pragma solidity 0.4.25;

// ----------------------------------------------------------------------------
// Safe maths
// ----------------------------------------------------------------------------
library SafeMath {
    function add(uint a, uint b) internal pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function sub(uint a, uint b) internal pure returns (uint c) {
        require(b <= a);
        c = a - b;
    }
    function mul(uint a, uint b) internal pure returns (uint c) {
        c = a * b;
        require(a == 0 || c / a == b);
    }
    function div(uint a, uint b) internal pure returns (uint c) {
        require(b > 0);
        c = a / b;
    }
}


// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
// ----------------------------------------------------------------------------
contract ERC20Interface {
    function totalSupply() public constant returns (uint);
    function balanceOf(address tokenOwner) public constant returns (uint balance);
    function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

// ----------------------------------------------------------------------------
// Owned contract
// ----------------------------------------------------------------------------
contract Owned {
    address public owner;
    address public newOwner;

    event OwnershipTransferred(address indexed _from, address indexed _to);

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

}

/**
 * @title MapCoin 
 */
contract MapCoin is ERC20Interface, Owned {
  using SafeMath for uint256;
  string  public symbol; 
  string  public name;
  uint8   public decimals;
  uint    internal _totalSupply;
  
  mapping(address => uint) balances;
  mapping(address => mapping(address => uint)) allowed;
  
    // ------------------------------------------------------------------------
    // Constructor
    // ------------------------------------------------------------------------
    constructor (address _owner) public {
        symbol = "MAP";
        name = "MapCoin";
        decimals = 18;
        owner = _owner;
        _totalSupply = 1e9; // 1 billion
        balances[owner] = totalSupply();
        emit Transfer(address(0),owner, totalSupply());
    }
    
    // donot accept any ethers
    function () external payable {
        revert();
    }

    /* ERC20Interface function's implementation */
    function totalSupply() public constant returns (uint){
       return _totalSupply* 10**uint(decimals);
    }
    
    // ------------------------------------------------------------------------
    // Get the token balance for account `tokenOwner`
    // ------------------------------------------------------------------------
    function balanceOf(address tokenOwner) public constant returns (uint balance) {
        return balances[tokenOwner];
    }

    // ------------------------------------------------------------------------
    // Transfer the balance from token owner's account to `to` account
    // - Owner's account must have sufficient balance to transfer
    // - 0 value transfers are allowed
    // ------------------------------------------------------------------------
    function transfer(address to, uint tokens) public returns (bool success) {
        // prevent transfer to 0x0, use burn instead
        require(to != 0x0);
        require(balances[msg.sender] >= tokens );
        require(balances[to] + tokens >= balances[to]);
        balances[msg.sender] = balances[msg.sender].sub(tokens);
        balances[to] = balances[to].add(tokens);
        emit Transfer(msg.sender,to,tokens);
        return true;
    }
    
    // ------------------------------------------------------------------------
    // Token owner can approve for `spender` to transferFrom(...) `tokens`
    // from the token owner's account
    // ------------------------------------------------------------------------
    function approve(address spender, uint tokens) public returns (bool success){
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender,spender,tokens);
        return true;
    }

    // ------------------------------------------------------------------------
    // Transfer `tokens` from the `from` account to the `to` account
    // 
    // The calling account must already have sufficient tokens approve(...)-d
    // for spending from the `from` account and
    // - From account must have sufficient balance to transfer
    // - Spender must have sufficient allowance to transfer
    // - 0 value transfers are allowed
    // ------------------------------------------------------------------------
    function transferFrom(address from, address to, uint tokens) public returns (bool success){
        require(tokens <= allowed[from][msg.sender]); //check allowance
        require(balances[from] >= tokens);
        balances[from] = balances[from].sub(tokens);
        balances[to] = balances[to].add(tokens);
        allowed[from][msg.sender] = allowed[from][msg.sender].sub(tokens);
        emit Transfer(from,to,tokens);
        return true;
    }
    // ------------------------------------------------------------------------
    // Returns the amount of tokens approved by the owner that can be
    // transferred to the spender's account
    // ------------------------------------------------------------------------
    function allowance(address tokenOwner, address spender) public constant returns (uint remaining) {
        return allowed[tokenOwner][spender];
    }

}