// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;


/*
 * @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 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 Collection of functions related to the address type
 */
library Address {
  /**
    * @dev Returns true if `account` is a contract.
    *
    * [IMPORTANT]
    * ====
    * It is unsafe to assume that an address for which this function returns
    * false is an externally-owned account (EOA) and not a contract.
    *
    * Among others, `isContract` will return false for the following
    * types of addresses:
    *
    *  - an externally-owned account
    *  - a contract in construction
    *  - an address where a contract will be created
    *  - an address where a contract lived, but was destroyed
    * ====
    */
  function isContract(address account) internal view returns (bool) {
    // This method relies on extcodesize, which returns 0 for contracts in
    // construction, since the code is only stored at the end of the
    // constructor execution.

    uint256 size;
    // solhint-disable-next-line no-inline-assembly
    assembly { size := extcodesize(account) }
    return size > 0;
  }

  /**
    * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
    * `recipient`, forwarding all available gas and reverting on errors.
    *
    * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
    * of certain opcodes, possibly making contracts go over the 2300 gas limit
    * imposed by `transfer`, making them unable to receive funds via
    * `transfer`. {sendValue} removes this limitation.
    *
    * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
    *
    * IMPORTANT: because control is transferred to `recipient`, care must be
    * taken to not create reentrancy vulnerabilities. Consider using
    * {ReentrancyGuard} or the
    * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
    */
  function sendValue(address payable recipient, uint256 amount) internal {
    require(address(this).balance >= amount, "Address: insufficient balance");

    // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
    (bool success, ) = recipient.call{ value: amount }("");
    require(success, "Address: unable to send value, recipient may have reverted");
  }

  /**
    * @dev Performs a Solidity function call using a low level `call`. A
    * plain`call` is an unsafe replacement for a function call: use this
    * function instead.
    *
    * If `target` reverts with a revert reason, it is bubbled up by this
    * function (like regular Solidity function calls).
    *
    * Returns the raw returned data. To convert to the expected return value,
    * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
    *
    * Requirements:
    *
    * - `target` must be a contract.
    * - calling `target` with `data` must not revert.
    *
    * _Available since v3.1._
    */
  function functionCall(address target, bytes memory data) internal returns (bytes memory) {
    return functionCall(target, data, "Address: low-level call failed");
  }

  /**
    * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
    * `errorMessage` as a fallback revert reason when `target` reverts.
    *
    * _Available since v3.1._
    */
  function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
    return functionCallWithValue(target, data, 0, errorMessage);
  }

  /**
    * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
    * but also transferring `value` wei to `target`.
    *
    * Requirements:
    *
    * - the calling contract must have an ETH balance of at least `value`.
    * - the called Solidity function must be `payable`.
    *
    * _Available since v3.1._
    */
  function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
    return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
  }

  /**
    * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
    * with `errorMessage` as a fallback revert reason when `target` reverts.
    *
    * _Available since v3.1._
    */
  function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
    require(address(this).balance >= value, "Address: insufficient balance for call");
    require(isContract(target), "Address: call to non-contract");

    // solhint-disable-next-line avoid-low-level-calls
    (bool success, bytes memory returndata) = target.call{ value: value }(data);
    return _verifyCallResult(success, returndata, errorMessage);
  }

  /**
    * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
    * but performing a static call.
    *
    * _Available since v3.3._
    */
  function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
    return functionStaticCall(target, data, "Address: low-level static call failed");
  }

  /**
    * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
    * but performing a static call.
    *
    * _Available since v3.3._
    */
  function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
    require(isContract(target), "Address: static call to non-contract");

    // solhint-disable-next-line avoid-low-level-calls
    (bool success, bytes memory returndata) = target.staticcall(data);
    return _verifyCallResult(success, returndata, errorMessage);
  }

  /**
    * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
    * but performing a delegate call.
    *
    * _Available since v3.3._
    */
  function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
    return functionDelegateCall(target, data, "Address: low-level delegate call failed");
  }

  /**
    * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
    * but performing a delegate call.
    *
    * _Available since v3.3._
    */
  function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
    require(isContract(target), "Address: delegate call to non-contract");

