/**
 * Home bootstrap reveal policy.
 *
 * The loading screen owns every wait before the page appears. Phase "account"
 * fetches account, model catalog and the session list; phase "prepare" fetches
 * the starter questions, today's starlanguage and the rectification entry
 * summary in parallel. The page is revealed once every applicable item has
 * settled, or when the prepare budget runs out — never with a spinner inside.
 */

import { parseSessionUrlQuery } from "./chat-session-url.ts";

export type BootstrapPhase = "account" | "prepare";

export type LandingSession = Readonly<{
  id: string;
  sessionType: string;
  messages: readonly unknown[];
}>;

export type LandingUrlAction = "keep" | "replace-selected" | "replace-clear" | "none";

/**
 * A rectification Case is opened only when the address bar names that session
 * (`?c=`), including refresh and a login return that restored the URL. Bare `/`
 * after login must not open the latest history item in the background.
 */
export function shouldAutoOpenRectificationSession(input: {
  readonly sessionType: string | undefined;
  readonly sessionId: string | undefined;
  readonly search: string;
}): boolean {
  if (input.sessionType !== "birth_time_rectification" || !input.sessionId) return false;
  return parseSessionUrlQuery(input.search).sessionId === input.sessionId;
}

/**
 * Default `/` landing prefers an empty consultation so the starter home can
 * center. Deep links and login-return URLs keep the requested session.
 */
export function resolveStarterHomeLandingSessionId(
  sessions: readonly LandingSession[],
  selectedId: string,
  urlAction: LandingUrlAction,
): string {
  if (urlAction === "keep" || urlAction === "replace-selected") return selectedId;
  const selected = sessions.find((session) => session.id === selectedId);
  if (selected?.sessionType !== "birth_time_rectification") return selectedId;
  const emptyConsultation = sessions.find(
    (session) => session.sessionType === "consultation" && session.messages.length === 0,
  );
  if (emptyConsultation) return emptyConsultation.id;
  const anyConsultation = sessions.find((session) => session.sessionType === "consultation");
  return anyConsultation?.id ?? selectedId;
}

export function starterHomeLandingNeedsConsultation(
  sessions: readonly LandingSession[],
  landingId: string,
  urlAction: LandingUrlAction,
): boolean {
  if (urlAction === "keep" || urlAction === "replace-selected") return false;
  const landing = sessions.find((session) => session.id === landingId);
  return !landing || landing.sessionType === "birth_time_rectification";
}

export const BOOTSTRAP_PREPARE_TIMEOUT_MS = 4000;
export const SESSION_PREFETCH_COUNT = 5;

export type BootstrapPrepareState = Readonly<{
  profileComplete: boolean;
  onboardingSettled: boolean;
  dailyStarlanguageApplicable: boolean;
  dailyStarlanguageSettled: boolean;
  entrySummarySettled: boolean;
  /** A URL-named rectification session must be opened and hydrated before reveal. */
  rectificationApplicable?: boolean;
  rectificationSettled?: boolean;
}>;

export function bootstrapPrepareSettled(state: BootstrapPrepareState): boolean {
  if (!state.entrySummarySettled) return false;
  if (state.rectificationApplicable && !state.rectificationSettled) return false;
  if (state.profileComplete && !state.onboardingSettled) return false;
  if (state.dailyStarlanguageApplicable && !state.dailyStarlanguageSettled) return false;
  return true;
}

export function bootstrapRevealDelayMs(now: number, prepareStartedAt: number | null, settled: boolean): number {
  if (settled) return 0;
  if (prepareStartedAt === null) return BOOTSTRAP_PREPARE_TIMEOUT_MS;
  return Math.max(0, BOOTSTRAP_PREPARE_TIMEOUT_MS - (now - prepareStartedAt));
}

export function bootstrapLoadingCopy(phase: BootstrapPhase): Readonly<{ title: string; detail: string }> {
  return phase === "prepare"
    ? { title: "正在准备对话", detail: "整理推荐问题、今日星语与对话记录" }
    : { title: "正在载入账户", detail: "同步个人资料与对话记录" };
}

export type PrefetchableSession = Readonly<{
  id: string;
  sessionType: string;
  messagesHydrated?: boolean;
}>;

export function sessionIdsToPrefetch(
  sessions: readonly PrefetchableSession[],
  activeSessionId: string,
  limit = SESSION_PREFETCH_COUNT,
): string[] {
  const ids: string[] = [];
  for (const session of sessions) {
    if (ids.length >= limit) break;
    if (session.id === activeSessionId) continue;
    if (session.messagesHydrated) continue;
    if (session.sessionType !== "consultation") continue;
    ids.push(session.id);
  }
  return ids;
}