Implement mail tracker system

* Implement mail tracking

Signed-off-by: Victor "multun" Collod <victor.collod@prologin.org>

* Implement task merging

* Add a mail tracker title format pattern

* Autocomplete task names

* Fix comment display

* Track notification answers

* Add a socket timeout for the mail worker

A mail worker is a long running application. And sometimes, the IMAP server
just hangs for hours for no apparent reason. imaplib doesn't enable setting
a timeout, and setting it globally seems fine.

* Only validate the merge form when submitted

* Redirect to the new form when merging

* Prettier task edit UI

* Make task merging optional

* Test mail tracking

* Update documentation for mail tracking

* Update dependencies

* Add the TODO_COMMENT_CLASSES setting

* Fix dependencies install order

* Remove debug leftovers, improve documentation

* Fail on missing from_address

todo/views/task_detail.py

@@ -1,15 +1,47 @@
+import bleach
 import datetime
 
-import bleach
+from django import forms
+from django.conf import settings
 from django.contrib import messages
 from django.contrib.auth.decorators import login_required, user_passes_test
 from django.core.exceptions import PermissionDenied
 from django.http import HttpResponse
-from django.shortcuts import get_object_or_404, redirect, render
+from django.shortcuts import get_object_or_404, redirect, render, redirect
+from django.urls import reverse
+from django.utils.decorators import method_decorator
 
 from todo.forms import AddEditTaskForm
 from todo.models import Comment, Task
-from todo.utils import send_email_to_thread_participants, toggle_task_completed, staff_check
+from todo.utils import send_email_to_thread_participants, toggle_task_completed, staff_check, user_can_read_task
+from todo.features import HAS_TASK_MERGE
+
+
+if HAS_TASK_MERGE:
+    from dal import autocomplete
+    from todo.views.task_autocomplete import TaskAutocomplete
+
+
+def handle_add_comment(request, task):
+    if not request.POST.get("add_comment"):
+        return
+
+    Comment.objects.create(
+        author=request.user,
+        task=task,
+        body=bleach.clean(request.POST["comment-body"], strip=True),
+    )
+
+    send_email_to_thread_participants(
+        task,
+        request.POST["comment-body"],
+        request.user,
+        subject='New comment posted on task "{}"'.format(task.title),
+    )
+
+    messages.success(
+        request, "Comment posted. Notification email sent to thread participants."
+    )
 
 
 @login_required
@@ -19,33 +51,55 @@ def task_detail(request, task_id: int) -> HttpResponse:
     """
 
     task = get_object_or_404(Task, pk=task_id)
-    comment_list = Comment.objects.filter(task=task_id)
+    comment_list = Comment.objects.filter(task=task_id).order_by('-date')
 
     # Ensure user has permission to view task. Admins can view all tasks.
     # Get the group this task belongs to, and check whether current user is a member of that group.
-    if task.task_list.group not in request.user.groups.all() and not request.user.is_staff:
+    if not user_can_read_task(task, request.user):
         raise PermissionDenied
 
-    # Save submitted comments
-    if request.POST.get("add_comment"):
-        Comment.objects.create(
-            author=request.user,
-            task=task,
-            body=bleach.clean(request.POST["comment-body"], strip=True),
-        )
+    # Handle task merging
+    if not HAS_TASK_MERGE:
+        merge_form = None
+    else:
+        class MergeForm(forms.Form):
+            merge_target = forms.ModelChoiceField(
+                queryset=Task.objects.all(),
+                widget=autocomplete.ModelSelect2(
+                    url=reverse("todo:task_autocomplete", kwargs={"task_id": task_id})
+                ),
+            )
 
-        send_email_to_thread_participants(
-            task,
-            request.POST["comment-body"],
-            request.user,
-            subject='New comment posted on task "{}"'.format(task.title),
-        )
-        messages.success(request, "Comment posted. Notification email sent to thread participants.")
+        # Handle task merging
+        if not request.POST.get("merge_task_into"):
+            merge_form = MergeForm()
+        else:
+            merge_form = MergeForm(request.POST)
+            if merge_form.is_valid():
+                merge_target = merge_form.cleaned_data["merge_target"]
+            if not user_can_read_task(merge_target, request.user):
+                raise PermissionDenied
+
+            task.merge_into(merge_target)
+            return redirect(reverse(
+                "todo:task_detail",
+                kwargs={"task_id": merge_target.pk}
+            ))
+
+    # Save submitted comments
+    handle_add_comment(request, task)
 
     # Save task edits
-    if request.POST.get("add_edit_task"):
+    if not request.POST.get("add_edit_task"):
         form = AddEditTaskForm(
-            request.user, request.POST, instance=task, initial={"task_list": task.task_list}
+            request.user, instance=task, initial={"task_list": task.task_list}
+        )
+    else:
+        form = AddEditTaskForm(
+            request.user,
+            request.POST,
+            instance=task,
+            initial={"task_list": task.task_list},
         )
 
         if form.is_valid():
@@ -54,10 +108,10 @@ def task_detail(request, task_id: int) -> HttpResponse:
             item.save()
             messages.success(request, "The task has been edited.")
             return redirect(
-                "todo:list_detail", list_id=task.task_list.id, list_slug=task.task_list.slug
+                "todo:list_detail",
+                list_id=task.task_list.id,
+                list_slug=task.task_list.slug,
             )
-    else:
-        form = AddEditTaskForm(request.user, instance=task, initial={"task_list": task.task_list})
 
     # Mark complete
     if request.POST.get("toggle_done"):
@@ -72,6 +126,13 @@ def task_detail(request, task_id: int) -> HttpResponse:
     else:
         thedate = datetime.datetime.now()
 
-    context = {"task": task, "comment_list": comment_list, "form": form, "thedate": thedate}
+    context = {
+        "task": task,
+        "comment_list": comment_list,
+        "form": form,
+        "merge_form": merge_form,
+        "thedate": thedate,
+        "comment_classes": getattr(settings, 'TODO_COMMENT_CLASSES', []),
+    }
 
     return render(request, "todo/task_detail.html", context)