// SPDX-License-Identifier: MIT
// Copied and adjusted from OpenZeppelin
// Adjustments:
// - modifications to support ERC-677
// - removed unnecessary require statements
// - removed GSN Context
// - upgraded to 0.8 to drop SafeMath
// - let name() and symbol() be implemented by subclass
// - infinite allowance support, with 2^255 and above considered infinite
// - use upper 32 bits of balance for flags
// - add a global settings variable

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./IERC677Receiver.sol";

/**
 * @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 `ERC20Mintable`.
 *
 * *For a detailed writeup see our guide [How to implement supply
 * mechanisms](https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226).*
 *
 * 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`.
 */

abstract contract ERC20Flaggable is IERC20 {

    // as Documented in /doc/infiniteallowance.md
    // 0x8000000000000000000000000000000000000000000000000000000000000000
    uint256 constant private INFINITE_ALLOWANCE = 2**255;

    uint256 private constant FLAGGING_MASK = 0xFFFFFFFF00000000000000000000000000000000000000000000000000000000;

    // Documentation of flags used by subclasses:
    // NOTE: flags denote the bit number that is being used and must be smaller than 32
    // ERC20Draggable: uint8 private constant FLAG_INDEX_VOTED = 1;
    // ERC20Recoverable: uint8 private constant FLAG_INDEX_CLAIM_PRESENT = 10;
    // ERCAllowlistable: uint8 private constant FLAG_INDEX_ALLOWLIST = 20;
    // ERCAllowlistable: uint8 private constant FLAG_INDEX_FORBIDDEN = 21;
    // ERCAllowlistable: uint8 private constant FLAG_INDEX_POWERLIST = 22;

    mapping (address => uint256) private _balances; // upper 32 bits reserved for flags

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    uint8 public override decimals;

    event NameChanged(string name, string symbol);

    constructor(uint8 _decimals) {
        decimals = _decimals;
    }

    /**
     * @dev See `IERC20.totalSupply`.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See `IERC20.balanceOf`.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return uint224 (_balances [account]);
    }

    function hasFlag(address account, uint8 number) external view returns (bool) {
        return hasFlagInternal(account, number);
    }

    function setFlag(address account, uint8 index, bool value) internal {
        uint256 flagMask = 1 << (index + 224);
        uint256 balance = _balances [account];
        if ((balance & flagMask == flagMask) != value) {
            _balances [account] = balance ^ flagMask;
        }
    }

    function hasFlagInternal(address account, uint8 number) internal view returns (bool) {
        uint256 flag = 0x1 << (number + 224);
        return _balances[account] & flag == flag;
    }

    /**
     * @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(msg.sender, recipient, amount);
        return true;
    }

    /**
     * @dev See `IERC20.allowance`.
     */
    function allowance(address owner, address spender) external view override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See `IERC20.approve`.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 value) external override returns (bool) {
        _approve(msg.sender, spender, value);
        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 `value`.
     * - the caller must have allowance for `sender`'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external override returns (bool) {
        _transfer(sender, recipient, amount);
        uint256 currentAllowance = _allowances[sender][msg.sender];
        if (currentAllowance < INFINITE_ALLOWANCE){
            // Only decrease the allowance if it was not set to 'infinite'
            // Documented in /doc/infiniteallowance.md
            _allowances[sender][msg.sender] = currentAllowance - amount;
        }
        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 {
        _beforeTokenTransfer(sender, recipient, amount);
        decreaseBalance(sender, amount);
        increaseBalance(recipient, amount);
        emit Transfer(sender, recipient, amount);
    }

    // ERC-677 functionality, can be useful for swapping and wrapping tokens
    function transferAndCall(address recipient, uint amount, bytes calldata data) external virtual returns (bool) {
        return transfer (recipient, amount) 
            && IERC677Receiver (recipient).onTokenTransfer (msg.sender, amount, data);
    }

    /** @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 recipient, uint256 amount) internal virtual {
        _beforeTokenTransfer(address(0), recipient, amount);
        _totalSupply += amount;
        increaseBalance(recipient, amount);
        emit Transfer(address(0), recipient, amount);
    }

    function increaseBalance(address recipient, uint256 amount) private {
        require(recipient != address(0x0), "0x0"); // use burn instead
        uint256 oldBalance = _balances[recipient];
        uint256 newBalance = oldBalance + amount;
        require(oldBalance & FLAGGING_MASK == newBalance & FLAGGING_MASK, "overflow");
        _balances[recipient] = newBalance;
    }

     /**
     * @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 {
        _beforeTokenTransfer(account, address(0), amount);

