// File: contracts/external/DividendDistributor.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import './IDividendDistributor.sol';
import './SafeMath.sol';
import './IERC20.sol';
import './ReentrancyGuard.sol';

contract DividendDistributor is IDividendDistributor, ReentrancyGuard {
    using SafeMath for uint256;

    event DividendDistributed(address shareholder, uint256 amount);

    address _token;

    struct Share {
        uint256 amount;
        uint256 totalExcluded;
        uint256 totalRealised;
    }

    address[] shareholders;
    mapping(address => uint256) shareholderIndexes;
    mapping(address => uint256) shareholderClaims;

    mapping(address => Share) public shares;

    uint256 public totalShares;
    uint256 public totalDividends;
    uint256 public totalDistributed;
    uint256 public dividendsPerShare;
    uint256 public dividendsPerShareAccuracyFactor = 10**36;

    uint256 public minPeriod = 1 hours;
    uint256 public minDistribution = 1 * (10**18);

    uint256 currentIndex;

    modifier onlyToken() {
        require(msg.sender == _token);
        _;
    }

    constructor() public {
        _token = msg.sender;
    }

    function setDistributionCriteria(
        uint256 _minPeriod,
        uint256 _minDistribution
    ) external override onlyToken {
        minPeriod = _minPeriod;
        minDistribution = _minDistribution;
    }

    function setShare(address shareholder, uint256 amount)
        external
        override
        onlyToken
    {
        if (shares[shareholder].amount > 0) {
            distributeDividend(payable(shareholder));
        }

        if (amount > 0 && shares[shareholder].amount == 0) {
            addShareholder(shareholder);
        } else if (amount == 0 && shares[shareholder].amount > 0) {
            removeShareholder(shareholder);
        }

        totalShares = totalShares.sub(shares[shareholder].amount).add(amount);
        shares[shareholder].amount = amount;

        shares[shareholder].totalExcluded = getCumulativeDividends(
            shares[shareholder].amount
        );
    }

    function deposit() external payable override onlyToken {
        totalDividends = totalDividends.add(msg.value);
        dividendsPerShare = dividendsPerShare.add(
            dividendsPerShareAccuracyFactor.mul(msg.value).div(totalShares)
        );
    }

    function distributeDividend(address payable shareholder) internal nonReentrant {
        if (shares[shareholder].amount == 0) {
            return;
        }

        uint256 amount = getUnpaidEarnings(shareholder);

        if (amount > 0) {
            totalDistributed = totalDistributed.add(amount);
            shareholder.transfer(amount);
            shareholderClaims[shareholder] = block.timestamp;
            shares[shareholder].totalRealised = shares[shareholder]
                .totalRealised
                .add(amount);
            shares[shareholder].totalExcluded = getCumulativeDividends(
                shares[shareholder].amount
            );

            emit DividendDistributed(shareholder, amount);
        }
    }

    function claimDividend() external {
        distributeDividend(msg.sender);
    }

    function getUnpaidEarnings(address shareholder)
        public
        view
        returns (uint256)
    {
        if (shares[shareholder].amount == 0) {
            return 0;
        }

        uint256 shareholderTotalDividends = getCumulativeDividends(
            shares[shareholder].amount
        );
        uint256 shareholderTotalExcluded = shares[shareholder].totalExcluded;

        if (shareholderTotalDividends <= shareholderTotalExcluded) {
            return 0;
        }

        return shareholderTotalDividends.sub(shareholderTotalExcluded);
    }

    function getCumulativeDividends(uint256 share)
        internal
        view
        returns (uint256)
    {
        return
            share.mul(dividendsPerShare).div(dividendsPerShareAccuracyFactor);
    }

    function addShareholder(address shareholder) internal {
        shareholderIndexes[shareholder] = shareholders.length;
        shareholders.push(shareholder);
    }

    function getShareholders()
        external
        view
        returns (address[] memory)
    {
        return shareholders;
    }

    function getShareholderAmount(address shareholder)
        external
        view
        returns (uint256)
    {
        return shares[shareholder].amount;
    }

    function removeShareholder(address shareholder) internal {
        shareholders[shareholderIndexes[shareholder]] = shareholders[
            shareholders.length - 1
        ];
        shareholderIndexes[
            shareholders[shareholders.length - 1]
        ] = shareholderIndexes[shareholder];
        shareholders.pop();
    }
}

// File: contracts/external/IDividendDistributor.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

interface IDividendDistributor {
    function setDistributionCriteria(
        uint256 _minPeriod,
        uint256 _minDistribution
    ) external;

    function setShare(address shareholder, uint256 amount) external;

    function deposit() external payable;

}

// File: contracts/external/SafeMath.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, 'SafeMath: addition overflow');

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, 'SafeMath: subtraction overflow');
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, 'SafeMath: multiplication overflow');

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, 'SafeMath: division by zero');
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, 'SafeMath: modulo by zero');
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: contracts/external/IERC20.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: contracts/external/ReentrancyGuard.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

abstract contract ReentrancyGuard {
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor() public {
        _status = _NOT_ENTERED;
    }

    modifier nonReentrant() {
        require(_status != _ENTERED, 'ReentrancyGuard: reentrant call');
        _status = _ENTERED;
        _;
        _status = _NOT_ENTERED;
    }

    modifier isHuman() {
        require(tx.origin == msg.sender, 'sorry humans only');
        _;
    }
}