Set up your contract

Setting up the Contract

This exact guide shows an example of custodial contract Algebra positions, meaning that we can interact with the Algebra Periphery by minting a position, adding more liquidity to an exact position, decreasing liquidity, and collecting commissions.

First, declare the solidity version used to compile the contract and abicoder v2 to allow arbitrary nested arrays and structs to be encoded and decoded in calldata, a feature that we use when transacting with a pool.

// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity =0.7.6;
pragma abicoder v2;

After that, import the contracts needed from the npm package installation.

import '@cryptoalgebra/core/contracts/interfaces/IAlgebraPool.sol';
import '@cryptoalgebra/core/contracts/libraries/TickMath.sol';
import '@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol';
import '@cryptoalgebra/periphery/contracts/interfaces/ISwapRouter.sol';
import '@cryptoalgebra/periphery/contracts/interfaces/INonfungiblePositionManager.sol';
import '@cryptoalgebra/periphery/contracts/libraries/TransferHelper.sol';
import '@cryptoalgebra/periphery/contracts/base/LiquidityManagement.sol';

Then, create a contract called LiquidityExamples and inherit both IERC721Receiver and LiquidityManagement.

For this case, we've chosen to hardcode the token contract addresses. Most likely, you would use an input parameter for this in production, allowing you to change the pools and tokens you are interacting with on a per-transaction basis.

contract LiquidityExamples is IERC721Receiver {

    address public constant DAI = 0x6B175474E89094C44Da98b954EedeAC495271d0F;
    address public constant USDC = 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48;

Declare an immutable public variable nonfungiblePositionManager of type INonfungiblePositionManager.

    INonfungiblePositionManager public immutable nonfungiblePositionManager;

Enabling ERC721 Interactions

EEvery NFT is identified by a unique uint256 ID inside the ERC-721 smart contract, declared as the tokenId

What is NFT?

To allow deposits of ERC721 expressions of liquidity, create a struct called Deposit, a mapping of uint256 to the Deposit struct, then declare that mapping as a public variable deposits.

    struct Deposit {
        address owner;
        uint128 liquidity;
        address token0;
        address token1;
    }

    mapping(uint256 => Deposit) public deposits;

The Constructor

Declare the constructor here, which is executed once when the contract is deployed. Our constructor hard codes the address of the non-fungible position manager interface, router, and the periphery immutable state constructor, which requires the factory and the address of WMATIC.

    constructor(
        INonfungiblePositionManager _nonfungiblePositionManager,
        address _factory,
        address _WMATIC
    ) PeripheryImmutableState(_factory, _WMATIC) {
        nonfungiblePositionManager = _nonfungiblePositionManager;
    }

Allowing custody of ERC721 tokens

To allow the contract to custody ERC721 tokens, implement the onERC721Received function within the inherited IERC721Receiver.sol contract.

IERC721Receiver Contract

The from identifier may be omitted because it is not used.

    function onERC721Received(
        address operator,
        address,
        uint256 tokenId,
        bytes calldata
    ) external override returns (bytes4) {
        // get position information
        _createDeposit(operator, tokenId);
        return this.onERC721Received.selector;
    }

Creating a Deposit

To add a Deposit instance to the deposits mapping, create an internal function called _createDeposit that destructures the positions struct returned by positions in nonfungiblePositionManager.sol. Pass the relevant variables token0, token1 and liquidity to the deposits mapping.

    function _createDeposit(address owner, uint256 tokenId) internal {
        (, , address token0, address token1, , , uint128 liquidity, , , , ) =
            nonfungiblePositionManager.positions(tokenId);

        // set the owner and data for position
        // operator is msg.sender
        deposits[tokenId] = Deposit({owner: owner, liquidity: liquidity, token0: token0, token1: token1});
    }

The Full Contract Setup

// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity =0.7.6;
pragma abicoder v2;

import '@cryptoalgebra/core/contracts/interfaces/IAlgebraPool.sol';
import '@cryptoalgebra/core/contracts/libraries/TickMath.sol';
import '@cryptoalgebra/periphery/contracts/libraries/TransferHelper.sol';
import '@cryptoalgebra/periphery/contracts/interfaces/INonfungiblePositionManager.sol';
import '@cryptoalgebra/periphery/contracts/base/LiquidityManagement.sol';
import '@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol';

contract LiquidityExamples is IERC721Receiver {
    address public constant DAI = 0x8f3Cf7ad23Cd3CaDbD9735AFf958023239c6A063;
    address public constant USDC = 0x2791Bca1f2de4661ED88A30C99A7a9449Aa84174;


    INonfungiblePositionManager public immutable nonfungiblePositionManager;

    /// @notice Represents the deposit of an NFT
    struct Deposit {
        address owner;
        uint128 liquidity;
        address token0;
        address token1;
    }

    /// @dev deposits[tokenId] => Deposit
    mapping(uint256 => Deposit) public deposits;

    constructor(
        INonfungiblePositionManager _nonfungiblePositionManager
    ) {
        nonfungiblePositionManager = _nonfungiblePositionManager;
    }

    // Implementing `onERC721Received` so this contract can receive custody of erc721 tokens
    function onERC721Received(
        address operator,
        address,
        uint256 tokenId,
        bytes calldata
    ) external override returns (bytes4) {
        // get position information

        _createDeposit(operator, tokenId);

        return this.onERC721Received.selector;
    }

    function _createDeposit(address owner, uint256 tokenId) internal {
        (, , address token0, address token1, , , uint128 liquidity, , , , ) =
            nonfungiblePositionManager.positions(tokenId);

        // set the owner and data for position
        // operator is msg.sender
        deposits[tokenId] = Deposit({owner: owner, liquidity: liquidity, token0: token0, token1: token1});
    }
}