Google Apps Script to automatically get stats (count of threads, age in days of oldest message) on Gmail inbox

inbox-stats.js

// Google Apps Script to automatically get stats within a Gmail inbox
// Stats logged: 
//   - current date & time 
//   - username / email address 
//   - # of message threads in inbox 
//   - Age in days of oldest message
 
// 1. Visit https://script.google.com and create a new project
// 2. Name the project 
// 3. Copy and paste this gist
// 4. Create a new Google Spreadsheet or reuse one

function inboxStats() {
  
  // get email address of user's inbox
  var userName = Session.getEffectiveUser().getEmail();
  
  // 5. Create a new Google Spreadsheet or reuse one and copy the URL
  // 6. Paste the URL of the gsheet below
  gsheetURL = 'gsheet-URL-goes-here'
  var dataSs = SpreadsheetApp.openByUrl(gsheetURL);
  
  // 5. Set the sheet name on the gsheet, copy and paste it below
  var sheetName = 'inboxStatsLogs'
  
  var sheet = dataSs.getSheetByName(sheetName); 
  var now = new Date();
  var oldest = now;
  var pageSize = 50;
  var start = 0;
  var threads;

  do {
    threads = GmailApp.getInboxThreads(start, pageSize);

    threads.forEach(function(thread) {
      oldest = thread.getLastMessageDate() < oldest ? thread.getLastMessageDate() : oldest;
    });

    start += pageSize;
    Utilities.sleep(1000);
  } while(threads.length > 0);
  
  // calculate age of oldest messag in days
  var ageOfOldest = dateDiffInDays(oldest, now);

  // get all threads in inbox as an array in order to count 
  var threadsCount = GmailApp.getInboxThreads();
  
  // Add a row of the spreadsheet's first sheet and include the following data:
  // current date & time | username / email address | # of message threads in inbox | Age in days of oldest message
  var logSheet = dataSs.getSheets()[0];
  logSheet.appendRow([now, userName,threadsCount.length,ageOfOldest]);
};

// Test
// 7. Test the script: Run > Run function > inboxStats

// Scheduling
// 8. Create triggers for the frequency you would like such as hourly or start & end of each day 


// Utilities
// compare dates only, ignore time of day
function dateDiffInDays(d1, d2) {
  return Math.round((datetimeToDate(d2) - datetimeToDate(d1)) / (1000 * 60 * 60 * 24));
}

// Create a date from a date-tiem
function datetimeToDate(d) {
  return new Date(d.getYear(), d.getMonth(), d.getDate());
}

// Thanks
// Mark Wilson for the date of oldest message technique
// https://github.com/mddub/google-apps-scripts/blob/master/log_oldest_email_age.gs

Rows 20 and 24 don't need terminal semicolons?