// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract ERC20Token {
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;
    mapping(address => uint256) public balances;
    mapping(address => mapping(address => uint256)) public allowed;

    address public owner;

    constructor(
        string memory _name,
        string memory _symbol,
        uint8 _decimals,
        uint256 _initialSupply
    ) {
        name = _name;
        symbol = _symbol;
        decimals = _decimals;
        totalSupply = _initialSupply * (10**uint256(_decimals));
        balances[msg.sender] = totalSupply;
        owner = address(0);
    }

    modifier onlyOwner {
        require(msg.sender == owner, "Must be creator");
        _;
    }

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    function balanceOf(address _owner) public view returns (uint256) {
        return balances[_owner];
    }

    function renounceOnwership() public onlyOwner {
        owner = address(0);
    }

    function transfer(address _to, uint256 _value) public returns (bool) {
        require(_to != address(0), "Invalid recipient address");
        require(balances[msg.sender] >= _value, "Insufficient balance");

        balances[msg.sender] -= _value;
        balances[_to] += _value;
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
        require(_from != address(0), "Invalid sender address");
        require(_to != address(0), "Invalid recipient address");
        require(balances[_from] >= _value, "Insufficient balance");
        require(allowed[_from][msg.sender] >= _value, "Allowance exceeded");

        balances[_from] -= _value;
        balances[_to] += _value;
        allowed[_from][msg.sender] -= _value;
        emit Transfer(_from, _to, _value);
        return true;
    }

    function allowance(address _owner, address _spender) public view returns (uint256) {
        return allowed[_owner][_spender];
    }

    function increaseAllowance(address _spender, uint256 _addedValue) public returns (bool) {
        allowed[msg.sender][_spender] += _addedValue;
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }

    function decreaseAllowance(address _spender, uint256 _subtractedValue) public returns (bool) {
        uint256 currentAllowance = allowed[msg.sender][_spender];
        require(currentAllowance >= _subtractedValue, "Allowance exceeded");
        allowed[msg.sender][_spender] = currentAllowance - _subtractedValue;
        emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
}