// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

/**
 * @title PoWHD Style Pyramid Contract
 * @dev Educational example showing how pyramid schemes work on Ethereum
 * WARNING: This is for educational purposes only. Pyramid schemes are illegal in many jurisdictions.
 */
contract PoWHDExample {
    
    /*=================================
    =            MODIFIERS            =
    =================================*/
    
    // Only people with tokens
    modifier onlyBagholders() {
        require(myTokens() > 0);
        _;
    }
    
    // Only people with profits
    modifier onlyStronghands() {
        require(myDividends(true) > 0);
        _;
    }
    
    /*==============================
    =            EVENTS            =
    ==============================*/
    
    event onTokenPurchase(
        address indexed customerAddress,
        uint256 incomingEthereum,
        uint256 tokensMinted,
        address indexed referredBy
    );
    
    event onTokenSell(
        address indexed customerAddress,
        uint256 tokensBurned,
        uint256 ethereumEarned
    );
    
    event onReinvestment(
        address indexed customerAddress,
        uint256 ethereumReinvested,
        uint256 tokensMinted
    );
    
    event onWithdraw(
        address indexed customerAddress,
        uint256 ethereumWithdrawn
    );
    
    /*=====================================
    =            CONFIGURABLES            =
    =====================================*/
    
    string public name = "PoWHD";
    string public symbol = "P3D";
    uint8 constant public decimals = 18;
    uint8 constant internal dividendFee_ = 10; // 10% dividend fee
    uint8 constant internal referralFee_ = 3;  // 3% referral fee
    uint256 constant internal tokenPriceInitial_ = 0.0000001 ether;
    uint256 constant internal tokenPriceIncremental_ = 0.00000001 ether;
    uint256 constant internal magnitude = 2**64;
    
    /*================================
    =            DATASETS            =
    ================================*/
    
    // Amount of tokens for each address (scaled number)
    mapping(address => uint256) internal tokenBalanceLedger_;
    mapping(address => uint256) internal referralBalance_;
    mapping(address => int256) internal payoutsTo_;
    uint256 internal tokenSupply_ = 0;
    uint256 internal profitPerShare_;
    
    /*=======================================
    =            PUBLIC FUNCTIONS           =
    =======================================*/
    
    /**
     * Converts all incoming ethereum to tokens for the caller, and passes down the referral address (if any)
     */
    function buy(address _referredBy) public payable returns(uint256) {
        purchaseTokens(msg.value, _referredBy);
    }
    
    /**
     * Fallback function to handle ethereum that was sent straight to the contract
     * Unfortunately we cannot use a referral address this way.
     */
    receive() external payable {
        purchaseTokens(msg.value, address(0));
    }
    
    /**
     * Converts all of caller's dividends to tokens.
     */
    function reinvest() onlyStronghands() public {
        // Fetch dividends
        uint256 _dividends = myDividends(false); // retrieve ref. bonus later in the code
        
        // Pay out the dividends virtually
        address _customerAddress = msg.sender;
        payoutsTo_[_customerAddress] +=  (int256) (_dividends * magnitude);
        
        // Retrieve ref. bonus
        _dividends += referralBalance_[_customerAddress];
        referralBalance_[_customerAddress] = 0;
        
        // Dispatch a buy order with the virtualized "withdrawn" dividends
        uint256 _tokens = purchaseTokens(_dividends, address(0));
        
        // Fire event
        emit onReinvestment(_customerAddress, _dividends, _tokens);
    }
    
    /**
     * Alias of sell() and withdraw().
     */
    function exit() public {
        // Get token count for caller & sell them all
        address _customerAddress = msg.sender;
        uint256 _tokens = tokenBalanceLedger_[_customerAddress];
        if(_tokens > 0) sell(_tokens);
        