        _totalSupply -= amount;
        decreaseBalance(account, amount);
        emit Transfer(account, address(0), amount);
    }

    function decreaseBalance(address sender, uint256 amount) private {
        uint256 oldBalance = _balances[sender];
        uint256 newBalance = oldBalance - amount;
        require(oldBalance & FLAGGING_MASK == newBalance & FLAGGING_MASK, "underflow");
        _balances[sender] = newBalance;
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is 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 value) internal {
        _allowances[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    /**
     * @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].
     */
     // solhint-disable-next-line no-empty-blocks
    function _beforeTokenTransfer(address from, address to, uint256 amount) virtual internal {
        // intentionally left blank
    }

}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./ERC20Flaggable.sol";
import "../utils/Ownable.sol";

contract ERC20Named is ERC20Flaggable, Ownable {

    string public override name;
    string public override symbol;

    constructor(string memory _symbol, string memory _name, uint8 _decimals, address _admin) ERC20Flaggable(_decimals) Ownable(_admin) {
        setNameInternal(_symbol, _name);
    }

    function setName(string memory _symbol, string memory _name) external onlyOwner {
        setNameInternal(_symbol, _name);
    }

    function setNameInternal(string memory _symbol, string memory _name) internal {
        symbol = _symbol;
        name = _name;
        emit NameChanged(_name, _symbol);
    }

}

/**
* SPDX-License-Identifier: LicenseRef-Aktionariat
*
* MIT License with Automated License Fee Payments
*
* Copyright (c) 2020 Aktionariat AG (aktionariat.com)
*
* Permission is hereby granted to any person obtaining a copy of this software
* and associated documentation files (the "Software"), to deal in the Software
* without restriction, including without limitation the rights to use, copy,
* modify, merge, publish, distribute, sublicense, and/or sell copies of the
* Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* - The above copyright notice and this permission notice shall be included in
*   all copies or substantial portions of the Software.
* - All automated license fee payments integrated into this and related Software
*   are preserved.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
pragma solidity ^0.8.0;

import "../ERC20/ERC20Flaggable.sol";
import "./IRecoveryHub.sol";
import "./IRecoverable.sol";

/**
 * @title Recoverable
 * In case of tokens that represent real-world assets such as shares of a company, one needs a way
 * to handle lost private keys. With physical certificates, courts can declare share certificates as
 * invalid so the company can issue replacements. Here, we want a solution that does not depend on
 * third parties to resolve such cases. Instead, when someone has lost a private key, he can use the
 * declareLost function on the recovery hub to post a deposit and claim that the shares assigned to a
 * specific address are lost.
 * If an attacker trying to claim shares belonging to someone else, they risk losing the deposit
 * as it can be claimed at anytime by the rightful owner.
 * Furthermore, if "getClaimDeleter" is defined in the subclass, the returned address is allowed to
 * delete claims, returning the collateral. This can help to prevent obvious cases of abuse of the claim
 * function, e.g. cases of front-running.
 * Most functionality is implemented in a shared RecoveryHub.
 */
abstract contract ERC20Recoverable is ERC20Flaggable, IRecoverable {

    uint8 private constant FLAG_CLAIM_PRESENT = 10;

    // ERC-20 token that can be used as collateral or 0x0 if disabled
    IERC20 public customCollateralAddress;
    // Rate the custom collateral currency is multiplied to be valued like one share.
    uint256 public customCollateralRate;

    uint256 constant CLAIM_PERIOD = 180 days;

    IRecoveryHub public immutable recovery;

    constructor(IRecoveryHub recoveryHub){
        recovery = recoveryHub;
    }

    /**
     * Returns the collateral rate for the given collateral type and 0 if that type
     * of collateral is not accepted. By default, only the token itself is accepted at
     * a rate of 1:1.
     *
     * Subclasses should override this method if they want to add additional types of
     * collateral.
     */
    function getCollateralRate(IERC20 collateralType) public override virtual view returns (uint256) {
        if (address(collateralType) == address(this)) {
            return 1;
        } else if (collateralType == customCollateralAddress) {
            return customCollateralRate;
        } else {
            return 0;
        }
    }

    function claimPeriod() external pure override returns (uint256){
        return CLAIM_PERIOD;
    }

