Contract Source Code:

// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;

abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }
    function _msgData() internal view virtual returns (bytes memory) {
        this; 
        return msg.data;
    }
}

pragma solidity >=0.6.0 <0.8.0;
interface IERC165 {
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

pragma solidity >=0.6.2 <0.8.0;
interface IERC721 is IERC165 {
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);
    function balanceOf(address owner) external view returns (uint256 balance);
    function ownerOf(uint256 tokenId) external view returns (address owner);
    function safeTransferFrom(address from, address to, uint256 tokenId) external;
    function transferFrom(address from, address to, uint256 tokenId) external;
    function approve(address to, uint256 tokenId) external;
    function getApproved(uint256 tokenId) external view returns (address operator);
    function setApprovalForAll(address operator, bool _approved) external;
    function isApprovedForAll(address owner, address operator) external view returns (bool);
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;
}

pragma solidity >=0.6.2 <0.8.0;
interface IERC721Metadata is IERC721 {
    function name() external view returns (string memory);
    function symbol() external view returns (string memory);
    function tokenURI(uint256 tokenId) external view returns (string memory);
}

pragma solidity >=0.6.2 <0.8.0;
interface IERC721Enumerable is IERC721 {
    function totalSupply() external view returns (uint256);
    function tokenOfOwnerByIndex(address owner, uint256 index) external view returns (uint256 tokenId);
    function tokenByIndex(uint256 index) external view returns (uint256);
}

pragma solidity >=0.6.0 <0.8.0;
interface IERC721Receiver {
    function onERC721Received(address operator, address from, uint256 tokenId, bytes calldata data) external returns (bytes4);
}

pragma solidity >=0.6.0 <0.8.0;
abstract contract ERC165 is IERC165 {
    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
    mapping(bytes4 => bool) private _supportedInterfaces;

    constructor () internal {
        _registerInterface(_INTERFACE_ID_ERC165);
    }
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return _supportedInterfaces[interfaceId];
    }
    function _registerInterface(bytes4 interfaceId) internal virtual {
        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
        _supportedInterfaces[interfaceId] = true;
    }
}
pragma solidity >=0.6.0 <0.8.0;
library SafeMath {
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (a == 0) return (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) return 0;
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        return a - b;
    }
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a / b;
    }
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a % b;
    }
}
pragma solidity >=0.6.2 <0.8.0;
library Address {
    function isContract(address account) internal view returns (bool) {
        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }
    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");
    }
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }
    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");
    }
    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);
    }
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");
        (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 {
            if (returndata.length > 0) {
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}
pragma solidity >=0.6.0 <0.8.0;
library EnumerableSet {
    struct Set {
        bytes32[] _values;
        mapping (bytes32 => uint256) _indexes;
    }
    function _add(Set storage set, bytes32 value) private returns (bool) {
