// SPDX-License-Identifier: MIT

pragma solidity >=0.8.0 <0.9.0;

abstract contract Ownable {
    address public owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor() {
        owner = msg.sender;
        emit OwnershipTransferred(address(0), msg.sender);
    }

    modifier onlyOwner() {
        require(owner == msg.sender, 'NOT_OWNER');
        _;
    }

    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), 'ZERO_ADDR');

        emit OwnershipTransferred(owner, newOwner);
        owner = newOwner;
    }
}

/**
 * @title EternalStorage
 * @dev This contract holds all the necessary state variables to carry out the storage of any contract.
 */
contract EternalStorage {
    mapping(bytes32 => uint256) private _uintStorage;
    mapping(bytes32 => string) private _stringStorage;
    mapping(bytes32 => address) private _addressStorage;
    mapping(bytes32 => bytes) private _bytesStorage;
    mapping(bytes32 => bool) private _boolStorage;
    mapping(bytes32 => int256) private _intStorage;

    // *** Getter Methods ***
    function getUint(bytes32 key) public view returns (uint256) {
        return _uintStorage[key];
    }

    function getString(bytes32 key) public view returns (string memory) {
        return _stringStorage[key];
    }

    function getAddress(bytes32 key) public view returns (address) {
        return _addressStorage[key];
    }

    function getBytes(bytes32 key) public view returns (bytes memory) {
        return _bytesStorage[key];
    }

    function getBool(bytes32 key) public view returns (bool) {
        return _boolStorage[key];
    }

    function getInt(bytes32 key) public view returns (int256) {
        return _intStorage[key];
    }

    // *** Setter Methods ***
    function _setUint(bytes32 key, uint256 value) internal {
        _uintStorage[key] = value;
    }

    function _setString(bytes32 key, string memory value) internal {
        _stringStorage[key] = value;
    }

    function _setAddress(bytes32 key, address value) internal {
        _addressStorage[key] = value;
    }

    function _setBytes(bytes32 key, bytes memory value) internal {
        _bytesStorage[key] = value;
    }

    function _setBool(bytes32 key, bool value) internal {
        _boolStorage[key] = value;
    }

    function _setInt(bytes32 key, int256 value) internal {
        _intStorage[key] = value;
    }

    // *** Delete Methods ***
    function _deleteUint(bytes32 key) internal {
        delete _uintStorage[key];
    }

    function _deleteString(bytes32 key) internal {
        delete _stringStorage[key];
    }

    function _deleteAddress(bytes32 key) internal {
        delete _addressStorage[key];
    }

    function _deleteBytes(bytes32 key) internal {
        delete _bytesStorage[key];
    }

    function _deleteBool(bytes32 key) internal {
        delete _boolStorage[key];
    }

    function _deleteInt(bytes32 key) internal {
        delete _intStorage[key];
    }
}

contract Burner {
    constructor(address tokenAddress, bytes32 salt) {
        BurnableMintableCappedERC20(tokenAddress).burn(salt);

        selfdestruct(payable(address(0)));
    }
}

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return payable(msg.sender);
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    mapping(address => uint256) public override balanceOf;

    mapping(address => mapping(address => uint256)) public override allowance;

    uint256 public override totalSupply;

    string public name;
    string public symbol;

    uint8 public immutable decimals;

    /**
     * @dev Sets the values for {name}, {symbol}, and {decimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(
        string memory name_,
        string memory symbol_,
        uint8 decimals_
    ) {
        name = name_;
        symbol = symbol_;
        decimals = decimals_;
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), allowance[sender][_msgSender()] - amount);
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, allowance[_msgSender()][spender] + addedValue);
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, allowance[_msgSender()][spender] - subtractedValue);
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal virtual {
        require(sender != address(0), 'ZERO_ADDR');
        require(recipient != address(0), 'ZERO_ADDR');

        _beforeTokenTransfer(sender, recipient, amount);

        balanceOf[sender] -= amount;
        balanceOf[recipient] += amount;
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), 'ZERO_ADDR');

        _beforeTokenTransfer(address(0), account, amount);

        totalSupply += amount;
        balanceOf[account] += amount;
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), 'ZERO_ADDR');

        _beforeTokenTransfer(account, address(0), amount);

        balanceOf[account] -= amount;
        totalSupply -= amount;
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), 'ZERO_ADDR');
        require(spender != address(0), 'ZERO_ADDR');

        allowance[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}
}

contract BurnableMintableCappedERC20 is ERC20, Ownable {
    uint256 public cap;

    bytes32 private constant PREFIX_TOKEN_FROZEN = keccak256('token-frozen');
    bytes32 private constant KEY_ALL_TOKENS_FROZEN = keccak256('all-tokens-frozen');

    event Frozen(address indexed owner);
    event Unfrozen(address indexed owner);

    constructor(
        string memory name,
        string memory symbol,
        uint8 decimals,
        uint256 capacity
    ) ERC20(name, symbol, decimals) Ownable() {
        cap = capacity;
    }

    function depositAddress(bytes32 salt) public view returns (address) {
        // This would be easier, cheaper, simpler, and result in  globally consistent deposit addresses for any salt (all chains, all tokens).
        // return address(uint160(uint256(keccak256(abi.encodePacked(bytes32(0x000000000000000000000000000000000000000000000000000000000000dead), salt)))));

        /* Convert a hash which is bytes32 to an address which is 20-byte long
        according to https://docs.soliditylang.org/en/v0.8.1/control-structures.html?highlight=create2#salted-contract-creations-create2 */
        return
            address(
                uint160(
                    uint256(
                        keccak256(
                            abi.encodePacked(
                                bytes1(0xff),
                                owner,
                                salt,
                                keccak256(abi.encodePacked(type(Burner).creationCode, abi.encode(address(this)), salt))
                            )
                        )
                    )
                )
            );
    }

    function mint(address account, uint256 amount) public onlyOwner {
        uint256 capacity = cap;
        require(capacity == 0 || totalSupply + amount <= capacity, 'CAP_EXCEEDED');

        _mint(account, amount);
    }

    function burn(bytes32 salt) public onlyOwner {
        address account = depositAddress(salt);
        _burn(account, balanceOf[account]);
    }

    function _beforeTokenTransfer(
        address,
        address,
        uint256
    ) internal view override {
        require(!EternalStorage(owner).getBool(KEY_ALL_TOKENS_FROZEN), 'IS_FROZEN');
        require(!EternalStorage(owner).getBool(keccak256(abi.encodePacked(PREFIX_TOKEN_FROZEN, symbol))), 'IS_FROZEN');
    }
}