> ## Documentation Index
> Fetch the complete documentation index at: https://docs.x402r.org/llms.txt
> Use this file to discover all available pages before exploring further.

# PaymentIndexRecorderHook

> Index payments by sequential count for on-chain queries and repeated refund requests

## Overview

PaymentIndexRecorderHook indexes payments by payer and receiver and stores the full `PaymentInfo` struct keyed by `paymentInfoHash`. Wire it into `AUTHORIZE_POST_ACTION_HOOK` on a `HookCombinator` (or directly when authorize is the only hook slot you use) so each new authorization registers itself for on-chain lookups.

## When to use

* You need on-chain payment lookups **without a subgraph**
* Other contracts need to read the full `PaymentInfo` for a hash, or page through every payment by payer / receiver
* You want a single chain-singleton index that aggregates across every operator routing through `HookCombinator`

**Skip when:** you're using a subgraph for payment queries, since the subgraph can derive indexes from events without the on-chain gas cost.

## State

```solidity theme={null}
mapping(bytes32 paymentInfoHash => AuthCaptureEscrow.PaymentInfo) private paymentInfoStore;
mapping(address payer    => mapping(uint256 index => bytes32 hash)) private payerPayments;
mapping(address payer    => uint256 count)                        public  payerPaymentCount;
mapping(address receiver => mapping(uint256 index => bytes32 hash)) private receiverPayments;
mapping(address receiver => uint256 count)                        public  receiverPaymentCount;
```

## Methods

```solidity theme={null}
function run(
    AuthCaptureEscrow.PaymentInfo calldata paymentInfo,
    uint256 /* amount */,
    address /* caller */,
    bytes calldata /* data */
) external {
    bytes32 hash = escrow.getHash(paymentInfo);
    paymentInfoStore[hash] = paymentInfo;
    payerPayments[paymentInfo.payer][payerPaymentCount[paymentInfo.payer]++] = hash;
    receiverPayments[paymentInfo.receiver][receiverPaymentCount[paymentInfo.receiver]++] = hash;
}

function getPaymentInfo(
    bytes32 paymentInfoHash
) external view returns (AuthCaptureEscrow.PaymentInfo memory);

function getPayerPayments(
    address payer,
    uint256 offset,
    uint256 count
) external view returns (AuthCaptureEscrow.PaymentInfo[] memory, uint256 total);

function getReceiverPayments(
    address receiver,
    uint256 offset,
    uint256 count
) external view returns (AuthCaptureEscrow.PaymentInfo[] memory, uint256 total);
```

`amount`, `caller`, and `data` are unused; they exist to satisfy `IHook.run`.

## Querying

```typescript theme={null}
const info = await paymentIndex.read.getPaymentInfo([paymentInfoHash])

const [payerInfos, total] = await paymentIndex.read.getPayerPayments([
  payer,
  0n,
  10n,
])
```

## Gas

**Cost:** \~175k gas per authorization (payer index + receiver index + full `PaymentInfo` SSTORE).

## Next Steps

<CardGroup cols={2}>
  <Card title="HookCombinator" icon="layer-group" href="/contracts/hooks/combinator">
    Combine with other hooks in a single slot.
  </Card>

  <Card title="Hooks Overview" icon="database" href="/contracts/hooks/overview">
    Compare recording strategies.
  </Card>
</CardGroup>