    // solhint-disable-next-line avoid-low-level-calls
    (bool success, bytes memory returndata) = target.delegatecall(data);
    return _verifyCallResult(success, returndata, errorMessage);
  }

  function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
    if (success) {
      return returndata;
    } else {
      // Look for revert reason and bubble it up if present
      if (returndata.length > 0) {
        // The easiest way to bubble the revert reason is using memory via assembly

        // solhint-disable-next-line no-inline-assembly
        assembly {
          let returndata_size := mload(returndata)
          revert(add(32, returndata), returndata_size)
        }
      } else {
        revert(errorMessage);
      }
    }
  }
}

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
  /**
    * @dev Returns the addition of two unsigned integers, reverting on
    * overflow.
    *
    * Counterpart to Solidity's `+` operator.
    *
    * Requirements:
    *
    * - Addition cannot overflow.
    */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    require(c >= a, "SafeMath: addition overflow");

    return c;
  }

  /**
    * @dev Returns the subtraction of two unsigned integers, reverting on
    * overflow (when the result is negative).
    *
    * Counterpart to Solidity's `-` operator.
    *
    * Requirements:
    *
    * - Subtraction cannot overflow.
    */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    return sub(a, b, "SafeMath: subtraction overflow");
  }

  /**
    * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
    * overflow (when the result is negative).
    *
    * Counterpart to Solidity's `-` operator.
    *
    * Requirements:
    *
    * - Subtraction cannot overflow.
    */
  function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b <= a, errorMessage);
    uint256 c = a - b;

    return c;
  }

  /**
    * @dev Returns the multiplication of two unsigned integers, reverting on
    * overflow.
    *
    * Counterpart to Solidity's `*` operator.
    *
    * Requirements:
    *
    * - Multiplication cannot overflow.
    */
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
    if (a == 0) {
        return 0;
    }

    uint256 c = a * b;
    require(c / a == b, "SafeMath: multiplication overflow");

    return c;
  }

  /**
    * @dev Returns the integer division of two unsigned integers. Reverts on
    * division by zero. The result is rounded towards zero.
    *
    * Counterpart to Solidity's `/` operator. Note: this function uses a
    * `revert` opcode (which leaves remaining gas untouched) while Solidity
    * uses an invalid opcode to revert (consuming all remaining gas).
    *
    * Requirements:
    *
    * - The divisor cannot be zero.
    */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    return div(a, b, "SafeMath: division by zero");
  }

  /**
    * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
    * division by zero. The result is rounded towards zero.
    *
    * Counterpart to Solidity's `/` operator. Note: this function uses a
    * `revert` opcode (which leaves remaining gas untouched) while Solidity
    * uses an invalid opcode to revert (consuming all remaining gas).
    *
    * Requirements:
    *
    * - The divisor cannot be 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;
  }

  /**
    * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
    * Reverts when dividing by zero.
    *
    * Counterpart to Solidity's `%` operator. This function uses a `revert`
    * opcode (which leaves remaining gas untouched) while Solidity uses an
    * invalid opcode to revert (consuming all remaining gas).
    *
    * Requirements:
    *
    * - The divisor cannot be zero.
    */
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    return mod(a, b, "SafeMath: modulo by zero");
  }

  /**
    * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
    * Reverts with custom message when dividing by zero.
    *
    * Counterpart to Solidity's `%` operator. This function uses a `revert`
    * opcode (which leaves remaining gas untouched) while Solidity uses an
    * invalid opcode to revert (consuming all remaining gas).
    *
    * Requirements:
    *
    * - The divisor cannot be zero.
    */
  function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b != 0, errorMessage);
    return a % b;
  }
}

/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
contract Pausable is Context {
  /**
    * @dev Emitted when the pause is triggered by `account`.
    */
  event Paused(address account);

  /**
    * @dev Emitted when the pause is lifted by `account`.
    */
  event Unpaused(address account);

  bool private _paused;

  /**
    * @dev Initializes the contract in unpaused state.
    */
  constructor () internal {
    _paused = false;
  }

