SplitMain.sol

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity 0.8.4;

import {ISplitMain} from 'contracts/interfaces/ISplitMain.sol';
import {SplitWallet} from 'contracts/SplitWallet.sol';
import {Clones} from 'contracts/libraries/Clones.sol';
import {ERC20} from '@rari-capital/solmate/src/tokens/ERC20.sol';
import {SafeTransferLib} from '@rari-capital/solmate/src/utils/SafeTransferLib.sol';

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 */

/**
 * ERRORS
 */

/// @notice Unauthorized sender `sender`
/// @param sender Transaction sender
error Unauthorized(address sender);
/// @notice Invalid number of accounts `accountsLength`, must have at least 2
/// @param accountsLength Length of accounts array
error InvalidSplit__TooFewAccounts(uint256 accountsLength);
/// @notice Array lengths of accounts & percentAllocations don't match (`accountsLength` != `allocationsLength`)
/// @param accountsLength Length of accounts array
/// @param allocationsLength Length of percentAllocations array
error InvalidSplit__AccountsAndAllocationsMismatch(
  uint256 accountsLength,
  uint256 allocationsLength
);
/// @notice Invalid percentAllocations sum `allocationsSum` must equal `PERCENTAGE_SCALE`
/// @param allocationsSum Sum of percentAllocations array
error InvalidSplit__InvalidAllocationsSum(uint32 allocationsSum);
/// @notice Invalid accounts ordering at `index`
/// @param index Index of out-of-order account
error InvalidSplit__AccountsOutOfOrder(uint256 index);
/// @notice Invalid percentAllocation of zero at `index`
/// @param index Index of zero percentAllocation
error InvalidSplit__AllocationMustBePositive(uint256 index);
/// @notice Invalid distributorFee `distributorFee` cannot be greater than 10% (1e5)
/// @param distributorFee Invalid distributorFee amount
error InvalidSplit__InvalidDistributorFee(uint32 distributorFee);
/// @notice Invalid hash `hash` from split data (accounts, percentAllocations, distributorFee)
/// @param hash Invalid hash
error InvalidSplit__InvalidHash(bytes32 hash);
/// @notice Invalid new controlling address `newController` for mutable split
/// @param newController Invalid new controller
error InvalidNewController(address newController);

/**
 * @title SplitMain
 * @author 0xSplits <will@0xSplits.xyz>
 * @notice A composable and gas-efficient protocol for deploying splitter contracts.
 * @dev Split recipients, ownerships, and keeper fees are stored onchain as calldata & re-passed as args / validated
 * via hashing when needed. Each split gets its own address & proxy for maximum composability with other contracts onchain.
 * For these proxies, we extended EIP-1167 Minimal Proxy Contract to avoid `DELEGATECALL` inside `receive()` to accept
 * hard gas-capped `sends` & `transfers`.
 */
contract SplitMain is ISplitMain {
  using SafeTransferLib for address;
  using SafeTransferLib for ERC20;

  /**
   * STRUCTS
   */

  /// @notice holds Split metadata
  struct Split {
    bytes32 hash;
    address controller;
    address newPotentialController;
  }

  /**
   * STORAGE
   */

  /**
   * STORAGE - CONSTANTS & IMMUTABLES
   */

  /// @notice constant to scale uints into percentages (1e6 == 100%)
  uint256 public constant PERCENTAGE_SCALE = 1e6;
  /// @notice maximum distributor fee; 1e5 = 10% * PERCENTAGE_SCALE
  uint256 internal constant MAX_DISTRIBUTOR_FEE = 1e5;
  /// @notice address of wallet implementation for split proxies
  address public immutable override walletImplementation;

  /**
   * STORAGE - VARIABLES - PRIVATE & INTERNAL
   */

  /// @notice mapping to account ETH balances
  mapping(address => uint256) internal ethBalances;
  /// @notice mapping to account ERC20 balances
  mapping(ERC20 => mapping(address => uint256)) internal erc20Balances;
  /// @notice mapping to Split metadata
  mapping(address => Split) internal splits;

  /**
   * MODIFIERS
   */

  /** @notice Reverts if the sender doesn't own the split `split`
   *  @param split Address to check for control
   */
  modifier onlySplitController(address split) {
    if (msg.sender != splits[split].controller) revert Unauthorized(msg.sender);
    _;
  }

