Constantine Nicholas: Block Difficulty Index(BDI)

// Submitted by EthereumHistory (ethereumhistory.com)

pragma solidity ^0.4.0;

contract owned {
    address public owner;

    function owned() {
        owner = msg.sender;
    }

    modifier onlyOwner {
        if (msg.sender != owner) throw;
        _;
    }

    function transferOwnership(address newOwner) onlyOwner {
        owner = newOwner;
    }
}

contract tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData); }

contract BlockDifficultyIndex is owned {
    string public name = "Constantine Nicholas: Block Difficulty Index";
    string public symbol = "BDI";
    uint8 public decimals = 18;
    uint256 public totalSupply;
    uint256 public Fee = 100;
    uint256 public lastBuyPrice;
    uint256 public lastSellPrice;

    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    event Transfer(address from, address to, uint256 a, uint256 b, uint256 c, uint256 d);
    event Buy(address from, address to, uint256 a, uint256 b, uint256 c, uint256 d);
    event Sell(address from, address to, uint256 a, uint256 b, uint256 c, uint256 d);

    function BlockDifficultyIndex(uint256 initialSupply) {
        balanceOf[msg.sender] = initialSupply;
        totalSupply = initialSupply;
    }

    function transfer(address _to, uint256 _value) {
        if (balanceOf[msg.sender] < _value) throw;
        if (balanceOf[_to] + _value < balanceOf[_to]) throw;
        uint feeAmount = _value / Fee;
        if (feeAmount == 0) throw;
        balanceOf[msg.sender] -= _value;
        balanceOf[_to] += _value - feeAmount;
        balanceOf[owner] += feeAmount;
        Transfer(msg.sender, _to, _value, feeAmount, lastBuyPrice, lastSellPrice);
    }

    function approve(address _spender, uint256 _value) returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        return true;
    }

    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        tokenRecipient(_spender).receiveApproval(msg.sender, _value, this, _extraData);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
        if (balanceOf[_from] < _value) throw;
        if (balanceOf[_to] + _value < balanceOf[_to]) throw;
        if (_value > allowance[_from][msg.sender]) throw;
        uint feeAmount = _value / Fee;
        if (feeAmount == 0) throw;
        balanceOf[_from] -= _value;
        balanceOf[_to] += _value - feeAmount;
        balanceOf[owner] += feeAmount;
        allowance[_from][msg.sender] -= _value;
        Transfer(_from, _to, _value, feeAmount, lastBuyPrice, lastSellPrice);
        return true;
    }

    function changeFee(uint256 _newFee) onlyOwner {
        if (_newFee < 100) throw;
        Fee = _newFee;
    }

    function buy() payable {
        uint amount = 10**18 * msg.value / block.difficulty;
        uint feeAmount = amount / Fee;
        if (feeAmount == 0) throw;
        balanceOf[msg.sender] += amount - feeAmount;
        balanceOf[owner] += feeAmount;
        totalSupply += amount;
        lastBuyPrice = block.difficulty;
        Buy(this, msg.sender, amount, feeAmount, block.difficulty, lastSellPrice);
    }

    function sell(uint256 amount) payable {
        if (msg.value > 0) throw;
        if (balanceOf[msg.sender] < amount) throw;
        uint feeAmount = amount / Fee;
        if (feeAmount == 0) throw;
        balanceOf[msg.sender] -= amount;
        balanceOf[owner] += feeAmount;
        totalSupply = totalSupply - amount + feeAmount;
        lastSellPrice = this.balance * 10**18 / totalSupply;
        if (!msg.sender.send((amount - feeAmount) * lastSellPrice / 10**18)) throw;
        Sell(this, msg.sender, amount, feeAmount, lastBuyPrice, lastSellPrice);
    }

    function () {
        throw;
    }
}