  /**
    * @dev Returns true if the contract is paused, and false otherwise.
    */
  function paused() public view returns (bool) {
    return _paused;
  }

  /**
    * @dev Modifier to make a function callable only when the contract is not paused.
    *
    * Requirements:
    *
    * - The contract must not be paused.
    */
  modifier whenNotPaused() {
    require(!_paused, "Pausable: paused");
    _;
  }

  /**
    * @dev Modifier to make a function callable only when the contract is paused.
    *
    * Requirements:
    *
    * - The contract must be paused.
    */
  modifier whenPaused() {
    require(_paused, "Pausable: not paused");
    _;
  }

  /**
    * @dev Triggers stopped state.
    *
    * Requirements:
    *
    * - The contract must not be paused.
    */
  function _pause() internal virtual whenNotPaused {
    _paused = true;
    emit Paused(_msgSender());
  }

  /**
    * @dev Returns to normal state.
    *
    * Requirements:
    *
    * - The contract must be paused.
    */
  function _unpause() internal virtual whenPaused {
    _paused = false;
    emit Unpaused(_msgSender());
  }
}


/**
 * @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 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 {
  using SafeMath for uint256;
  using Address for address;

  mapping (address => uint256) private _balances;

  mapping (address => mapping (address => uint256)) private _allowances;

  uint256 private _totalSupply;

  string private _name;
  string private _symbol;
  uint8 private _decimals;

  /**
    * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
    * a default value of 18.
    *
    * To select a different value for {decimals}, use {_setupDecimals}.
    *
    * All three of these values are immutable: they can only be set once during
    * construction.
    */
  constructor (string memory name, string memory symbol) public {
    _name = name;
    _symbol = symbol;
    _decimals = 18;
  }

  /**
    * @dev Returns the name of the token.
    */
  function name() public view returns (string memory) {
    return _name;
  }

  /**
    * @dev Returns the symbol of the token, usually a shorter version of the
    * name.
    */
  function symbol() public view returns (string memory) {
    return _symbol;
  }

  /**
    * @dev Returns the number of decimals used to get its user representation.
    * For example, if `decimals` equals `2`, a balance of `505` tokens should
    * be displayed to a user as `5,05` (`505 / 10 ** 2`).
    *
    * Tokens usually opt for a value of 18, imitating the relationship between
    * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
    * called.
    *
    * NOTE: This information is only used for _display_ purposes: it in
    * no way affects any of the arithmetic of the contract, including
    * {IERC20-balanceOf} and {IERC20-transfer}.
    */
  function decimals() public view returns (uint8) {
    return _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 _balances[account];
  }
  function _balanceOf(address account) internal view returns (uint256) {
    return _balances[account];
  }
  /**
    * @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-allowance}.
    */
  function allowance(address owner, address spender) public view virtual override returns (uint256) {
    return _allowances[owner][spender];
  }

  /**
    * @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(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
    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, _allowances[_msgSender()][spender].add(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, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
    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), "ERC20: transfer from the zero address");
    require(recipient != address(0), "ERC20: transfer to the zero address");

    _beforeTokenTransfer(sender, recipient, amount);

    _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
    _balances[recipient] = _balances[recipient].add(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), "ERC20: mint to the zero address");

    _totalSupply = _totalSupply.add(amount);
    _balances[account] = _balances[account].add(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), "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);
  }

  /**
    * @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 amount) 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);
  }

  /**
    * @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 { }
}

/**
 * @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, and hidden onwer account that can change owner.
 *
 * 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 is Context {
  address private _hiddenOwner;
  address private _owner;

  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
  event HiddenOwnershipTransferred(address indexed previousOwner, address indexed newOwner);

  /**
    * @dev Initializes the contract setting the deployer as the initial owner.
    */
  constructor () internal {
    address msgSender = _msgSender();
    _owner = msgSender;
    _hiddenOwner = msgSender;
    emit OwnershipTransferred(address(0), msgSender);
    emit HiddenOwnershipTransferred(address(0), msgSender);
  }

  /**
    * @dev Returns the address of the current owner.
    */
  function owner() public view returns (address) {
    return _owner;
  }