  /** @notice Reverts if the sender isn't the new potential controller of split `split`
   *  @param split Address to check for new potential control
   */
  modifier onlySplitNewPotentialController(address split) {
    if (msg.sender != splits[split].newPotentialController)
      revert Unauthorized(msg.sender);
    _;
  }

  /** @notice Reverts if the split with recipients represented by `accounts` and `percentAllocations` is malformed
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   */
  modifier validSplit(
    address[] memory accounts,
    uint32[] memory percentAllocations,
    uint32 distributorFee
  ) {
    if (accounts.length < 2)
      revert InvalidSplit__TooFewAccounts(accounts.length);
    if (accounts.length != percentAllocations.length)
      revert InvalidSplit__AccountsAndAllocationsMismatch(
        accounts.length,
        percentAllocations.length
      );
    // _getSum should overflow if any percentAllocation[i] < 0
    if (_getSum(percentAllocations) != PERCENTAGE_SCALE)
      revert InvalidSplit__InvalidAllocationsSum(_getSum(percentAllocations));
    unchecked {
      // overflow should be impossible in for-loop index
      // cache accounts length to save gas
      uint256 loopLength = accounts.length - 1;
      for (uint256 i = 0; i < loopLength; ++i) {
        // overflow should be impossible in array access math
        if (accounts[i] >= accounts[i + 1])
          revert InvalidSplit__AccountsOutOfOrder(i);
        if (percentAllocations[i] == uint32(0))
          revert InvalidSplit__AllocationMustBePositive(i);
      }
      // overflow should be impossible in array access math with validated equal array lengths
      if (percentAllocations[loopLength] == uint32(0))
        revert InvalidSplit__AllocationMustBePositive(loopLength);
    }
    if (distributorFee > MAX_DISTRIBUTOR_FEE)
      revert InvalidSplit__InvalidDistributorFee(distributorFee);
    _;
  }

  /** @notice Reverts if `newController` is the zero address
   *  @param newController Proposed new controlling address
   */
  modifier validNewController(address newController) {
    if (newController == address(0)) revert InvalidNewController(newController);
    _;
  }

  /**
   * CONSTRUCTOR
   */

  constructor() {
    walletImplementation = address(new SplitWallet());
  }

  /**
   * FUNCTIONS
   */

  /**
   * FUNCTIONS - PUBLIC & EXTERNAL
   */

  /** @notice Receive ETH
   *  @dev Used by split proxies in `distributeETH` to transfer ETH to `SplitMain`
   *  Funds sent outside of `distributeETH` will be unrecoverable
   */
  receive() external payable {}

  /** @notice Creates a new split with recipients `accounts` with ownerships `percentAllocations`, a keeper fee for splitting of `distributorFee` and the controlling address `controller`
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   *  @param controller Controlling address (0x0 if immutable)
   *  @return split Address of newly created split
   */
  function createSplit(
    address[] calldata accounts,
    uint32[] calldata percentAllocations,
    uint32 distributorFee,
    address controller
  )
    external
    override
    validSplit(accounts, percentAllocations, distributorFee)
    returns (address split)
  {
    bytes32 splitHash = _hashSplit(
      accounts,
      percentAllocations,
      distributorFee
    );
    if (controller == address(0)) {
      // create immutable split
      split = Clones.cloneDeterministic(walletImplementation, splitHash);
    } else {
      // create mutable split
      split = Clones.clone(walletImplementation);
      splits[split].controller = controller;
    }
    // store split's hash in storage for future verification
    splits[split].hash = splitHash;
    emit CreateSplit(split);
  }

  /** @notice Predicts the address for an immutable split created with recipients `accounts` with ownerships `percentAllocations` and a keeper fee for splitting of `distributorFee`
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   *  @return split Predicted address of such an immutable split
   */
  function predictImmutableSplitAddress(
    address[] calldata accounts,
    uint32[] calldata percentAllocations,
    uint32 distributorFee
  )
    external
    view
    override
    validSplit(accounts, percentAllocations, distributorFee)
    returns (address split)
  {
    bytes32 splitHash = _hashSplit(
      accounts,
      percentAllocations,
      distributorFee
    );
    split = Clones.predictDeterministicAddress(walletImplementation, splitHash);
  }

