/**
 * Warm the Home snapshot from a secondary page (BUG-1104).
 *
 * BUG-1040's warm return only works after Home has cold-started once in this
 * document. A tab that opens on /chart, /ephemeris, /reports or /people (a
 * refresh, a shared link, the post-login landing of a deep link) has no
 * snapshot, so its first 「新建对话」 plays the whole loading ring.
 *
 * While such a page sits idle, fetch exactly what `isCompleteHomeWarmSnapshot`
 * requires — the model catalog and the rectification entry summary — with the
 * same client helpers the cold start uses, and write it through the same
 * `writeHomeWarmSnapshot`. Read-only GETs only: no fallback PATCH, no
 * consultation recovery. Those still run in Home's warm refresh after landing.
 * The cursor is left to the provider's own boot (`listBoot: null`).
 *
 * Pure module state, no React.
 */

import { fetchModelCatalog, fetchRectificationEntrySummary } from "./home-cloud-sync";
import { isCompleteHomeWarmSnapshot, readHomeWarmSnapshot, writeHomeWarmSnapshot } from "./home-warm-snapshot";
import type { PublicLanguageModelCatalog } from "./public-models";
import type { RectificationEntrySummary } from "./rectification-entry";

export type HomeWarmPrefetchIo = Readonly<{
  fetchModelCatalog: (signal?: AbortSignal) => Promise<PublicLanguageModelCatalog>;
  fetchRectificationEntrySummary: (signal?: AbortSignal) => Promise<RectificationEntrySummary | null>;
}>;

const defaultIo: HomeWarmPrefetchIo = { fetchModelCatalog, fetchRectificationEntrySummary };

let inflight: { accountId: string; promise: Promise<boolean> } | null = null;

/**
 * Fill the snapshot for `accountId` unless it is already complete. Resolves to
 * true when this call wrote a complete snapshot. Any failure leaves nothing
 * behind: the next Home simply takes the unchanged cold path.
 * `isCurrent` is asked again before writing, so an account switch, sign-out
 * or a Home that mounted meanwhile never receives a late write.
 */
export function prefetchHomeWarmSnapshot(
  accountId: string,
  isCurrent: () => boolean,
  io: HomeWarmPrefetchIo = defaultIo,
  signal?: AbortSignal,
): Promise<boolean> {
  if (!accountId || isCompleteHomeWarmSnapshot(readHomeWarmSnapshot(accountId))) return Promise.resolve(false);
  if (inflight && inflight.accountId === accountId) return inflight.promise;
  const promise = (async () => {
    try {
      const [modelCatalog, summary] = await Promise.all([
        io.fetchModelCatalog(signal),
        // Same settle rule as the cold start: a failed summary reads as the default card.
        io.fetchRectificationEntrySummary(signal).catch(() => null),
      ]);
      if (signal?.aborted || !isCurrent()) return false;
      if (isCompleteHomeWarmSnapshot(readHomeWarmSnapshot(accountId))) return false;
      const next = { accountId, modelCatalog, entrySummary: summary, entrySummarySettled: true, sessionsCursor: null, listBoot: null };
      if (!isCompleteHomeWarmSnapshot(next)) return false;
      writeHomeWarmSnapshot(next);
      return true;
    } catch {
      return false;
    } finally {
      inflight = null;
    }
  })();
  inflight = { accountId, promise };
  return promise;
}

export function resetHomeWarmPrefetchForTests(): void {
  inflight = null;
}