time.js

let timeHtmlElement = document.getElementById("clock");

//example time pattern
//"%A, %B %Y | %H:%M:%S"

var _state = {
    patternLoaded: false,
    currentPattern: ""
}

const timeMeridianModes = {
    AM_PM_UPPERCASE: 0,
    AM_PM_LOWERCASE: 1,
};

const constStrings = {
    AM_UPPERCASE: "AM",
    AM_LOWERCASE: "am",
    PM_UPPERCASE: "PM",
    PM_LOWERCASE: "pm",
};


var SavedTimeOptions = {};

var TimeUtils = {
    currentTime: new Date(),
    /**
     * @return {string}
     */
    A: function () {
        return this.currentTime.toLocaleString("en-us",
            {weekday: "short"});
    },
    a: function () {
        return this.currentTime.toLocaleString("en-us",
            {weekday: "long"});
    },
    b: function () {
        return this.currentTime.toLocaleString("en-us",
            {month: "short"});
    },
    /**
     * @return {string}
     */
    B: function () {
        return this.currentTime.toLocaleString("en-us",
            {month: "long"});
    },
    c: function () {
        return `${window["TimeUtils"]["a"]()} ${window["TimeUtils"]["b"]()} ${window["TimeUtils"]["d"]()} ${window["TimeUtils"]["T"]()} ${window["TimeUtils"]["G"]()}`;
    },
    //Year divided by 100 and truncated to integer (00-99)
    /**
     * @return {number}
     */
    C: function () {
        return parseInt(this.currentTime.getFullYear() / 100);
    },
    //Day of the month, zero-padded (01-31)
    d: function () {
        return this.currentTime.toLocaleString("en-us",
            {day: "2-digit"});

    },
    //	Short MM/DD/YY date, equivalent to %m/%d/%y
    /**
     * @return {string}
     */
    D: function () {
        return `${this.currentTime.getMonth()}/${this.currentTime.getDate()}/${this.currentTime.getFullYear()}`;
    },
    //Day of the month, space-padded ( 1-31)
    e: function () {
        return this.currentTime.getDate();
    },
    //	Short YYYY-MM-DD date, equivalent to %Y-%m-%d
    /**
     * @return {string}
     */
    F: function () {
        return `${this.currentTime.getFullYear()}-${this.currentTime.getMonth()}-${this.currentTime.getDate()}`;

    },
    //day of the month postfix (th, nd, rd, etc)
    f: function () {
        return dayPostFixNew(this.currentTime.getDate());

    },
    //Week-based year, last two digits (00-99)
    g: function () {
        return this.currentTime.getFullYear();
    },
    //	Week-based year
    /**
     * @return {string}
     */
    G: function () {
        return this.currentTime.toLocaleString("en-us",
            {year: "numeric"});
    },

    //Abbreviated month name * (same as %b)
    h: function () {
        return this.currentTime.toLocaleString("en-us",
            {month: "short"});
    },
    //Hour in 24h format (00-23)
    /**
     * @return {number}
     */
    H: function () {
        return this.currentTime.getHours();
    },
    //Hour in 12h format (01-12)
    /**
     * @return {number}
     */
    I: function () {
        return convertTo12HRFormat(this.currentTime.getHours());
    },
    //Day of the year (001-366)
    j: function () {
        return this.currentTime.getDate();
    },
    //Month as a decimal number (01-12)
    m: function () {
        return this.currentTime.getMonth();
    },
    //Minute (00-59)
    /**
     * @return {number}
     */
    M: function () {
        return digitCorrectionNew(this.currentTime.getMinutes());
    },
    //AM or PM designation
    //works
    p: function () {
        return resolveAmPmNew(this.currentTime.getHours(), timeMeridianModes.AM_PM_UPPERCASE);
    },
    //12-hour clock time *
    r: function () {
        return `${this.currentTime.getHours()}:${this.currentTime.getMinutes()}:${this.currentTime.getSeconds()} ${resolveAmPmNew(this.currentTime.getHours(), timeMeridianModes.AM_PM_LOWERCASE)}`
    },
    /**
     * @return {string}
     */
    R: function () {
        let minNow = this.currentTime.getMinutes();
        let hrsNow = this.currentTime.getHours(2);
        return `${hrsNow}:${minNow}`;
    },
    //Second (00-61)
    /**
     * @return {number}
     */
    S: function () {
        return digitCorrectionNew(this.currentTime.getSeconds());
    },
    //ISO 8601 time format (HH:MM:SS), equivalent to %H:%M:%S
    /**
     * @return {string}
     */
    T: function () {
        let minNow = this.currentTime.getMinutes();
        let hrsNow = this.currentTime.getHours();
        let secNow = this.currentTime.getSeconds();
        return `${hrsNow}:${minNow}:${secNow}`;
    },
    //ISO 8601 weekday as number with Monday as 1 (1-7)
    u: function () {
        return this.currentTime.getDay();
    },
    //Week number with the first Sunday as the first day of week one (00-53)
    U: function () {
        //not implemented
    },
    //ISO 8601 week number (01-53)
    V: function () {
        //not implemented
    },
    //Weekday as a decimal number with Sunday as 0 (0-6)
    w: function () {
        return this.currentTime.getDay();
    },
    //Week number with the first Monday as the first day of week one (00-53)
    W: function () {
        //not implemented
    },
    //Date representation
    x: function () {
        return window["TimeUtils"]["D"]();
    },
    //Time representation
    /**
     * @return {string}
     */
    X: function () {
        return `${this.currentTime.getMinutes()}:${this.currentTime.getHours()}:${this.getSeconds()}`;
    },
    //Year, last two digits (00-99)
    y: function () {
        return this.currentTime.toLocaleString("en-us", {"year": "2-digit"});
    },
    //Year
    /**
     * @return {number}
     */
    Y: function () {
        return this.currentTime.getFullYear();
    },
    //ISO 8601 offset from UTC in timezone (1 minute=1, 1 hour=100)
    // If timezone cannot be determined, no characters
    z: function () {
        return this.currentTime.getTimezoneOffset()
    },
    //Timezone name or abbreviation *
    // If timezone cannot be determined, no characters
    /**
     * @return {string}
     */
    Z: function () {
        return Intl.DateTimeFormat().resolvedOptions().timeZone;
    },

