script.js

document.getElementById("submitButton").addEventListener("click", function() {
    try {
        const rawData = document.getElementById("userInput").value;
        const ics_events = genorateEvents(rawData);
        if (ics_events === "") {
            alert("No valid course data found. Please check your input.");
            return;
        }
        const ics_file = wrapEvents(ics_events);
        genorateDownloadLink(ics_file);
    } catch (error) {
        alert("An error occured! Check your input and try again.");
        console.error(error)
    }
});

function genorateEvents(rawData) {
    const lines = rawData.split('\n');
    const events = [];
    let currentBlock = [];

    for (const line of lines) {
        if (line.trim() === '' && currentBlock.length === 0) {
            continue;
        }

        currentBlock.push(line);

        if (line.includes('CRN:')) {
            const event = parseScheduleBlock(currentBlock.join('\n'));
            if (event) {
                events.push(formatEvent(event));
            }
            currentBlock = [];
        }
    }

    return events.join('');
}

function parseScheduleBlock(blockText) {
    const titleLine = blockText.split('\n').find(line => line.includes('Class Begin:')) || '';
    const markdownTitleMatch = titleLine.match(/^\[([^\]]+)\]/);
    const title = markdownTitleMatch ? markdownTitleMatch[1].trim() : titleLine.split('|')[0].trim();

    const waitlistMatch = blockText.match(/Waitlist Position:\s*(\d+)/i);
    if (waitlistMatch && parseInt(waitlistMatch[1], 10) > 0) {
        return null;
    }

    const timeLine = blockText.split('\n').find(line => line.includes('Type: Class') && line.includes(' - ')) || '';
    if (timeLine.includes('TBA')) {
        return null;
    }

    const scheduleLine = blockText.split('\n').find(line => line.includes('--') && /Monday|Tuesday|Wednesday|Thursday|Friday|Saturday|Sunday/.test(line)) || '';
    const scheduleMatch = scheduleLine.match(/([0-9]{2}\/\d{2}\/\d{4})\s*--\s*([0-9]{2}\/\d{2}\/\d{4})\s+(.+)$/);
    if (!scheduleMatch) {
        return null;
    }

    const timeMatch = timeLine.match(/(\d{1,2}:\d{2}\s*[AP]M)\s*-\s*(\d{1,2}:\d{2}\s*[AP]M)/i);
    if (!timeMatch) {
        return null;
    }

    const locationMatch = timeLine.match(/Location:\s*(.+)$/i);
    const location = locationMatch ? locationMatch[1].trim() : '';

    const instructorLine = blockText.split('\n').find(line => line.startsWith('Instructor:')) || '';
    const instructor = instructorLine
        .replace(/^Instructor:\s*/i, '')
        .replace(/\[([^\]]+)\]\([^)]+\)/g, '$1')
        .replace(/\s*\([^)]+\)\s*$/g, '')
        .trim();

    const dayMap = {
        monday: 'M',
        tuesday: 'T',
        wednesday: 'W',
        thursday: 'R',
        friday: 'F',
        saturday: 'S',
        sunday: 'U'
    };
    const days = scheduleMatch[3]
        .split(',')
        .map(day => dayMap[day.trim().toLowerCase()])
        .filter(Boolean);

    if (days.length === 0) {
        const legacyDayMatch = blockText.match(/[MTWRFSU]+/g);
        if (legacyDayMatch) {
            days.push(...legacyDayMatch[0].split(''));
        }
    }

    return {
        title: title,
        startTime: timeMatch[1].trim(),
        endTime: timeMatch[2].trim(),
        days: days,
        location: location,
        startDate: scheduleMatch[1].trim(),
        endDate: scheduleMatch[2].trim(),
        instructor: instructor
    };
}

function firstOccurrenceOnOrAfter(dateStr, days) {
    const dayIndices = {
        U: 0,
        M: 1,
        T: 2,
        W: 3,
        R: 4,
        F: 5,
        S: 6
    };
    const [month, day, year] = dateStr.split('/').map(Number);
    const date = new Date(Date.UTC(year, month - 1, day));
    for (let i = 0; i < 7; i++) {
        const letterForDow = Object.keys(dayIndices).find(letter => dayIndices[letter] === date.getUTCDay());
        if (days.includes(letterForDow)) break;
        date.setUTCDate(date.getUTCDate() + 1);
    }
    const adjMonth = String(date.getUTCMonth() + 1).padStart(2, '0');
    const adjDay = String(date.getUTCDate()).padStart(2, '0');
    return `${adjMonth}/${adjDay}/${date.getUTCFullYear()}`;
}

function formatEvent(event) {
    const uid = generateUID()
    const title = event.title;
    const location = event.location;
    const startDate = firstOccurrenceOnOrAfter(event.startDate, event.days);
    const endDate = formatDate(event.endDate, event.endTime, true);
    const startTime = formatDate(startDate, event.startTime, false);
    const endTime = formatDate(startDate, event.endTime, false);
    const byDay = event.days.map(d => ({
        M: 'MO',
        T: 'TU',
        W: 'WE',
        R: 'TH',
        F: 'FR',
        S: 'SA',
        U: 'SU'
    } [d])).join(',');
    const instructor = event.instructor;

