Post Chargebee plan upgrades and downgrades to Slack

from clickruntime import on_event, credentials, notify, state

def from_chargebee(event):
    return event.header("Authorization") == credentials.secret("CHARGEBEE_WEBHOOK_AUTH")  # "Basic ..." set on the webhook

@on_event
def handle(event):
    if not from_chargebee(event):
        return {"posted": False, "reason": "unauthorised"}
    body = event.json
    if body["event_type"] not in ("subscription_created", "subscription_changed"):
        return {"posted": False}
    c, sub = body["content"]["customer"], body["content"]["subscription"]
    plan = next((i["item_price_id"] for i in sub["subscription_items"] if i.get("item_type") == "plan"),
                sub["subscription_items"][0]["item_price_id"])
    mrr = sub.get("mrr", 0)
    before = state.get(f"sub:{sub['id']}")
    state.set(f"sub:{sub['id']}", {"plan": plan, "mrr": mrr})
    if body["event_type"] == "subscription_created" or not before or (before["plan"] == plan and before["mrr"] == mrr):
        return {"posted": False}
    diff = (mrr - before["mrr"]) / 100
    kind = "⬆️ Upgrade" if diff > 0 else "⬇️ Downgrade" if diff < 0 else "🔁 Plan change"
    name = c.get("company") or f"{c.get('first_name', '')} {c.get('last_name', '')}".strip() or c.get("email", c["id"])
    notify.slack(f"{kind}: {name} moved from {before['plan']} to {plan}. "
                 f"MRR {diff:+,.2f} {sub['currency_code']} (now {sub['currency_code']} {mrr / 100:,.2f})", channel="#revenue")
    return {"posted": True, "subscription": sub["id"]}