from datetime import datetime, timedelta, timezone

from app.models import EventEdition


def _fmt_ics(dt: datetime) -> str:
    if dt.tzinfo is None:
        dt = dt.replace(tzinfo=timezone.utc)
    return dt.strftime("%Y%m%dT%H%M%SZ")


def build_ics(edition: EventEdition, page_url: str) -> str:
    start = edition.event_date or datetime.now(timezone.utc) + timedelta(days=7)
    end = start + timedelta(hours=4)
    uid = f"desi-clans-{edition.slug}@bengaluru"
    location = edition.venue_name or edition.city
    summary = edition.title.replace(",", "\\,")
    desc = (edition.meta_description or edition.description or edition.title).replace("\n", "\\n")

    lines = [
        "BEGIN:VCALENDAR",
        "VERSION:2.0",
        "PRODID:-//Desi Clans//Bengaluru Events//EN",
        "CALSCALE:GREGORIAN",
        "METHOD:PUBLISH",
        "BEGIN:VEVENT",
        f"UID:{uid}",
        f"DTSTAMP:{_fmt_ics(datetime.now(timezone.utc))}",
        f"DTSTART:{_fmt_ics(start)}",
        f"DTEND:{_fmt_ics(end)}",
        f"SUMMARY:{summary}",
        f"DESCRIPTION:{desc} — {page_url}",
        f"LOCATION:{location}",
        f"URL:{page_url}",
        "END:VEVENT",
        "END:VCALENDAR",
    ]
    return "\r\n".join(lines) + "\r\n"