staking/contracts/StakeManager.sol

// SPDX-License-Identifier: MIT

pragma solidity 0.8.19;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract StakeManager is ERC20 {

    ERC20 stakedToken;

    uint256 public constant MP_APY = 1; 
    uint256 public constant STAKE_APY = 1; 
    uint256 public constant MAX_BOOST = 1; 
    uint256 public constant MAX_MP = 1; 
    mapping (address => Account) accounts;

    struct Account {
        uint256 lockUntil;
        uint256 balance;
        uint256 multiplier;
        uint256 lastAccured;
        uint256 epoch;
    }

    struct Epoch {
        uint256 startTime;
        uint256 totalReward;    
    }

    uint256 currentEpoch;
    uint256 pendingReward;
    uint256 public totalSupply;
    
    uint256 public constant EPOCH_SIZE = 1 week;

    mapping (uint256 => Epoch) epoch;
    mapping (address => Account) accounts;


    constructor() {
        epoch[0].startTime = now();
    }

    function increaseBalance(uint256 _amount, uint256 _time) external {
        Account storage account = accounts[msg.sender];
        uint256 increasedMultiplier = _amount * (_time + 1);
        account.balance += _amount;
        account.multiplier += mp;
        account.lastAccured = now();
        account.lockUntil = now() + _time;

        multiplierSupply += increasedMultiplier;
        totalSupply += _amount;
    }


    function decreaseBalance(uint256 _amount) external {
        Account storage account = accounts[msg.sender];
        uint256 reducedMultiplier = (_amount * account.multiplier) / account.balance;
        account.multiplier -= reducedMultiplier;
        account.balance -= _amount;

        multiplierSupply -= reducedMultiplier;
        totalSupply -= _amount;
    }

    /**
     * Locks entire balance for more amount of time.
     * @param _time amount of time to lock from now.
     */
    function balanceLock(uint256 _time) external {
        Account storage account = accounts[msg.sender];
        require(now() + _time > account.lockUntil, "Cannot decrease lock time");

        //if balance still locked, multipliers must be minted from difference of time.
        uint256 dT = account.lockUntil > now() ? now() + _time - account.lockUntil : _time); 
        account.lockUntil =  now() + _time;
        uint256 increasedMultiplier = _amount * dT;

        account.multiplier += increasedMultiplier;
        multiplierSupply += increasedMultiplier;
    }

    /**
     * @dev Function called to increase the Multiplier Points of a Vault
     * @param _vault 
     */
    function mintMultiplierPoints(address _vault) external {
        Account storage account = accounts[msg.sender];
        uint256 lastCall = now() - account.lastAccured; 
        uint256 increasedMultiplier = checkMaxMultiplier(
            account.balance * (MP_APY * lastCall),  
            account.multiplier);
        account.lastAccured = now();
        account.multiplier += increasedMultiplier;
        multiplierSupply += increasedMultiplier;
    }

    function executeEpochReward() external {
        if(now() > epoch[currentEpoch].startTime + EPOCH_SIZE){
            uint256 epochReward = stakedToken.balanceOf(this) - pendingReward;
            epoch[currentEpoch].totalReward = epochReward;
            pendingReward += epochReward;
            currentEpoch++;
            epoch[currentEpoch].startTime = now();
        }

    }

    function executeUserReward(address _vault, uint256 _limitEpoch) external {
        Account storage account = accounts[msg.sender];
        uint256 userReward;
        uint256 userEpoch = account.epoch
        require(_limitEpoch <= currentEpoch, "Epoch not reached");
        require(_limitEpoch > userEpoch, "Epoch already claimed");
        uint256 totalShare = this.totalSupply + this.multiplierSupply;
        uint256 userShare = account.balance + account.multiplier;
        uint256 userRatio = userShare / totalShare; //TODO: might lose precision, multiply by 100 and divide back later?
        for (; userEpoch < _limitEpoch; userEpoch++) {
            userReward += userRatio * epoch[userEpoch].totalReward;
        }
        account.epoch = userEpoch;
        pendingReward -= userReward;
        stakedToken.transfer(_vault, userReward);
    }

    function checkMaxMultiplier(uint256 _increasedMultiplier, uint256 _currentMp) private view returns(uint256 _maxToIncrease) {
        uint256 newMp = _increasedMultiplier + _currentMp;
        return newMp > MAX_MP ? MAX_MP - newMp : _increasedMultiplier;
    }

}