        if (!_contains(set, value)) {
            set._values.push(value);
            set._indexes[value] = set._values.length;
            return true;
        } else {
            return false;
        }
    }
    function _remove(Set storage set, bytes32 value) private returns (bool) {
        uint256 valueIndex = set._indexes[value];
        if (valueIndex != 0) { 
            uint256 toDeleteIndex = valueIndex - 1;
            uint256 lastIndex = set._values.length - 1;
            bytes32 lastvalue = set._values[lastIndex];
            set._values[toDeleteIndex] = lastvalue;
            set._indexes[lastvalue] = toDeleteIndex + 1;
            set._values.pop();
            delete set._indexes[value];
            return true;
        } else {
            return false;
        }
    }
    function _contains(Set storage set, bytes32 value) private view returns (bool) {
        return set._indexes[value] != 0;
    }
    function _length(Set storage set) private view returns (uint256) {
        return set._values.length;
    }
    function _at(Set storage set, uint256 index) private view returns (bytes32) {
        require(set._values.length > index, "EnumerableSet: index out of bounds");
        return set._values[index];
    }
    struct Bytes32Set {
        Set _inner;
    }
    function add(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _add(set._inner, value);
    }    
    function remove(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _remove(set._inner, value);
    }
    function contains(Bytes32Set storage set, bytes32 value) internal view returns (bool) {
        return _contains(set._inner, value);
    }
    function length(Bytes32Set storage set) internal view returns (uint256) {
        return _length(set._inner);
    }
    function at(Bytes32Set storage set, uint256 index) internal view returns (bytes32) {
        return _at(set._inner, index);
    }
    struct AddressSet {
        Set _inner;
    }
    function add(AddressSet storage set, address value) internal returns (bool) {
        return _add(set._inner, bytes32(uint256(uint160(value))));
    }
    function remove(AddressSet storage set, address value) internal returns (bool) {
        return _remove(set._inner, bytes32(uint256(uint160(value))));
    }
    function contains(AddressSet storage set, address value) internal view returns (bool) {
        return _contains(set._inner, bytes32(uint256(uint160(value))));
    }
    function length(AddressSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }
    function at(AddressSet storage set, uint256 index) internal view returns (address) {
        return address(uint160(uint256(_at(set._inner, index))));
    }
    struct UintSet {
        Set _inner;
    }
    function add(UintSet storage set, uint256 value) internal returns (bool) {
        return _add(set._inner, bytes32(value));
    }
    function remove(UintSet storage set, uint256 value) internal returns (bool) {
        return _remove(set._inner, bytes32(value));
    }
    function contains(UintSet storage set, uint256 value) internal view returns (bool) {
        return _contains(set._inner, bytes32(value));
    }
    function length(UintSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }
    function at(UintSet storage set, uint256 index) internal view returns (uint256) {
        return uint256(_at(set._inner, index));
    }
}
pragma solidity >=0.6.0 <0.8.0;
library EnumerableMap {
    struct MapEntry {
        bytes32 _key;
        bytes32 _value;
    }
    struct Map {
        MapEntry[] _entries;
        mapping (bytes32 => uint256) _indexes;
    }
    function _set(Map storage map, bytes32 key, bytes32 value) private returns (bool) {
        uint256 keyIndex = map._indexes[key];

