Get a Telegram warning about tomorrow's calendar clashes

from datetime import datetime, timedelta
from zoneinfo import ZoneInfo
from google.oauth2.credentials import Credentials
from googleapiclient.discovery import build
from clickruntime import on_trigger, credentials, http

CALENDARS = {"primary": "work", "you.personal@gmail.com": "personal"}
TZ, CHAT_ID, MIN_GAP = ZoneInfo("Europe/Berlin"), "123456789", 10

def tg(method, **params):
    r = http.post(f"https://api.telegram.org/bot{credentials.secret('TELEGRAM_BOT_TOKEN')}/{method}", json=params)
    r.raise_for_status()
    return r.json()["result"]

@on_trigger
def run(event):
    cal = build("calendar", "v3", credentials=Credentials(credentials.connection("google", "work")), cache_discovery=False)
    start = datetime.now(TZ).replace(hour=0, minute=0, second=0, microsecond=0) + timedelta(days=1)
    events = []
    for cid, label in CALENDARS.items():
        for e in cal.events().list(calendarId=cid, timeMin=start.isoformat(), timeMax=(start + timedelta(days=1)).isoformat(),
                                   singleEvents=True, orderBy="startTime").execute().get("items", []):
            me = next((a for a in e.get("attendees", []) if a.get("self")), {})
            if "dateTime" not in e["start"] or e.get("transparency") == "transparent" or me.get("responseStatus") == "declined":
                continue
            events.append((datetime.fromisoformat(e["start"]["dateTime"]).astimezone(TZ),
                           datetime.fromisoformat(e["end"]["dateTime"]).astimezone(TZ), e.get("summary", "(no title)"), label))
    events.sort()
    issues = []
    for i, (s1, e1, t1, l1) in enumerate(events):
        for s2, e2, t2, l2 in events[i + 1:]:
            if s2 < e1:
                issues.append(f"• {s1:%H:%M} {t1} overlaps {s2:%H:%M} {t2} ({l2})")
            elif (s2 - e1) < timedelta(minutes=MIN_GAP):
                issues.append(f"• {t1} ends {e1:%H:%M}, {s2:%H:%M} {t2} starts ({int((s2 - e1).total_seconds() // 60)} min gap)")
            else:
                break
    if issues:
        tg("sendMessage", chat_id=CHAT_ID, text=f"⚠️ Tomorrow has {len(issues)} clashes\n" + "\n".join(issues))
    return {"clashes": len(issues)}