};

function parseTimePattern() {
    let finalTimeString;
    if (!_state.patternLoaded) {
        let testTimePattern = userSettings.clockPatternStr;
        finalTimeString = testTimePattern;
        if (testTimePattern !== "" && testTimePattern !== undefined) {
            for (let c = 0; c < testTimePattern.length - 1; c++) {
                if (testTimePattern[c] === "%" &&
                    (testTimePattern.charCodeAt(c + 1) >= 65 &&
                        testTimePattern.charCodeAt(c + 1) <= 122)) {
                    SavedTimeOptions[testTimePattern[c + 1]] = true;
                }
            }
            _state.patternLoaded = true;
            _state.currentPattern = finalTimeString;
            finalTimeString = getActualTime();
        }
    } else {
        finalTimeString = getActualTime();
    }
    return finalTimeString;
}


function getActualTime() {
    let timeString = _state.currentPattern;
    TimeUtils.currentTime = new Date();
    for (let setOption in SavedTimeOptions) {
        if (SavedTimeOptions[setOption] === true) {
            timeString = timeString.replace("%" + setOption,
                TimeUtils[setOption]());
        }
    }
    return timeString;
}

function convertTo12HRFormat(hrs) {
    if (hrs === 0) {
        hrs = 12;
    } else if (hrs === 12) {
    } else {
        hrs -= 12;
    }
    return hrs;
}

function resolveAmPmNew(hrsNow, caseMode) {
    let amPmString;
    hrsNow = convertTo12HRFormat(hrsNow);
    if (hrsNow === 0) {
        amPmString = timeMeridianModes.AM_PM_UPPERCASE ? constStrings.AM_UPPERCASE : constStrings.AM_LOWERCASE
    } else if (hrsNow < 12) {
        amPmString = caseMode === timeMeridianModes.AM_PM_UPPERCASE ? constStrings.AM_UPPERCASE : constStrings.AM_LOWERCASE;
    } else if (hrsNow === 12) {
        amPmString = timeMeridianModes.AM_PM_UPPERCASE ? constStrings.PM_UPPERCASE : constStrings.PM_LOWERCASE;
    } else {
        amPmString = timeMeridianModes.AM_PM_UPPERCASE ? constStrings.PM_UPPERCASE : constStrings.PM_LOWERCASE;
    }
    return amPmString;
}

function digitCorrectionNew(c) {
    return c < 10 ? c = "0" + c : c;
}

function dayPostFixNew(day) {
    let dayPostFix = "";
    if (day < 4) {
        switch (day) {
            case 1:
                dayPostFix = "st";
                break;
            case 2:
                dayPostFix = "nd";
                break;
            default:
                dayPostFix = "rd";
                break;
        }
    } else if (day > 20) {
        if (!(day % 11))
            dayPostFix = "nd";
        else if (day === 23 || day === 33)
            dayPostFix = "rd";
        else if (day === 21 || day === 31)
            dayPostFix = "st";
        else
            dayPostFix = "th";
    } else {
        dayPostFix = "th";
    }
    return dayPostFix;
}

function initTimeScript(mode) {
    timeHtmlElement.innerHTML = "Today is " + parseTimePattern();
    let t = setTimeout(function () {
        initTimeScript()
    }, 500);
}