        if (keyIndex == 0) {
            map._entries.push(MapEntry({ _key: key, _value: value }));
            map._indexes[key] = map._entries.length;
            return true;
        } else {
            map._entries[keyIndex - 1]._value = value;
            return false;
        }
    }
    function _remove(Map storage map, bytes32 key) private returns (bool) {
        uint256 keyIndex = map._indexes[key];

        if (keyIndex != 0) { 
            uint256 toDeleteIndex = keyIndex - 1;
            uint256 lastIndex = map._entries.length - 1;
            MapEntry storage lastEntry = map._entries[lastIndex];
            map._entries[toDeleteIndex] = lastEntry;
            map._indexes[lastEntry._key] = toDeleteIndex + 1; 
            map._entries.pop();
            delete map._indexes[key];
            return true;
        } else {
            return false;
        }
    }
    function _contains(Map storage map, bytes32 key) private view returns (bool) {
        return map._indexes[key] != 0;
    }
    function _length(Map storage map) private view returns (uint256) {
        return map._entries.length;
    }
    function _at(Map storage map, uint256 index) private view returns (bytes32, bytes32) {
        require(map._entries.length > index, "EnumerableMap: index out of bounds");

        MapEntry storage entry = map._entries[index];
        return (entry._key, entry._value);
    }
    function _tryGet(Map storage map, bytes32 key) private view returns (bool, bytes32) {
        uint256 keyIndex = map._indexes[key];
        if (keyIndex == 0) return (false, 0); // Equivalent to contains(map, key)
        return (true, map._entries[keyIndex - 1]._value); // All indexes are 1-based
    }
    function _get(Map storage map, bytes32 key) private view returns (bytes32) {
        uint256 keyIndex = map._indexes[key];
        require(keyIndex != 0, "EnumerableMap: nonexistent key"); // Equivalent to contains(map, key)
        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
    }
    function _get(Map storage map, bytes32 key, string memory errorMessage) private view returns (bytes32) {
        uint256 keyIndex = map._indexes[key];
        require(keyIndex != 0, errorMessage); // Equivalent to contains(map, key)
        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
    }
    struct UintToAddressMap {
        Map _inner;
    }
    function set(UintToAddressMap storage map, uint256 key, address value) internal returns (bool) {
        return _set(map._inner, bytes32(key), bytes32(uint256(uint160(value))));
    }
    function remove(UintToAddressMap storage map, uint256 key) internal returns (bool) {
        return _remove(map._inner, bytes32(key));
    }
    function contains(UintToAddressMap storage map, uint256 key) internal view returns (bool) {
        return _contains(map._inner, bytes32(key));
    }
    function length(UintToAddressMap storage map) internal view returns (uint256) {
        return _length(map._inner);
    }
    function at(UintToAddressMap storage map, uint256 index) internal view returns (uint256, address) {
        (bytes32 key, bytes32 value) = _at(map._inner, index);
        return (uint256(key), address(uint160(uint256(value))));
    }
    function tryGet(UintToAddressMap storage map, uint256 key) internal view returns (bool, address) {
        (bool success, bytes32 value) = _tryGet(map._inner, bytes32(key));
        return (success, address(uint160(uint256(value))));
    }
    function get(UintToAddressMap storage map, uint256 key) internal view returns (address) {
        return address(uint160(uint256(_get(map._inner, bytes32(key)))));
    }
    function get(UintToAddressMap storage map, uint256 key, string memory errorMessage) internal view returns (address) {
        return address(uint160(uint256(_get(map._inner, bytes32(key), errorMessage))));
    }
}
pragma solidity >=0.6.0 <0.8.0;
library Strings {
    
    function toString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        uint256 index = digits - 1;
        temp = value;
        while (temp != 0) {
            buffer[index--] = bytes1(uint8(48 + temp % 10));
            temp /= 10;
        }
        return string(buffer);
    }
}
pragma solidity >=0.6.0 <0.8.0;
contract ERC721 is Context, ERC165, IERC721, IERC721Metadata, IERC721Enumerable {
    using SafeMath for uint256;
    using Address for address;
    using EnumerableSet for EnumerableSet.UintSet;
    using EnumerableMap for EnumerableMap.UintToAddressMap;
    using Strings for uint256;
    bytes4 private constant _ERC721_RECEIVED = 0x150b7a02;
    mapping (address => EnumerableSet.UintSet) private _holderTokens;
    EnumerableMap.UintToAddressMap private _tokenOwners;
    mapping (uint256 => address) private _tokenApprovals;
    mapping (address => mapping (address => bool)) private _operatorApprovals;
    string private _name;
    string private _symbol;
    mapping (uint256 => string) private _tokenURIs;
    string private _baseURI;
    bytes4 private constant _INTERFACE_ID_ERC721 = 0x80ac58cd;
    bytes4 private constant _INTERFACE_ID_ERC721_METADATA = 0x5b5e139f;
    bytes4 private constant _INTERFACE_ID_ERC721_ENUMERABLE = 0x780e9d63;
    constructor (string memory name_, string memory symbol_) public {
        _name = name_;
        _symbol = symbol_;
        _registerInterface(_INTERFACE_ID_ERC721);
        _registerInterface(_INTERFACE_ID_ERC721_METADATA);
        _registerInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
    }
    function balanceOf(address owner) public view virtual override returns (uint256) {
        require(owner != address(0), "ERC721: balance query for the zero address");
        return _holderTokens[owner].length();
    }
    function ownerOf(uint256 tokenId) public view virtual override returns (address) {
        return _tokenOwners.get(tokenId, "ERC721: owner query for nonexistent token");
    }
    function name() public view virtual override returns (string memory) {
        return _name;
    }
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }
    function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
        require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");

        string memory _tokenURI = _tokenURIs[tokenId];
        string memory base = baseURI();

