Group Tasks Shared Completion (#10515)

* WIP(groups): add shared completion prop
Also fix an issue where the Needs Approval toggle would not read/save 
correctly.

* fix(groups): save group options on task create
Also, correct count of assigned members when viewing user is among 
assignments

* fix(groups): display correct messages in two places

* fix(tasks): eliminate console error related to filtering
Also localize a group plans string

* WIP(groups): implement single completion for approval workflow

* WIP(groups): Add shared completion handling to no-approval-needed flow

* WIP(groups): cover approval flow case for all-assigned
Also save new field on initial task creation

* fix(tasks): use default sharedCompletion value when creating tasks

* WIP(tests): non-working draft test

* Added completed todo to group query

* WIP(group-tasks): fix bugs, add tests

* refactor(group-tasks): deleteMany op, add more tests

* refactor(group-tasks): move shared completion handling to lib

* WIP(group-tasks): broken refactor

* WIP(group-tasks): await all the things

* Turned complete master task to save

* WIP(group-tasks): show completed

* fix(filtering): don't try to filter if no list is passed

* refactor(group-tasks): load completed to-dos on demand, not at start

* fix(group-tasks): don't double up on repeat visits

* fix(group-tasks): include brief explanation in dropdown

* fix(group-tasks): improve wording some more

website/server/libs/groupTasks.js

@@ -0,0 +1,61 @@
+import * as Tasks from '../models/task';
+
+const SHARED_COMPLETION = {
+  default: 'recurringCompletion',
+  single: 'singleCompletion',
+  every: 'allAssignedCompletion',
+};
+
+async function _completeMasterTask (masterTask) {
+  masterTask.completed = true;
+  await masterTask.save();
+}
+
+async function _deleteUnfinishedTasks (groupMemberTask) {
+  await Tasks.Task.deleteMany({
+    'group.taskId': groupMemberTask.group.taskId,
+    $and: [
+      {userId: {$exists: true}},
+      {userId: {$ne: groupMemberTask.userId}},
+    ],
+  }).exec();
+}
+
+async function _evaluateAllAssignedCompletion (masterTask) {
+  let completions;
+  if (masterTask.group.approval && masterTask.group.approval.required) {
+    completions = await Tasks.Task.count({
+      'group.taskId': masterTask._id,
+      'group.approval.approved': true,
+    }).exec();
+    completions++;
+  } else {
+    completions = await Tasks.Task.count({
+      'group.taskId': masterTask._id,
+      completed: true,
+    }).exec();
+  }
+  if (completions >= masterTask.group.assignedUsers.length) {
+    await _completeMasterTask(masterTask);
+  }
+}
+
+async function handleSharedCompletion (groupMemberTask) {
+  let masterTask = await Tasks.Task.findOne({
+    _id: groupMemberTask.group.taskId,
+  }).exec();
+
+  if (!masterTask || !masterTask.group || masterTask.type !== 'todo') return;
+
+  if (masterTask.group.sharedCompletion === SHARED_COMPLETION.single) {
+    await _deleteUnfinishedTasks(groupMemberTask);
+    await _completeMasterTask(masterTask);
+  } else if (masterTask.group.sharedCompletion === SHARED_COMPLETION.every) {
+    await _evaluateAllAssignedCompletion(masterTask);
+  }
+}
+
+export {
+  SHARED_COMPLETION,
+  handleSharedCompletion,
+};