// File: @gelatonetwork/core/contracts/external/Ownable.sol



// "SPDX-License-Identifier: UNLICENSED"
pragma solidity ^0.6.10;

/**
 * @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.
 *
 * 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 private _owner;

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

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

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Returns true if the caller is the current owner.
     */
    function isOwner() public view returns (bool) {
        return msg.sender == _owner;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

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

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     */
    function _transferOwnership(address newOwner) internal virtual {
        require(
            newOwner != address(0),
            "Ownable: new owner is the zero address"
        );
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: @gelatonetwork/core/contracts/external/SafeMath.sol



// "SPDX-License-Identifier: UNLICENSED"
pragma solidity ^0.6.10;

/**
 * @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.
     *
     * _Available since v2.4.0._
     */
    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.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        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.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}
// File: @openzeppelin/contracts/GSN/Context.sol



// 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;
    }
}

// File: @openzeppelin/contracts/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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;
    }
}

// File: @openzeppelin/contracts/token/ERC20/ERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../GSN/Context.sol";
import "./IERC20.sol";
import "../../math/SafeMath.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 {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;

    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];
    }

    /**
     * @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");

        _beforeTokenTransfer(address(0), account, amount);

        _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");

        _beforeTokenTransfer(account, address(0), amount);

        _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 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 Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }

    /**
     * @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 { }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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);
}

// File: contracts/OracleAggregator.sol



// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.6.10;

import { Ownable } from "@gelatonetwork/core/contracts/external/Ownable.sol";
import { SafeMath } from "@gelatonetwork/core/contracts/external/SafeMath.sol";
import { ERC20 } from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import { IOracle } from "./interfaces/IOracle.sol";

// solhint-disable max-states-count
contract OracleAggregator is Ownable {
  using SafeMath for uint256;

  // solhint-disable var-name-mixedcase
  address private constant ETH = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
  // solhint-disable var-name-mixedcase
  address private constant USD = 0x7354C81fbCb229187480c4f497F945C6A312d5C3;

  string public constant version = "v1.0.0";

  address public immutable WETH;

  mapping(address => mapping(address => address)) private _tokenPairAddress;
  mapping(address => uint256) private _nrOfDecimalsUSD;

  // solhint-disable function-max-lines
  constructor(
    address _weth,
    address[] memory _inTokens,
    address[] memory _outTokens,
    address[] memory _oracles,
    address[] memory _stablecoins,
    uint256[] memory _decimals
  ) public {
    WETH = _weth;
    addTokens(_inTokens, _outTokens, _oracles);
    addStablecoins(_stablecoins, _decimals);
    // required token pairs
    require(_tokenPairAddress[ETH][USD] != address(0));
    require(_tokenPairAddress[USD][ETH] != address(0));
  }

  function addTokens(
    address[] memory _inTokens,
    address[] memory _outTokens,
    address[] memory _oracles
  ) public onlyOwner {
    require(
      _inTokens.length == _outTokens.length &&
        _inTokens.length == _oracles.length
    );
    for (uint256 i = 0; i < _inTokens.length; i++) {
      _tokenPairAddress[_inTokens[i]][_outTokens[i]] = _oracles[i];
    }
  }

  function addStablecoins(
    address[] memory _stablecoins,
    uint256[] memory _decimals
  ) public onlyOwner {
    require(_stablecoins.length == _decimals.length);
    for (uint256 i = 0; i < _stablecoins.length; i++) {
      _nrOfDecimalsUSD[_stablecoins[i]] = _decimals[i];
    }
  }

  // solhint-disable function-max-lines
  // solhint-disable code-complexity
  /// @dev expected return amount of outToken from amountIn of inToken
  function getExpectedReturnAmount(
    uint256 amountIn,
    address inToken,
    address outToken
  ) public view returns (uint256 returnAmount, uint256 outTokenDecimals) {
    // sanity checks
    require(amountIn > 0, "OracleAggregator: amountIn is Zero");
    require(inToken != address(0), "OracleAggregator: inToken is Zero");
    require(outToken != address(0), "OracleAggregator: outToken is Zero");

    // convert WETH to ETH
    if (inToken == WETH) {
      inToken = ETH;
    }
    if (outToken == WETH) {
      outToken = ETH;
    }

    // decimals of inToken
    uint256 inTokenDecimals;
    (inTokenDecimals, outTokenDecimals) = _getDecimals(inToken, outToken);

    // store outToken address if it is a stablecoin
    address stableCoinAddress =
      _nrOfDecimalsUSD[outToken] > 0 ? outToken : address(0);