    /**
     * Allows subclasses to set a custom collateral besides the token itself.
     * The collateral must be an ERC-20 token that returns true on successful transfers and
     * throws an exception or returns false on failure.
     * Also, do not forget to multiply the rate in accordance with the number of decimals of the collateral.
     * For example, rate should be 7*10**18 for 7 units of a collateral with 18 decimals.
     */
    function _setCustomClaimCollateral(IERC20 collateral, uint256 rate) internal {
        customCollateralAddress = collateral;
        if (address(customCollateralAddress) == address(0)) {
            customCollateralRate = 0; // disabled
        } else {
            require(rate > 0, "zero");
            customCollateralRate = rate;
        }
    }

    function getClaimDeleter() virtual public view returns (address);

    function transfer(address recipient, uint256 amount) override(ERC20Flaggable, IERC20) virtual public returns (bool) {
        require(super.transfer(recipient, amount), "transfer");
        if (hasFlagInternal(msg.sender, FLAG_CLAIM_PRESENT)){
            recovery.clearClaimFromToken(msg.sender);
        }
        return true;
    }

    function notifyClaimMade(address target) external override {
        require(msg.sender == address(recovery), "not recovery");
        setFlag(target, FLAG_CLAIM_PRESENT, true);
    }

    function notifyClaimDeleted(address target) external override {
        require(msg.sender == address(recovery), "not recovery");
        setFlag(target, FLAG_CLAIM_PRESENT, false);
    }

    function deleteClaim(address lostAddress) external {
        require(msg.sender == getClaimDeleter(), "not claim deleter");
        recovery.deleteClaim(lostAddress);
    }

    function recover(address oldAddress, address newAddress) external override {
        require(msg.sender == address(recovery), "not recovery");
        _transfer(oldAddress, newAddress, balanceOf(oldAddress));
    }

}

/**
* SPDX-License-Identifier: MIT
*
* Copyright (c) 2016-2019 zOS Global Limited
*
*/
pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see `ERC20Detailed`.
 */

interface IERC20 {

    // Optional functions
    function name() external view returns (string memory);

    function symbol() external view returns (string memory);

    function decimals() external view returns (uint8);

    /**
     * @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.
     *
     * > 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);

}

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

interface IERC677Receiver {
    
    function onTokenTransfer(address from, uint256 amount, bytes calldata data) external returns (bool);

}

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

import "../ERC20/IERC20.sol";

interface IRecoverable is IERC20{

    function claimPeriod() external view returns (uint256);
    
    function notifyClaimMade(address target) external;

    function notifyClaimDeleted(address target) external;

    function getCollateralRate(IERC20 collateral) external view returns(uint256);

    function recover(address oldAddress, address newAddress) external;

}

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

interface IRecoveryHub {

    function setRecoverable(bool flag) external;
    
    // deletes claim and transfers collateral back to claimer
    function deleteClaim(address target) external;

    // clears claim and transfers collateral to holder
    function clearClaimFromToken(address holder) external;

}

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

interface IShares {
	function burn(uint256) external;

	function totalShares() external view returns (uint256);
}

// SPDX-License-Identifier: MIT
//
// From https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol
//
// Modifications:
// - Replaced Context._msgSender() with msg.sender
// - Made leaner
// - Extracted interface

pragma solidity ^0.8.0;

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
contract Ownable {

    address public owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor (address initialOwner) {
        owner = initialOwner;
        emit OwnershipTransferred(address(0), owner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) external onlyOwner {
        emit OwnershipTransferred(owner, newOwner);
        owner = newOwner;
    }

    modifier onlyOwner() {
        require(owner == msg.sender, "not owner");
        _;
    }
}

/**
* SPDX-License-Identifier: LicenseRef-Aktionariat
*
* MIT License with Automated License Fee Payments
*
* Copyright (c) 2020 Aktionariat AG (aktionariat.com)
*
* Permission is hereby granted to any person obtaining a copy of this software
* and associated documentation files (the "Software"), to deal in the Software
* without restriction, including without limitation the rights to use, copy,
* modify, merge, publish, distribute, sublicense, and/or sell copies of the
* Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* - The above copyright notice and this permission notice shall be included in
*   all copies or substantial portions of the Software.
* - All automated license fee payments integrated into this and related Software
*   are preserved.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
pragma solidity ^0.8.0;

import "../ERC20/ERC20Named.sol";
import "../ERC20/IERC677Receiver.sol";
import "../recovery/ERC20Recoverable.sol";
import "../shares/IShares.sol";

/**
 * @title CompanyName AG Shares
 * @author Luzius Meisser, luzius@aktionariat.com
 *
 * These tokens represent ledger-based securities according to article 973d of the Swiss Code of Obligations.
 * This smart contract serves as an ownership registry, enabling the token holders to register them as
 * shareholders in the issuer's shareholder registry. This is equivalent to the traditional system
 * of having physical share certificates kept at home by the shareholders and a shareholder registry run by
 * the company. Just like with physical certificates, the owners of the tokens are the owners of the shares.
 * However, in order to exercise their rights (for example receive a dividend), shareholders must register
 * themselves. For example, in case the company pays out a dividend to a previous shareholder because
 * the current shareholder did not register, the company cannot be held liable for paying the dividend to
 * the "wrong" shareholder. In relation to the company, only the registered shareholders count as such.
 */
contract Shares is ERC20Recoverable, ERC20Named, IShares{