    const icsContent = `
  BEGIN:VEVENT
  UID:${uid}
  DTSTAMP:20240101T000000Z
  SUMMARY:${title}
  DESCRIPTION:Scheduled Class with ${instructor}
  LOCATION:${location}
  DTSTART;TZID=America/New_York:${startTime}
  DTEND;TZID=America/New_York:${endTime}
  RRULE:FREQ=WEEKLY;BYDAY=${byDay};UNTIL=${endDate}Z
  STATUS:CONFIRMED
  SEQUENCE:0
  TRANSP:OPAQUE
  BEGIN:VALARM
  TRIGGER:-PT15M
  ACTION:DISPLAY
  END:VALARM
  END:VEVENT`;
    return icsContent;
}

function getEasternOffsetMinutes(utcGuess) {
    const dtf = new Intl.DateTimeFormat('en-US', {
        timeZone: 'America/New_York',
        hourCycle: 'h23',
        year: 'numeric',
        month: '2-digit',
        day: '2-digit',
        hour: '2-digit',
        minute: '2-digit',
        second: '2-digit'
    });
    const parts = dtf.formatToParts(utcGuess).reduce((acc, p) => {
        if (p.type !== 'literal') acc[p.type] = p.value;
        return acc;
    }, {});
    const asIfUTC = Date.UTC(parts.year, parts.month - 1, parts.day, parts.hour, parts.minute, parts.second);
    return (asIfUTC - utcGuess.getTime()) / 60000;
}

function formatDate(date, time, UTC) {
    let year;
    let month;
    let day;

    if (date.includes('/')) {
        const dateParts = date.split('/');
        month = dateParts[0].padStart(2, '0');
        day = dateParts[1].padStart(2, '0');
        year = dateParts[2];
    } else {
        const monthMap = {
            Jan: '01',
            Feb: '02',
            Mar: '03',
            Apr: '04',
            May: '05',
            Jun: '06',
            Jul: '07',
            Aug: '08',
            Sep: '09',
            Oct: '10',
            Nov: '11',
            Dec: '12'
        };

        const [monthStr, dayWithComma, parsedYear] = date.split(' ');
        day = dayWithComma.replace(',', '').padStart(2, '0');
        month = monthMap[monthStr];
        year = parsedYear;
    }

    const [hour, minutePart] = time.split(':');
    const [minute, meridian] = minutePart.split(' ');
    let h = parseInt(hour, 10);
    if (meridian.toLowerCase() === 'pm' && h !== 12) {
        h += 12;
    }
    if (meridian.toLowerCase() === 'am' && h === 12) {
        h = 0;
    }

    if (!UTC) {
        const formattedDate = `${year}${month}${day}`;
        const formattedTime = `${String(h).padStart(2, '0')}${minute}00`;
        return `${formattedDate}T${formattedTime}`;
    }

    const naiveUTC = new Date(Date.UTC(Number(year), Number(month) - 1, Number(day), h, Number(minute)));
    const offsetMinutes = getEasternOffsetMinutes(naiveUTC);
    const actualUTC = new Date(naiveUTC.getTime() - offsetMinutes * 60000);

    const y = actualUTC.getUTCFullYear();
    const mo = String(actualUTC.getUTCMonth() + 1).padStart(2, '0');
    const d = String(actualUTC.getUTCDate()).padStart(2, '0');
    const hh = String(actualUTC.getUTCHours()).padStart(2, '0');
    const mm = String(actualUTC.getUTCMinutes()).padStart(2, '0');
    return `${y}${mo}${d}T${hh}${mm}00`;
}

function wrapEvents(events) {
    var wrapped_events = `
  BEGIN:VCALENDAR
  VERSION:2.0
  PRODID:-//CalendarGenerator//EN
  CALSCALE:GREGORIAN
  ${events}
  END:VCALENDAR`;
    var lines = wrapped_events.split('\n');
    var cleaned_content = '';
    for (var line of lines) {
        line = line.trim();
        if (line !== '') {
            cleaned_content += line + '\r\n';
        }
    }
    return cleaned_content
}

function generateUID() {
    return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
        const r = Math.random() * 16 | 0,
            v = c === 'x' ? r : (r & 0x3 | 0x8);
        return v.toString(16);
    }) + '@northeastern.edu';
}

function genorateDownloadLink(ics_file) {
    const blob = new Blob([ics_file], {
        type: 'text/calendar'
    });
    const link = document.createElement('a');
    link.href = URL.createObjectURL(blob);
    link.download = 'calendar.ics';
    document.body.appendChild(link);
    link.click();
    document.body.removeChild(link);
}