// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

library SafeMath {
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }
    
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

interface IERC20 {
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    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);
}

abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }
}

abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    function owner() public view returns (address) {
        return _owner;
    }

    modifier onlyOwner() {
        require(_owner == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

abstract contract Pausable is Context, Ownable {
    event Paused(address account);
    event Unpaused(address account);

    bool private _paused;

    constructor () internal {
        _paused = false;
    }

    function paused() public view returns (bool) {
        return _paused;
    }

    modifier whenNotPaused() {
        require(!_paused, "Pausable: paused");
        _;
    }


    modifier whenPaused() {
        require(_paused, "Pausable: not paused");
        _;
    }


    function _pause() internal virtual onlyOwner whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }


    function _unpause() internal virtual onlyOwner whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

contract ERC20 is Context, IERC20, Pausable {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;
    
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;
    
    constructor (string memory name_, string memory symbol_, uint256 totalSupply_) public { 
        name = name_;
        symbol = symbol_;
        decimals = 18;

        _mint(owner(), totalSupply_ * (10 ** uint256(decimals)));
        emit Transfer(address(0), owner(), totalSupply);
    }

    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }
    
    function mint(address account, uint256 amount) onlyOwner public virtual returns (bool) {
        _mint(account, amount);
        return true;
    }

    function burn(uint256 amount) onlyOwner public virtual returns (bool) {
        _burn(_msgSender(), amount);
        return true;
    }

    function pause() public virtual {
        _pause();
    }
    
    function unpause() public virtual {
        _unpause();
    }

    function _transfer(address sender, address recipient, uint256 amount) whenNotPaused internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    function _mint(address account, uint256 amount) whenNotPaused internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        totalSupply = totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    function _burn(address account, uint256 amount) whenNotPaused internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        totalSupply = totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    function _approve(address owner, address spender, uint256 amount) whenNotPaused internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");
        
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
}