    string public terms;

    uint256 public override totalShares; // total number of shares, maybe not all tokenized
    uint256 public invalidTokens;

    event Announcement(string message);
    event TokensDeclaredInvalid(address indexed holder, uint256 amount, string message);
    event ChangeTerms(string terms);
    event ChangeTotalShares(uint256 total);

    constructor(
        string memory _symbol,
        string memory _name,
        string memory _terms,
        uint256 _totalShares,
        address _owner,
        IRecoveryHub _recoveryHub
    )
        ERC20Named(_symbol, _name, 0, _owner) 
        ERC20Recoverable(_recoveryHub)
    {
        totalShares = _totalShares;
        terms = _terms;
        invalidTokens = 0;
        _recoveryHub.setRecoverable(false); 
    }

    function setTerms(string memory _terms) external onlyOwner {
        terms = _terms;
        emit ChangeTerms(_terms);
    }

    /**
     * Declares the number of total shares, including those that have not been tokenized and those
     * that are held by the company itself. This number can be substiantially higher than totalSupply()
     * in case not all shares have been tokenized. Also, it can be lower than totalSupply() in case some
     * tokens have become invalid.
     */
    function setTotalShares(uint256 _newTotalShares) external onlyOwner() {
        require(_newTotalShares >= totalValidSupply(), "below supply");
        totalShares = _newTotalShares;
        emit ChangeTotalShares(_newTotalShares);
    }

    /**
     * Allows the issuer to make public announcements that are visible on the blockchain.
     */
    function announcement(string calldata message) external onlyOwner() {
        emit Announcement(message);
    }

    /**
     * See parent method for collateral requirements.
     */
    function setCustomClaimCollateral(IERC20 collateral, uint256 rate) external onlyOwner() {
        super._setCustomClaimCollateral(collateral, rate);
    }

    function getClaimDeleter() public override view returns (address) {
        return owner;
    }

    /**
     * Signals that the indicated tokens have been declared invalid (e.g. by a court ruling in accordance
     * with article 973g of the Swiss Code of Obligations) and got detached from
     * the underlying shares. Invalid tokens do not carry any shareholder rights any more.
     *
     * This function is purely declarative. It does not technically immobilize the affected tokens as
     * that would give the issuer too much power.
     */
    function declareInvalid(address holder, uint256 amount, string calldata message) external onlyOwner() {
        uint256 holderBalance = balanceOf(holder);
        require(amount <= holderBalance, "amount too high");
        invalidTokens += amount;
        emit TokensDeclaredInvalid(holder, amount, message);
    }

    /**
     * The total number of valid tokens in circulation. In case some tokens have been declared invalid, this
     * number might be lower than totalSupply(). Also, it will always be lower than or equal to totalShares().
     */
    function totalValidSupply() public view returns (uint256) {
        return totalSupply() - invalidTokens;
    }

    /**
     * Allows the company to tokenize shares and transfer them e.g to the draggable contract and wrap them.
     * If these shares are newly created, setTotalShares must be called first in order to adjust the total number of shares.
     */
    function mintAndCall(address shareholder, address callee, uint256 amount, bytes calldata data) external {
        mint(callee, amount);
        require(IERC677Receiver(callee).onTokenTransfer(shareholder, amount, data));
    }

    function mint(address target, uint256 amount) public onlyOwner {
        _mint(target, amount);
    }

    function _mint(address account, uint256 amount) internal virtual override {
        require(totalValidSupply() + amount <= totalShares, "total");
        super._mint(account, amount);
    }

    function transfer(address to, uint256 value) virtual override(ERC20Recoverable, ERC20Flaggable) public returns (bool) {
        return super.transfer(to, value);
    }

    /**
     * Transfers _amount tokens to the company and burns them.
     * The meaning of this operation depends on the circumstances and the fate of the shares does
     * not necessarily follow the fate of the tokens. For example, the company itself might call
     * this function to implement a formal decision to destroy some of the outstanding shares.
     * Also, this function might be called by an owner to return the shares to the company and
     * get them back in another form under an according agreement (e.g. printed certificates or
     * tokens on a different blockchain). It is not recommended to call this function without
     * having agreed with the company on the further fate of the shares in question.
     */
    function burn(uint256 _amount) override external {
        _transfer(msg.sender, address(this), _amount);
        _burn(address(this), _amount);
    }

}

{
  "compilationTarget": {
    "src/shares/Shares.sol": "Shares"
  },
  "evmVersion": "london",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs",
    "useLiteralContent": true
  },
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}