Sync an outside calendar feed into Google Calendar

from google.oauth2.credentials import Credentials
from googleapiclient.discovery import build
from clickruntime import on_trigger, credentials, http

ICS_URL = "https://example.com/events.ics"
CALENDAR_ID = "imports-calendar-id@group.calendar.google.com"

def parse_ics(text):
    text = text.replace("\r\n ", "").replace("\n ", "")
    for block in text.split("BEGIN:VEVENT")[1:]:
        fields = dict(l.split(":", 1) for l in block.split("END:VEVENT")[0].splitlines() if ":" in l)
        yield {k.split(";")[0]: v for k, v in fields.items()}

def when(v):
    if "T" not in v:
        return {"date": f"{v[:4]}-{v[4:6]}-{v[6:8]}"}
    return {"dateTime": f"{v[:4]}-{v[4:6]}-{v[6:8]}T{v[9:11]}:{v[11:13]}:{v[13:15]}" + ("Z" if v.endswith("Z") else ""),
            "timeZone": "UTC"}

@on_trigger
def run(event):
    cal = build("calendar", "v3", credentials=Credentials(credentials.connection("google", "work")), cache_discovery=False)
    feed = {e["UID"]: e for e in parse_ics(http.get(ICS_URL).text)}
    existing = {e["extendedProperties"]["private"]["uid"]: e for e in cal.events().list(
        calendarId=CALENDAR_ID, privateExtendedProperty="source=ics", maxResults=2500).execute()["items"]}
    added = updated = removed = 0
    for uid, e in feed.items():
        body = {"summary": e.get("SUMMARY", ""), "location": e.get("LOCATION", ""),
                "start": when(e["DTSTART"]), "end": when(e.get("DTEND", e["DTSTART"])),
                "extendedProperties": {"private": {"source": "ics", "uid": uid}}}
        if uid not in existing:
            cal.events().insert(calendarId=CALENDAR_ID, body=body).execute(); added += 1
        elif existing[uid]["summary"] != body["summary"] or existing[uid]["start"] != body["start"]:
            cal.events().patch(calendarId=CALENDAR_ID, eventId=existing[uid]["id"], body=body).execute(); updated += 1
    for uid in existing.keys() - feed.keys():
        cal.events().delete(calendarId=CALENDAR_ID, eventId=existing[uid]["id"]).execute(); removed += 1
    return {"added": added, "updated": updated, "removed": removed}