date.ts

// ----- Imports ----- //

import { Option, some, none } from '@guardian/types/option';


// ----- Setup ----- //

const days = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];
const months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];


// ----- Functions ----- //

function isToday(date: Date): boolean {
    const today = new Date();
    return (date.toDateString() === today.toDateString());
}

function isWithin24Hours(date: Date): boolean {
    const today = new Date();
    return (date.valueOf() > (today.valueOf() - (24 * 60 * 60 * 1000)));
}

function isWithinPastWeek(date: Date): boolean {
    const daysAgo = new Date().valueOf() - (7 * 24 * 60 * 60 * 1000);
    return date.valueOf() >= daysAgo;
}

function isWithinPastYear(date: Date): boolean {
    const weeksAgo = new Date().valueOf() - (52 * 7 * 24 * 60 * 60 * 1000);
    return date.valueOf() >= weeksAgo;
}

function isValidDate(date: Date): boolean {
    if (Object.prototype.toString.call(date) !== '[object Date]') {
        return false;
    }
    return !isNaN(date.getTime());
}

function makeRelativeDate(date: Date): string | null {
    const then: Date = new Date(date);
    const now: Date = new Date();

    if (!isValidDate(then)) {
        return null;
    }

    const delta: number = parseInt(`${(now.valueOf() - then.valueOf()) / 1000}`, 10);

    if (delta < 0) {
        return null;
    } else if (delta < 55) {
        return `${delta}s`;
    } else if (delta < (55 * 60)) {
        const minutesAgo = Math.round(delta / 60);

        if (minutesAgo === 1) {
            return 'Now';
        } else {
            return `${minutesAgo}m ago`;
        }
    } else if (isToday(then) || isWithin24Hours(then)) {
        const hoursAgo = Math.round(delta / 3600);
        return `${hoursAgo}h ago`;
    } else if (isWithinPastWeek(then)) {
        const daysAgo = Math.round(delta / 3600 / 24);
        return `${daysAgo}d ago`;
    } else if (isWithinPastYear(then)) {
        const weeksAgo = Math.round(delta / 3600 / 24 / 7);
        return `${weeksAgo}w ago`;
    } else {
        const yearsAgo = Math.round(delta / 3600 / 24 / 7 / 52);
        return `${yearsAgo}y ago`;
    }
}

const day = (date: Date): string =>
    days[date.getUTCDay()];

const month = (date: Date): string =>
    months[date.getUTCMonth()];

const padZero = (n: number): string =>
    n < 10 ? `0${n}` : n.toString();

const time = (date: Date): string =>
    `${padZero(date.getUTCHours())}.${padZero(date.getUTCMinutes())}`;

const format = (date: Date): string =>
    `${day(date)} ${date.getUTCDate()} ${month(date)} ${date.getUTCFullYear()} ${time(date)} UTC`;

function fromString(date: string): Option<Date> {
    try {
        return some(new Date(date));
    } catch(e) {
        return none;
    }
}


// ----- Exports ----- //

export {
    makeRelativeDate,
    format as formatDate,
    isValidDate,
    fromString,
}