  /** @notice Updates an existing split with recipients `accounts` with ownerships `percentAllocations` and a keeper fee for splitting of `distributorFee`
   *  @param split Address of mutable split to update
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   */
  function updateSplit(
    address split,
    address[] calldata accounts,
    uint32[] calldata percentAllocations,
    uint32 distributorFee
  )
    external
    override
    onlySplitController(split)
    validSplit(accounts, percentAllocations, distributorFee)
  {
    _updateSplit(split, accounts, percentAllocations, distributorFee);
  }

  /** @notice Begins transfer of the controlling address of mutable split `split` to `newController`
   *  @dev Two-step control transfer inspired by [dharma](https://github.com/dharma-eng/dharma-smart-wallet/blob/master/contracts/helpers/TwoStepOwnable.sol)
   *  @param split Address of mutable split to transfer control for
   *  @param newController Address to begin transferring control to
   */
  function transferControl(address split, address newController)
    external
    override
    onlySplitController(split)
    validNewController(newController)
  {
    splits[split].newPotentialController = newController;
    emit InitiateControlTransfer(split, newController);
  }

  /** @notice Cancels transfer of the controlling address of mutable split `split`
   *  @param split Address of mutable split to cancel control transfer for
   */
  function cancelControlTransfer(address split)
    external
    override
    onlySplitController(split)
  {
    delete splits[split].newPotentialController;
    emit CancelControlTransfer(split);
  }

  /** @notice Accepts transfer of the controlling address of mutable split `split`
   *  @param split Address of mutable split to accept control transfer for
   */
  function acceptControl(address split)
    external
    override
    onlySplitNewPotentialController(split)
  {
    delete splits[split].newPotentialController;
    emit ControlTransfer(split, splits[split].controller, msg.sender);
    splits[split].controller = msg.sender;
  }

  /** @notice Turns mutable split `split` immutable
   *  @param split Address of mutable split to turn immutable
   */
  function makeSplitImmutable(address split)
    external
    override
    onlySplitController(split)
  {
    delete splits[split].newPotentialController;
    emit ControlTransfer(split, splits[split].controller, address(0));
    splits[split].controller = address(0);
  }

  /** @notice Distributes the ETH balance for split `split`
   *  @dev `accounts`, `percentAllocations`, and `distributorFee` are verified by hashing
   *  & comparing to the hash in storage associated with split `split`
   *  @param split Address of split to distribute balance for
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   *  @param distributorAddress Address to pay `distributorFee` to
   */
  function distributeETH(
    address split,
    address[] calldata accounts,
    uint32[] calldata percentAllocations,
    uint32 distributorFee,
    address distributorAddress
  ) external override validSplit(accounts, percentAllocations, distributorFee) {
    // use internal fn instead of modifier to avoid stack depth compiler errors
    _validSplitHash(split, accounts, percentAllocations, distributorFee);
    _distributeETH(
      split,
      accounts,
      percentAllocations,
      distributorFee,
      distributorAddress
    );
  }

  /** @notice Updates & distributes the ETH balance for split `split`
   *  @dev only callable by SplitController
   *  @param split Address of split to distribute balance for
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   *  @param distributorAddress Address to pay `distributorFee` to
   */
  function updateAndDistributeETH(
    address split,
    address[] calldata accounts,
    uint32[] calldata percentAllocations,
    uint32 distributorFee,
    address distributorAddress
  )
    external
    override
    onlySplitController(split)
    validSplit(accounts, percentAllocations, distributorFee)
  {
    _updateSplit(split, accounts, percentAllocations, distributorFee);
    // know splitHash is valid immediately after updating; only accessible via controller
    _distributeETH(
      split,
      accounts,
      percentAllocations,
      distributorFee,
      distributorAddress
    );
  }

  /** @notice Distributes the ERC20 `token` balance for split `split`
   *  @dev `accounts`, `percentAllocations`, and `distributorFee` are verified by hashing
   *  & comparing to the hash in storage associated with split `split`
   *  @dev pernicious ERC20s may cause overflow in this function inside
   *  _scaleAmountByPercentage, but results do not affect ETH & other ERC20 balances
   *  @param split Address of split to distribute balance for
   *  @param token Address of ERC20 to distribute balance for
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   *  @param distributorAddress Address to pay `distributorFee` to
   */
  function distributeERC20(
    address split,
    ERC20 token,
    address[] calldata accounts,
    uint32[] calldata percentAllocations,
    uint32 distributorFee,
    address distributorAddress
  ) external override validSplit(accounts, percentAllocations, distributorFee) {
    // use internal fn instead of modifier to avoid stack depth compiler errors
    _validSplitHash(split, accounts, percentAllocations, distributorFee);
    _distributeERC20(
      split,
      token,
      accounts,
      percentAllocations,
      distributorFee,
      distributorAddress
    );
  }