        // If there is no base URI, return the token URI.
        if (bytes(base).length == 0) {
            return _tokenURI;
        }
        // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
        if (bytes(_tokenURI).length > 0) {
            return string(abi.encodePacked(base, _tokenURI));
        }
        // If there is a baseURI but no tokenURI, concatenate the tokenID to the baseURI.
        return string(abi.encodePacked(base, tokenId.toString()));
    }
    function baseURI() internal view virtual returns (string memory) {
        return _baseURI;
    }
    function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
        return _holderTokens[owner].at(index);
    }
    function totalSupply() public view virtual override returns (uint256) {
        // _tokenOwners are indexed by tokenIds, so .length() returns the number of tokenIds
        return _tokenOwners.length();
    }
    function tokenByIndex(uint256 index) public view virtual override returns (uint256) {
        (uint256 tokenId, ) = _tokenOwners.at(index);
        return tokenId;
    }
    function approve(address to, uint256 tokenId) public virtual override {
        address owner = ERC721.ownerOf(tokenId);
        require(to != owner, "ERC721: approval to current owner");

        require(_msgSender() == owner || ERC721.isApprovedForAll(owner, _msgSender()),
            "ERC721: approve caller is not owner nor approved for all"
        );

        _approve(to, tokenId);
    }
    function getApproved(uint256 tokenId) public view virtual override returns (address) {
        require(_exists(tokenId), "ERC721: approved query for nonexistent token");

        return _tokenApprovals[tokenId];
    }
    function setApprovalForAll(address operator, bool approved) public virtual override {
        require(operator != _msgSender(), "ERC721: approve to caller");

        _operatorApprovals[_msgSender()][operator] = approved;
        emit ApprovalForAll(_msgSender(), operator, approved);
    }
    function isApprovedForAll(address owner, address operator) public view virtual override returns (bool) {
        return _operatorApprovals[owner][operator];
    }
    function transferFrom(address from, address to, uint256 tokenId) public virtual override {
        //solhint-disable-next-line max-line-length
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");

        _transfer(from, to, tokenId);
    }
    function safeTransferFrom(address from, address to, uint256 tokenId) public virtual override {
        safeTransferFrom(from, to, tokenId, "");
    }
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public virtual override {
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
        _safeTransfer(from, to, tokenId, _data);
    }
    function _safeTransfer(address from, address to, uint256 tokenId, bytes memory _data) internal virtual {
        _transfer(from, to, tokenId);
        require(_checkOnERC721Received(from, to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
    }
    function _exists(uint256 tokenId) internal view virtual returns (bool) {
        return _tokenOwners.contains(tokenId);
    }
    function _isApprovedOrOwner(address spender, uint256 tokenId) internal view virtual returns (bool) {
        require(_exists(tokenId), "ERC721: operator query for nonexistent token");
        address owner = ERC721.ownerOf(tokenId);
        return (spender == owner || getApproved(tokenId) == spender || ERC721.isApprovedForAll(owner, spender));
    }
    function _safeMint(address to, uint256 tokenId) internal virtual {
        _safeMint(to, tokenId, "");
    }
    function _safeMint(address to, uint256 tokenId, bytes memory _data) internal virtual {
        _mint(to, tokenId);
        require(_checkOnERC721Received(address(0), to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
    }
    function _mint(address to, uint256 tokenId) internal virtual {
        require(to != address(0), "ERC721: mint to the zero address");
        require(!_exists(tokenId), "ERC721: token already minted");
        _beforeTokenTransfer(address(0), to, tokenId);
        _holderTokens[to].add(tokenId);
        _tokenOwners.set(tokenId, to);
        emit Transfer(address(0), to, tokenId);
    }
    function _burn(uint256 tokenId) internal virtual {
        address owner = ERC721.ownerOf(tokenId); 
        _beforeTokenTransfer(owner, address(0), tokenId);
        _approve(address(0), tokenId);
        if (bytes(_tokenURIs[tokenId]).length != 0) {
            delete _tokenURIs[tokenId];
        }
        _holderTokens[owner].remove(tokenId);
        _tokenOwners.remove(tokenId);
        emit Transfer(owner, address(0), tokenId);
    }
    function _transfer(address from, address to, uint256 tokenId) internal virtual {
        require(ERC721.ownerOf(tokenId) == from, "ERC721: transfer of token that is not own"); 
        require(to != address(0), "ERC721: transfer to the zero address");
        _beforeTokenTransfer(from, to, tokenId);
        _approve(address(0), tokenId);
        _holderTokens[from].remove(tokenId);
        _holderTokens[to].add(tokenId);
        _tokenOwners.set(tokenId, to);
        emit Transfer(from, to, tokenId);
    }
    function _setTokenURI(uint256 tokenId, string memory _tokenURI) internal virtual {
        require(_exists(tokenId), "ERC721Metadata: URI set of nonexistent token");
        _tokenURIs[tokenId] = _tokenURI;
    }
    function _setBaseURI(string memory baseURI_) internal virtual {
        _baseURI = baseURI_;
    }
    function _checkOnERC721Received(address from, address to, uint256 tokenId, bytes memory _data)
        private returns (bool)
    {
        if (!to.isContract()) {
            return true;
        }
        bytes memory returndata = to.functionCall(abi.encodeWithSelector(
            IERC721Receiver(to).onERC721Received.selector,
            _msgSender(),
            from,
            tokenId,
            _data
        ), "ERC721: transfer to non ERC721Receiver implementer");
        bytes4 retval = abi.decode(returndata, (bytes4));
        return (retval == _ERC721_RECEIVED);
    }
    function _approve(address to, uint256 tokenId) internal virtual {
        _tokenApprovals[tokenId] = to;
        emit Approval(ERC721.ownerOf(tokenId), to, tokenId); // internal owner
    }
    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal virtual { }
}




