Create the Google Calendar event links of the courses on the NTU "My Schedule" page.

createNTUCourseEvents.js

javascript: (() => {
  /**
   * This script is used to create the Google Calendar event links of the
   * courses on the NTU "My Schedule" page.
   */
  if (
    location.href !== "https://nol.ntu.edu.tw/nol/coursesearch/myschedule.php"
  ) {
    return;
  }
  let locationTimeIdx = null;
  let table = null;

  /**
   * Get course name and the information link from the row of the course table.
   *
   * @param {HTMLElement} row
   * @returns {[String, String]}
   */
  function getCourseNameAndLinkFromRow(row) {
    /* assume the first link in the row is the course name */
    const courseNameElm = row.getElementsByTagName("a")[0];
    const url = new URL(courseNameElm.href);
    const keys = Array.from(url.searchParams.keys());
    keys.forEach((key) => {
      if (!["course_id", "semester"].includes(key)) {
        url.searchParams.delete(key);
      }
    });
    return [courseNameElm.innerText, url.href];
  }

  /**
   * Get the link of COOL platform from the row of the course table.
   *
   * @param {HTMLElement} row
   * @returns {String=}
   */
  function getCoolLink(row) {
    return row.querySelector('a[href*="cool.ntu.edu.tw"]')?.href;
  }

  /**
   * Parse the locations and time from the row of the course table.
   *
   * @param {HTMLElement} row
   * @returns {[String, String[], String][]}
   */
  function getLocationAndTime(row) {
    const timeAndLocationPattern =
      /([一二三四五六日])(([0-9]|10|[A-D])(,([0-9]|10|[A-D]))*)\((.+?)\)/g;
    if (locationTimeIdx == null) {
      locationTimeIdx = -1;
      Array.from(row.getElementsByTagName("td")).some((elm) => {
        locationTimeIdx += 1;
        const istimeAndLocation = timeAndLocationPattern.test(elm.innerText);
        timeAndLocationPattern.lastIndex = 0;
        return istimeAndLocation;
      });
    }
    return [
      ...row
        .getElementsByTagName("td")
        [locationTimeIdx].innerText.matchAll(timeAndLocationPattern),
    ].map((res) => [res[1], res[2].split(","), res[6]]);
  }

  /**
   * Convert the orders of the class to numbers.
   * E.g. "1" => 1, "A" => 11
   *
   * @param {String[]} classNo
   * @returns {Number[]}
   */
  function parseClassNo(classNo) {
    const parsedClassNo = classNo.map((c) => {
      if (/^[ABCD]$/.test(c)) {
        return c.charCodeAt(0) - "A".charCodeAt(0) + 11;
      }
      return parseInt(c);
    });
    for (let i = 1; i < parsedClassNo.length; ++i) {
      if (parsedClassNo[i] !== parsedClassNo[i - 1] + 1) {
        throw new Error(
          `Class No. are not strictly increasing: [${parsedClassNo}]`
        );
      }
    }
    return parsedClassNo;
  }

  /**
   * Compose Google Calendar Event link from the information of the course.
   *
   * @param {String} courseName
   * @param {String} link
   * @param {String=} coolLink
   * @param {[String, String[], String][]} locationAndTimePairs
   * @param {String=} calendarID
   * @returns {URL[]}
   */
  function composeUrl(courseName, link, coolLink, locationAndTimePairs, calendarID) {
    return locationAndTimePairs.map(([weekDay, classNo, location]) => {
      const setToStartOfClass = (dateObj, classNoIdx) => {
        const classStartTimeTable = [
          [7, 10],
          [8, 10],
          [9, 10],
          [10, 20],
          [11, 20],
          [12, 20],
          [13, 20],
          [14, 20],
          [15, 30],
          [16, 30],
          [17, 30],
          [18, 25],
          [19, 20],
          [20, 15],
          [21, 00],
        ];
        dateObj.setHours(classStartTimeTable[classNoIdx][0]);
        dateObj.setMinutes(classStartTimeTable[classNoIdx][1]);
      };
      const parsedClassNo = parseClassNo(classNo);
      const classStartTime = new Date(firstDate);
      classStartTime.setDate(classStartTime.getDate() + dayOffsetMap[weekDay]);
      setToStartOfClass(classStartTime, parsedClassNo[0]);
      const classEndTime = new Date(classStartTime);
      setToStartOfClass(classEndTime, parsedClassNo[parsedClassNo.length - 1]);
      classEndTime.setMinutes(classEndTime.getMinutes() + 50);

