export const SESSION_URL_QUERY_KEY = "c";
export const NEW_CHAT_QUERY_KEY = "new";
/**
 * Legacy key only. Until BUG-1052 a 401 or a secondary-page link stashed the
 * current `?c=` here and a bare `/` reopened it. Nothing writes it any more;
 * bootstrap removes a leftover value so an old tab cannot keep a stale id.
 */
export const SESSION_URL_RETURN_STORAGE_KEY = "jyotisha.session-url-return";
export const SESSION_MISSING_NOTICE = "该对话不存在或已被删除";
export const SESSION_LOOKUP_FAILED_NOTICE = "这条对话暂时读不到，请稍后重试。";
export const SESSION_URL_ID_PATTERN = /^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;

export type SessionUrlQuery = {
  readonly present: boolean;
  readonly sessionId: string | null;
};

export type BootstrapSessionSelection = {
  readonly sessionId: string;
  readonly urlAction: "keep" | "replace-clear" | "none" | "lookup" | "new-chat";
  readonly missing: boolean;
};

/**
 * The one new-chat intent. The read-only sidebar and /people「和 TA 对话」 both
 * link here; the person rides on the current-subject store, not the URL.
 * Bootstrap turns it into a local empty consultation, so no older session is
 * reopened (BUG-1015/1038).
 */
export function newChatHref(): string {
  return "/?new=1";
}

export function parseNewChatIntent(search: string): boolean {
  const params = new URLSearchParams(search.startsWith("?") ? search.slice(1) : search);
  return params.has(NEW_CHAT_QUERY_KEY);
}

export function parseSessionUrlQuery(search: string): SessionUrlQuery {
  const params = new URLSearchParams(search.startsWith("?") ? search.slice(1) : search);
  if (!params.has(SESSION_URL_QUERY_KEY)) {
    return { present: false, sessionId: null };
  }
  const raw = params.get(SESSION_URL_QUERY_KEY) ?? "";
  return {
    present: true,
    sessionId: SESSION_URL_ID_PATTERN.test(raw) ? raw : null,
  };
}

export function sessionHref(search: string, sessionId: string | null, pathname = "/"): string {
  const params = new URLSearchParams(search.startsWith("?") ? search.slice(1) : search);
  params.delete(NEW_CHAT_QUERY_KEY);
  if (sessionId) params.set(SESSION_URL_QUERY_KEY, sessionId);
  else params.delete(SESSION_URL_QUERY_KEY);
  const query = params.toString();
  const path = pathname || "/";
  return query ? `${path}?${query}` : path;
}

export function writeSessionUrl(sessionId: string | null, mode: "push" | "replace") {
  const { location, history } = globalThis.window;
  const next = sessionHref(location.search, sessionId, location.pathname);
  const current = `${location.pathname}${location.search}`;
  if (current === next) return;
  if (mode === "push") history.pushState(null, "", next);
  else history.replaceState(null, "", next);
}

/** Removes a stash an older build left behind (BUG-1052). Never read back. */
export function clearLoginSessionReturn() {
  try {
    globalThis.sessionStorage.removeItem(SESSION_URL_RETURN_STORAGE_KEY);
  } catch {
    // Ignore private-mode quota errors.
  }
}

/**
 * Where a full load of `/` lands (BUG-1052): `?new=1` → a new chat; `?c=` →
 * that conversation (shared links, sidebar links, refresh inside a
 * conversation); anything else — login, a typed address, a bookmark, a
 * refresh of bare `/` — → the blank starter home. There is no stored
 * "return to the last conversation" any more.
 */
export function resolveBootstrapSessionSelection(input: {
  readonly listedIds: readonly string[];
  readonly defaultSessionId: string;
  readonly search: string;
}): BootstrapSessionSelection {
  if (parseNewChatIntent(input.search)) {
    return { sessionId: input.defaultSessionId, urlAction: "new-chat", missing: false };
  }
  const query = parseSessionUrlQuery(input.search);
  if (query.present) {
    if (query.sessionId && input.listedIds.includes(query.sessionId)) {
      return { sessionId: query.sessionId, urlAction: "keep", missing: false };
    }
    if (query.sessionId) {
      return { sessionId: query.sessionId, urlAction: "lookup", missing: false };
    }
    return { sessionId: input.defaultSessionId, urlAction: "replace-clear", missing: true };
  }
  return { sessionId: input.defaultSessionId, urlAction: "none", missing: false };
}

/** Outcome of looking up a `?c=` id that is not in the loaded page (BUG-705). */
export function bootstrapSelectionFromLookup(
  status: "found" | "missing" | "unavailable",
  requestedId: string,
  defaultSessionId: string,
): BootstrapSessionSelection {
  if (status === "found") return { sessionId: requestedId, urlAction: "keep", missing: false };
  if (status === "missing") return { sessionId: defaultSessionId, urlAction: "replace-clear", missing: true };
  return { sessionId: defaultSessionId, urlAction: "none", missing: false };
}