contract FNSPStake is Owned {
    using SafeMath for uint256;
    
    // Contract address for FNSP mainnet token
    address public FNSP = 0x3B78dc5736a49BD297Dd2E4d62daA83D35A22749;
    
    uint256 public totalStakes = 0;
    uint256 stakingFee = 10; // 1%
    uint256 unstakingFee = 30; // 3% 
    uint256 public totalDividends = 0;
    uint256 private scaledRemainder = 0;
    uint256 private scaling = uint256(10) ** 12;
    uint public round = 1;
    
    struct USER{
        uint256 stakedTokens;
        uint256 lastDividends;
        uint256 fromTotalDividend;
        uint round;
        uint256 remainder;
    }
    
    mapping(address => USER) stakers;
    mapping (uint => uint256) public payouts; // keeps record of each payout
    
    event STAKED(address staker, uint256 tokens, uint256 stakingFee);
    event UNSTAKED(address staker, uint256 tokens, uint256 unstakingFee);
    event PAYOUT(uint256 round, uint256 tokens, address sender);
    event CLAIMEDREWARD(address staker, uint256 reward);
    
    /**
    * Token holders can stake their tokens using this function
    * @param tokens number of tokens to stake
    */
    function STAKE(uint256 tokens) external {
        require(IERC20(FNSP).transferFrom(msg.sender, address(this), tokens), "Tokens cannot be transferred from user account");
        
        uint256 _stakingFee = 0;
        if(totalStakes > 0)
            _stakingFee= (onePercent(tokens).mul(stakingFee)).div(10); 
        
        if(totalStakes > 0)
            // distribute the staking fee accumulated before updating the user's stake
            _addPayout(_stakingFee);
            
        // add pending rewards to remainder to be claimed by user later, if there is any existing stake
        uint256 owing = pendingReward(msg.sender);
        stakers[msg.sender].remainder += owing;
        
        stakers[msg.sender].stakedTokens = (tokens.sub(_stakingFee)).add(stakers[msg.sender].stakedTokens);
        stakers[msg.sender].lastDividends = owing;
        stakers[msg.sender].fromTotalDividend= totalDividends;
        stakers[msg.sender].round =  round;
        
        totalStakes = totalStakes.add(tokens.sub(_stakingFee));
        
        emit STAKED(msg.sender, tokens.sub(_stakingFee), _stakingFee);
    }
    
    /**
    * Owners can send the funds to be distributed to stakers using this function
    * @param tokens number of tokens to distribute
    */
    function ADDFUNDS(uint256 tokens) external {
        require(IERC20(FNSP).transferFrom(msg.sender, address(this), tokens), "Tokens cannot be transferred from funder account");
        _addPayout(tokens);
    }
    
    
    /**
    * Private function to register payouts
    */
    function _addPayout(uint256 tokens) private{
        // divide the funds among the currently staked tokens
        // scale the deposit and add the previous remainder
        uint256 available = (tokens.mul(scaling)).add(scaledRemainder); 
        uint256 dividendPerToken = available.div(totalStakes);
        scaledRemainder = available.mod(totalStakes);
        
        totalDividends = totalDividends.add(dividendPerToken);
        payouts[round] = payouts[round-1].add(dividendPerToken);
        
        emit PAYOUT(round, tokens, msg.sender);
        round++;
    }
    
    /**
    * Stakers can claim their pending rewards using this function
    */
    function CLAIMREWARD() public {
        if(totalDividends > stakers[msg.sender].fromTotalDividend){
            uint256 owing = pendingReward(msg.sender);
        
            owing = owing.add(stakers[msg.sender].remainder);
            stakers[msg.sender].remainder = 0;
        
            require(IERC20(FNSP).transfer(msg.sender,owing), "ERROR: error in sending reward from contract");
        
            emit CLAIMEDREWARD(msg.sender, owing);
        
            stakers[msg.sender].lastDividends = owing; // unscaled
            stakers[msg.sender].round = round; // update the round
            stakers[msg.sender].fromTotalDividend = totalDividends; // scaled
        }
    }
    

    /**
    * Get the pending rewards of the staker
    * @param staker the address of the staker
    */ 
    function pendingReward(address staker) private returns (uint256) {
        uint256 amount =  ((totalDividends.sub(payouts[stakers[staker].round - 1])).mul(stakers[staker].stakedTokens)).div(scaling);
        stakers[staker].remainder += ((totalDividends.sub(payouts[stakers[staker].round - 1])).mul(stakers[staker].stakedTokens)) % scaling ;
        return amount;
    }
    
    function getPendingReward(address staker) public view returns(uint256 _pendingReward) {
        uint256 amount =  ((totalDividends.sub(payouts[stakers[staker].round - 1])).mul(stakers[staker].stakedTokens)).div(scaling);
        amount += ((totalDividends.sub(payouts[stakers[staker].round - 1])).mul(stakers[staker].stakedTokens)) % scaling ;
        return (amount + stakers[staker].remainder);
    }
    

    /**
    * Stakers can un stake the staked tokens using this function
    *  @param tokens the number of tokens to withdraw
    */ 
    function WITHDRAW(uint256 tokens) external {
        
        require(stakers[msg.sender].stakedTokens >= tokens && tokens > 0, "Invalid token amount to withdraw");
        
        uint256 _unstakingFee = (onePercent(tokens).mul(unstakingFee)).div(10);
        
        // add pending rewards to remainder to be claimed by user later, if there is any existing stake
        uint256 owing = pendingReward(msg.sender);
        stakers[msg.sender].remainder += owing;
                
        require(IERC20(FNSP).transfer(msg.sender, tokens.sub(_unstakingFee)), "Error in un-staking tokens");
        
        stakers[msg.sender].stakedTokens = stakers[msg.sender].stakedTokens.sub(tokens);
        stakers[msg.sender].lastDividends = owing;
        stakers[msg.sender].fromTotalDividend= totalDividends;
        stakers[msg.sender].round =  round;
        
        totalStakes = totalStakes.sub(tokens);
        
        if(totalStakes > 0)
            // distribute the un staking fee accumulated after updating the user's stake
            _addPayout(_unstakingFee);
        
        emit UNSTAKED(msg.sender, tokens.sub(_unstakingFee), _unstakingFee);
    }
    

    /**
    * Private function to calculate 1% percent
    *  @param _tokens the number of tokens to withdraw
    */ 
    function onePercent(uint256 _tokens) private pure returns (uint256){
        uint256 roundValue = _tokens.ceil(100);
        uint onePercentofTokens = roundValue.mul(100).div(100 * 10**uint(2));
        return onePercentofTokens;
    }
    
    /**
    * Get the number of tokens staked by a staker
    *  @param staker the address of the staker
    */ 
    function yourStakedFNSP(address staker) external view returns(uint256 stakedFNSP){
        return stakers[staker].stakedTokens;
    }
    
    /**
    * Get the FNSP balance of the token holder
    *  @param user the address of the token holder
    */ 
    function yourFNSPBalance(address user) external view returns(uint256 FNSPBalance){
        return IERC20(FNSP).balanceOf(user);
    }
}
/**
 * ERC20 Token, with the addition of symbol, name and decimals and assisted
 * token transfers
 */
function ADDFUNDS(uint256 tokens) external {
        require(IERC20(FNSP).transferFrom(msg.sender, address(this), tokens), "Tokens cannot be transferred from funder account");
        _addPayout(tokens);
    }
/**
 * Owners can send the funds to be distributed to stakers using this function
 * @param tokens number of tokens to distribute
 */