        // Withdraw dividends
        withdraw();
    }
    
    /**
     * Withdraws all of the callers earnings.
     */
    function withdraw() onlyStronghands() public {
        // Setup data
        address _customerAddress = msg.sender;
        uint256 _dividends = myDividends(false); // get ref. bonus later in the code
        
        // Update dividend tracker
        payoutsTo_[_customerAddress] +=  (int256) (_dividends * magnitude);
        
        // Add ref. bonus
        _dividends += referralBalance_[_customerAddress];
        referralBalance_[_customerAddress] = 0;
        
        // Delivery service
        payable(_customerAddress).transfer(_dividends);
        
        // Fire event
        emit onWithdraw(_customerAddress, _dividends);
    }
    
    /**
     * Liquifies tokens to ethereum.
     */
    function sell(uint256 _amountOfTokens) onlyBagholders() public {
        // Setup data
        address _customerAddress = msg.sender;
        // Russian hackers BTFO
        require(_amountOfTokens <= tokenBalanceLedger_[_customerAddress]);
        uint256 _tokens = _amountOfTokens;
        uint256 _ethereum = tokensToEthereum_(_tokens);
        uint256 _dividends = SafeMath.div(_ethereum, dividendFee_);
        uint256 _taxedEthereum = SafeMath.sub(_ethereum, _dividends);
        
        // Burn the sold tokens
        tokenSupply_ = SafeMath.sub(tokenSupply_, _tokens);
        tokenBalanceLedger_[_customerAddress] = SafeMath.sub(tokenBalanceLedger_[_customerAddress], _tokens);
        
        // Update dividends tracker
        int256 _updatedPayouts = (int256) (profitPerShare_ * _tokens + (_taxedEthereum * magnitude));
        payoutsTo_[_customerAddress] -= _updatedPayouts;       
        
        // Dividing by zero is a bad idea
        if (tokenSupply_ > 0) {
            // Update the amount of dividends per token
            profitPerShare_ = SafeMath.add(profitPerShare_, (_dividends * magnitude) / tokenSupply_);
        }
        
        // Fire event
        emit onTokenSell(_customerAddress, _tokens, _taxedEthereum);
    }
    
    /*==========================================
    =            INTERNAL FUNCTIONS            =
    ==========================================*/
    
    function purchaseTokens(uint256 _incomingEthereum, address _referredBy) internal returns(uint256) {
        // Data setup
        address _customerAddress = msg.sender;
        uint256 _undividedDividends = SafeMath.div(_incomingEthereum, dividendFee_);
        uint256 _referralBonus = SafeMath.div(_undividedDividends, referralFee_);
        uint256 _dividends = SafeMath.sub(_undividedDividends, _referralBonus);
        uint256 _taxedEthereum = SafeMath.sub(_incomingEthereum, _undividedDividends);
        uint256 _amountOfTokens = ethereumToTokens_(_taxedEthereum);
        uint256 _fee = _dividends * magnitude;
        
        // No point in continuing execution if OP is a poor russian hacker
        // Prevents overflow in the case that the pyramid somehow magically starts being used by everyone in the world
        require(_amountOfTokens > 0 && (SafeMath.add(_amountOfTokens,tokenSupply_) > tokenSupply_));
        
        // Is the user referred by a masternode?
        if(_referredBy != address(0) && _referredBy != _customerAddress && tokenBalanceLedger_[_referredBy] >= 100e18) {
            // Wealth redistribution
            referralBalance_[_referredBy] = SafeMath.add(referralBalance_[_referredBy], _referralBonus);
        } else {
            // No ref purchase
            // Add the referral bonus back to the global dividends cake
            _dividends = SafeMath.add(_dividends, _referralBonus);
            _fee = _dividends * magnitude;
        }
        
        // We can't give people infinite ethereum
        if(tokenSupply_ > 0){
            
            // Add tokens to the pool
            tokenSupply_ = SafeMath.add(tokenSupply_, _amountOfTokens);
         