    // convert any stablecoin addresses to USD address
    (inToken, outToken) = _convertUSD(inToken, outToken);

    if (outToken == ETH || outToken == USD) {
      // when outToken is ETH or USD
      returnAmount = _handleConvertToEthOrUsd(
        amountIn,
        inToken,
        outToken,
        inTokenDecimals,
        stableCoinAddress
      );
    } else {
      // when outToken is not ETH or USD
      returnAmount = _handleConvertToToken(
        amountIn,
        inToken,
        outToken,
        inTokenDecimals
      );
    }

    return (returnAmount, outTokenDecimals);
  }

  function _handleConvertToEthOrUsd(
    uint256 amountIn,
    address inToken,
    address outToken,
    uint256 inTokenDecimals,
    address stableCoinAddress
  ) private view returns (uint256 returnAmount) {
    // oracle of inToken vs outToken exists
    // e.g. calculating KNC/ETH
    // and KNC/ETH oracle exists
    if (_tokenPairAddress[inToken][outToken] != address(0)) {
      (uint256 price, uint256 nrOfDecimals) = _getRate(inToken, outToken);
      returnAmount = stableCoinAddress != address(0)
        ? _matchStableCoinDecimal(
          stableCoinAddress,
          amountIn,
          nrOfDecimals,
          0,
          price,
          1
        )
        : amountIn.mul(price);

      return returnAmount.div(10**inTokenDecimals);
    } else {
      // direct oracle of inToken vs outToken does not exist
      // e.g. calculating UNI/USD
      // UNI/ETH and USD/ETH oracles available
      (address pairA, address pairB) = _checkAvailablePair(inToken, outToken);
      if (pairA == address(0) && pairB == address(0)) return (0);
      (uint256 priceA, ) = _getRate(inToken, pairA);
      (uint256 priceB, uint256 nrOfDecimals) = _getRate(outToken, pairB);

      nrOfDecimals = stableCoinAddress != address(0)
        ? _nrOfDecimalsUSD[stableCoinAddress]
        : nrOfDecimals;

      returnAmount = amountIn.mul(priceA.mul(10**nrOfDecimals)).div(priceB);
      if (outToken != ETH) {
        return returnAmount.div(10**inTokenDecimals);
      } else {
        return returnAmount.div(10**_nrOfDecimalsUSD[USD]);
      }
    }
  }

  function _handleConvertToToken(
    uint256 amountIn,
    address inToken,
    address outToken,
    uint256 inTokenDecimals
  ) private view returns (uint256 returnAmount) {
    (address pairA, address pairB) = _checkAvailablePair(inToken, outToken);
    if (pairA == address(0) && pairB == address(0)) return (0);
    // oracle of inToken/ETH, outToken/ETH || inToken/USD, outToken/USD exists
    // e.g. calculating KNC/UNI where
    // KNC/ETH and UNI/ETH oracles available
    if (pairA == pairB) {
      (uint256 priceA, uint256 nrOfDecimals) = _getRate(inToken, pairA);

      (uint256 priceB, ) = _getRate(outToken, pairB);

      returnAmount = amountIn.mul(priceA.mul(10**nrOfDecimals)).div(priceB);
      if (pairA == ETH) {
        return returnAmount.div(10**inTokenDecimals);
      } else {
        return returnAmount.div(10**_nrOfDecimalsUSD[USD]);
      }
    } else if (pairA == ETH && pairB == USD) {
      // oracle of inToken/ETH and outToken/USD exists
      // e.g. calculating UNI/SXP where
      // UNI/ETH and SXP/USD oracles available
      (uint256 priceA, ) = _getRate(inToken, pairA);
      (uint256 priceETHUSD, ) = _getRate(ETH, USD);
      (uint256 priceB, ) = _getRate(outToken, pairB);

      returnAmount = amountIn.mul(priceA.mul(priceETHUSD)).div(priceB);
      return returnAmount.div(10**inTokenDecimals);
    } else if (pairA == USD && pairB == ETH) {
      // oracle of inToken/USD and outToken/ETH exists
      // e.g. calculating SXP/UNI where
      // SXP/USD and UNI/ETH oracles available
      uint256 numerator;
      {
        (uint256 priceA, uint256 nrOfDecimals) = _getRate(inToken, pairA);

