Hiero Hooks

// SPDX-License-Identifier: Apache-2.0
pragma solidity >=0.4.9 <0.9.0;
pragma experimental ABIEncoderV2;

/// The interface for a generic EVM hook.
interface IHieroHook {
    /// The context the hook is executing in
    struct HookContext {
        /// The address of the entity the hook is executing on behalf of
        address owner;
        /// The fee the transaction payer was charged for the triggering transaction
        uint256 txnFee;
        /// The gas cost the transaction payer was charged for specifically this hook
        uint256 gasCost;
        /// The memo of the triggering transaction
        string memo;
        /// Any extra call data passed to the hook
        bytes data;
    }
}

// SPDX-License-Identifier: Apache-2.0
pragma solidity >=0.4.9 <0.9.0;
pragma experimental ABIEncoderV2;

import './IHieroHook.sol';

/// The interface for an account allowance hook invoked once before a CryptoTransfer.
interface IHieroAccountAllowanceHook {
    /// A single balance adjustment in the range of a Hiero native token
    struct AccountAmount {
        address account;
        int64 amount;
    }

    /// A single NFT ownership change
    struct NftTransfer {
        address sender;
        address receiver;
        int64 serialNo;
    }

    /// A zero-sum list of balance adjustments for a Hiero-native token
    struct TokenTransferList {
        address token;
        AccountAmount[] adjustments;
        NftTransfer[] nftTransfers;
    }

    /// Combines HBAR and HTS asset transfers
    struct Transfers {
        AccountAmount[] hbarAdjustments;
        TokenTransferList[] tokens;
    }

    /// Combines the full proposed transfers for a Hiero transaction,
    /// including both its direct transfers and the implied HIP-18
    /// custom fee transfers.
    struct ProposedTransfers {
        Transfers direct;
        Transfers customFee;
    }

    /// Decides if the proposed transfers are allowed.
    /// @param context The context of the hook call
    /// @param proposedTransfers The proposed transfers
    /// @return true if the proposed transfers are allowed, false or revert otherwise
    function allow(
        IHieroHook.HookContext calldata context,
        ProposedTransfers memory proposedTransfers
    ) external payable returns (bool);
}

// SPDX-License-Identifier: Apache-2.0
pragma solidity >=0.4.9 <0.9.0;
pragma experimental ABIEncoderV2;

import './IHieroHook.sol';
import './IHieroAccountAllowanceHook.sol';

/// The interface for an account allowance hook invoked both before and after a CryptoTransfer.
interface IHieroAccountAllowancePrePostHook {
    /// Decides if the proposed transfers are allowed BEFORE the CryptoTransfer
    /// business logic is performed.
    /// @param context The context of the hook call
    /// @param proposedTransfers The proposed transfers
    /// @return true if the proposed transfers are allowed, false or revert otherwise
    function allowPre(
        IHieroHook.HookContext calldata context,
        IHieroAccountAllowanceHook.ProposedTransfers memory proposedTransfers
    ) external payable returns (bool);

    /// Decides if the proposed transfers are allowed AFTER the CryptoTransfer
    /// business logic is performed.
    /// @param context The context of the hook call
    /// @param proposedTransfers The proposed transfers
    /// @return true if the proposed transfers are allowed, false or revert otherwise
    function allowPost(
        IHieroHook.HookContext calldata context,
        IHieroAccountAllowanceHook.ProposedTransfers memory proposedTransfers
    ) external payable returns (bool);
}

// SPDX-License-Identifier: Apache-2.0
pragma solidity ^0.8.0;

import './IHieroHook.sol';
import './IHieroAccountAllowanceHook.sol';

contract SimpleAllowanceHook is IHieroAccountAllowanceHook {

    modifier onlyHookContext() {
        require(address(this) == address(0x16d), "Hook can only run in network context");
        _;
    }

    function allow(
        IHieroHook.HookContext calldata context,
        ProposedTransfers memory proposedTransfers
    ) external payable override onlyHookContext returns (bool) {
        // Allow all transfers unconditionally
        return true;
    }
}

// SPDX-License-Identifier: Apache-2.0
pragma solidity ^0.8.0;

import './IHieroHook.sol';
import './IHieroAccountAllowanceHook.sol';
import './IHieroAccountAllowancePrePostHook.sol';

contract AuditHook is IHieroAccountAllowancePrePostHook {

    modifier onlyHookContext() {
        require(address(this) == address(0x16d), "Hook can only run in network context");
        _;
    }

    function allowPre(
        IHieroHook.HookContext calldata context,
        IHieroAccountAllowanceHook.ProposedTransfers memory proposedTransfers
    ) external payable override onlyHookContext returns (bool) {
        // Validate proposed transfers before execution
        // For example, check that the owner is not debited more than a threshold
        return true;
    }

    function allowPost(
        IHieroHook.HookContext calldata context,
        IHieroAccountAllowanceHook.ProposedTransfers memory proposedTransfers
    ) external payable override onlyHookContext returns (bool) {
        // Verify state after the transfer completed
        // For example, confirm balances changed as expected
        return true;
    }
}