// script forked from https://gist.github.com/jamesramsay/9298cf3f4ac584a3dc05
// to start timed execution: select "Install" from the menu above and hit "run"
// to stop timed execution: select "Uninstall" from the menu above and hit "run"
// to initialize a batch run ad-hoc and immediately: select "_processNextBatch" from the menu above and hit "run"

const LABELS_TO_DELETE = [
  // ... list of labels ...
  // 'test-delete-after-label',
  'spammy-alerts',
  // 'delete-after-30d',
  // TODO - add support for different time bombs
  // 'delete-after-7d',
  // 'delete-after-1d',
  // TODO - add support for archive
  // 'archive-after-30d',
  // 'archive-after-7d',
];

// Constants for trigger names
const DAILY_TRIGGER_NAME = "dailyProcessTrigger";
const DELAYED_BATCH_TRIGGER_NAME = "delayedBatchTrigger";

// timezone probably doesn't really matter if we're only working in days.
const TIMEZONE = "America/Los Angeles";

// Batch size and timing configuration
const MAX_THREADS_TO_PROCESS_PER_BATCH = 500; // max argument size is 500
const MINUTES_TO_WAIT_BETWEEN_BATCHES = 5; // TODO - why?

const DELETE_AFTER_DAYS = 30;
function _getPurgeBeforeDate() {
  const today = new Date();
  // TODO - change DELETE_AFTER_DAYS based on the label
  const age = new Date(today.setDate(today.getDate() - DELETE_AFTER_DAYS));
  return Utilities.formatDate(age, TIMEZONE, "yyyy-MM-dd");
}

function _processNextBatch() {
  console.log('START process next batch');

  // Clear all batch triggers
  _clearAllDelayedBatchTriggers();
  _processEmails();

  console.log('FINISH process batch');
}

function _processEmails() {
  let threadsProcessedCount = 0;
  const threadsProcessedPerLabel = {};

  const purgeBeforeDate = _getPurgeBeforeDate()

  LABELS_TO_DELETE.forEach(function(label) {
    const threadBudgetLeftForThisBatch = MAX_THREADS_TO_PROCESS_PER_BATCH - threadsProcessedCount;
    if (threadBudgetLeftForThisBatch <= 0) {
      return; // Skip this label if the maximum number of threads to process has been reached
    }

    const search = 'label:' + label + ' before:' + purgeBeforeDate;
    console.log('Searching for threads with label: ' + label);
    const threads = GmailApp.search(search, 0, threadBudgetLeftForThisBatch);
    const threadsToDeleteCount = threads.length;

    console.log('Found ' + threadsToDeleteCount + ' threads to delete for label: ' + label);
    for (let i = 0; i < threadsToDeleteCount; i++) {
      // NB: this moves the thread to the trash. so thread will not get *permanently* deleted 
      //     until 30 days *after* it gets moved to the trash.
      threads[i].moveToTrash();
    }

    threadsProcessedCount += threadsToDeleteCount;
    threadsProcessedPerLabel[label] = (threadsProcessedPerLabel[label] || 0) + threadsToDeleteCount;
  });

  // Log the deleted email count per label
  console.log('Deleted emails from labels:');
  for (let label in threadsProcessedPerLabel) {
    console.log('  ' + label + ': ' + threadsProcessedPerLabel[label]);
  }

  // Schedule another run if we hit the processing limit.
  // NB: Since we're only loading up to MAX_THREADS_TO_PROCESS_PER_BATCH at a time, we don't 
  //     know if there are more threads to process in the next execution. So, if we reach the limit, 
  //     there are *probably* more threads to process. It's possible there's no more left but it's not 
  //     a big deal to just run it again.
  if (threadsProcessedCount >= MAX_THREADS_TO_PROCESS_PER_BATCH) {
    // TODO - when would threadsProcessedCount be above MAX_THREADS_TO_PROCESS?
    console.log("Reached processing limit, scheduling next batch...");
    ScriptApp.newTrigger(DELAYED_BATCH_TRIGGER_NAME)
             .timeBased()
             .after(MINUTES_TO_WAIT_BETWEEN_BATCHES * 60 * 1000)
             .create();
  } else {
    console.log('Did not reach batch limit, no follow-up needed.');
  }
}

function _clearAllDelayedBatchTriggers() {
  // cancel all delayed jobs
  const existingTriggers = ScriptApp.getProjectTriggers();
  console.log('Checking for triggers other than the daily trigger...');
  let foundDelayedBatchTrigger = false;
  for (let i = 0; i < existingTriggers.length; i++) {
    const trigger = existingTriggers[i];
    if (trigger.getHandlerFunction() === DELAYED_BATCH_TRIGGER_NAME) {
      ScriptApp.deleteTrigger(trigger);
      console.log('Deleted delayed batch trigger: ' + trigger.getUniqueId());
      foundDelayedBatchTrigger = true;
    }
  }
  if (!foundDelayedBatchTrigger) {
    console.log('No delayed batch triggers found.')
  }
}


function dailyProcessTrigger() {
  // run this daily to initiate the auto delete process
  console.log('START run daily deletion process for Gmail threads...');
  
  _processNextBatch();

  console.log('FINISH run daily deletion process.');
}

function delayedBatchTrigger() {
  // run this to start the process again if we didn't finish the first time
  console.log('START process delayed batch');

  _processNextBatch();

  console.log('FINISH process delayed batch');
}

function Install() {
  console.log('Installing triggers...');

  // Clear all existing triggers before setting up new ones
  Uninstall();

  // Set up the new daily trigger
  ScriptApp.newTrigger(DAILY_TRIGGER_NAME)
           .timeBased()
           .everyDays(1)
           .create();

  console.log('Installation complete.');
}

function Uninstall() {
  console.log('Uninstalling all triggers...');

  const triggers = ScriptApp.getProjectTriggers();
  for (let i = 0; i < triggers.length; i++) {
    ScriptApp.deleteTrigger(triggers[i]);
  }

  console.log('All triggers have been removed.');
}