pragma solidity ^0.5.8;


import './SafeMath.sol';


contract Token {
    uint256 public totalSupply;
    
    function balanceOf(address _owner) public view returns (uint256 balance);
    function transfer(address _to, uint256 _value) public returns (bool success);
    function transferFrom(address _from, address _to, uint256 _value) public returns(bool success);
    
    function approve(address _spender, uint256 _value) public returns (bool success);
    
    function allowance(address _owner, address _spender) public view returns (uint256 remaining);
    
    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}

contract KentCoin is Token {
    
    using SafeMath for uint256;
    
    string  public name;
    uint8   public decimals;
    string  public symbol;
    
    constructor() public {
        totalSupply = 3*(10**8)*(10**18);
        balances[msg.sender] = totalSupply;
        
        name = "KentCoin";
        decimals = 18;
        symbol = "KTC";
    }
    
    function transfer(address _to, uint256 _value) public returns (bool success) {
        require(balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]);
        require(_to != address(0x0));
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }
    
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value);
        require(_to != address(0x0));
        balances[_from] = balances[_from].sub(_value);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(_from, _to, _value);
        return true;
    }
    
    function balanceOf(address _owner) public view returns (uint256 balance) {
        return balances[_owner];
    }
    
    function approve(address _spender, uint256 _value) public returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
    
    function increaseApproval(address _spender, uint256 _value) public returns (bool success) {
        allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_value);
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
    
    function decreaseApproval(address _spender, uint256 _value) public returns (bool success) {
        if (_value > allowed[msg.sender][_spender]) {
            allowed[msg.sender][_spender] = 0;
        } else {
            allowed[msg.sender][_spender] = allowed[msg.sender][_spender].sub(_value);
        }
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
    
    function allowance(address _owner, address _spender) public view returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }
    
    mapping (address => uint256) balances;
    mapping (address => mapping(address => uint256)) allowed;
}