Track PayPal refunds in Slack

from clickruntime import on_event, credentials, http, notify

API = "https://api-m.paypal.com"

def paypal_headers():
    resp = http.post(f"{API}/v1/oauth2/token", data={"grant_type": "client_credentials"},
                     auth=(credentials.secret("PAYPAL_CLIENT_ID"), credentials.secret("PAYPAL_CLIENT_SECRET")))
    resp.raise_for_status()
    return {"Authorization": f"Bearer {resp.json()['access_token']}"}

@on_event
def handle(event):
    body = event.json
    if body.get("event_type") != "PAYMENT.CAPTURE.REFUNDED":
        return {"posted": False}
    headers = paypal_headers()
    refund = http.get(f"{API}/v2/payments/refunds/{body['resource']['id']}", headers=headers).json()
    capture_url = next(l["href"] for l in refund["links"] if l["rel"] == "up")
    capture = http.get(capture_url, headers=headers).json()
    order_id = capture["supplementary_data"]["related_ids"]["order_id"]
    payer = http.get(f"{API}/v2/checkout/orders/{order_id}", headers=headers).json()["payer"]
    amount = refund["amount"]
    notify.slack(f"↩️ Refund of {amount['currency_code']} {amount['value']} to {payer['email_address']}\n"
                 f"Original transaction: {capture['id']}", channel="#finance")
    return {"refund": refund["id"]}