// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;

// RevertingERC20 reverts on errors
contract RevertingERC20Mock {
    string public symbol;
    string public name;
    uint8 public immutable decimals;
    uint256 public totalSupply;
    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

    constructor(
        string memory name_,
        string memory symbol_,
        uint8 decimals_,
        uint256 supply
    ) public {
        name = name_;
        symbol = symbol_;
        decimals = decimals_;
        totalSupply = supply;
        balanceOf[msg.sender] = supply;
    }

    function transfer(address to, uint256 amount) public returns (bool success) {
        require(balanceOf[msg.sender] >= amount, "TokenB: balance too low");
        require(amount >= 0, "TokenB: amount should be > 0");
        require(balanceOf[to] + amount >= balanceOf[to], "TokenB: overflow detected");
        balanceOf[msg.sender] -= amount;
        balanceOf[to] += amount;
        emit Transfer(msg.sender, to, amount);
        return true;
    }

    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) public returns (bool success) {
        require(balanceOf[from] >= amount, "TokenB: balance too low");
        require(allowance[from][msg.sender] >= amount, "TokenB: allowance too low");
        require(amount >= 0, "TokenB: amount should be >= 0");
        require(balanceOf[to] + amount >= balanceOf[to], "TokenB: overflow detected");
        balanceOf[from] -= amount;
        allowance[from][msg.sender] -= amount;
        balanceOf[to] += amount;
        emit Transfer(from, to, amount);
        return true;
    }

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