pragma solidity ^0.4.16;

contract owned {
    address public owner;

    function owned() public {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address newOwner) onlyOwner public {
        owner = newOwner;
    }
}


contract ERC20Basic {
    function totalSupply() public constant returns (uint supply);
    function balanceOf( address who ) public constant returns (uint value);
    function allowance( address owner, address spender ) public constant returns (uint _allowance);

    function transfer( address to, uint value) public returns (bool ok);
    function transferFrom( address from, address to, uint value) public returns (bool ok);
    function approve( address spender, uint value ) public returns (bool ok);

    // This generates a public event on the blockchain that will notify clients
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval( address indexed owner, address indexed spender, uint value);
    // This notifies clients about the amount burnt
    event Burn(address indexed from, uint256 value);
}

contract TokenERC20  is ERC20Basic{
    // Public variables of the token
    string public name;
    string public symbol;
    uint8 public decimals = 4;
    uint256 _supply;
    mapping (address => uint256)   _balances;
    mapping (address => mapping (address => uint256)) _allowance;

    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    function TokenERC20(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol,
        uint8 decimal
    ) public {
        _supply = initialSupply * 10 ** uint256(decimal);  // Update total supply with the decimal amount
        _balances[msg.sender] = _supply;                // Give the creator all initial tokens
        name = tokenName;                                   // Set the name for display purposes
        symbol = tokenSymbol;                               // Set the symbol for display purposes
        decimals = decimal;
    }
    function totalSupply() public constant returns (uint256) {
        return _supply;
    }
    function balanceOf(address src) public constant returns (uint256) {
        return _balances[src];
    }
    function allowance(address src, address guy) public constant returns (uint256) {
        return _allowance[src][guy];
    }
    /**
     * Internal transfer, only can be called by this contract
     */
    function _transfer(address _from, address _to, uint _value) internal {
        // Prevent transfer to 0x0 address. Use burn() instead
        require(_to != 0x0);
        // Check if the sender has enough
        require(_balances[_from] >= _value);
        // Check for overflows
        require(_balances[_to] + _value > _balances[_to]);
        // Save this for an assertion in the future
        uint previousBalances = _balances[_from] + _balances[_to];
        // Subtract from the sender
        _balances[_from] -= _value;
        // Add the same to the recipient
        _balances[_to] += _value;
        Transfer(_from, _to, _value);
        // Asserts are used to use static analysis to find bugs in your code. They should never fail
        assert(_balances[_from] + _balances[_to] == previousBalances);
    }

    /**
     * Transfer tokens
     *
     * Send `_value` tokens to `_to` from your account
     *
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transfer(address _to, uint256 _value) public returns (bool){
        _transfer(msg.sender, _to, _value);
        return true;
    }

    /**
     * Transfer tokens from other address
     *
     * Send `_value` tokens to `_to` in behalf of `_from`
     *
     * @param _from The address of the sender
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= _allowance[_from][msg.sender]);     // Check allowance
        _allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);
        return true;
    }

    /**
     * Set allowance for other address
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf
     *
     * @param _spender The address authorized to spend
     * @param _value the max amount they can spend
     */
    function approve(address _spender, uint256 _value) public returns (bool success) {
        _allowance[msg.sender][_spender] = _value;
        return true;
    }

    /**
     * Set allowance for other address and notify
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf, and then ping the contract about it
     *
     * @param _spender The address authorized to spend
     * @param _value the max amount they can spend
     */
    function approveAndCall(address _spender, uint256 _value)
        public returns (bool success) {
        if (approve(_spender, _value)) {
            Approval(msg.sender, _spender, _value);
            return true;
        }
    }

    /**
     * Destroy tokens
     *
     * Remove `_value` tokens from the system irreversibly
     *
     * @param _value the amount of money to burn
     */
    function burn(uint256 _value) public returns (bool success) {
        require(_balances[msg.sender] >= _value);   // Check if the sender has enough
        _balances[msg.sender] -= _value;            // Subtract from the sender
        _supply -= _value;                      // Updates totalSupply
        Burn(msg.sender, _value);
        return true;
    }