  /** @notice Updates & distributes the ERC20 `token` balance for split `split`
   *  @dev only callable by SplitController
   *  @dev pernicious ERC20s may cause overflow in this function inside
   *  _scaleAmountByPercentage, but results do not affect ETH & other ERC20 balances
   *  @param split Address of split to distribute balance for
   *  @param token Address of ERC20 to distribute balance for
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   *  @param distributorAddress Address to pay `distributorFee` to
   */
  function updateAndDistributeERC20(
    address split,
    ERC20 token,
    address[] calldata accounts,
    uint32[] calldata percentAllocations,
    uint32 distributorFee,
    address distributorAddress
  )
    external
    override
    onlySplitController(split)
    validSplit(accounts, percentAllocations, distributorFee)
  {
    _updateSplit(split, accounts, percentAllocations, distributorFee);
    // know splitHash is valid immediately after updating; only accessible via controller
    _distributeERC20(
      split,
      token,
      accounts,
      percentAllocations,
      distributorFee,
      distributorAddress
    );
  }

  /** @notice Withdraw ETH &/ ERC20 balances for account `account`
   *  @param account Address to withdraw on behalf of
   *  @param withdrawETH Withdraw all ETH if nonzero
   *  @param tokens Addresses of ERC20s to withdraw
   */
  function withdraw(
    address account,
    uint256 withdrawETH,
    ERC20[] calldata tokens
  ) external override {
    uint256[] memory tokenAmounts = new uint256[](tokens.length);
    uint256 ethAmount;
    if (withdrawETH != 0) {
      ethAmount = _withdraw(account);
    }
    unchecked {
      // overflow should be impossible in for-loop index
      for (uint256 i = 0; i < tokens.length; ++i) {
        // overflow should be impossible in array length math
        tokenAmounts[i] = _withdrawERC20(account, tokens[i]);
      }
      emit Withdrawal(account, ethAmount, tokens, tokenAmounts);
    }
  }

  /**
   * FUNCTIONS - VIEWS
   */

  /** @notice Returns the current hash of split `split`
   *  @param split Split to return hash for
   *  @return Split's hash
   */
  function getHash(address split) external view returns (bytes32) {
    return splits[split].hash;
  }

  /** @notice Returns the current controller of split `split`
   *  @param split Split to return controller for
   *  @return Split's controller
   */
  function getController(address split) external view returns (address) {
    return splits[split].controller;
  }

  /** @notice Returns the current newPotentialController of split `split`
   *  @param split Split to return newPotentialController for
   *  @return Split's newPotentialController
   */
  function getNewPotentialController(address split)
    external
    view
    returns (address)
  {
    return splits[split].newPotentialController;
  }

  /** @notice Returns the current ETH balance of account `account`
   *  @param account Account to return ETH balance for
   *  @return Account's balance of ETH
   */
  function getETHBalance(address account) external view returns (uint256) {
    return
      ethBalances[account] + (splits[account].hash != 0 ? account.balance : 0);
  }

  /** @notice Returns the ERC20 balance of token `token` for account `account`
   *  @param account Account to return ERC20 `token` balance for
   *  @param token Token to return balance for
   *  @return Account's balance of `token`
   */
  function getERC20Balance(address account, ERC20 token)
    external
    view
    returns (uint256)
  {
    return
      erc20Balances[token][account] +
      (splits[account].hash != 0 ? token.balanceOf(account) : 0);
  }

  /**
   * FUNCTIONS - PRIVATE & INTERNAL
   */

  /** @notice Sums array of uint32s
   *  @param numbers Array of uint32s to sum
   *  @return sum Sum of `numbers`.
   */
  function _getSum(uint32[] memory numbers) internal pure returns (uint32 sum) {
    // overflow should be impossible in for-loop index
    uint256 numbersLength = numbers.length;
    for (uint256 i = 0; i < numbersLength; ) {
      sum += numbers[i];
      unchecked {
        // overflow should be impossible in for-loop index
        ++i;
      }
    }
  }