      const url = new URL(
        "https://www.google.com/calendar/event?action=TEMPLATE"
      );
      url.searchParams.set("text", courseName);
      const toGoogleCalendarDateString = (time) => {
        const year = time.getUTCFullYear();
        const month = `${time.getUTCMonth() + 1}`.padStart(2, "0");
        const date = `${time.getUTCDate()}`.padStart(2, "0");
        const hour = `${time.getUTCHours()}`.padStart(2, "0");
        const minute = `${time.getUTCMinutes()}`.padStart(2, "0");
        return `${year}${month}${date}T${hour}${minute}00Z`;
      };
      url.searchParams.set(
        "dates",
        `${toGoogleCalendarDateString(
          classStartTime
        )}/${toGoogleCalendarDateString(classEndTime)}`
      );
      url.searchParams.set("location", location);
      let description = link;
      if (coolLink != null) {
        description += `\n\ncool: ${coolLink}`;
      }
      url.searchParams.set("details", description);
      url.searchParams.set("recur", "RRULE:FREQ=WEEKLY;COUNT=16");
      if (calendarID !== null) {
        url.searchParams.set("src", calendarID);
      }
      return url;
    });
  }

  /**
   * @param {String} html representing a single element
   * @return {Element}
   */
  function htmlToElement(html) {
    const template = document.createElement("template");
    html = html.trim(); /* Never return a text node of whitespace as the result */
    template.innerHTML = html;
    return template.content.firstChild;
  }

  if (window.googleCalendarLinksHaveAdded != null) return;

  let firstDate = prompt(
    "Please enter the first day of this semester:",
    "20220905"
  );
  if (firstDate == null || firstDate == "") {
    return;
  }
  firstDate = new Date(
    firstDate.substring(0, 4),
    firstDate.substring(4, 6) - 1,
    firstDate.substring(6, 8)
  );
  if (isNaN(firstDate)) {
    /* invalid input */
    return;
  }
  const firstDay = firstDate.getDay();
  const dayOffsetMap = {
    日: (7 - firstDay) % 7,
    一: (8 - firstDay) % 7,
    二: (9 - firstDay) % 7,
    三: (10 - firstDay) % 7,
    四: (11 - firstDay) % 7,
    五: (12 - firstDay) % 7,
    六: (13 - firstDay) % 7,
  };

  const calendarID = prompt(
    "Target calendar ID (optional):",
    ""
  );
  if (calendarID == null) {
    return;
  }


  table = document.getElementsByTagName("table")[0];
  let rows = table.getElementsByTagName("tr");

  /* Update header */
  const header = rows[0];
  const addToGoogleCalendarCell = `
    <td>
      加到
      <br>
      Google
      <br>
      日曆
    </td>
   `;
  header.insertBefore(
    htmlToElement(addToGoogleCalendarCell),
    header.children[header.children.length - 1]
  );

  /* Update foot */
  const foot = rows[rows.length - 1];
  const footCell = foot.getElementsByTagName("td")[0];
  footCell.setAttribute("colspan", footCell.getAttribute("colspan") - -1);

  rows = Array.from(rows);
  rows.shift();
  rows.pop();
  rows.forEach((row) => {
    const [courseName, link] = getCourseNameAndLinkFromRow(row);
    const coolLink = getCoolLink(row);
    const locationAndTimePairs = getLocationAndTime(row);
    console.debug(courseName, link, coolLink, locationAndTimePairs);
    const urls = composeUrl(courseName, link, coolLink, locationAndTimePairs, calendarID);
    const newCell = document.createElement("td");
    if (urls.length === 1) {
      newCell.append(
        htmlToElement(`<a target="_blank" href="${urls[0].href}">活動</a>`)
      );
    } else {
      urls.forEach((url, idx) => {
        if (idx > 0) {
          newCell.append(document.createElement("br"));
        }
        newCell.append(
          htmlToElement(
            `<a target="_blank" href="${urls[idx].href}">活動${idx + 1}</a>`
          )
        );
      });
    }
    row.insertBefore(newCell, row.children[row.children.length - 1]);
  });

  window.googleCalendarLinksHaveAdded = true;
})();