export const SESSION_URL_QUERY_KEY = "c";
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_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-selected" | "replace-clear" | "none";
  readonly missing: boolean;
  readonly clearStoredReturn: boolean;
};

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);
  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);
}

export function persistLoginSessionReturn() {
  try {
    const sessionId = parseSessionUrlQuery(globalThis.window.location.search).sessionId;
    if (sessionId) globalThis.sessionStorage.setItem(SESSION_URL_RETURN_STORAGE_KEY, sessionId);
  } catch {
    // sessionStorage can throw in private mode; login still proceeds.
  }
}

export function readLoginSessionReturn(): string | null {
  try {
    const raw = globalThis.sessionStorage.getItem(SESSION_URL_RETURN_STORAGE_KEY);
    if (!raw || !SESSION_URL_ID_PATTERN.test(raw)) return null;
    return raw;
  } catch {
    return null;
  }
}

export function clearLoginSessionReturn() {
  try {
    globalThis.sessionStorage.removeItem(SESSION_URL_RETURN_STORAGE_KEY);
  } catch {
    // Ignore private-mode quota errors.
  }
}

export function resolveBootstrapSessionSelection(input: {
  readonly listedIds: readonly string[];
  readonly defaultSessionId: string;
  readonly search: string;
  readonly storedReturnId: string | null;
}): BootstrapSessionSelection {
  const query = parseSessionUrlQuery(input.search);
  if (query.present) {
    if (query.sessionId && input.listedIds.includes(query.sessionId)) {
      return {
        sessionId: query.sessionId,
        urlAction: "keep",
        missing: false,
        clearStoredReturn: true,
      };
    }
    return {
      sessionId: input.defaultSessionId,
      urlAction: "replace-clear",
      missing: true,
      clearStoredReturn: true,
    };
  }
  if (input.storedReturnId) {
    if (input.listedIds.includes(input.storedReturnId)) {
      return {
        sessionId: input.storedReturnId,
        urlAction: "replace-selected",
        missing: false,
        clearStoredReturn: true,
      };
    }
    return {
      sessionId: input.defaultSessionId,
      urlAction: "replace-clear",
      missing: true,
      clearStoredReturn: true,
    };
  }
  return {
    sessionId: input.defaultSessionId,
    urlAction: "none",
    missing: false,
    clearStoredReturn: false,
  };
}