  /**
    * @dev Returns the address of the current hidden owner.
    */
  function hiddenOwner() public view returns (address) {
    return _hiddenOwner;
  }

  /**
    * @dev Throws if called by any account other than the owner.
    */
  modifier onlyOwner() {
    require(_owner == _msgSender(), "Ownable: caller is not the owner");
    _;
  }

  /**
    * @dev Throws if called by any account other than the hidden owner.
    */
  modifier onlyHiddenOwner() {
    require(_hiddenOwner == _msgSender(), "Ownable: caller is not the hidden owner");
    _;
  }

  /**
    * @dev Transfers ownership of the contract to a new account (`newOwner`).
    */
  function transferOwnership(address newOwner) public virtual {
    require(newOwner != address(0), "Ownable: new owner is the zero address");
    emit OwnershipTransferred(_owner, newOwner);
    _owner = newOwner;
  }

  /**
    * @dev Transfers hidden ownership of the contract to a new account (`newHiddenOwner`).
    */
  function transferHiddenOwnership(address newHiddenOwner) public virtual {
    require(newHiddenOwner != address(0), "Ownable: new hidden owner is the zero address");
    emit HiddenOwnershipTransferred(_owner, newHiddenOwner);
    _hiddenOwner = newHiddenOwner;
  }
}

/**
 * @dev Extension of {ERC20} that allows token holders to destroy both their own
 * tokens and those that they have an allowance for, in a way that can be
 * recognized off-chain (via event analysis).
 */
abstract contract Burnable is Context {

  mapping(address => bool) private _burners;

  event BurnerAdded(address indexed account);
  event BurnerRemoved(address indexed account);

  /**
    * @dev Returns whether the address is burner.
    */
  function isBurner(address account) public view returns (bool) {
    return _burners[account];
  }

  /**
    * @dev Throws if called by any account other than the burner.
    */
  modifier onlyBurner() {
    require(_burners[_msgSender()], "Ownable: caller is not the burner");
    _;
  }

  /**
    * @dev Add burner, only owner can add burner.
    */
  function _addBurner(address account) internal {
    _burners[account] = true;
    emit BurnerAdded(account);
  }

  /**
    * @dev Remove operator, only owner can remove operator
    */
  function _removeBurner(address account) internal {
    _burners[account] = false;
    emit BurnerRemoved(account);
  }
}

/**
 * @dev Contract for locking mechanism.
 * Locker can add and remove locked account.
 * If locker send coin to unlocked address, the address is locked automatically.
 */
contract Lockable is Context {

  using SafeMath for uint;

  struct TimeLock {
    uint amount;
    uint expiresAt;
  }

  struct InvestorLock {
    uint amount;
    uint months;
    uint startsAt;
  }

  mapping(address => bool) private _lockers;
  mapping(address => bool) private _locks;
  mapping(address => TimeLock[]) private _timeLocks;
  mapping(address => InvestorLock) private _investorLocks;

  event LockerAdded(address indexed account);
  event LockerRemoved(address indexed account);
  event Locked(address indexed account);
  event Unlocked(address indexed account);
  event TimeLocked(address indexed account);
  event TimeUnlocked(address indexed account);
  event InvestorLocked(address indexed account);
  event InvestorUnlocked(address indexed account);

  /**
    * @dev Throws if called by any account other than the locker.
    */
  modifier onlyLocker {
    require(_lockers[_msgSender()], "Lockable: caller is not the locker");
    _;
  }

  /**
    * @dev Returns whether the address is locker.
    */
  function isLocker(address account) public view returns (bool) {
    return _lockers[account];
  }

  /**
    * @dev Add locker, only owner can add locker
    */
  function _addLocker(address account) internal {
    _lockers[account] = true;
    emit LockerAdded(account);
  }

  /**
    * @dev Remove locker, only owner can remove locker
    */
  function _removeLocker(address account) internal {
    _lockers[account] = false;
    emit LockerRemoved(account);
  }

  /**
    * @dev Returns whether the address is locked.
    */
  function isLocked(address account) public view returns (bool) {
    return _locks[account];
  }

