Per-month quota for email-sending

Fix #34

phonehome/migrations/0002_installation_email_quota_usage.py

@@ -0,0 +1,18 @@
+# Generated by Django 4.2.21 on 2025-07-28 12:04
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("phonehome", "0001_b_squashed_initial"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="installation",
+            name="email_quota_usage",
+            field=models.TextField(default='{"per_month": {}}'),
+        ),
+    ]

phonehome/models.py

@@ -1,6 +1,10 @@
+import json
 import uuid
 
 from django.db import models
+from bugsink.transaction import immediate_atomic
+
+from bugsink.app_settings import get_settings
 
 
 class Installation(models.Model):
@@ -12,6 +16,29 @@ class Installation(models.Model):
 
     silence_email_system_warning = models.BooleanField(default=False)
 
+    email_quota_usage = models.TextField(null=False, default='{"per_month": {}}')
+
+    @classmethod
+    @immediate_atomic(only_if_needed=True)  # minimalize write-lock-hogging (while being callable within atomic blocks)
+    def check_and_inc_email_quota(cls, date):
+        obj = cls.objects.first()
+
+        email_quota_usage = json.loads(obj.email_quota_usage)
+
+        key = date.strftime('%Y-%m')
+        if key not in email_quota_usage["per_month"]:
+            email_quota_usage['per_month'] = {key: 0}  # full overwrite: no need to keep old info around.
+
+        if (get_settings().MAX_EMAILS_PER_MONTH is not None
+                and email_quota_usage['per_month'][key] >= get_settings().MAX_EMAILS_PER_MONTH):
+            return False
+
+        email_quota_usage['per_month'][key] += 1
+
+        obj.email_quota_usage = json.dumps(email_quota_usage)
+        obj.save()
+        return True
+
 
 class OutboundMessage(models.Model):
     attempted_at = models.DateTimeField(auto_now_add=True)