# Integration

## L1->L2

To send funds L1->L2, call the `sendToL2` [method](https://github.com/hop-protocol/contracts/blob/8cefc3975115b6e3e706dd110670badad954a3bd/contracts/bridges/L1_Bridge.sol#L109) on the L1 Bridge contract:

{% hint style="info" %}
The `relayer` and `relayerFee` are ***required*** for most routes. You can get these values from the Hop SDK.
{% endhint %}

```solidity
sendToL2(
    uint256 chainId,
    address recipient,
    uint256 amount,
    uint256 amountOutMin,
    uint256 deadline,
    address relayer,
    uint256 relayerFee
)
```

### L2->L1 and L2->L2

To send funds L2->L1 or L2->L2, call the `swapAndSend` [method](https://github.com/hop-protocol/contracts/blob/8cefc3975115b6e3e706dd110670badad954a3bd/contracts/bridges/L2_AmmWrapper.sol#L58) on the L2 AMM Wrapper contract:

```solidity
swapAndSend(
    uint256 chainId,
    address recipient,
    uint256 amount,
    uint256 bonderFee,
    uint256 amountOutMin,
    uint256 deadline,
    uint256 destinationAmountOutMin,
    uint256 destinationDeadline
)
```

Note: **Do not set `destinationAmountOutMin` and `destinationDeadline` when sending to L1 because there is no AMM on L1, otherwise the computed transferId will be invalid and the transfer will be unbondable.** These parameters should be set to `0` when sending to L1.

### L2 hTokens->L2 or L2 hTokens -> L1

To send hTokens L2->L2 or hTokens L2->L1, call the `send` [method](https://github.com/hop-protocol/contracts/blob/8cefc3975115b6e3e706dd110670badad954a3bd/contracts/bridges/L2_Bridge.sol#L117) on the L2 Bridge contract:

```solidity
send(
    uint256 chainId,
    address recipient,
    uint256 amount,
    uint256 bonderFee,
    uint256 amountOutMin,
    uint256 deadline
)
```

Note: There are no hTokens on L1 so sending L2 hUSDC to L1 means you'll receive USDC on L1.

Note: **Do not set `amountOutMin` and `deadline` when sending to L1 because there is no AMM on L1, otherwise the computed transferId will be invalid and the transfer will be unbondable.** These parameters should be set to `0` when sending to L1.

### Sending ETH vs Token

When sending native asset from source chain (ie ETH on Ethereum, Optimism, Arbitrum, or XDAI on Gnosis Chain, or MATIC on Polygon), set the transaction `value` to match the `amount` parameter.

### swapAndSend vs send

`swapAndSend` (on L2 AMM Wrapper) on the source chain swaps your canonical token (eg USDC) to hTokens (eg hUSDC) and burns the hTokens and then you receive the canonical tokens (eg USDC) on the destination chain.

`send` on (on L2 Bridge) is for only dealing with hTokens. The `send` method on the source chain takes your hTokens (ie hUSDC), burns the hTokens and then you receive hTokens (eg hUSDC) on the destination chain.

swapAndSend is what you'd want to use most of the time since the canonical tokens are what users are interested in.

### Calling Hop from smart contract for transfers

Some good examples you can check out as a reference are:

* [InstaDapp](https://instadapp.io/) DSA connector contracts ([helpers.sol](https://github.com/Instadapp/dsa-connectors/blob/b0a9c6f8333eb2252a49f3c6ac4900ab03db8d21/contracts/mainnet/connectors/hop/helpers.sol#L38))
* [movr](https://www.movr.network/) bridge aggregator contracts ([Hop.sol](https://polygonscan.com/address/0x2b42AFFD4b7C14d9B7C2579229495c052672Ccd3#code))
* [LI.FI](https://li.fi/) bridge aggregator contracts ([HopFacet.sol](https://polygonscan.com/address/0xc46304a0b2accc4462d9bdcaa0f6bf632510d617#code))

## AMM Deposit

Use the [`addLiquidity`](https://github.com/hop-protocol/contracts/blob/156dc60557349da9fe0785c369ab3fda0bf01288/contracts/saddle/Swap.sol#L406C23-L406C23) method on the Swap contract.

```solidity
Swap.addLiquidity(
    amounts, // array of amounts of tokens to LP, should be an array of 2 elements containing the amount of canonical tokens and h-tokens, e.g. ['100000000', '0'],
    minToMint, // min amount of LP tokens to receive,
    deadline // e.g. use 10 minutes from now in unix seconds
)
```

## AMM Withdraw

```solidity
Swap.removeLiquidityOneToken(
    tokenAmount, // amount of LP tokens to burn
    tokenIndex, // token to receive; use 0 for canonical token, use 1 for h-token
    minAmount, // minimum amount to receive
    deadline // e.g. use 10 minutes from now in unix seconds
)
```

Use the [`removeLiquidityOneToken`](https://github.com/hop-protocol/contracts/blob/156dc60557349da9fe0785c369ab3fda0bf01288/contracts/saddle/Swap.sol#L447) method on the Swap contract. You can also use the [`removeLiquidity`](https://github.com/hop-protocol/contracts/blob/156dc60557349da9fe0785c369ab3fda0bf01288/contracts/saddle/Swap.sol#L430C14-L430C29) method to receive proportional canonical tokens and h-tokens.

### Contract addresses

The L1 Bridge addresses, L2 Bridge addresses, L2 AMM wrapper addresses, AMM addresses (Saddle Swap contracts), and other Hop contract addresses can be found on this link:

{% content-ref url="contract-addresses" %}
[contract-addresses](https://docs.hop.exchange/developer-docs/smart-contracts/contract-addresses)
{% endcontent-ref %}

### Calculating Bonder Fee

There's a REST API you can use to get estimated bonder fee. See [API docs](https://docs.hop.exchange/developer-docs/api/api).

{% content-ref url="../api/api" %}
[api](https://docs.hop.exchange/developer-docs/api/api)
{% endcontent-ref %}

### Getting transfer status

There's a REST API you can use to get transfer status. See [API docs](https://docs.hop.exchange/developer-docs/api/api).

{% content-ref url="../api/api" %}
[api](https://docs.hop.exchange/developer-docs/api/api)
{% endcontent-ref %}