Staking limits

core/contracts/Acre.sol

@@ -2,6 +2,7 @@
 pragma solidity ^0.8.21;
 
 import "@openzeppelin/contracts/token/ERC20/extensions/ERC4626.sol";
+import "@openzeppelin/contracts/access/Ownable.sol";
 
 /// @title Acre
 /// @notice This contract implements the ERC-4626 tokenized vault standard. By
@@ -14,12 +15,96 @@ import "@openzeppelin/contracts/token/ERC20/extensions/ERC4626.sol";
 ///      of yield-bearing vaults. This contract facilitates the minting and
 ///      burning of shares (stBTC), which are represented as standard ERC20
 ///      tokens, providing a seamless exchange with tBTC tokens.
-contract Acre is ERC4626 {
+contract Acre is ERC4626, Ownable {
+    struct StakingParameters {
+        // Minimum amount for a single deposit operation.
+        uint256 minimumDepositAmount;
+        // Maximum total amount of tBTC token held by Acre.
+        uint256 maximumTotalAssets;
+    }
+
+    StakingParameters public stakingParameters;
+
     event StakeReferral(bytes32 indexed referral, uint256 assets);
+    event StakingParametersUpdated(
+        uint256 minimumDepositAmount,
+        uint256 maximumTotalAssets
+    );
 
     constructor(
-        IERC20 tbtc
-    ) ERC4626(tbtc) ERC20("Acre Staked Bitcoin", "stBTC") {}
+        IERC20 tbtc,
+        address initialOwner
+    )
+        ERC4626(tbtc)
+        ERC20("Acre Staked Bitcoin", "stBTC")
+        Ownable(initialOwner)
+    {
+        stakingParameters.minimumDepositAmount = 0.01 ether; // 0.01 tBTC
+        stakingParameters.maximumTotalAssets = 25 ether; // 25 tBTC
+    }
+
+    /// @notice Updates parameters of staking.
+    /// @dev Requirements:
+    ///      - Minimum deposit amount must be greater than zero,
+    ///      - Minimum deposit amount must be greater than or equal to the
+    ///        minimum deposit amount in the tBTC system,
+    ///      - Maximum total assets must be greater than zero.
+    /// @param minimumDepositAmount New value of the minimum deposit amount. It
+    ///        is the minimum amount for a single deposit operation.
+    /// @param maximumTotalAssets New value of the maximum total assets amount.
+    ///        It is the maximum amount of the tBTC token that the Acre can
+    ///        hold.
+    function updateStakingParameters(
+        uint256 minimumDepositAmount,
+        uint256 maximumTotalAssets
+    ) external onlyOwner {
+        require(
+            minimumDepositAmount > 0,
+            "Minimum deposit amount must be greater than zero"
+        );
+
+        // TODO: Do we need this requirement?
+        require(
+            minimumDepositAmount >= _getTBTCSystemMinDepositAmount(),
+            "Minimum deposit amount must be greater than or to the equal minimum deposit amount in tBTC system"
+        );
+
+        require(
+            maximumTotalAssets > 0,
+            "Maximum total assets amount must be greater than zero"
+        );
+
+        stakingParameters.minimumDepositAmount = minimumDepositAmount;
+        stakingParameters.maximumTotalAssets = maximumTotalAssets;
+
+        emit StakingParametersUpdated(minimumDepositAmount, maximumTotalAssets);
+    }
+
+    function deposit(
+        uint256 assets,
+        address receiver
+    ) public override returns (uint256) {
+        require(
+            assets >= stakingParameters.minimumDepositAmount,
+            "Amount is less than minimum"
+        );
+
+        return super.deposit(assets, receiver);
+    }
+
+    function mint(
+        uint256 shares,
+        address receiver
+    ) public override returns (uint256) {
+        uint256 assets = super.mint(shares, receiver);
+
+        require(
+            assets >= stakingParameters.minimumDepositAmount,
+            "Amount is less than minimum"
+        );
+
+        return assets;
+    }
 
     /// @notice Stakes a given amount of tBTC token and mints shares to a
     ///         receiver.
@@ -43,4 +128,36 @@ contract Acre is ERC4626 {
 
         return shares;
     }
+
+    /// @notice Returns the maximum amount of the tBTC token that can be
+    ///         deposited into the vault for the receiver, through a deposit
+    ///         call. It takes into account the staking parameter, maximum total
+    ///         assets, which determines the total amount of tBTC token held by
+    ///         Acre.
+    /// @return The maximum amount of the tBTC token.
+    function maxDeposit(address) public view override returns (uint256) {
+        return stakingParameters.maximumTotalAssets - totalAssets();
+    }
+
+    /// @notice Returns the maximum amount of the vault shares that can be
+    ///         minted for the receiver, through a mint call.
+    /// @dev Since the Acre contract limits the maximum total tBTC tokens this
+    ///      function converts the maximum deposit amount to shares.
+    /// @return The maximum amount of the vault shares.
+    function maxMint(address receiver) public view override returns (uint256) {
+        return previewDeposit(maxDeposit(receiver));
+    }
+
+    function _getTBTCSystemMinDepositAmount() private pure returns (uint256) {
+        // TODO: Implement if we want to make sure the minimum deposit amount is
+        // greater than or equal the minimum dposit amount in the tBTC system.
+
+        // (uint64 depositDustThreshold, , , ) = tbtcBridge.depositParameters();
+
+        // // The `depositDustThreshold` is in satoshi so we need to cast to tBTC
+        // // decimals.
+        // return 10 ** (ERC20(asset()).decimals() - 8) * depositDustThreshold;
+
+        return 0.01 ether; // 0.01 tBTC
+    }
 }

core/deploy/01_deploy_acre.ts

@@ -9,7 +9,7 @@ const func: DeployFunction = async (hre: HardhatRuntimeEnvironment) => {
 
   await deployments.deploy("Acre", {
     from: deployer,
-    args: [tbtc.address],
+    args: [tbtc.address, deployer],
     log: true,
     waitConfirmations: 1,
   })