pragma solidity >=0.6.0 <0.8.0;
abstract contract Ownable is Context {
    address private _owner;

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

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

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

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the 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 {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}



pragma solidity ^0.7.0;
contract MaestroBannersNFT is ERC721, Ownable {    
    using SafeMath for uint256;
    uint256 public constant MAX_NFTS = 9999;  //10000 when including tokenID = 0
    uint256 public NFTCost = 40000000000000000; // 0.05 ETH
    uint256 public NFTCost3_Discount = 36000000000000000; // 0.045 ETH (if ordering 3 or 4 banners)
    uint256 public NFTCost5_Discount = 34000000000000000; // 0.043 ETH (if ordering 5, 6, 7, 8 or 9 banners)
    uint256 public NFTCost10_Discount = 32000000000000000; // 0.040 ETH (if ordering 10 banners)
    uint public constant maxNFTPurchase = 10;    
    uint256 public constant MAX_PRESALE = 2999; //Tokens of other contract
    bool public SALE_ACTIVE = false;
    bool public PRESALE_ACTIVE = false;
    uint256 public PRESALE_SUPPLY = 2999;
    address ownerAcct = 0x24A6CA874f5ed2c61BbfC8286343d32437a7565C;     
    address MaestroPupsAddress = 0x874Dd3F2317bEaBb4f069b42B539010c54B195eC;
    uint256[] public nftPreSaleSupply = new uint256[](PRESALE_SUPPLY);
   
   
   
    function preSaleMintNFTBulk(address toAccount, uint256[] memory tokenIds) public {
        require (PRESALE_ACTIVE, "The PRE-SALE is CLOSED");
        require (totalSupply().add(tokenIds.length) <= PRESALE_SUPPLY, "The number of NFTs claimed exceeds to alloted supply of PRE-SALE NFTs.");
        uint i = 0;
        for (i = 0; i < tokenIds.length; i++) {
            presaleMintNFT(toAccount, tokenIds[i]);
        }       
    }
    function presaleMintNFT(address toAccount, uint256 tokenId) public {
        require (PRESALE_ACTIVE, "The PRE-SALE is CLOSED");
        require (IERC721(MaestroPupsAddress).ownerOf(tokenId) == toAccount, "This account does not own the token ID of the NFT they are claiming.");   
        require (totalSupply().add(1) <= PRESALE_SUPPLY, "The number of NFTs claimed exceeds to alloted supply of PRE-SALE NFTs.");
        require ((nftPreSaleSupply[tokenId] != 1), "This MaestroPup Token has already been claimed");
        
        uint256 mindex = totalSupply();
        if (totalSupply() <= PRESALE_SUPPLY) {
            _mint(toAccount, mindex);
            nftPreSaleSupply[tokenId] = 1;
        }        
        if (mindex >= PRESALE_SUPPLY) {
            PRESALE_ACTIVE = false;
        }
    }    
    function mintNFT(uint numberOfTokens) public payable {
        uint256 price = NFTCost;
        if (numberOfTokens >= 3 && numberOfTokens < 5) {
            price = NFTCost3_Discount;
        }
        else if (numberOfTokens >= 5 &&  numberOfTokens < 10) {
            price = NFTCost5_Discount;
        }
        else if (numberOfTokens >= 10) {
            price = NFTCost10_Discount;
        }

