Flag declined Paddle payments in Slack

from clickruntime import on_event, credentials, http, state, notify

import hashlib, hmac

def paddle_signed(event):
    parts = dict(p.split("=", 1) for p in event.header("Paddle-Signature").split(";"))
    expected = hmac.new(credentials.secret("PADDLE_WEBHOOK_SECRET").encode(),
                        f"{parts['ts']}:{event.body}".encode(), hashlib.sha256).hexdigest()
    return hmac.compare_digest(expected, parts["h1"])

@on_event
def handle(event):
    if not paddle_signed(event):
        return {"posted": False, "reason": "bad signature"}
    txn = event.json["data"]
    if state.get(f"alerted:{txn['id']}"):
        return {"posted": False, "reason": "already alerted"}
    customer = http.get(f"https://api.paddle.com/customers/{txn['customer_id']}",
                        headers={"Authorization": f"Bearer {credentials.secret('PADDLE_API_KEY')}"}).json()["data"]
    reason = next((p.get("error_code") for p in reversed(txn.get("payments", [])) if p.get("error_code")), "unknown")
    amount = int(txn["details"]["totals"]["grand_total"]) / 100
    notify.slack(f"💳 Payment failed: {customer['email']}, {txn['currency_code']} {amount:,.2f}, reason: {reason}",
                 channel="#billing")
    state.set(f"alerted:{txn['id']}", True)
    return {"transaction": txn["id"]}