// File: github/dn3010/staking-contracts/YieldFarm.sol



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

// import "@openzeppelin/contracts-ethereum-package/contracts/math/SafeMath.sol";
import "@openzeppelin/contracts/utils/math/SafeMath.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "./IStaking.sol";

contract YieldFarm {
    // lib
    using SafeMath for uint256;
    using SafeMath for uint128;

    // constants
    uint256 public constant TOTAL_DISTRIBUTED_AMOUNT = 62_500_000;
    uint256 public constant NR_OF_EPOCHS = 25;
    uint128 public constant EPOCHS_DELAYED_FROM_STAKING_CONTRACT = 0;

    // addreses
    address private _lpTokenAddress;
    address private _communityVault;

    // contracts
    IERC20 private _sylo;
    IStaking private _staking;

    uint256[] private epochs = new uint256[](NR_OF_EPOCHS + 1);
    uint256 private _totalAmountPerEpoch;
    uint128 public lastInitializedEpoch;
    mapping(address => uint128) private lastEpochIdHarvested;
    uint256 public epochDuration;
    uint256 public epochStart;

    // events
    event MassHarvest(
        address indexed user,
        uint256 epochsHarvested,
        uint256 totalValue
    );
    event Harvest(
        address indexed user,
        uint128 indexed epochId,
        uint256 amount
    );

    // constructor
    constructor(
        address syloTokenAddress,
        address lpTokenAddress,
        address stakeContract,
        address communityVault
    ) {
        require(syloTokenAddress != address(0), "Sylo token address is required");
        require(lpTokenAddress != address(0), "LP token address is required");
        require(stakeContract != address(0), "Stake address is required");
        require(communityVault != address(0), "Community Vault address is required");

        _sylo = IERC20(syloTokenAddress);
        _lpTokenAddress = lpTokenAddress;
        _staking = IStaking(stakeContract);
        _communityVault = communityVault;
        epochDuration = _staking.epochDuration();
        epochStart =
            _staking.epoch1Start() +
            epochDuration.mul(EPOCHS_DELAYED_FROM_STAKING_CONTRACT);
        _totalAmountPerEpoch = 
            TOTAL_DISTRIBUTED_AMOUNT
                .mul(10**18)
                .div(NR_OF_EPOCHS);
    }

    // public methods
    // public method to harvest all the unharvested epochs until current epoch - 1
    function massHarvest() external returns (uint256) {
        uint256 totalDistributedValue;
        uint256 epochId = _getEpochId().sub(1); // fails in epoch 0
        // force max number of epochs
        if (epochId > NR_OF_EPOCHS) {
            epochId = NR_OF_EPOCHS;
        }

        for (
            uint128 i = lastEpochIdHarvested[msg.sender] + 1;
            i <= epochId;
            i++
        ) {
            // i = epochId
            // compute distributed Value and do one single transfer at the end
            totalDistributedValue += _harvest(i);
        }

        emit MassHarvest(
            msg.sender,
            epochId - lastEpochIdHarvested[msg.sender],
            totalDistributedValue
        );

        if (totalDistributedValue > 0) {
            bool success = _sylo.transferFrom(
                _communityVault,
                msg.sender,
                totalDistributedValue
            );
            require(success, "Failed to transfer mass harvest reward");
        }

        return totalDistributedValue;
    }

    function harvest(uint128 epochId) external returns (uint256) {
        // checks for requested epoch
        require(_getEpochId() > epochId, "This epoch is in the future");
        require(epochId <= NR_OF_EPOCHS, "Maximum number of epochs is 12");
        require(
            lastEpochIdHarvested[msg.sender].add(1) == epochId,
            "Harvest in order"
        );
        uint256 userReward = _harvest(epochId);
        if (userReward > 0) {
            bool success = _sylo.transferFrom(_communityVault, msg.sender, userReward);
            require(success, "Failed to transfer harvest reward");
        }
        emit Harvest(msg.sender, epochId, userReward);
        return userReward;
    }

    // views
    // calls to the staking smart contract to retrieve the epoch total pool size
    function getPoolSize(uint128 epochId) external view returns (uint256) {
        return _getPoolSize(epochId);
    }

    function getCurrentEpoch() external view returns (uint256) {
        return _getEpochId();
    }

    // calls to the staking smart contract to retrieve user balance for an epoch
    function getEpochStake(address userAddress, uint128 epochId)
        external
        view
        returns (uint256)
    {
        return _getUserBalancePerEpoch(userAddress, epochId);
    }

    function userLastEpochIdHarvested() external view returns (uint256) {
        return lastEpochIdHarvested[msg.sender];
    }

    // internal methods

    function _initEpoch(uint128 epochId) internal {
        require(
            lastInitializedEpoch.add(1) == epochId,
            "Epoch can be init only in order"
        );
        lastInitializedEpoch = epochId;
        // call the staking smart contract to init the epoch
        epochs[epochId] = _getPoolSize(epochId);
    }

    function _harvest(uint128 epochId) internal returns (uint256) {
        // try to initialize an epoch. if it can't it fails
        // if it fails either user either a Plug account will init not init epochs
        if (lastInitializedEpoch < epochId) {
            _initEpoch(epochId);
        }
        // Set user state for last harvested
        lastEpochIdHarvested[msg.sender] = epochId;
        // compute and return user total reward. For optimization reasons the transfer have been moved to an upper layer (i.e. massHarvest needs to do a single transfer)

        // exit if there is no stake on the epoch
        if (epochs[epochId] == 0) {
            return 0;
        }
        return
            _totalAmountPerEpoch
                .mul(_getUserBalancePerEpoch(msg.sender, epochId))
                .div(epochs[epochId]);
    }

    // retrieve _lpTokenAddress token balance
    function _getPoolSize(uint128 epochId) internal view returns (uint256) {
        return
            _staking.getEpochPoolSize(
                _lpTokenAddress,
                _stakingEpochId(epochId)
            );
    }

    // retrieve _lpTokenAddress token balance per user per epoch
    function _getUserBalancePerEpoch(address userAddress, uint128 epochId)
        internal
        view
        returns (uint256)
    {
        return
            _staking.getEpochUserBalance(
                userAddress,
                _lpTokenAddress,
                _stakingEpochId(epochId)
            );
    }

    // compute epoch id from block.timestamp and epochStart date
    function _getEpochId() internal view returns (uint128 epochId) {
        if (block.timestamp < epochStart) {
            return 0;
        }
        epochId = uint128(
            block.timestamp.sub(epochStart).div(epochDuration).add(1)
        );
    }

    // get the staking epoch
    function _stakingEpochId(uint128 epochId) internal pure returns (uint128) {
        return epochId + EPOCHS_DELAYED_FROM_STAKING_CONTRACT;
    }
}

// File: github/dn3010/staking-contracts/IStaking.sol



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

interface IStaking {
    function getEpochId(uint timestamp) external view returns (uint); // get epoch id
    function getEpochUserBalance(address user, address token, uint128 epoch) external view returns(uint);
    function getEpochPoolSize(address token, uint128 epoch) external view returns (uint);
    function epoch1Start() external view returns (uint);
    function epochDuration() external view returns (uint);
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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: @openzeppelin/contracts/utils/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is no longer needed starting with Solidity 0.8. The compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // 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 (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @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) {
        return a + b;
    }

    /**
     * @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 a - b;
    }

    /**
     * @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) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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 a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting 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) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}