Get a monthly revenue report

from datetime import datetime, timezone
import stripe
from clickruntime import on_trigger, credentials, state, notify

@on_trigger
def run(event):
    stripe.api_key = credentials.secret("STRIPE_API_KEY")
    end = datetime.now(timezone.utc).replace(day=1, hour=0, minute=0, second=0, microsecond=0)
    start = end.replace(year=end.year - 1, month=12) if end.month == 1 else end.replace(month=end.month - 1)
    window = {"gte": int(start.timestamp()), "lt": int(end.timestamp())}
    gross = refunds = 0
    for t in stripe.BalanceTransaction.list(created=window, limit=100).auto_paging_iter():
        if t.type in ("charge", "payment"):
            gross += t.amount
        elif t.type in ("refund", "payment_refund"):
            refunds -= t.amount
    subs = list(stripe.Subscription.list(status="all", limit=100).auto_paging_iter())
    new = sum(1 for s in subs if window["gte"] <= s.created < window["lt"])
    cancelled = sum(1 for s in subs if s.canceled_at and window["gte"] <= s.canceled_at < window["lt"])
    now = {"gross": gross, "refunds": refunds, "net": gross - refunds, "new": new, "cancelled": cancelled}
    prev = state.get("last_month") or {}
    fmt = lambda k, money: (f"${now[k] / 100:,.2f}" if money else str(now[k])) + (
        f" (was {'$' + format(prev[k] / 100, ',.2f') if money else prev[k]})" if k in prev else "")
    notify.email_me(f"Stripe revenue for {start:%B %Y}", "\n".join([
        f"Gross: {fmt('gross', True)}", f"Refunds: {fmt('refunds', True)}", f"Net: {fmt('net', True)}",
        f"New subscriptions: {fmt('new', False)}", f"Cancelled: {fmt('cancelled', False)}"]))
    state.set("last_month", now)
    return now