// SPDX-License-Identifier: MIT

pragma solidity 0.8.18;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "./StakeVault.sol";

contract StakeManager is Ownable {

    struct Account {
        uint256 lockUntil;
        uint256 balance;
        uint256 multiplier;
        uint256 lastMint;
        uint256 epoch;
        address rewardAddress;
    }

    struct Epoch {
        uint256 startTime;
        uint256 epochReward;   
        uint256 totalSupply; 
    }

    uint256 public constant EPOCH_SIZE = 1 weeks;
    uint256 public constant YEAR = 365 days; 
    uint256 public constant MP_APY = 1; 
    uint256 public constant STAKE_APY = 1; 
    uint256 public constant MAX_BOOST = 4; 
    uint256 public constant MAX_MP = 1; 

    mapping (address => Account) accounts;
    mapping (uint256 => Epoch) epochs;
    mapping (bytes32 => bool) isVault;

    
    uint256 public currentEpoch;
    uint256 public pendingReward;
    uint256 public multiplierSupply;
    uint256 public stakeSupply;
    StakeManager public migration;
    StakeManager public immutable oldManager;
    ERC20 public immutable stakedToken;
    modifier onlyVault {
        require(isVault[msg.sender.codehash], "Not a vault");
        _;
    }

    constructor(ERC20 _stakedToken, StakeManager _oldManager) Ownable()  {
        epochs[0].startTime = block.timestamp;
        oldManager = _oldManager;
        stakedToken = _stakedToken;
    }

    /**
     * Increases balance of msg.sender;
     * @param _amount Amount of balance to be decreased.
     * @param _time Seconds from block.timestamp to lock balance.
     */
    function stake(uint256 _amount, uint256 _time) external onlyVault {
        Account storage account = accounts[msg.sender];
        processAccount(account, currentEpoch);
        account.balance += _amount;
        account.rewardAddress = StakeVault(msg.sender).owner();
        mintIntialMultiplier(account, _time, _amount, 1);
        stakeSupply += _amount;
    }

    /**
     * Decreases balance of msg.sender;
     * @param _amount Amount of balance to be decreased
     */
    function unstake(uint256 _amount) external onlyVault {
        Account storage account = accounts[msg.sender];
        require(account.lockUntil <= block.timestamp, "Funds are locked");
        processAccount(account, currentEpoch);
        uint256 reducedMultiplier = (_amount * account.multiplier) / account.balance;
        account.multiplier -= reducedMultiplier;
        account.balance -= _amount;
        multiplierSupply -= reducedMultiplier;
        stakeSupply -= _amount;
    }

    /**
     * @notice Locks entire balance for more amount of time.
     * @param _time amount of time to lock from now.
     */
    function lock(uint256 _time) external onlyVault {
        Account storage account = accounts[msg.sender];
        processAccount(account, currentEpoch);
        require(block.timestamp + _time > account.lockUntil, "Cannot decrease lock time");
        mintIntialMultiplier(account, _time, account.balance, 0);
    }

    /**
     * @notice leave without processing account
     */
    function leave() external onlyVault {
        require(address(migration) != address(0), "Leave only during migration");
        Account memory account = accounts[msg.sender];
        delete accounts[msg.sender];
        multiplierSupply -= account.multiplier;
        stakeSupply -= account.balance;
    }

    /**
     * @notice Release rewards for current epoch and increase epoch.
     */
    function executeEpoch() external {
        processEpoch();
    }

    /**
     * @notice Execute rewards for account until limit has reached
     * @param _vault Referred account
     * @param _limitEpoch Until what epoch it should be executed
     */
    function executeAccount(address _vault, uint256 _limitEpoch) external {
        processAccount(accounts[_vault], _limitEpoch); 
    }
    
    /**
     * @notice Enables a contract class to interact with staking functions
     * @param _codehash bytecode hash of contract
     */
    function setVault(bytes32 _codehash) external onlyOwner {
        isVault[_codehash] = true;  
    }
    /**
     * @notice Migrate account to new manager.
     */
    function migrate() external onlyVault returns (StakeManager newManager) {
        require(address(migration) != address(0), "Migration not available");
        Account storage account = accounts[msg.sender];
        stakedToken.approve(address(migration), account.balance);
        migration.migrate(msg.sender, account);
        delete accounts[msg.sender];
        return migration;
    }

    /**
     * @dev Only callable from old manager.
     * @notice Migrate account from old manager
     * @param _vault Account address
     * @param _account Account data
     */
    function migrate(address _vault, Account memory _account) external {
        require(msg.sender == address(oldManager), "Unauthorized");
        stakedToken.transferFrom(address(oldManager), address(this), _account.balance);
        accounts[_vault] = _account;
     }

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

    function processEpoch() private {
        if(block.timestamp >= epochEnd()){
            //finalize current epoch
            epochs[currentEpoch].epochReward = epochReward();
            epochs[currentEpoch].totalSupply = totalSupply();
            pendingReward += epochs[currentEpoch].epochReward;
            //create new epoch
            currentEpoch++;
            epochs[currentEpoch].startTime = block.timestamp;
        }
    }

    function processAccount(Account storage account, uint256 _limitEpoch) private {
        processEpoch();
        require(address(migration) == address(0), "Contract ended, please migrate");
        require(_limitEpoch <= currentEpoch, "Non-sense call");
        uint256 userReward;
        uint256 userEpoch = account.epoch;
        for (Epoch memory iEpoch = epochs[userEpoch]; userEpoch < _limitEpoch; userEpoch++) {
            //mint multipliers to that epoch
            mintMultiplier(account, iEpoch.startTime + EPOCH_SIZE);
            uint256 userSupply = account.balance + account.multiplier;
            uint256 userShare = userSupply / iEpoch.totalSupply; //TODO: might lose precision, multiply by 100 and divide back later?
            userReward += userShare * iEpoch.epochReward; 
        }
        account.epoch = userEpoch;
        if(userReward > 0){
            pendingReward -= userReward;
            stakedToken.transfer(account.rewardAddress, userReward);
        }
        mintMultiplier(account, block.timestamp);
    }


    function mintMultiplier(Account storage account, uint256 processTime) private {
        uint256 deltaTime = processTime - account.lastMint; 
        account.lastMint = processTime;
        uint256 increasedMultiplier = calcMaxMultiplierIncrease(
            account.balance * (MP_APY * deltaTime),  
            account.multiplier);
        account.multiplier += increasedMultiplier;
        multiplierSupply += increasedMultiplier;
    }

    function mintIntialMultiplier(Account storage account, uint256 lockTime, uint256 amount, uint256 initMint) private {
        //if balance still locked, multipliers must be minted from difference of time.
        uint256 dT = account.lockUntil > block.timestamp ? block.timestamp + lockTime - account.lockUntil : lockTime; 
        account.lockUntil =  block.timestamp + lockTime;
        uint256 increasedMultiplier = amount * ((dT/YEAR)+initMint); 
        account.lastMint = block.timestamp;
        account.multiplier += increasedMultiplier;
        multiplierSupply += increasedMultiplier;
    }

    function totalSupply() public view returns (uint256) {
        return multiplierSupply + stakeSupply;
    }

    function epochReward() public view returns (uint256) {
        return stakedToken.balanceOf(address(this)) - pendingReward;
    }

    function epochEnd() public view returns (uint256) {
        return epochs[currentEpoch].startTime + EPOCH_SIZE;
    }

}