import { parseSafeXml, type ParsedXmlElement } from "@/worker/xml/parser";
import { CALDAV_NS, DAV_NS, qname, sameQName } from "@/worker/xml/namespaces";
import { elementsByQName, firstTextByQName, namedElement, namedElementChildren, textContent } from "@/worker/xml/tree";

export interface CalendarCollectionCreateRequest {
  displayName: string | null;
  timezoneIcal: string | null;
}

export function calendarCollectionCreateRequest(
  xml: string,
  maxBytes: number,
  method: "MKCALENDAR" | "MKCOL",
): CalendarCollectionCreateRequest {
  // RFC 4791 5.3.1 lets MKCALENDAR accept an empty body. RFC 5689 MKCOL requires
  // an extended body containing the desired resourcetype, so empty MKCOL must
  // not be used as a calendar-creation shortcut.
  if (xml.trim().length === 0) {
    if (method === "MKCOL") {
      throw new Error("MKCOL requires an RFC 5689 body with a calendar resourcetype");
    }
    return { displayName: null, timezoneIcal: null };
  }

  const { root: rootElement } = parseSafeXml(xml, maxBytes);
  const root = namedElement(rootElement);
  if (method === "MKCALENDAR" && !sameQName(root.qname, qname(CALDAV_NS, "mkcalendar"))) {
    throw new Error("Invalid MKCALENDAR body");
  }
  if (method === "MKCOL" && !sameQName(root.qname, qname(DAV_NS, "mkcol"))) throw new Error("Invalid MKCOL body");
  if (
    method === "MKCOL" &&
    !elementsByQName(root.element, qname(DAV_NS, "resourcetype"), root.namespaces).some(hasCalendarResourceType)
  ) {
    throw new Error("MKCOL requires a calendar resourcetype");
  }

  return {
    displayName: firstTextByQName(root.element, qname(DAV_NS, "displayname"), root.namespaces),
    timezoneIcal: calendarTimezoneIcal(root.element, root.namespaces),
  };
}

function hasCalendarResourceType(entry: { element: ParsedXmlElement; namespaces: Record<string, string> }): boolean {
  return namedElementChildren(entry.element, entry.namespaces).some((child) =>
    sameQName(child.qname, qname(CALDAV_NS, "calendar")),
  );
}

function calendarTimezoneIcal(element: ParsedXmlElement, namespaces: Record<string, string>): string | null {
  const timezone = elementsByQName(element, qname(CALDAV_NS, "calendar-timezone"), namespaces).at(0);
  if (!timezone) return null;
  const value = textContent(timezone.element).trim();
  if (!value) throw new Error("CALDAV:calendar-timezone must not be empty");
  const lines = value
    .replace(/\r\n/g, "\n")
    .replace(/\r/g, "\n")
    .split("\n")
    .map((line) => line.trim());
  if (!lines.some((line) => line.toUpperCase() === "BEGIN:VTIMEZONE")) {
    throw new Error("CALDAV:calendar-timezone must contain a VTIMEZONE component");
  }
  const tzid = lines
    .map((line) => /^TZID(?:;[^:]*)?:(.+)$/i.exec(line)?.[1]?.trim())
    .find((entry): entry is string => Boolean(entry));
  if (!tzid) throw new Error("CALDAV:calendar-timezone VTIMEZONE must include TZID");
  try {
    new Intl.DateTimeFormat("en-US", { timeZone: tzid }).format(new Date(0));
  } catch {
    throw new Error(`Unsupported CALDAV:calendar-timezone TZID ${tzid}`);
  }
  return value;
}