pragma solidity ^0.4.0;

/**
public - 안 밖에서 자유롭게 접근가능
internal - 계약서 안에서 실행 가능한 함수를 통해서만 접근 가능
external - 외부 계약서의 트랜잭션을 통해서만 접근 가능
private - 계약서 내부일지라도 다른데서 상속받은 함수들이 아닌 순수 계약서만의 함수에서만 접근 가능
 */

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

contract RankingballToken {
	// Token 의 Public 변수 들
    string public standard = "Rankingball Token";
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;

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

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approved(address spender, uint value);

    function RankingballToken (uint256 initialSupply, string tokenName, uint8 decimalUnits, string tokenSymbol) public {
        balanceOf[msg.sender] = initialSupply;
        totalSupply = initialSupply;
        name = tokenName;
        symbol = tokenSymbol;
        decimals = decimalUnits;
    }

	/**
	 * Token 이체, only can be called by this contract
	 */
    function _transfer(address _from, address _to, uint256 _value) internal {
		//if (balanceOf[msg.sender] < _value) throw; // throw deprecated
		//if (balanceOf[_to] + _value < balanceOf[_to]) throw; // throw deprecated

		// prevent transfer to 0x0 address. Use burn() instead
        require(_to != 0x0);
		// check if the sender has enough
        require(balanceOf[_from] >= _value);
		// check for overflows
        require(balanceOf[_to] + _value > balanceOf[_to]);

        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        emit Transfer(_from, _to, _value);
    }

	/**
     * 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 {
        _transfer(msg.sender, _to, _value);
    }

	/* 특정 Contract 가 내 대신 Token 을 쓸 수 있도록 함 */
    function approve(address _spender, uint256 _value) public returns (bool success_) {
        allowance[msg.sender][_spender] = _value;
        return true;
    }

	/* Approve 받은 Contract 에게 알림 */
    function approveAndCall(address _spender, uint256 _value, bytes _extraData) public returns (bool success_) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            emit Approved(_spender, _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
     *
     * Contract 가 Token 을 가져가려 함
     */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success_) {
		//if (balanceOf[_from] < _value) throw;
		//if (balanceOf[_to] + _value < balanceOf[_to]) throw;
		//if (_value > allowance[_from][msg.sender]) throw;
		/*
		// check if the sender has enough
        require(balanceOf[_from] >= _value);
		// check for overflows
        require(balanceOf[_to] + _value > balanceOf[_to]);
		// check allowance
        require(_value <= allowance[_from][msg.sender]);

        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        allowance[_from][msg.sender] -= _value;

		emit Transfer(_from, _to, _value);*/

        // check allowance
        require(_value <= allowance[_from][msg.sender]);
        allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);

        return true;
    }
}