// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.0;

contract TokenAuthorization {
    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    event Transfer(address indexed from, address indexed to, uint256 amount);
    event Approval(address indexed owner, address indexed spender, uint256 amount);

    uint256 private _totalSupply;

    constructor(uint256 initialSupply) {
        _totalSupply = initialSupply;
        _balances[msg.sender] = initialSupply;
    }

    function totalSupply() external view returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) external view returns (uint256) {
        return _balances[account];
    }

    function transfer(address to, uint256 amount) external returns (bool) {
        require(to != address(0), "Invalid recipient");
        require(amount <= _balances[msg.sender], "Insufficient balance");

        _balances[msg.sender] -= amount;
        _balances[to] += amount;

        emit Transfer(msg.sender, to, amount);
        return true;
    }

    function approve(address spender, uint256 amount) external returns (bool) {
        _allowances[msg.sender][spender] = amount;

        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function allowance(address owner, address spender) external view returns (uint256) {
        return _allowances[owner][spender];
    }

    function transferFrom(address from, address to, uint256 amount) external returns (bool) {
        require(to != address(0), "Invalid recipient");
        require(amount <= _balances[from], "Insufficient balance");
        require(amount <= _allowances[from][msg.sender], "Insufficient allowance");

        _balances[from] -= amount;
        _balances[to] += amount;
        _allowances[from][msg.sender] -= amount;

        emit Transfer(from, to, amount);
        return true;
    }
}