pragma solidity ^0.6.12;
import "./String.sol";

library DateTime {
    using String for string;

    struct _DateTime {
        uint16 year;
        uint8 month;
        uint8 day;
        uint8 hour;
        uint8 minute;
        uint8 second;
        uint8 weekday;
    }

    uint256 constant DAY_IN_SECONDS = 86400;
    uint256 constant YEAR_IN_SECONDS = 31536000;
    uint256 constant LEAP_YEAR_IN_SECONDS = 31622400;

    uint256 constant HOUR_IN_SECONDS = 3600;
    uint256 constant MINUTE_IN_SECONDS = 60;

    uint16 constant ORIGIN_YEAR = 1970;

    function isLeapYear(uint16 year) internal pure returns (bool) {
        if (year % 4 != 0) {
            return false;
        }
        if (year % 100 != 0) {
            return true;
        }
        if (year % 400 != 0) {
            return false;
        }
        return true;
    }

    function leapYearsBefore(uint256 year) internal pure returns (uint256) {
        year -= 1;
        return year / 4 - year / 100 + year / 400;
    }

    function getDaysInMonth(uint8 month, uint16 year)
        internal
        pure
        returns (uint8)
    {
        if (
            month == 1 ||
            month == 3 ||
            month == 5 ||
            month == 7 ||
            month == 8 ||
            month == 10 ||
            month == 12
        ) {
            return 31;
        } else if (month == 4 || month == 6 || month == 9 || month == 11) {
            return 30;
        } else if (isLeapYear(year)) {
            return 29;
        } else {
            return 28;
        }
    }

    function parseTimestamp(uint256 timestamp)
        internal
        pure
        returns (_DateTime memory dt)
    {
        uint256 secondsAccountedFor = 0;
        uint256 buf;
        uint8 i;

        // Year
        dt.year = getYear(timestamp);
        buf = leapYearsBefore(dt.year) - leapYearsBefore(ORIGIN_YEAR);

        secondsAccountedFor += LEAP_YEAR_IN_SECONDS * buf;
        secondsAccountedFor += YEAR_IN_SECONDS * (dt.year - ORIGIN_YEAR - buf);

        // Month
        uint256 secondsInMonth;
        for (i = 1; i <= 12; i++) {
            secondsInMonth = DAY_IN_SECONDS * getDaysInMonth(i, dt.year);
            if (secondsInMonth + secondsAccountedFor > timestamp) {
                dt.month = i;
                break;
            }
            secondsAccountedFor += secondsInMonth;
        }

        // Day
        for (i = 1; i <= getDaysInMonth(dt.month, dt.year); i++) {
            if (DAY_IN_SECONDS + secondsAccountedFor > timestamp) {
                dt.day = i;
                break;
            }
            secondsAccountedFor += DAY_IN_SECONDS;
        }

        // Hour
        dt.hour = getHour(timestamp);

        // Minute
        dt.minute = getMinute(timestamp);

        // Second
        dt.second = getSecond(timestamp);

        // Day of week.
        dt.weekday = getWeekday(timestamp);
    }

    function getYear(uint256 timestamp) internal pure returns (uint16) {
        uint256 secondsAccountedFor = 0;
        uint16 year;
        uint256 numLeapYears;

        // Year
        year = uint16(ORIGIN_YEAR + timestamp / YEAR_IN_SECONDS);
        numLeapYears = leapYearsBefore(year) - leapYearsBefore(ORIGIN_YEAR);

        secondsAccountedFor += LEAP_YEAR_IN_SECONDS * numLeapYears;
        secondsAccountedFor +=
            YEAR_IN_SECONDS *
            (year - ORIGIN_YEAR - numLeapYears);

        while (secondsAccountedFor > timestamp) {
            if (isLeapYear(uint16(year - 1))) {
                secondsAccountedFor -= LEAP_YEAR_IN_SECONDS;
            } else {
                secondsAccountedFor -= YEAR_IN_SECONDS;
            }
            year -= 1;
        }
        return year;
    }

    function getMonth(uint256 timestamp) internal pure returns (uint8) {
        return parseTimestamp(timestamp).month;
    }

    function getDay(uint256 timestamp) internal pure returns (uint8) {
        return parseTimestamp(timestamp).day;
    }

    function getHour(uint256 timestamp) internal pure returns (uint8) {
        return uint8((timestamp / 60 / 60) % 24);
    }

    function getMinute(uint256 timestamp) internal pure returns (uint8) {
        return uint8((timestamp / 60) % 60);
    }

    function getSecond(uint256 timestamp) internal pure returns (uint8) {
        return uint8(timestamp % 60);
    }

    function getWeekday(uint256 timestamp) internal pure returns (uint8) {
        return uint8((timestamp / DAY_IN_SECONDS + 4) % 7);
    }

    function convertTimestampToDateTime(uint256 _timestamp)
        internal
        pure
        returns (string memory)
    {
        string memory prefix = "0";
        string memory year = ToString(getYear(_timestamp));
        string memory month = getMonth(_timestamp) < 10
            ? prefix.append(ToString(getMonth(_timestamp)))
            : ToString(getMonth(_timestamp));
        string memory day = getDay(_timestamp) < 10
            ? prefix.append(ToString(getDay(_timestamp)))
            : ToString(getDay(_timestamp));
        string memory hour = getHour(_timestamp) < 10
            ? prefix.append(ToString(getHour(_timestamp)))
            : ToString(getHour(_timestamp));
        string memory minute = getMinute(_timestamp) < 10
            ? prefix.append(ToString(getMinute(_timestamp)))
            : ToString(getMinute(_timestamp));
        string memory second = getSecond(_timestamp) < 10
            ? prefix.append(ToString(getSecond(_timestamp)))
            : ToString(getSecond(_timestamp));
        string memory date = year.append("-").append(month).append("-").append(
            day
        );
        string memory time = hour.append(":").append(minute).append(":").append(
            second
        );
        return date.append("T").append(time);
    }

    function ToString(uint16 _i) internal pure returns (string memory) {
        if (_i == 0) {
            return "0";
        }
        uint256 j = _i;
        uint256 len;
        while (j != 0) {
            len++;
            j /= 10;
        }
        bytes memory bstr = new bytes(len);
        uint256 k = len;
        while (_i != 0) {
            k = k - 1;
            uint8 temp = (48 + uint8(_i - (_i / 10) * 10));
            bytes1 b1 = bytes1(temp);
            bstr[k] = b1;
            _i /= 10;
        }
        return string(bstr);
    }
}