// SPDX-License-Identifier: MIT
// https://seniorblockchain.io
// Security-Contact: security@seniorblockchain.io

pragma solidity ^0.8.20;

interface ISenior {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function allowance(address owner, address spender) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract Senior is ISenior {
    using SafeMath for uint256;

    string public name = "Senior";
    string public symbol = "SNR";
    uint8 public decimals = 18;
    uint256 private _totalSupply = 256000000 * 10**uint256(decimals);

    mapping(address => uint256) private balances;
    mapping(address => mapping(address => uint256)) private allowances;

    constructor(address initialRecipient) {
        balances[initialRecipient] = _totalSupply;
        emit Transfer(address(0), initialRecipient, _totalSupply);
    }

    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address tokenOwner) public view override returns (uint256) {
        return balances[tokenOwner];
    }

    function transfer(address recipient, uint256 amount) public override returns (bool) {
        require(amount <= balances[msg.sender], "Insufficient balance");
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    function approve(address spender, uint256 amount) public override returns (bool) {
        allowances[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function allowance(address owner, address spender) public view override returns (uint256) {
        return allowances[owner][spender];
    }

    function transferFrom(address sender, address recipient, uint256 amount) public override returns (bool) {
        require(amount <= balances[sender], "Insufficient balance");
        require(amount <= allowances[sender][msg.sender], "Allowance exceeded");
        _transfer(sender, recipient, amount);
        _approve(sender, msg.sender, allowances[sender][msg.sender].sub(amount));
        return true;
    }

    function _transfer(address sender, address recipient, uint256 amount) internal {
        balances[sender] = balances[sender].sub(amount);
        balances[recipient] = balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    function _approve(address owner, address spender, uint256 amount) internal {
        allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
}

library SafeMath {
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "Subtraction overflow");
        return a - b;
    }

    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "Addition overflow");
        return c;
    }
}