    /**
     * Destroy tokens from other account
     *
     * Remove `_value` tokens from the system irreversibly on behalf of `_from`.
     *
     * @param _from the address of the sender
     * @param _value the amount of money to burn
     */
    function burnFrom(address _from, uint256 _value) public returns (bool success) {
        require(_balances[_from] >= _value);                // Check if the targeted balance is enough
        require(_value <= _allowance[_from][msg.sender]);    // Check allowance
        _balances[_from] -= _value;                         // Subtract from the targeted balance
        _allowance[_from][msg.sender] -= _value;             // Subtract from the sender's allowance
        _supply -= _value;                              // Update totalSupply
        Burn(_from, _value);
        return true;
    }
}

/******************************************/
/*       ADVANCED TOKEN STARTS HERE       */
/******************************************/

contract DYITToken is owned, TokenERC20 {

    uint256 public sellPrice = 0.00000001 ether ; //设置代币的卖的价格等于一个以太币
    uint256 public buyPrice = 0.00000001 ether ;//设置代币的买的价格等于一个以太币
    
    mapping (address => bool) public _frozenAccount;

    /* This generates a public event on the blockchain that will notify clients */
    event FrozenFunds(address target, bool frozen);

    /* Initializes contract with initial supply tokens to the creator of the contract */
   function DYITToken(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol,
        uint8 decimal
    ) TokenERC20(initialSupply, tokenName, tokenSymbol,decimal) public {
        _balances[msg.sender] = _supply;  
    }
    
    /* Internal transfer, only can be called by this contract */
    function _transfer(address _from, address _to, uint _value) internal {
        require (_to != 0x0);                               // Prevent transfer to 0x0 address. Use burn() instead
        require (_balances[_from] >= _value);               // Check if the sender has enough
        require (_balances[_to] + _value > _balances[_to]); // Check for overflows
        require(!_frozenAccount[_from]);                     // Check if sender is frozen
        require(!_frozenAccount[_to]);                       // Check if recipient is frozen
        _balances[_from] -= _value;                         // Subtract from the sender
        _balances[_to] += _value;                           // Add the same to the recipient
        Transfer(_from, _to, _value);
    }

    /// @notice Create `mintedAmount` tokens and send it to `target`
    /// @param target Address to receive the tokens
    /// @param mintedAmount the amount of tokens it will receive
    function mintToken(address target, uint256 mintedAmount) onlyOwner public {
        _balances[target] += mintedAmount;
        _supply += mintedAmount;
        Transfer(0, owner, mintedAmount);
        Transfer(owner, target, mintedAmount);
    }

    /// @notice `freeze? Prevent | Allow` `target` from sending & receiving tokens
    /// @param target Address to be frozen
    /// @param freeze either to freeze it or not
    function freezeAccount(address target, bool freeze) onlyOwner public {
        _frozenAccount[target] = freeze;
        FrozenFunds(target, freeze);
    }
    /**
     * 实现账户间，代币的转移
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transfer(address _to, uint256 _value) public returns (bool){
        _transfer(msg.sender, _to, _value);
        return true;
    }
    
    /// @notice Allow users to buy tokens for `newBuyPrice` eth and sell tokens for `newSellPrice` eth
    /// @param newSellPrice Price the users can sell to the contract
    /// @param newBuyPrice Price users can buy from the contract
    function setPrices(uint256 newSellPrice, uint256 newBuyPrice) onlyOwner public {
        sellPrice = newSellPrice;
        buyPrice = newBuyPrice;
    }

    /// @notice Buy tokens from contract by sending ether
    function buy() payable public {
        uint amount = msg.value / buyPrice;               // calculates the amount
        _transfer(owner, msg.sender, amount);              // makes the transfers
    }

    /// @notice Sell `amount` tokens to contract
    /// @param amount amount of tokens to be sold
    function sell(uint256 amount) public {
        require(owner.balance >= amount * sellPrice);      // checks if the contract has enough ether to buy
        _transfer(msg.sender, owner, amount);              // makes the transfers
        msg.sender.transfer(amount * sellPrice);          // sends ether to the seller. It's important to do this last to avoid recursion attacks
    }
}