Send polite payment reminders by email and text

from google.oauth2.credentials import Credentials
from googleapiclient.discovery import build
from twilio.rest import Client
import base64
from datetime import date
from clickruntime import on_trigger, credentials, http, state

OVERDUE = "https://billing.example.com/api/overdue"
STAGES = [(3, "a friendly reminder"), (10, "a second reminder"), (21, "a final reminder")]
FROM = "+15005550006"

def sms(to, body):
    return Client(credentials.secret("TWILIO_ACCOUNT_SID"), credentials.secret("TWILIO_AUTH_TOKEN")).messages.create(to=to, from_=FROM, body=body)
gmail = lambda: build("gmail", "v1", credentials=Credentials(credentials.connection("google", "work")), cache_discovery=False).users()

def send_email(to, subject, text):
    gmail().messages().send(userId="me", body={"raw": base64.urlsafe_b64encode(f"To: {to}\r\nSubject: {subject}\r\n\r\n{text}".encode()).decode()}).execute()

@on_trigger
def run(event):
    items = http.get(OVERDUE, headers={"Authorization": f"Bearer {credentials.secret('BILLING_TOKEN')}"}).json()
    sent = 0
    for it in items:
        days = (date.today() - date.fromisoformat(it["due_date"])).days
        stage = max((i for i, (d, _) in enumerate(STAGES) if days >= d), default=-1)
        if stage < 0 or (state.get(f"stage:{it['id']}") or -1) >= stage:
            continue
        text = f"Hi {it['name']}, this is {STAGES[stage][1]} that {it['amount']} was due on {it['due_date']}. Pay here: {it['pay_url']}"
        send_email(it["email"], f"Payment reminder: {it['amount']}", text)
        if it.get("phone"): sms(it["phone"], text[:300])
        state.set(f"stage:{it['id']}", stage); sent += 1
    return {"sent": sent}