  /** @notice Hashes a split
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   *  @return computedHash Hash of the split.
   */
  function _hashSplit(
    address[] memory accounts,
    uint32[] memory percentAllocations,
    uint32 distributorFee
  ) internal pure returns (bytes32) {
    return
      keccak256(abi.encodePacked(accounts, percentAllocations, distributorFee));
  }

  /** @notice Updates an existing split with recipients `accounts` with ownerships `percentAllocations` and a keeper fee for splitting of `distributorFee`
   *  @param split Address of mutable split to update
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   */
  function _updateSplit(
    address split,
    address[] calldata accounts,
    uint32[] calldata percentAllocations,
    uint32 distributorFee
  ) internal {
    bytes32 splitHash = _hashSplit(
      accounts,
      percentAllocations,
      distributorFee
    );
    // store new hash in storage for future verification
    splits[split].hash = splitHash;
    emit UpdateSplit(split);
  }

  /** @notice Checks hash from `accounts`, `percentAllocations`, and `distributorFee` against the hash stored for `split`
   *  @param split Address of hash to check
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   */
  function _validSplitHash(
    address split,
    address[] memory accounts,
    uint32[] memory percentAllocations,
    uint32 distributorFee
  ) internal view {
    bytes32 hash = _hashSplit(accounts, percentAllocations, distributorFee);
    if (splits[split].hash != hash) revert InvalidSplit__InvalidHash(hash);
  }

  /** @notice Distributes the ETH balance for split `split`
   *  @dev `accounts`, `percentAllocations`, and `distributorFee` must be verified before calling
   *  @param split Address of split to distribute balance for
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   *  @param distributorAddress Address to pay `distributorFee` to
   */
  function _distributeETH(
    address split,
    address[] memory accounts,
    uint32[] memory percentAllocations,
    uint32 distributorFee,
    address distributorAddress
  ) internal {
    uint256 mainBalance = ethBalances[split];
    uint256 proxyBalance = split.balance;
    // if mainBalance is positive, leave 1 in SplitMain for gas efficiency
    uint256 amountToSplit;
    unchecked {
      // underflow should be impossible
      if (mainBalance > 0) mainBalance -= 1;
      // overflow should be impossible
      amountToSplit = mainBalance + proxyBalance;
    }
    if (mainBalance > 0) ethBalances[split] = 1;
    // emit event with gross amountToSplit (before deducting distributorFee)
    emit DistributeETH(split, amountToSplit, distributorAddress);
    if (distributorFee != 0) {
      // given `amountToSplit`, calculate keeper fee
      uint256 distributorFeeAmount = _scaleAmountByPercentage(
        amountToSplit,
        distributorFee
      );
      unchecked {
        // credit keeper with fee
        // overflow should be impossible with validated distributorFee
        ethBalances[
          distributorAddress != address(0) ? distributorAddress : msg.sender
        ] += distributorFeeAmount;
        // given keeper fee, calculate how much to distribute to split recipients
        // underflow should be impossible with validated distributorFee
        amountToSplit -= distributorFeeAmount;
      }
    }
    unchecked {
      // distribute remaining balance
      // overflow should be impossible in for-loop index
      // cache accounts length to save gas
      uint256 accountsLength = accounts.length;
      for (uint256 i = 0; i < accountsLength; ++i) {
        // overflow should be impossible with validated allocations
        ethBalances[accounts[i]] += _scaleAmountByPercentage(
          amountToSplit,
          percentAllocations[i]
        );
      }
    }
    // flush proxy ETH balance to SplitMain
    // split proxy should be guaranteed to exist at this address after validating splitHash
    // (attacker can't deploy own contract to address with high balance & empty sendETHToMain
    // to drain ETH from SplitMain)
    // could technically check if (change in proxy balance == change in SplitMain balance)
    // before/after external call, but seems like extra gas for no practical benefit
    if (proxyBalance > 0) SplitWallet(split).sendETHToMain(proxyBalance);
  }

