SSE Service

Manages Server-Sent Event connections, enabling client registration and event broadcasting.

### Hooks Service

Fetches CoW Hooks execution data from Dune Analytics across multiple blockchains and time periods.

### Affiliate Stats Service

Aggregates affiliate performance metrics. Provides statistics and export functionality for affiliate program data in CSV or JSON formats.

## Setup Pattern

Services utilize factory functions that handle repository configuration automatically:

```typescript theme={null}
import {
  getCacheRepository,
  getErc20Repository,
  getUsdRepository,
} from '@cowprotocol/services';

// Factory functions handle all wiring
const cache = getCacheRepository();
const erc20Repo = getErc20Repository(cache);
const usdRepo = getUsdRepository(cache, erc20Repo);
```

## Dependency Injection Setup

The dependency injection container binds service interfaces to implementations using exported symbols:

```typescript theme={null}
import { Container } from 'inversify';

const container = new Container();
container.bind(usdServiceSymbol).to(UsdServiceImpl);
container.bind(slippageServiceSymbol).to(SlippageServiceImpl);
```

## Best Practices

1. **Inject interfaces rather than implementations** - Enables testing and flexibility
2. **Handle null responses gracefully** - Repositories may return null for missing data
3. **Leverage factory functions** - Use provided factory functions for consistent wiring
4. **Set reasonable timeouts** - For external service calls
5. **Cache at the repository level** - Not within services themselves