// SPDX-License-Identifier: MIT

pragma solidity ^0.8.13;

import "@openzeppelin/contracts/utils/Context.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

/**
 * @title PaymentSplitter
 * @dev This contract allows to split Ether payments among a group of accounts. The sender does not need to be aware
 * that the Ether will be split in this way, since it is handled transparently by the contract.
 *
 * The split can be in equal parts or in any other arbitrary proportion. The way this is specified is by assigning each
 * account to a number of shares. Of all the Ether that this contract receives, each account will then be able to claim
 * an amount proportional to the percentage of total shares they were assigned.
 *
 * `PaymentSplitter` follows a _pull payment_ model. This means that payments are not automatically forwarded to the
 * accounts but kept in this contract, and the actual transfer is triggered as a separate step by calling the {release}
 * function.
 *
 * NOTE: This contract assumes that ERC20 tokens will behave similarly to native tokens (Ether). Rebasing tokens, and
 * tokens that apply fees during transfers, are likely to not be supported as expected. If in doubt, we encourage you
 * to run tests before sending real value to this contract.
 */
contract PaymentSplitter is Context {
  event PayeeAdded(address account, uint256 shares);
  event PaymentReleased(address to, uint256 amount);
  event ERC20PaymentReleased(IERC20 indexed token, address to, uint256 amount);
  event PaymentReceived(address from, uint256 amount);

  uint256 private _totalShares;
  uint256 private _totalReleased;

  mapping(address => uint256) private _shares;
  mapping(address => uint256) private _released;
  address[] private _payees;

  mapping(IERC20 => uint256) private _erc20TotalReleased;
  mapping(IERC20 => mapping(address => uint256)) private _erc20Released;

  /**
   * @dev Creates an instance of `PaymentSplitter` where each account in `payees` is assigned the number of shares at
   * the matching position in the `shares` array.
   *
   * All addresses in `payees` must be non-zero. Both arrays must have the same non-zero length, and there must be no
   * duplicates in `payees`.
   */
  constructor(address[] memory payees, uint256[] memory shares_) payable {
    require(
      payees.length == shares_.length,
      "PaymentSplitter: payees and shares length mismatch"
    );
    require(payees.length > 0, "PaymentSplitter: no payees");

    for (uint256 i = 0; i < payees.length; i++) {
      _addPayee(payees[i], shares_[i]);
    }
  }

  /**
   * @dev The Ether received will be logged with {PaymentReceived} events. Note that these events are not fully
   * reliable: it's possible for a contract to receive Ether without triggering this function. This only affects the
   * reliability of the events, and not the actual splitting of Ether.
   *
   * To learn more about this see the Solidity documentation for
   * https://solidity.readthedocs.io/en/latest/contracts.html#fallback-function[fallback
   * functions].
   */
  receive() external payable virtual {
    emit PaymentReceived(_msgSender(), msg.value);
  }

  /**
   * @dev Getter for the total shares held by payees.
   */
  function totalShares() public view returns (uint256) {
    return _totalShares;
  }

  /**
   * @dev Getter for the total amount of Ether already released.
   */
  function totalReleased() public view returns (uint256) {
    return _totalReleased;
  }

  /**
   * @dev Getter for the total amount of `token` already released. `token` should be the address of an IERC20
   * contract.
   */
  function totalReleased(IERC20 token) public view returns (uint256) {
    return _erc20TotalReleased[token];
  }

  /**
   * @dev Getter for the amount of shares held by an account.
   */
  function shares(address account) public view returns (uint256) {
    return _shares[account];
  }

  /**
   * @dev Getter for the amount of Ether already released to a payee.
   */
  function released(address account) public view returns (uint256) {
    return _released[account];
  }

  /**
   * @dev Getter for the amount of `token` tokens already released to a payee. `token` should be the address of an
   * IERC20 contract.
   */
  function released(IERC20 token, address account)
    public
    view
    returns (uint256)
  {
    return _erc20Released[token][account];
  }

  /**
   * @dev Getter for the address of the payee number `index`.
   */
  function payee(uint256 index) public view returns (address) {
    return _payees[index];
  }

  /**
   * @dev Triggers a transfer to `account` of the amount of Ether they are owed, according to their percentage of the
   * total shares and their previous withdrawals.
   */
  function release(address payable account) public virtual {
    require(_shares[account] > 0, "PaymentSplitter: account has no shares");

    uint256 totalReceived = address(this).balance + totalReleased();
    uint256 payment = _pendingPayment(
      account,
      totalReceived,
      released(account)
    );

    require(payment != 0, "PaymentSplitter: account is not due payment");

    _released[account] += payment;
    _totalReleased += payment;

    Address.sendValue(account, payment);
    emit PaymentReleased(account, payment);
  }

  /**
   * @dev Triggers a transfer to `account` of the amount of `token` tokens they are owed, according to their
   * percentage of the total shares and their previous withdrawals. `token` must be the address of an IERC20
   * contract.
   */
  function release(IERC20 token, address account) public virtual {
    require(_shares[account] > 0, "PaymentSplitter: account has no shares");

    uint256 totalReceived = token.balanceOf(address(this)) +
      totalReleased(token);
    uint256 payment = _pendingPayment(
      account,
      totalReceived,
      released(token, account)
    );

    require(payment != 0, "PaymentSplitter: account is not due payment");

    _erc20Released[token][account] += payment;
    _erc20TotalReleased[token] += payment;

    SafeERC20.safeTransfer(token, account, payment);
    emit ERC20PaymentReleased(token, account, payment);
  }

  /**
   * @dev internal logic for computing the pending payment of an `account` given the token historical balances and
   * already released amounts.
   */
  function _pendingPayment(
    address account,
    uint256 totalReceived,
    uint256 alreadyReleased
  ) private view returns (uint256) {
    return (totalReceived * _shares[account]) / _totalShares - alreadyReleased;
  }

  /**
   * @dev Add a new payee to the contract.
   * @param account The address of the payee to add.
   * @param shares_ The number of shares owned by the payee.
   */
  function _addPayee(address account, uint256 shares_) private {
    require(
      account != address(0),
      "PaymentSplitter: account is the zero address"
    );
    require(shares_ > 0, "PaymentSplitter: shares are 0");
    require(
      _shares[account] == 0,
      "PaymentSplitter: account already has shares"
    );

    _payees.push(account);
    _shares[account] = shares_;
    _totalShares = _totalShares + shares_;
    emit PayeeAdded(account, shares_);
  }
}
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