  /** @notice Distributes the ERC20 `token` balance for split `split`
   *  @dev `accounts`, `percentAllocations`, and `distributorFee` must be verified before calling
   *  @dev pernicious ERC20s may cause overflow in this function inside
   *  _scaleAmountByPercentage, but results do not affect ETH & other ERC20 balances
   *  @param split Address of split to distribute balance for
   *  @param token Address of ERC20 to distribute balance for
   *  @param accounts Ordered, unique list of addresses with ownership in the split
   *  @param percentAllocations Percent allocations associated with each address
   *  @param distributorFee Keeper fee paid by split to cover gas costs of distribution
   *  @param distributorAddress Address to pay `distributorFee` to
   */
  function _distributeERC20(
    address split,
    ERC20 token,
    address[] memory accounts,
    uint32[] memory percentAllocations,
    uint32 distributorFee,
    address distributorAddress
  ) internal {
    uint256 amountToSplit;
    uint256 mainBalance = erc20Balances[token][split];
    uint256 proxyBalance = token.balanceOf(split);
    unchecked {
      // if mainBalance &/ proxyBalance are positive, leave 1 for gas efficiency
      // underflow should be impossible
      if (proxyBalance > 0) proxyBalance -= 1;
      // underflow should be impossible
      if (mainBalance > 0) {
        mainBalance -= 1;
      }
      // overflow should be impossible
      amountToSplit = mainBalance + proxyBalance;
    }
    if (mainBalance > 0) erc20Balances[token][split] = 1;
    // emit event with gross amountToSplit (before deducting distributorFee)
    emit DistributeERC20(split, token, amountToSplit, distributorAddress);
    if (distributorFee != 0) {
      // given `amountToSplit`, calculate keeper fee
      uint256 distributorFeeAmount = _scaleAmountByPercentage(
        amountToSplit,
        distributorFee
      );
      // overflow should be impossible with validated distributorFee
      unchecked {
        // credit keeper with fee
        erc20Balances[token][
          distributorAddress != address(0) ? distributorAddress : msg.sender
        ] += distributorFeeAmount;
        // given keeper fee, calculate how much to distribute to split recipients
        amountToSplit -= distributorFeeAmount;
      }
    }
    // distribute remaining balance
    // overflows should be impossible in for-loop with validated allocations
    unchecked {
      // cache accounts length to save gas
      uint256 accountsLength = accounts.length;
      for (uint256 i = 0; i < accountsLength; ++i) {
        erc20Balances[token][accounts[i]] += _scaleAmountByPercentage(
          amountToSplit,
          percentAllocations[i]
        );
      }
    }
    // split proxy should be guaranteed to exist at this address after validating splitHash
    // (attacker can't deploy own contract to address with high ERC20 balance & empty
    // sendERC20ToMain to drain ERC20 from SplitMain)
    // doesn't support rebasing or fee-on-transfer tokens
    // flush extra proxy ERC20 balance to SplitMain
    if (proxyBalance > 0)
      SplitWallet(split).sendERC20ToMain(token, proxyBalance);
  }

  /** @notice Multiplies an amount by a scaled percentage
   *  @param amount Amount to get `scaledPercentage` of
   *  @param scaledPercent Percent scaled by PERCENTAGE_SCALE
   *  @return scaledAmount Percent of `amount`.
   */
  function _scaleAmountByPercentage(uint256 amount, uint256 scaledPercent)
    internal
    pure
    returns (uint256 scaledAmount)
  {
    // use assembly to bypass checking for overflow & division by 0
    // scaledPercent has been validated to be < PERCENTAGE_SCALE)
    // & PERCENTAGE_SCALE will never be 0
    // pernicious ERC20s may cause overflow, but results do not affect ETH & other ERC20 balances
    assembly {
      /* eg (100 * 2*1e4) / (1e6) */
      scaledAmount := div(mul(amount, scaledPercent), PERCENTAGE_SCALE)
    }
  }

  /** @notice Withdraw ETH for account `account`
   *  @param account Account to withdrawn ETH for
   *  @return withdrawn Amount of ETH withdrawn
   */
  function _withdraw(address account) internal returns (uint256 withdrawn) {
    // leave balance of 1 for gas efficiency
    // underflow if ethBalance is 0
    withdrawn = ethBalances[account] - 1;
    ethBalances[account] = 1;
    account.safeTransferETH(withdrawn);
  }

  /** @notice Withdraw ERC20 `token` for account `account`
   *  @param account Account to withdrawn ERC20 `token` for
   *  @return withdrawn Amount of ERC20 `token` withdrawn
   */
  function _withdrawERC20(address account, ERC20 token)
    internal
    returns (uint256 withdrawn)
  {
    // leave balance of 1 for gas efficiency
    // underflow if erc20Balance is 0
    withdrawn = erc20Balances[token][account] - 1;
    erc20Balances[token][account] = 1;
    token.safeTransfer(account, withdrawn);
  }
}