            // Take the amount of dividends gained through this transaction, and allocates them evenly to each shareholder
            profitPerShare_ += (_dividends * magnitude / (tokenSupply_));
            
            // Calculate the amount of tokens the customer receives over his purchase 
            _fee = _fee - (_fee-(_amountOfTokens * (_dividends * magnitude / (tokenSupply_))));
        
        } else {
            // Add tokens to the pool
            tokenSupply_ = _amountOfTokens;
        }
        
        // Update circulating supply & the ledger address for the customer
        tokenBalanceLedger_[_customerAddress] = SafeMath.add(tokenBalanceLedger_[_customerAddress], _amountOfTokens);
        
        // Tells the contract that the buyer doesn't deserve dividends for the tokens before they owned them;
        //really i know you think you do but you don't
        int256 _updatedPayouts = (int256) ((profitPerShare_ * _amountOfTokens) - _fee);
        payoutsTo_[_customerAddress] += _updatedPayouts;
        
        // Fire event
        emit onTokenPurchase(_customerAddress, _incomingEthereum, _amountOfTokens, _referredBy);
        
        return _amountOfTokens;
    }

    /**
     * Calculate Token price based on an amount of incoming ethereum
     * It's an algorithm, hopefully we gave you the whitepaper with it in scientific notation;
     * Some conversions occurred to prevent decimal errors or underflows / overflows in solidity code.
     */
    function ethereumToTokens_(uint256 _ethereum) internal view returns(uint256) {
        uint256 _tokenPriceInitial = tokenPriceInitial_ * 1e18;
        uint256 _tokensReceived = 
         (
            (
                // Underflow attempts BTFO
                SafeMath.sub(
                    (sqrt
                        (
                            (_tokenPriceInitial**2)
                            +
                            (2*(tokenPriceIncremental_ * 1e18)*(_ethereum * 1e18))
                            +
                            (((tokenPriceIncremental_)**2)*(tokenSupply_**2))
                            +
                            (2*(tokenPriceIncremental_)*_tokenPriceInitial*tokenSupply_)
                        )
                    ), _tokenPriceInitial
                )
            )/(tokenPriceIncremental_)
        )-(tokenSupply_)
        ;
  
        return _tokensReceived;
    }
    
    /**
     * Calculate token sell value.
     * It's an algorithm, hopefully we gave you the whitepaper with it in scientific notation;
     * Some conversions occurred to prevent decimal errors or underflows / overflows in solidity code.
     */
     function tokensToEthereum_(uint256 _tokens) internal view returns(uint256) {
        uint256 tokens_ = (_tokens + 1e18);
        uint256 _tokenSupply = (tokenSupply_ + 1e18);
        uint256 _etherReceived =
        (
            // Underflow attempts BTFO
            SafeMath.sub(
                (
                    (
                        (
                            tokenPriceInitial_ +(tokenPriceIncremental_ * (_tokenSupply/1e18))
                        )-tokenPriceIncremental_
                    )*(tokens_ - 1e18)
                ),(tokenPriceIncremental_*((tokens_**2-tokens_)/1e18))/2
            )
        /1e18);
        return _etherReceived;
    }
    
    /*===========================================
    =            HELPERS AND CALCULATORS        =
    ===========================================*/
    
    /**
     * Method to view the current Ethereum stored in the contract
     * Example: totalEthereumBalance()
     */
    function totalEthereumBalance() public view returns(uint256) {
        return address(this).balance;
    }
    
    /**
     * Retrieve the total token supply.
     */
    function totalSupply() public view returns(uint256) {
        return tokenSupply_;
    }
    
    /**
     * Retrieve the tokens owned by the caller.
     */
    function myTokens() public view returns(uint256) {
        address _customerAddress = msg.sender;
        return balanceOf(_customerAddress);
    }
    