        (uint256 priceUSDETH, uint256 nrOfDecimalsUSDETH) = _getRate(USD, ETH);

        numerator = priceUSDETH
          .mul(10**(nrOfDecimalsUSDETH.sub(nrOfDecimals)))
          .mul(priceA)
          .div(10**nrOfDecimalsUSDETH);
      }
      (uint256 priceB, ) = _getRate(outToken, pairB);
      returnAmount = amountIn.mul(numerator).div(priceB);
      return returnAmount;
    }
  }

  /// @dev check the available oracles for token a & b
  /// and choose which oracles to use
  function _checkAvailablePair(address inToken, address outToken)
    private
    view
    returns (address, address)
  {
    if (
      _tokenPairAddress[inToken][USD] != address(0) &&
      _tokenPairAddress[outToken][USD] != address(0)
    ) {
      return (USD, USD);
    } else if (
      _tokenPairAddress[inToken][ETH] != address(0) &&
      _tokenPairAddress[outToken][ETH] != address(0)
    ) {
      return (ETH, ETH);
    } else if (
      _tokenPairAddress[inToken][ETH] != address(0) &&
      _tokenPairAddress[outToken][USD] != address(0)
    ) {
      return (ETH, USD);
    } else if (
      _tokenPairAddress[inToken][USD] != address(0) &&
      _tokenPairAddress[outToken][ETH] != address(0)
    ) {
      return (USD, ETH);
    } else {
      return (address(0), address(0));
    }
  }

  function _getDecimals(address inToken, address _outToken)
    private
    view
    returns (uint256 inTokenDecimals, uint256 outTokenDecimals)
  {
    // decimals of inToken
    if (inToken != ETH && inToken != USD) {
      try ERC20(inToken).decimals() returns (uint8 _inputDecimals) {
        inTokenDecimals = uint256(_inputDecimals);
      } catch {
        revert("OracleAggregator: ERC20.decimals() revert");
      }
    } else {
      if (inToken != ETH) {
        inTokenDecimals = _nrOfDecimalsUSD[USD];
      } else {
        inTokenDecimals = 18;
      }
    }

    // decimals of outToken
    if (_outToken != ETH && _outToken != USD) {
      try ERC20(_outToken).decimals() returns (uint8 _outputDecimals) {
        outTokenDecimals = uint256(_outputDecimals);
      } catch {
        revert("OracleAggregator: ERC20.decimals() revert");
      }
    } else {
      if (_outToken != ETH) {
        outTokenDecimals = _nrOfDecimalsUSD[USD];
      } else {
        outTokenDecimals = 18;
      }
    }
  }

  function _getRate(address inToken, address outToken)
    private
    view
    returns (uint256 tokenPrice, uint256 nrOfDecimals)
  {
    if (inToken == outToken) {
      return (1, 0);
    } else {
      IOracle priceFeed = IOracle(_tokenPairAddress[inToken][outToken]);
      tokenPrice = uint256(priceFeed.latestAnswer());
      nrOfDecimals = priceFeed.decimals();
    }
  }

  /// @dev converting all usd pegged stablecoins to single USD address
  function _convertUSD(address inToken, address outToken)
    private
    view
    returns (address, address)
  {
    if (_nrOfDecimalsUSD[inToken] > 0 && _nrOfDecimalsUSD[outToken] > 0) {
      return (USD, USD);
    } else if (_nrOfDecimalsUSD[inToken] > 0) {
      return (USD, outToken);
    } else if (_nrOfDecimalsUSD[outToken] > 0) {
      return (inToken, USD);
    } else {
      return (inToken, outToken);
    }
  }

  /// @dev modify nrOfDecimlas and amount to follow stableCoin's nrOfDecimals
  function _matchStableCoinDecimal(
    address stableCoinAddress,
    uint256 amount,
    uint256 nrOfDecimals,
    uint256 padding,
    uint256 returnRateA,
    uint256 returnRateB
  ) private view returns (uint256 returnAmount) {
    uint256 div =
      _nrOfDecimalsUSD[stableCoinAddress] > nrOfDecimals
        ? 10**(_nrOfDecimalsUSD[stableCoinAddress].sub(nrOfDecimals))
        : 10**(nrOfDecimals.sub(_nrOfDecimalsUSD[stableCoinAddress]));
    returnAmount = _nrOfDecimalsUSD[stableCoinAddress] > nrOfDecimals
      ? amount.mul(returnRateA.mul(10**padding)).div(returnRateB).mul(div)
      : amount.mul(returnRateA.mul(10**padding)).div(returnRateB).div(div);
  }
}

// File: contracts/interfaces/IOracle.sol



// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.6.10;

interface IOracle {
    function latestAnswer() external view returns (uint256);

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