// SPDX-License-Identifier: MIT
pragma solidity 0.8.7;

/// @notice Basic ERC20 implementation.
contract TestERC20 {
    string public name;
    string public symbol;
    uint8 public constant decimals = 18;
    uint256 public totalSupply;

    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;

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

    constructor(string memory _name, string memory _symbol, uint256 _totalSupply) {
        name = _name;
        symbol = _symbol;
        totalSupply = _totalSupply;
        balanceOf[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }

    function approve(address to, uint256 amount) external returns (bool) {
        allowance[msg.sender][to] = amount;
        emit Approval(msg.sender, to, amount);
        return true;
    }

    function transfer(address to, uint256 amount) external returns (bool) {
        balanceOf[msg.sender] -= amount;
        balanceOf[to] += amount;
        emit Transfer(msg.sender, to, amount);
        return true;
    }

    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) external returns (bool) {
        if (allowance[from][msg.sender] != type(uint256).max)
            allowance[from][msg.sender] -= amount;

        balanceOf[from] -= amount;
        balanceOf[to] += amount;
        emit Transfer(from, to, amount);
        return true;
    }
}