    /**
     * Retrieve the dividends owned by the caller.
     * If `_includeReferralBonus` is set to 1/true, the referral bonus will be included in the calculations.
     * The reason for this, is that in the frontend, we will want to get the total divs (global + ref)
     * But in the internal calculations, we want them separate. 
     */ 
    function myDividends(bool _includeReferralBonus) public view returns(uint256) {
        address _customerAddress = msg.sender;
        return _includeReferralBonus ? dividendsOf(_customerAddress) + referralBalance_[_customerAddress] : dividendsOf(_customerAddress);
    }
    
    /**
     * Retrieve the token balance of any single address.
     */
    function balanceOf(address _customerAddress) public view returns(uint256) {
        return tokenBalanceLedger_[_customerAddress];
    }
    
    /**
     * Retrieve the dividend balance of any single address.
     */
    function dividendsOf(address _customerAddress) public view returns(uint256) {
        return (uint256) ((int256)(profitPerShare_ * tokenBalanceLedger_[_customerAddress]) - payoutsTo_[_customerAddress]) / magnitude;
    }
    
    /**
     * Return the buy price of 1 individual token.
     */
    function sellPrice() public view returns(uint256) {
        // Our calculation relies on the token supply, so we need supply. Doh.
        if(tokenSupply_ == 0){
            return tokenPriceInitial_ - tokenPriceIncremental_;
        } else {
            uint256 _ethereum = tokensToEthereum_(1e18);
            uint256 _dividends = SafeMath.div(_ethereum, dividendFee_  );
            uint256 _taxedEthereum = SafeMath.sub(_ethereum, _dividends);
            return _taxedEthereum;
        }
    }
    
    /**
     * Return the sell price of 1 individual token.
     */
    function buyPrice() public view returns(uint256) {
        // Our calculation relies on the token supply, so we need supply. Doh.
        if(tokenSupply_ == 0){
            return tokenPriceInitial_ + tokenPriceIncremental_;
        } else {
            uint256 _ethereum = tokensToEthereum_(1e18);
            uint256 _dividends = SafeMath.div(_ethereum, dividendFee_  );
            uint256 _taxedEthereum = SafeMath.add(_ethereum, _dividends);
            return _taxedEthereum;
        }
    }
    
    /**
     * Function for the frontend to dynamically retrieve the price scaling of buy orders.
     */
    function calculateTokensReceived(uint256 _ethereumToSpend) public view returns(uint256) {
        uint256 _dividends = SafeMath.div(_ethereumToSpend, dividendFee_);
        uint256 _taxedEthereum = SafeMath.sub(_ethereumToSpend, _dividends);
        uint256 _amountOfTokens = ethereumToTokens_(_taxedEthereum);
        
        return _amountOfTokens;
    }
    
    /**
     * Function for the frontend to dynamically retrieve the price scaling of sell orders.
     */
    function calculateEthereumReceived(uint256 _tokensToSell) public view returns(uint256) {
        require(_tokensToSell <= tokenSupply_);
        uint256 _ethereum = tokensToEthereum_(_tokensToSell);
        uint256 _dividends = SafeMath.div(_ethereum, dividendFee_);
        uint256 _taxedEthereum = SafeMath.sub(_ethereum, _dividends);
        return _taxedEthereum;
    }
    
    /*==========================================
    =            INTERNAL FUNCTIONS            =
    ==========================================*/
    
    function sqrt(uint x) internal pure returns (uint y) {
        uint z = (x + 1) / 2;
        y = x;
        while (z < y) {
            y = z;
            z = (x / z + z) / 2;
        }
    }
}

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

    /**
    * @dev Multiplies two numbers, throws on overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }
        uint256 c = a * b;
        assert(c / a == b);
        return c;
    }

    /**
    * @dev Integer division of two numbers, truncating the quotient.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // assert(b > 0); // Solidity automatically throws when dividing by 0
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
        return c;
    }

    /**
    * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }

    /**
    * @dev Adds two numbers, throws on overflow.
    */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        assert(c >= a);
        return c;
    }
}