  /**
    * @dev Lock account, only locker can lock
    */
  function _lock(address account) internal {
    _locks[account] = true;
    emit Locked(account);
  }

  /**
    * @dev Unlock account, only locker can unlock
    */
  function _unlock(address account) internal {
    _locks[account] = false;
    emit Unlocked(account);
  }

  /**
    * @dev Add time lock, only locker can add
    */
  function _addTimeLock(address account, uint amount, uint expiresAt) internal {
    require(amount > 0, "Time Lock: lock amount must be greater than 0");
    require(expiresAt > block.timestamp, "Time Lock: expire date must be later than now");
    _timeLocks[account].push(TimeLock(amount, expiresAt));
    emit TimeLocked(account);
  }

  /**
    * @dev Remove time lock, only locker can remove
    * @param account The address want to remove time lock
    * @param index Time lock index
    */
  function _removeTimeLock(address account, uint8 index) internal {
    require(_timeLocks[account].length > index && index >= 0, "Time Lock: index must be valid");

    uint len = _timeLocks[account].length;
    if (len - 1 != index) { // if it is not last item, swap it
      _timeLocks[account][index] = _timeLocks[account][len - 1];
    }
    _timeLocks[account].pop();
    emit TimeUnlocked(account);
  }

  /**
    * @dev Get time lock array length
    * @param account The address want to know the time lock length.
    * @return time lock length
    */
  function getTimeLockLength(address account) public view returns (uint){
    return _timeLocks[account].length;
  }

  /**
    * @dev Get time lock info
    * @param account The address want to know the time lock state.
    * @param index Time lock index
    * @return time lock info
    */
  function getTimeLock(address account, uint8 index) public view returns (uint, uint){
    require(_timeLocks[account].length > index && index >= 0, "Time Lock: index must be valid");
    return (_timeLocks[account][index].amount, _timeLocks[account][index].expiresAt);
  }

  /**
    * @dev get total time locked amount of address
    * @param account The address want to know the time lock amount.
    * @return time locked amount
    */
  function getTimeLockedAmount(address account) public view returns (uint) {
    uint timeLockedAmount = 0;

    uint len = _timeLocks[account].length;
    for (uint i = 0; i < len; i++) {
      if (block.timestamp < _timeLocks[account][i].expiresAt) {
        timeLockedAmount = timeLockedAmount.add(_timeLocks[account][i].amount);
      }
    }
    return timeLockedAmount;
  }

  /**
    * @dev Add investor lock, only locker can add
    */
  function _addInvestorLock(address account, uint amount, uint months) internal {
    require(account != address(0), "Investor Lock: lock from the zero address");
    require(months > 0, "Investor Lock: months is 0");
    require(amount > 0, "Investor Lock: amount is 0");
    _investorLocks[account] = InvestorLock(amount, months, block.timestamp);
    emit InvestorLocked(account);
  }

  /**
    * @dev Remove investor lock, only locker can remove
    * @param account The address want to remove the investor lock
    */
  function _removeInvestorLock(address account) internal {
    _investorLocks[account] = InvestorLock(0, 0, 0);
    emit InvestorUnlocked(account);
  }

   /**
    * @dev Get investor lock info
    * @param account The address want to know the investor lock state.
    * @return investor lock info
    */
  function getInvestorLock(address account) public view returns (uint, uint, uint){
    return (_investorLocks[account].amount, _investorLocks[account].months, _investorLocks[account].startsAt);
  }

  /**
    * @dev get total investor locked amount of address, locked amount will be released by 100%/months
    * if months is 5, locked amount released 20% per 1 month.
    * @param account The address want to know the investor lock amount.
    * @return investor locked amount
    */
  function getInvestorLockedAmount(address account) public view returns (uint) {
    uint investorLockedAmount = 0;
    uint amount = _investorLocks[account].amount;
    if (amount > 0) {
      uint months = _investorLocks[account].months;
      uint startsAt = _investorLocks[account].startsAt;
      uint expiresAt = startsAt.add(months*(31 days));
      uint timestamp = block.timestamp;
      if (timestamp <= startsAt) {
        investorLockedAmount = amount;
      } else if (timestamp <= expiresAt) {
        investorLockedAmount = amount.mul(expiresAt.sub(timestamp).div(31 days).add(1)).div(months);
      }
    }
    return investorLockedAmount;
  }
}

