pragma solidity ^0.4.11;

contract owned { address public owner;

  function owned() {
      owner = msg.sender;
  }

  modifier onlyOwner {
      require(msg.sender == owner);
      _;
  }

  function transferOwnership(address newOwner) onlyOwner {
      owner = newOwner;
  }
}

contract tokenRecipient { function receiveApproval(address from, uint256 value, address token, bytes extraData); }

contract token { 
    string public name; string public symbol; uint8 public decimals; uint256 public totalSupply;

  /* This creates an array with all balances */
  mapping (address => uint256) public balanceOf;
  mapping (address => mapping (address => uint256)) public allowance;

  /* This generates a public event on the blockchain that will notify clients */
  event Transfer(address indexed from, address indexed to, uint256 value);

  /* This notifies clients about the amount burnt */
  event Burn(address indexed from, uint256 value);

  /* Initializes contract with initial supply tokens to the creator of the contract */
  function token(
      uint256 initialSupply,
      string tokenName,
      uint8 decimalUnits,
      string tokenSymbol
      ) {
      balanceOf[msg.sender] = initialSupply;              // Give the creator all initial tokens
      totalSupply = initialSupply;                        // Update total supply
      name = tokenName;                                   // Set the name for display purposes
      symbol = tokenSymbol;                               // Set the symbol for display purposes
      decimals = decimalUnits;                            // Amount of decimals for display purposes
  }

  /* 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 (balanceOf[_from] > _value);                // Check if the sender has enough
      require (balanceOf[_to] + _value > balanceOf[_to]); // Check for overflows
      balanceOf[_from] -= _value;                         // Subtract from the sender
      balanceOf[_to] += _value;                            // Add the same to the recipient
      Transfer(_from, _to, _value);
  }

  /// @notice 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) {
      _transfer(msg.sender, _to, _value);
  }

  /// @notice 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) returns (bool success) {
      require (_value < allowance[_from][msg.sender]);     // Check allowance
      allowance[_from][msg.sender] -= _value;
      _transfer(_from, _to, _value);
      return true;
  }

  /// @notice 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)
      returns (bool success) {
      allowance[msg.sender][_spender] = _value;
      return true;
  }

  /// @notice 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
  /// @param _extraData some extra information to send to the approved contract
  function approveAndCall(address _spender, uint256 _value, bytes _extraData)
      returns (bool success) {
      tokenRecipient spender = tokenRecipient(_spender);
      if (approve(_spender, _value)) {
          spender.receiveApproval(msg.sender, _value, this, _extraData);
          return true;
      }
  }        

  /// @notice Remove `_value` tokens from the system irreversibly
  /// @param _value the amount of money to burn
  function burn(uint256 _value) returns (bool success) {
      require (balanceOf[msg.sender] > _value);            // Check if the sender has enough
      balanceOf[msg.sender] -= _value;                      // Subtract from the sender
      totalSupply -= _value;                                // Updates totalSupply
      Burn(msg.sender, _value);
      return true;
  }

  function burnFrom(address _from, uint256 _value) returns (bool success) {
      require(balanceOf[_from] >= _value);                // Check if the targeted balance is enough
      require(_value <= allowance[_from][msg.sender]);    // Check allowance
      balanceOf[_from] -= _value;                         // Subtract from the targeted balance
      allowance[_from][msg.sender] -= _value;             // Subtract from the sender's allowance
      totalSupply -= _value;                              // Update totalSupply
      Burn(_from, _value);
      return true;
  }
}

contract NetkingToken is owned, token {

  uint256 public sellPrice;
  uint256 public buyPrice;

  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 NetkingToken(
      uint256 initialSupply,
      string tokenName,
      uint8 decimalUnits,
      string tokenSymbol
  ) token (initialSupply, tokenName, decimalUnits, tokenSymbol) {}

  /* 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 (balanceOf[_from] > _value);                // Check if the sender has enough
      require (balanceOf[_to] + _value > balanceOf[_to]); // Check for overflows
      require(!frozenAccount[_from]);                     // Check if sender is frozen
      require(!frozenAccount[_to]);                       // Check if recipient is frozen
      balanceOf[_from] -= _value;                         // Subtract from the sender
      balanceOf[_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 {
      balanceOf[target] += mintedAmount;
      totalSupply += mintedAmount;
      Transfer(0, this, mintedAmount);
      Transfer(this, 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 {
      frozenAccount[target] = freeze;
      FrozenFunds(target, freeze);
  }

  /// @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 {
      sellPrice = newSellPrice;
      buyPrice = newBuyPrice;
  }

  /// @notice Buy tokens from contract by sending ether
  function buy() payable {
      uint amount = msg.value / buyPrice;               // calculates the amount
      _transfer(this, msg.sender, amount);              // makes the transfers
  }

  /// @notice Sell `amount` tokens to contract
  /// @param amount amount of tokens to be sold
  function sell(uint256 amount) {
      require(this.balance >= amount * sellPrice);      // checks if the contract has enough ether to buy
      _transfer(msg.sender, this, 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
  }
}