From 927094ee410eeb2927c56d8ae0f7c7b2996f7e2e Mon Sep 17 00:00:00 2001
From: Adam Goldsmith <adam@adamgoldsmith.name>
Date: Mon, 7 Dec 2020 18:02:46 -0500
Subject: [PATCH] Add per-user Reminder model and adjust sendNotifications to
 use it

---
 tasks/admin.py                                |  3 +-
 .../management/commands/sendNotifications.py  | 47 +++++++++++++++----
 tasks/migrations/0002_reminder.py             | 25 ++++++++++
 tasks/models.py                               | 18 +++++++
 4 files changed, 83 insertions(+), 10 deletions(-)
 create mode 100644 tasks/migrations/0002_reminder.py

diff --git a/tasks/admin.py b/tasks/admin.py
index 197063c..4d246f2 100644
--- a/tasks/admin.py
+++ b/tasks/admin.py
@@ -1,6 +1,6 @@
 from django.contrib import admin
 
-from .models import Tool, Task, Event
+from .models import Tool, Task, Reminder, Event
 
 admin.site.register(Tool)
 
@@ -10,4 +10,5 @@ class TaskAdmin(admin.ModelAdmin):
     prepopulated_fields = {"slug": ("name",)}
 
 
+admin.site.register(Reminder)
 admin.site.register(Event)
diff --git a/tasks/management/commands/sendNotifications.py b/tasks/management/commands/sendNotifications.py
index 12e7177..69cf37c 100644
--- a/tasks/management/commands/sendNotifications.py
+++ b/tasks/management/commands/sendNotifications.py
@@ -1,20 +1,49 @@
 import smtplib
 
 from email.message import EmailMessage
+from itertools import groupby
 
 from django.core.management.base import BaseCommand, CommandError
-from tasks.models import Tool, Task, Event
+from tasks.models import Tool, Task, Event, Reminder
 
 
 class Command(BaseCommand):
     help = 'Sends any notifications for upcoming and overdue tasks'
 
-    # TODO: actually send notifications
+    def _send_email(self, to, subject, content):
+        msg = EmailMessage()
+        msg.set_content(content)
+        msg['Subject'] = subject
+        msg['From'] = 'adam@adamgoldsmith.name'
+        msg['To'] = to
+
+        with smtplib.SMTP("localhost") as server:
+            server.send_message(msg)
+
+    def _active_reminders(self):
+        for reminder in Reminder.objects.all():
+            if reminder.should_remind:
+                yield reminder
+
+    def _format_reminder_lines(self, reminders):
+        for reminder in reminders:
+            next_date = reminder.task.next_recurrence.strftime('%Y-%m-%d')
+            yield f"  - {reminder.task.name} - {next_date}"
+
     def handle(self, *args, **options):
-        for tool in Tool.objects.all():
-            print(tool.name)
-            for task in tool.task_set.all():
-                print('==>', task.name, 'next:', task.next_recurrence())
-                if task.is_overdue():
-                    self.stdout.write(self.style.SUCCESS(
-                        f'Sending Notification for task {task.name}'))
+        reminders_per_user = {
+            user: sorted(reminders, key=lambda r: r.task.next_recurrence)
+            for user, reminders in groupby(self._active_reminders(), lambda r: r.user)
+        }
+
+        for user, reminders in reminders_per_user.items():
+            self.stdout.write(self.style.SUCCESS(
+                f'Sending notification for {len(reminders)} task(s) to {user}'))
+
+            contents = "The following tasks are upcoming or overdue:\n\n" + \
+                ('\n'.join(self._format_reminder_lines(reminders)))
+
+            self._send_email(
+                user.email,
+                f'[CMS Tool Maintenance] {len(reminders)} tasks are upcoming or overdue!',
+                contents)
diff --git a/tasks/migrations/0002_reminder.py b/tasks/migrations/0002_reminder.py
new file mode 100644
index 0000000..a33dc33
--- /dev/null
+++ b/tasks/migrations/0002_reminder.py
@@ -0,0 +1,25 @@
+# Generated by Django 3.1.4 on 2020-12-07 21:13
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+        ('tasks', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Subscription',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('days_before', models.IntegerField()),
+                ('task', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='tasks.task')),
+                ('user', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL)),
+            ],
+        ),
+    ]
diff --git a/tasks/models.py b/tasks/models.py
index dd64343..89ec706 100644
--- a/tasks/models.py
+++ b/tasks/models.py
@@ -58,6 +58,24 @@ class Task(models.Model):
             return next_rec < datetime.now()
 
 
+class Reminder(models.Model):
+    user = models.ForeignKey(get_user_model(), on_delete=models.CASCADE)
+    task = models.ForeignKey(Task, on_delete=models.CASCADE)
+    days_before = models.IntegerField()
+
+    class Meta:
+        # Django doesn't support multiple-column primary keys
+        unique_together = (("user", "task"),)
+
+    @property
+    def should_remind(self):
+        time_until_overdue = self.task.next_recurrence - datetime.now()
+        return self.task.is_overdue or (time_until_overdue.days <= self.days_before)
+
+    def __str__(self):
+        return f"{self.user}-{self.task}, {self.days_before} day(s)"
+
+
 class Event(models.Model):
     task = models.ForeignKey(Task, on_delete=models.CASCADE)
     user = models.ForeignKey(get_user_model(), on_delete=models.CASCADE)