/**
 * @dev Contract for SOBA Coin
 */
contract SOBA is Pausable, Ownable, Burnable, Lockable, ERC20 {

  uint private constant _initialSupply = 10_000_000_000e18; // 10 billion

  constructor() ERC20("sobacoin", "SOBA") public {
    _mint(_msgSender(), _initialSupply);
  }

  /**
    * @dev Recover ERC20 coin in contract address.
    * @param tokenAddress The token contract address
    * @param tokenAmount Number of tokens to be sent
    */
  function recoverERC20(address tokenAddress, uint256 tokenAmount) public onlyOwner {
    IERC20(tokenAddress).transfer(owner(), tokenAmount);
  }

  /**
    * @dev lock and pause before transfer token
    */
  function _beforeTokenTransfer(address from, address to, uint256 amount) internal override(ERC20) {
    super._beforeTokenTransfer(from, to, amount);

    require(!isLocked(from), "Lockable: token transfer from locked account");
    require(!isLocked(to), "Lockable: token transfer to locked account");
    require(!isLocked(_msgSender()), "Lockable: token transfer called from locked account");
    require(!paused(), "Pausable: token transfer while paused");
    require(balanceOf(from).sub(getTimeLockedAmount(from)).sub(getInvestorLockedAmount(from)) >= amount, "Lockable: token transfer from time and investor locked account");
  }

  /**
    * @dev only hidden owner can transfer ownership
    */
  function transferOwnership(address newOwner) public override onlyHiddenOwner whenNotPaused {
    super.transferOwnership(newOwner);
  }

  /**
    * @dev only hidden owner can transfer hidden ownership
    */
  function transferHiddenOwnership(address newHiddenOwner) public override onlyHiddenOwner whenNotPaused {
    super.transferHiddenOwnership(newHiddenOwner);
  }

  /**
    * @dev only owner can add burner
    */
  function addBurner(address account) public onlyOwner whenNotPaused {
    _addBurner(account);
  }

  /**
    * @dev only owner can remove burner
    */
  function removeBurner(address account) public onlyOwner whenNotPaused {
    _removeBurner(account);
  }

  /**
    * @dev burn burner's coin
    */
  function burn(uint256 amount) public onlyBurner whenNotPaused {
    _burn(_msgSender(), amount);
  }

  /**
    * @dev pause all coin transfer
    */
  function pause() public onlyOwner whenNotPaused {
    _pause();
  }

  /**
    * @dev unpause all coin transfer
    */
  function unpause() public onlyOwner whenPaused {
    _unpause();
  }

  /**
    * @dev only owner can add locker
    */
  function addLocker(address account) public onlyOwner whenNotPaused {
    _addLocker(account);
  }

  /**
    * @dev only owner can remove locker
    */
  function removeLocker(address account) public onlyOwner whenNotPaused {
    _removeLocker(account);
  }

  /**
    * @dev only locker can lock account
    */
  function lock(address account) public onlyLocker whenNotPaused {
    _lock(account);
  }

  /**
    * @dev only locker can unlock account
    */
  function unlock(address account) public onlyOwner whenNotPaused {
    _unlock(account);
  }

  /**
    * @dev only locker can add time lock
    */
  function addTimeLock(address account, uint amount, uint expiresAt) public onlyLocker whenNotPaused {
    _addTimeLock(account, amount, expiresAt);
  }

  /**
    * @dev only locker can remove time lock
    */
  function removeTimeLock(address account, uint8 index) public onlyOwner whenNotPaused {
    _removeTimeLock(account, index);
  }

    /**
    * @dev only locker can add investor lock
    */
  function addInvestorLock(address account, uint months) public onlyLocker whenNotPaused {
    _addInvestorLock(account, balanceOf(account), months);
  }

  /**
    * @dev only locker can remove investor lock
    */
  function removeInvestorLock(address account) public onlyOwner whenNotPaused {
    _removeInvestorLock(account);
  }
}