contract ChainHeros is ERC721Enumerable, Ownable {
    using SafeMath for uint256;
    using Address for address;
    using Strings for uint256;

    uint256 public constant NFT_PRICE = 80000000000000000; // 0.08 ETH
    uint public constant MAX_NFT_PURCHASE = 50;
    uint256 public MAX_SUPPLY = 10000;
    bool public saleIsActive = false;

    string private _baseURIExtended;
    mapping(uint256 => string) _tokenURIs;
    mapping(address => bool) minted;
    mapping(address => uint256) purchased;

    modifier mintOnlyOnce() {
        require(!minted[_msgSender()], 'Can only mint once');
        minted[_msgSender()] = true;
        _;
    }

    constructor() ERC721('ChainHeros', 'CHEROS') {}

    function flipSaleState() public onlyOwner {
        saleIsActive = !saleIsActive;
    }

    function withdraw() public onlyOwner {
        uint256 balance = address(this).balance;
        payable(msg.sender).transfer(balance);
    }


    function mint(uint numberOfTokens) public payable {
        require(purchased[msg.sender].add(numberOfTokens) <= MAX_NFT_PURCHASE, 'Can only mint up to 50 per address');
        require(saleIsActive, 'Sale is not active at the moment');
        require(numberOfTokens > 0, "Number of tokens can not be less than or equal to 0");
        require(totalSupply().add(numberOfTokens) <= MAX_SUPPLY, "Purchase would exceed max supply of Muds");
        require(numberOfTokens <= MAX_NFT_PURCHASE,"Can only mint up to 50 per purchase");
        require(NFT_PRICE.mul(numberOfTokens) == msg.value, "Sent ether value is incorrect");
        purchased[msg.sender] = purchased[msg.sender].add(numberOfTokens);
        for (uint i = 0; i < numberOfTokens; i++) {
            _safeMint(msg.sender, totalSupply());
        }
    }

    function mintForFree() public mintOnlyOnce {
        require(saleIsActive, 'Sale is not active at the moment');
        require(totalSupply().add(1) <= MAX_SUPPLY, 'Purchase would exceed max supply of Muds');
        _safeMint(msg.sender, totalSupply());
    }

    function _baseURI() internal view virtual override returns (string memory) {
        return _baseURIExtended;
    }

    // Sets base URI for all tokens, only able to be called by contract owner
    function setBaseURI(string memory baseURI_) external onlyOwner {
        _baseURIExtended = baseURI_;
    }

    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 setBaseURI(string memory baseURI_) external onlyOwner {
    _baseURIExtended = baseURI_;
}

// Sets base URI for all tokens, only able to be called by contract owner