pragma solidity ^0.4.21;

library SafeMath {
	function mul(uint256 a, uint256 b) internal pure returns (uint256) {
		if (a == 0) {
			return 0;
		}
		uint256 c = a * b;
		assert(c / a == b);
		return c;
	}

	function div(uint256 a, uint256 b) internal pure 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 pure returns (uint256) {
		assert(b <= a);
		return a - b;
	}

	function add(uint256 a, uint256 b) internal pure returns (uint256) {
		uint256 c = a + b;
		assert(c >= a);
		return c;
	}
}

contract ERC20Basic {
	uint256 public totalSupply;
	function balanceOf(address who) public view returns (uint256);
	function transfer(address to, uint256 value) public returns (bool);
	event Transfer(address indexed from, address indexed to, uint256 value);
}

contract ERC20 is ERC20Basic {
	function allowance(address owner, address spender) public view returns (uint256);
	function transferFrom(address from, address to, uint256 value) public returns (bool);
	function approve(address spender, uint256 value) public returns (bool);
	event Approval(address indexed owner, address indexed spender, uint256 value);
}

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) public returns (bool) {
		require(_to != address(0));
		require(_value <= balances[msg.sender]);

		// SafeMath.sub will throw if there is not enough balance.
		balances[msg.sender] = balances[msg.sender].sub(_value);
		balances[_to] = balances[_to].add(_value);
		emit 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) public view returns (uint256 balance) {
		return balances[_owner];
	}
}

contract WoodToken is ERC20, BasicToken {
	// Public variables of the token
    string public name;
    string public symbol;
    uint8 public decimals = 0;

	mapping (address => mapping (address => uint256)) internal allowed;
	
	event Burn(address indexed burner, uint256 value);
	
	/**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    function WoodToken(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) public {
        totalSupply = initialSupply * 10 ** uint256(decimals);          // Update total supply with the decimal amount
		balances[msg.sender] = balances[msg.sender].add(totalSupply);   // Give the creator all initial tokens           
        name = tokenName;                                               // Set the name for display purposes
        symbol = tokenSymbol;                                           // Set the symbol for display purposes
    }
	
	/**
	* @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 amount of tokens to be transferred
	*/
	function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
		require(_to != address(0));
		require(_value <= balances[_from]);
		require(_value <= allowed[_from][msg.sender]);

		balances[_from] = balances[_from].sub(_value);
		balances[_to] = balances[_to].add(_value);
		allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
		emit Transfer(_from, _to, _value);
		return true;
	}
	
	/**
	* @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
	*
	* Beware that changing an allowance with this method brings the risk that someone may use both the old
	* and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
	* race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
	* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
	* @param _spender The address which will spend the funds.
	* @param _value The amount of tokens to be spent.
	*/
	function approve(address _spender, uint256 _value) public returns (bool) {
		allowed[msg.sender][_spender] = _value;
		emit 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 specifying the amount of tokens still available for the spender.
	*/
	function allowance(address _owner, address _spender) public view returns (uint256) {
		return allowed[_owner][_spender];
	}
	
	/**
     * @dev Burns a specific amount of tokens.
     * @param _value The amount of token to be burned.
     */
    function burn(uint256 _value) public {
        require(_value <= balances[msg.sender]);
        // no need to require value <= totalSupply, since that would imply the
        // sender's balance is greater than the totalSupply, which *should* be an assertion failure

        address burner = msg.sender;
        balances[burner] = balances[burner].sub(_value);
        totalSupply = totalSupply.sub(_value);
        emit Burn(burner, _value);
    }
}