/**
 * @title METTA platform token & preICO crowdsale implementasion
 * @author Maxim Akimov - <devstylesoftware@gmail.com>
 * @author Dmitrii Bykov - <bykoffdn@gmail.com>
 */

pragma solidity ^0.4.18;

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {
    
	function mul(uint256 a, uint256 b) internal constant returns (uint256) {
		uint256 c = a * b;
		assert(a == 0 || c / a == b);
		return c;
	}

	function div(uint256 a, uint256 b) internal constant 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;
	}

	function sub(uint256 a, uint256 b) internal constant returns (uint256) {
		assert(b <= a);
		return a - b;
	}

	function add(uint256 a, uint256 b) internal constant returns (uint256) {
		uint256 c = a + b;
		assert(c >= a);
		return c;
	}
  
}

/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
	uint256 public totalSupply;
	function balanceOf(address who) constant returns (uint256);
	function transfer(address to, uint256 value) returns (bool);
	event Transfer(address indexed from, address indexed to, uint256 value);
}

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 is ERC20Basic {
	function allowance(address owner, address spender) constant returns (uint256);
	function transferFrom(address from, address to, uint256 value) returns (bool);
	function approve(address spender, uint256 value) returns (bool);
	event Approval(address indexed owner, address indexed spender, uint256 value);
}

/**
 * @title Basic token
 * @dev Basic version of StandardToken, with no allowances. 
 */
contract BasicToken is ERC20Basic {
    
	using SafeMath for uint256;

	mapping(address => uint256) balances;

	/**
	* @dev transfer token for a specified address
	* @param _to The address to transfer to.
	* @param _value The amount to be transferred.
	*/
	function transfer(address _to, uint256 _value) returns (bool) {
		balances[msg.sender] = balances[msg.sender].sub(_value);
		balances[_to] = balances[_to].add(_value);
		Transfer(msg.sender, _to, _value);
		return true;
	}

	/**
	* @dev Gets the balance of the specified address.
	* @param _owner The address to query the the balance of. 
	* @return An uint256 representing the amount owned by the passed address.
	*/
	function balanceOf(address _owner) constant returns (uint256 balance) {
		return balances[_owner];
	}

}

/**
 * @title Standard ERC20 token
 * @dev Implementation of the basic standard token.
 * @dev https://github.com/ethereum/EIPs/issues/20
 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
contract StandardToken is ERC20, BasicToken {

	mapping (address => mapping (address => uint256)) allowed;

	/**
	* @dev Transfer tokens from one address to another
	* @param _from address The address which you want to send tokens from
	* @param _to address The address which you want to transfer to
	* @param _value uint256 the amout of tokens to be transfered
	*/
	function transferFrom(address _from, address _to, uint256 _value) returns (bool) {
	  
		var _allowance = allowed[_from][msg.sender];

		// Check is not needed because sub(_allowance, _value) will already throw if this condition is not met
		// require (_value <= _allowance);

		balances[_to] = balances[_to].add(_value);
		balances[_from] = balances[_from].sub(_value);
		allowed[_from][msg.sender] = _allowance.sub(_value);
		Transfer(_from, _to, _value);
		return true;
	}

	/**
	* @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender.
	* @param _spender The address which will spend the funds.
	* @param _value The amount of tokens to be spent.
	*/
	function approve(address _spender, uint256 _value) returns (bool) {

		// To change the approve amount you first have to reduce the addresses`
		//  allowance to zero by calling `approve(_spender, 0)` if it is not
		//  already 0 to mitigate the race condition described here:
		//  https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
		require((_value == 0) || (allowed[msg.sender][_spender] == 0));

		allowed[msg.sender][_spender] = _value;
		Approval(msg.sender, _spender, _value);
		return true;
	}

	/**
	* @dev Function to check the amount of tokens that an owner allowed to a spender.
	* @param _owner address The address which owns the funds.
	* @param _spender address The address which will spend the funds.
	* @return A uint256 specifing the amount of tokens still available for the spender.
	*/
	function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
		return allowed[_owner][_spender];
	}

}

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
    
	address public owner;
	address public ownerCandidat;

	/**
	* @dev The Ownable constructor sets the original `owner` of the contract to the sender
	* account.
	*/
	function Ownable() {
		owner = msg.sender;
		
	}

	/**
	* @dev Throws if called by any account other than the owner.
	*/
	modifier onlyOwner() {
		require(msg.sender == owner);
		_;
	}

	/**
	* @dev Allows the current owner to transfer control of the contract to a newOwner.
	* @param newOwner The address to transfer ownership to.
	*/
	function transferOwnership(address newOwner) onlyOwner {
		require(newOwner != address(0));      
		ownerCandidat = newOwner;
	}
	/**
	* @dev Allows safe change current owner to a newOwner.
	*/
	function confirmOwnership()  {
		require(msg.sender == ownerCandidat);      
		owner = msg.sender;
	}

}

/**
 * @title Burnable Token
 * @dev Token that can be irreversibly burned (destroyed).
 */
contract BurnableToken is StandardToken, Ownable {
 
	/**
	* @dev Burns a specific amount of tokens.
	* @param _value The amount of token to be burned.
	*/
	function burn(uint256 _value) public onlyOwner {
		require(_value > 0);

		address burner = msg.sender;    
										

		balances[burner] = balances[burner].sub(_value);
		totalSupply = totalSupply.sub(_value);
		Burn(burner, _value);
	}

	event Burn(address indexed burner, uint indexed value);
 
}
 
contract MettaCoin is BurnableToken {
 
	string public constant name = "TOKEN METTA";   
	string public constant symbol = "METTA";   
	uint32 public constant decimals = 18;    
	uint256 public constant initialSupply = 300000000 * 1 ether;

	function MettaCoin() {
		totalSupply = initialSupply;
		balances[msg.sender] = initialSupply;
	}    
  
}