npm package: @frinkly/payment-detection
Description: Payment detection using ethers.
Latest version: 0.37.1

# @frinkly/payment-detection

`@frinkly/payment-detection` is a typescript library part of the [Request Network protocol](https://github.com/RequestNetwork/requestNetwork).
It contains the implementation of request-related events interpretations, typically onchain payments of requests.

The interpretation of events is specified by the payment extension added to the request. [Cf. advanced-logic specifications](../advanced-logic/specs/).

# Balance and events

If a payment network has been given to the request, the payment detection can be done.

Based on information found in the payment network state, and included manual payment declarations, the library will perform queries and feed the property `balance` of the request with:

- `balance`: the detected amount paid on the request, in request currency
- `events`: all the payments, payment declarations, refunds, and other balance-related events with the amount, timestamp etc...

# Retrievers and detectors

This library relies on two concepts:

- **Retrievers** perform RPC or TheGraph calls and fetch relevant events. Balance-impacting events are fetched with `InfoRetrievers`, implementing the `getTransferEvents()` method (cf. [IPaymentRetriever](./src/types.ts))
- **Payment detectors** implement the interface **PaymentTypes.IPaymentNetwork**, with the method `getBalance()`, which calls retrievers and interpret events according to the payment network (cf. [Abstract PaymentDetectorBase](./src/payment-detector-base.ts)). `getBalance()` returns the balance as well as events: payments, refunds, and possibly other events (declarations, escrow events...)

## PaymentDetectorBase

A good part of the logic is implemented in the abstract class `PaymentDetectorBase`:

```typescript
export abstract class PaymentDetectorBase<
  TExtension extends ExtensionTypes.IExtension,
  TPaymentEventParameters,
> implements PaymentTypes.IPaymentNetwork<TPaymentEventParameters>
{
  public async getBalance(
    request: RequestLogicTypes.IRequest,
  ): Promise<PaymentTypes.IBalanceWithEvents<TPaymentEventParameters>> {
    // ...

    // getEvents() should be implemented by children payment detectors, and use appropriate retrievers
    // For example: RPC or The Graph based retriever
    const rawEvents = await this.getEvents(request);
    // ...
    // computeBalance() sums up all payment events and deduces all refunds.
    const balance = this.computeBalance(events).toString();

    return {
      balance,
      events,
    };
  }
}
```

[cf. full implementation](./src/payment-detector-base.ts)

## Subgraph-based payment retrievers

For TheGraph-based information retrieval, a client can be retrieved using `getTheGraphClient()` in `./src/thegraph/index.ts`. It provides a strongly typed interface, generated based on the queries in `/src/thegraph/queries`.

The automated type generation is configured within files `./codegen.yml` (for EVM chains) and `./codegen-near.yml` (for Near) and output in `./src/thegraph/generated`. It depends on the deployed subgraphes schema and on the queries.

The code generation is included in the pre-build script and can be run manually:

```
yarn codegen
```

# Test

The ETH `InfoRetriever` tests require explorer API keys. Before running the
payment-detection tests, define `DISABLE_API_TESTS` or define all required
explorer API keys.

```bash
export DISABLE_API_TESTS=1
# OR
export EXPLORER_API_KEY_MAINNET=
export EXPLORER_API_KEY_RINKEBY=
export EXPLORER_API_KEY_FUSE=
export EXPLORER_API_KEY_MATIC=
export EXPLORER_API_KEY_FANTOM=

yarn run test
```