habitica-self-host/website/server/libs/groupTasks.js

import * as Tasks from '../models/task'; // eslint-disable-line import/no-cycle

async function handleSharedCompletion (teamTask) {
  if (teamTask.type === 'reward') return;
  const incompleteTask = await Tasks.Task.findOne({
    'group.taskId': teamTask._id,
    userId: { $exists: true },
    completed: false,
  }, { _id: 1 }).exec();
  if (!incompleteTask) {
    teamTask.completed = true;
    teamTask.save();
  }
}

export {
  handleSharedCompletion,
};