Task Reminder with Google Apps Script

file.gs.js

const USERS_SHEET_NAME = "users",
    TASKS_SHEET_NAME = "tasks",
    SPREADSHEET_URL = "https://docs.google.com/spreadsheets/d/abc123456/edit", /* TODO(Developer): Replace the spreadsheet ID */
    /* Use `SpreadsheetApp.getActiveSpreadsheet()` if the Apps Script was created from a Google Sheet. */
    spreadsheet = SpreadsheetApp.openByUrl(SPREADSHEET_URL);

const getEmailByNickname = (() => {
    const usersSheet = spreadsheet.getSheetByName(USERS_SHEET_NAME);
          
    let userEmailTable = {};

    for (let i = 2; i <= usersSheet.getLastRow(); ++i) {
        userEmailTable[usersSheet.getRange(i, 1).getValue()] = usersSheet.getRange(i, 2).getValue();
    }

    return nickname => userEmailTable[nickname];
})();

function getAllUserNicknames() {
    let usersSheet = spreadsheet.getSheetByName(USERS_SHEET_NAME);

    let users = [];
    for (let i = 2; i <= usersSheet.getLastRow(); ++i) {
        let nickname = usersSheet.getRange(i, 1).getValue();

        if ((nickname in users) === false) {
            users.push(nickname);
        }
    }

    return users;
}

function getTasks() {
    const tasksSheet = spreadsheet.getSheetByName(TASKS_SHEET_NAME);
          
    let tasks = {};

    for (let i = 2; i <= tasksSheet.getLastRow(); ++i) {
        const task = {
            name: tasksSheet.getRange(i, 1).getValue(),
            limit: new Date(Date.parse(tasksSheet.getRange(i, 2).getValue())),
            charge: tasksSheet.getRange(i, 3).getValue(),
            progress: tasksSheet.getRange(i, 4).getValue()
        };

        if (task.progress >= 100) {
            continue;
        }

        if (task.charge in tasks) {
            tasks[task.charge].push(task);
        } else {
            tasks[task.charge] = [task];
        }
    }

    return tasks;
}

function getTaskState(task) { // 1: Overdue, 2: Due Today, 3: Not due yet
    let today = new Date();
    
    today.setHours(0);
    today.setMinutes(0);
    today.setSeconds(0);
    today.setMilliseconds(0);

    // Overdue
    if (task.limit.getTime() < today.getTime()) {
        return 1;
    }

    // Due Today
    if (task.limit.getTime() === today.getTime()) {
        return 2;
    }

    // Not due yet
    return 3;
}

function getFormatedDate(date) {
    const months = [
        "January",
        "Febuary",
        "March",
        "April",
        "May",
        "June",
        "July",
        "August",
        "Sepetember",
        "October",
        "November",
        "December"
    ];

    return `${months[date.getMonth()]} ${date.getDate()}, ${date.getFullYear()}`;
}

function getFormatedTask(task, embed_nickname) {
    if (embed_nickname === true) {
        return `${task.name} [Assignment Name: ${task.charge}][Due Date: ${getFormatedDate(task.limit)}][Progress: ${task.progress}%]\n`;
    }

    return `${task.name} [Due Date: ${getFormatedDate(task.limit)}][Progress: ${task.progress}%]\n`;
}

function sendTaskReminderEmail2Individual() {
    const tasks = getTasks();

    for (const recipient in tasks) {
        let overdue = "",
            today = "",
            need2Do = "";

        for (let i = 0; i < tasks[recipient].length; ++i) {
            let task = tasks[recipient][i];

            if (!task) {
                continue;
            }

            switch (getTaskState(task)) {
                case 1:
                    overdue += getFormatedTask(task);
                    break;
                case 2:
                    today += getFormatedTask(task);
                    break;
                case 3:
                    need2Do += getFormatedTask(task);
                    break;
            }
        }

        const body = "Task Reminder\n" +
            `Add tasks and change progress from ${SPREADSHEET_URL}.\n\n` +
            `========= Overdue =========\n${overdue}\n` +
            `======== Due Today ========\n${today}\n` +
            `======== Need 2 Do ========\n${need2Do}`;

        sendEmail(
            getEmailByNickname(recipient),
            `Task Reminder For ${recipient}`,
            body
        );
    }
}

function sendTaskReminderMail2All() { // Everyone
    let tasks = getTasks(),
        overdue = "",
        today = "",
        need2Do = "";

    for (let charge in tasks) {
        for (let i = 0; i < tasks[charge].length; ++i) {
            let task = tasks[charge][i];

            if (!task) {
                continue;
            }

            switch (getTaskState(task)) {
                case 1:
                    overdue += getFormatedTask(task, true);
                    break;
                case 2:
                    today += getFormatedTask(task, true);
                    break;
                case 3:
                    need2Do += getFormatedTask(task, true);
                    break;
            }
        }
    }

    const body = "Task Reminder\n" +
        `Add tasks and change progress from ${SPREADSHEET_URL}.\n\n` +
        `========= Overdue =========\n${overdue}\n` +
        `======== Due Today ========\n${today}\n` +
        `======== Need 2 Do ========\n${need2Do}`;

    const nicknames = getAllUserNicknames();

    for (const nickname of nicknames) {
        sendEmail(
            getEmailByNickname(nickname),
            "Task Reminder",
            body
        );
    }
}


function sendEmail(recipient, title, body) {
    MailApp.sendEmail(recipient, `[Automatic Email]${title}`, body);
}