        require(SALE_ACTIVE, "Sale must be active to mint an NFT");
        require(numberOfTokens > 0 && numberOfTokens <= maxNFTPurchase, "Can only mint 10 tokens at a time");
        require(totalSupply().add(numberOfTokens) <= MAX_NFTS, "Purchase would exceed max supply of NFTs");
        require(msg.value >= price.mul(numberOfTokens), "Ether value sent is not correct");
        
        for(uint i = 0; i < numberOfTokens; i++) {
            uint mintIndex = totalSupply();
            if (totalSupply() < MAX_NFTS) {
                _safeMint(msg.sender, mintIndex);
            }
        }

        if (totalSupply() >= MAX_NFTS) {
            SALE_ACTIVE = false;
        }

    }    
    function AllPreSaleTokensClaimed() external view returns(uint256[] memory) {
        return nftPreSaleSupply;
    }
    function PresaleTokenClaimed(uint256 tokenId) public view returns (bool) {
        return (nftPreSaleSupply[tokenId] > 0);
    }
    uint public nftReserve = 75;    
    
    constructor() ERC721("MaestroBanners", "MBAN") {}
    
    function withdraw() public onlyOwner {
        uint balance = address(this).balance;
        msg.sender.transfer(balance);    
    }  
    function GetPresaleState() public view returns (bool) { return PRESALE_ACTIVE; }    
    function GetSaleState() public view returns (bool) { return SALE_ACTIVE; }
    function tokensOfOwner(address _owner) external view returns(uint256[] memory ) { 
        uint256 tokenCount = balanceOf(_owner);
        if (tokenCount == 0) {
            return new uint256[](0);
        } else {
            uint256[] memory result = new uint256[](tokenCount);
            uint256 index;
            for (index = 0; index < tokenCount; index++) {
                result[index] = tokenOfOwnerByIndex(_owner, index);
            }
            return result;
        }
    }

    function GetNFTCosts() public view returns (uint256[] memory) {
        uint256[] memory r = new uint256[](4);
        r[0] = NFTCost;
        r[1] = NFTCost3_Discount;
        r[2] = NFTCost5_Discount;
        r[3] =  NFTCost10_Discount;
        return r;
    }

    function setNFTCost(uint256 nft1Gwei, uint256 nft3Gwei, uint256 nft5Gwei, uint256 nft10Gwei) public onlyOwner {
        NFTCost = nft1Gwei;
        NFTCost3_Discount= nft3Gwei;
        NFTCost5_Discount= nft5Gwei;
        NFTCost10_Discount= nft10Gwei;
    }
    address NULL_ADDRESS;
    function ownerMintTokenToAddress(address toAccount, uint256 tokenId) public onlyOwner {
        require(ownerOf(tokenId) == NULL_ADDRESS, "This Token Id has already been claimed");
        require(ownerOf(tokenId) == address(0), "2-This Token Id has already been claimed");
        require(tokenId <= MAX_NFTS, "Token ID exceeds maximum amount in the collection.");
        require(tokenId >= 0, "Token ID cannot be less than 0.");
        _mint(toAccount, tokenId);
    }
    function reserveNFTs(address _to, uint256 _reserveAmount) public onlyOwner {         
        uint supply = totalSupply();
        require(totalSupply().add(_reserveAmount) <= MAX_NFTS, "The requested amount to reserve exceeds the total NFT supply");

        for (uint i = 0; i < _reserveAmount; i++) {
            _safeMint(_to, supply + i);
        }
        nftReserve = nftReserve.sub(_reserveAmount);        
    }
    function changeMaestroPupContract(address _contract) public onlyOwner { MaestroPupsAddress = _contract; }
    function setBaseURI(string memory uri) external onlyOwner { _setBaseURI(uri); }
    function flipSaleState() public onlyOwner { SALE_ACTIVE = !SALE_ACTIVE; }
    function flipPreSaleState() public onlyOwner { PRESALE_ACTIVE = !PRESALE_ACTIVE; }  
    
}