Get warned before Stripe free trials end

import time
import stripe
from datetime import datetime, timezone
from clickruntime import on_trigger, credentials, notify, report_fetched

DAYS = 3

@on_trigger
def run(event):
    stripe.api_key = credentials.secret("STRIPE_API_KEY")
    cutoff = time.time() + DAYS * 86400
    ending = []
    for sub in stripe.Subscription.list(status="trialing", limit=100,
                                        expand=["data.customer", "data.default_payment_method"]).auto_paging_iter():
        if sub.trial_end and sub.trial_end <= cutoff:
            ending.append(sub)
    report_fetched(len(ending))
    if not ending:
        return {"ending": 0}

    def line(s):
        plan = s["items"]["data"][0]["price"].get("nickname") or s["items"]["data"][0]["price"]["id"]
        day = datetime.fromtimestamp(s.trial_end, timezone.utc).strftime("%a %d %b")
        return f"- {s.customer.email} · {plan} · ends {day}"

    has_card = lambda s: bool(s.default_payment_method or s.customer.invoice_settings.default_payment_method)
    no_card = [line(s) for s in ending if not has_card(s)]
    card = [line(s) for s in ending if has_card(s)]
    body = "No card on file:\n" + ("\n".join(no_card) or "- none") + "\n\nCard saved:\n" + ("\n".join(card) or "- none")
    notify.email_me(f"{len(ending)} Stripe trials end in the next {DAYS} days", body)
    return {"ending": len(ending)}