Add recurring Stripe donations

This uses Stripe's Subscriptions capability to set up recurring
donations. Requires setting up a Product for the recurring donation, and
defining its product ID in the INI file.

tildes/production.ini.example

@@ -23,6 +23,8 @@ redis.sessions.timeout = 3600
 
 sqlalchemy.url = postgresql+psycopg2://tildes:@:6432/tildes
 
+stripe.recurring_donation_product_id = prod_ProductID
+
 tildes.default_user_comment_label_weight = 1.0
 tildes.welcome_message_sender = Deimos
 

tildes/scss/modules/_form.scss

@@ -1,6 +1,12 @@
 // Copyright (c) 2018 Tildes contributors <code@tildes.net>
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
+.form-group {
+  .form-radio {
+    margin-left: 1rem;
+  }
+}
+
 .form-narrow {
   max-width: 20rem;
 
@@ -97,6 +103,10 @@ textarea.form-input {
   }
 }
 
+.form-radio {
+  display: block;
+}
+
 .form-search .form-input {
   margin-right: 0.4rem;
 }

tildes/tildes/templates/donate_stripe.jinja2

@@ -17,6 +17,22 @@
 <form class="form-narrow" method="post" data-js-stripe-donate-form>
   <input type="hidden" name="csrf_token" value="{{ get_csrf_token() }}">
 
+  <div class="form-group">
+    <label class="form-label">Donation type</label>
+    <label class="form-radio">
+      <input type="radio" name="interval" value="onetime" checked>
+      <i class="form-icon"></i> One time
+    </label>
+    <label class="form-radio">
+      <input type="radio" name="interval" value="month">
+      <i class="form-icon"></i> Monthly
+    </label>
+    <label class="form-radio">
+      <input type="radio" name="interval" value="year">
+      <i class="form-icon"></i> Yearly
+    </label>
+  </div>
+
   <div class="form-group">
     <label class="form-label" for="amount">Donation amount (must be at least $1)</label>
 

tildes/tildes/views/donate.py

@@ -37,18 +37,23 @@ def get_donate_stripe(request: Request) -> dict:
     {
         "amount": Float(required=True, validate=Range(min=1.0)),
         "currency": String(required=True, validate=OneOf(("CAD", "USD"))),
+        "interval": String(required=True, validate=OneOf(("onetime", "month", "year"))),
     }
 )
-def post_donate_stripe(request: Request, amount: int, currency: str) -> dict:
+def post_donate_stripe(
+    request: Request, amount: int, currency: str, interval: str
+) -> dict:
     """Process a Stripe donation."""
     try:
         stripe.api_key = request.registry.settings["api_keys.stripe.secret"]
         publishable_key = request.registry.settings["api_keys.stripe.publishable"]
+        product_id = request.registry.settings["stripe.recurring_donation_product_id"]
     except KeyError:
         raise HTTPInternalServerError
 
     incr_counter("donation_initiations", type="stripe")
 
+    if interval == "onetime":
         session = stripe.checkout.Session.create(
             payment_method_types=["card"],
             line_items=[
@@ -63,6 +68,34 @@ def post_donate_stripe(request: Request, amount: int, currency: str) -> dict:
             success_url="https://tildes.net/donate_success",
             cancel_url="https://docs.tildes.net/donate",
         )
+    else:
+        product = stripe.Product.retrieve(product_id)
+        existing_plans = stripe.Plan.list(product=product, active=True, limit=100)
+
+        # look through existing plans to see if there's already a matching one, or
+        # create a new plan if not
+        for existing_plan in existing_plans:
+            if (
+                existing_plan.amount == int(amount * 100)
+                and existing_plan.currency == currency.lower()
+                and existing_plan.interval == interval
+            ):
+                plan = existing_plan
+                break
+        else:
+            plan = stripe.Plan.create(
+                amount=int(amount * 100),
+                currency=currency,
+                interval=interval,
+                product=product,
+            )
+
+        session = stripe.checkout.Session.create(
+            payment_method_types=["card"],
+            subscription_data={"items": [{"plan": plan.id}]},
+            success_url="https://tildes.net/donate_success",
+            cancel_url="https://docs.tildes.net/donate",
+        )
 
     return {"publishable_key": publishable_key, "session_id": session.id}