function mint(address to, uint256 value) public onlyOwner returns (bool) {
        require(block.timestamp >= mintBegintime);
        require(value > 0);

        if (mintPerday > 0) {
            uint256 currentMax = (block.timestamp - mintBegintime).mul(mintPerday) / (3600 * 24);
            uint256 leave = currentMax.sub(mintTotal);
            require(leave >= value);
        }

        mintTotal = mintTotal.add(value);
        if (mintMax > 0 && mintTotal > mintMax) {
            revert();
        }

        _mint(to, value);
        emit Mint(to, value);
        return true;
    }