sub-amigo

A Django app that tracks software subscriptions and fires reminders before they renew. It works out when to call your notification adapter and what to pass it. You write the adapter.

---

Install

uv add sub-amigo
# or
pip install sub-amigo

Add to INSTALLED_APPS and run migrations:

INSTALLED_APPS = [
    ...
    "sub_amigo",
]

python manage.py migrate

---

Write an adapter

Subclass BaseNotificationAdapter and implement send(). Return True on success, False on failure. Do not raise exceptions.

# myapp/adapters.py
import logging
from django.core.mail import send_mail
from django.conf import settings
from sub_amigo import BaseNotificationAdapter, NotificationPayload

logger = logging.getLogger(__name__)


class EmailAdapter(BaseNotificationAdapter):
    def send(self, payload: NotificationPayload) -> bool:
        try:
            send_mail(
                subject=payload.subject,
                message=payload.message,
                from_email=settings.DEFAULT_FROM_EMAIL,
                recipient_list=[payload.recipient],
            )
            return True
        except Exception:
            logger.exception("Reminder failed for %s", payload.recipient)
            return False

NotificationPayload has four fields:

Field	Description
recipient	The value from Subscription.recipient_ref, passed through unchanged
subject	Pre-rendered subject line
message	Fully-rendered body text
metadata	Dict with subscription_id, billing_date, days_before, cost, currency

---

Configure

# settings.py
SUB_AMIGO_ADAPTER = "myapp.adapters.EmailAdapter"

---

Schedule

Run once a day via cron or a task scheduler:

python manage.py process_reminders

To process a specific date instead of today:

python manage.py process_reminders --date 2024-08-01

With Celery beat:

# celery.py
app.conf.beat_schedule = {
    "process-reminders": {
        "task": "myapp.tasks.process_reminders",
        "schedule": crontab(hour=8, minute=0),
    },
}

# myapp/tasks.py
from celery import shared_task
from sub_amigo.engine import SubscriptionReminderEngine
from myapp.adapters import EmailAdapter


@shared_task
def process_reminders():
    SubscriptionReminderEngine(adapter=EmailAdapter()).process_daily_reminders()

---

Processing result

process_reminders() and process_daily_reminders() both return a ProcessingResult:

result = amigo.process_reminders()
print(result.succeeded)  # reminders sent
print(result.failed)     # adapter returned False or template error
print(result.skipped)    # already sent for this billing cycle
print(result.processed)  # total rules evaluated

Field	Type	Description
run_date	date	The date the engine ran against
processed	int	Total rules evaluated
succeeded	int	Reminders sent successfully
failed	int	Adapter failures or template errors
skipped	int	Already sent for this billing cycle
results	list[ReminderResult]	Per-rule detail

Each ReminderResult has rule_id, subscription_id, subscription_name, success, skipped, and error.

---

Create subscriptions

The SubAmigo class is the quickest way to get started. It creates the subscription and its reminder rules in one call and exposes process_reminders() on the same object.

from datetime import date
from decimal import Decimal
from sub_amigo.service import SubAmigo
from myapp.adapters import EmailAdapter

amigo = SubAmigo(adapter=EmailAdapter())

sub = amigo.subscribe(
    name="GitHub Teams",
    cost=Decimal("4.00"),
    currency="USD",
    next_billing_date=date(2024, 8, 1),
    recipient_ref="billing@example.com",
    owner_ref="team-42",
    remind_days_before=[7, 3, 0],  # uses the default template
)

# Run reminders (call this daily)
result = amigo.process_reminders()

For custom message templates per rule, use reminder_specs instead:

from sub_amigo.service import ReminderSpec

sub = amigo.subscribe(
    name="GitHub Teams",
    cost=Decimal("4.00"),
    next_billing_date=date(2024, 8, 1),
    recipient_ref="billing@example.com",
    reminder_specs=[
        ReminderSpec(days_before=7, message_template="One week until {subscription_name} renews."),
        ReminderSpec(days_before=0, message_template="{subscription_name} charges today ({cost} {currency})."),
    ],
)

Both arguments can be mixed. remind_days_before uses the default template; reminder_specs uses whatever you provide.

Template variables

Variable	Value
{subscription_name}	Name of the subscription
{cost}	Billing amount
{currency}	ISO 4217 currency code
{next_billing_date}	Next billing date, YYYY-MM-DD
{days_before}	Days until billing
{description}	Subscription description, may be empty

---

Advance the billing date

After a subscription charges, move it to the next cycle:

sub.advance_billing_date().save()

Interval	Behaviour
monthly	One calendar month forward, month-end dates handled correctly
annually	One calendar year forward
custom	Forward by billing_interval_days days

---

Signals

sub-amigo fires Django signals after every reminder attempt so your app can react without subclassing anything.

from django.dispatch import receiver
from sub_amigo.signals import reminder_sent, reminder_failed

@receiver(reminder_sent)
def log_to_datadog(sender, subscription, rule, payload, log, **kwargs):
    datadog.increment("reminders.sent", tags=[f"sub:{subscription.name}"])

@receiver(reminder_failed)
def alert_on_call(sender, subscription, rule, error, log, **kwargs):
    pagerduty.trigger(f"{subscription.name} reminder failed: {error}")

reminder_sent kwargs:

kwarg	Type
subscription	Subscription
rule	ReminderRule
payload	NotificationPayload
log	NotificationLog

reminder_failed kwargs:

kwarg	Type
subscription	Subscription
rule	ReminderRule
error	str
log	NotificationLog

reminder_failed fires on both adapter failures and template render errors.

---

Idempotency

NotificationLog records every fired reminder keyed on (reminder_rule, billing_cycle_date). That pair has a unique constraint, so running process_daily_reminders() twice on the same date does not send duplicates. The engine checks before calling the adapter; the database constraint enforces it regardless.

---

Model reference

Subscription

Field	Type	Notes
id	UUID	Auto-generated
name	CharField
cost	DecimalField
currency	CharField	ISO 4217, default "USD"
billing_interval	CharField	monthly / annually / custom
billing_interval_days	PositiveIntegerField	Required when billing_interval = "custom", min 1
next_billing_date	DateField
status	CharField	active / paused / cancelled
recipient_ref	CharField	Passed to your adapter unchanged
owner_ref	CharField	Optional, for multi-tenant filtering
metadata	JSONField	Arbitrary app-specific data

ReminderRule

Field	Type	Notes
subscription	ForeignKey	Cascade delete
days_before	PositiveSmallIntegerField	0 fires on the billing date; unique per subscription
message_template	TextField	str.format_map() template
is_active	BooleanField

NotificationLog

Read-only ledger. One row per reminder fired.

---

Direct model access

For data migrations, bulk imports, management commands, or admin actions, you can work with the ORM directly.

from sub_amigo.models import Subscription, ReminderRule, BillingInterval

sub = Subscription.objects.create(
    name="GitHub Teams",
    cost="4.00",
    currency="USD",
    billing_interval=BillingInterval.MONTHLY,
    next_billing_date=date(2024, 8, 1),
    recipient_ref="billing@example.com",
)

ReminderRule.objects.create(
    subscription=sub,
    days_before=7,
    message_template="{subscription_name} renews on {next_billing_date}.",
)

SubAmigo.subscribe() does the same thing internally. Reach for the ORM when you need finer control or are operating outside a request cycle.

---

Requirements

• Python 3.12+
• Django 5.0+
• python-dateutil 2.9+

---

Licence

MIT