"use client";

import type { TranscriptDetail } from "../lib/transcripts";
import { channelRef, readerFor } from "../lib/archive/readers";
import { idbGet, idbPutBatch } from "./transcriptStore";
import { makeId, splitId } from "./originId";

// The manifest -> slugToPage -> page walk is the ArchiveReader's
// (lib/archive/reader.ts), including the per-channel manifest PromiseMap and
// the byte-budgeted page LRU. What stays here is what is genuinely the
// viewer's: the per-id memo, the in-flight dedupe, and warming IndexedDB with
// every record of a page we already paid for.
const resolved = new Map<string, TranscriptDetail>();
const inFlight = new Map<string, Promise<TranscriptDetail>>();

// `id` is an OriginId: a bare "channelSlug/videoId" for same-origin content, or
// "origin\tchannelSlug/videoId" for a federated cross-origin video. Maps and
// the IDB store are keyed by the full id, so origins never collide.
export function fetchTranscript(id: string): Promise<TranscriptDetail> {
  const hit = resolved.get(id);
  if (hit) return Promise.resolve(hit);
  const flying = inFlight.get(id);
  if (flying) return flying;

  const p = load(id).then((detail) => {
    resolved.set(id, detail);
    inFlight.delete(id);
    return detail;
  });
  p.catch(() => {
    inFlight.delete(id);
  });
  inFlight.set(id, p);
  return p;
}

async function load(id: string): Promise<TranscriptDetail> {
  const stored = await idbGet(id);
  if (stored) return stored;
  const { origin, slug } = splitId(id);
  const slashIdx = slug.indexOf("/");
  if (slashIdx < 0) throw new Error(`Malformed transcript slug: ${slug}`);
  const channelSlug = slug.slice(0, slashIdx);
  const videoId = slug.slice(slashIdx + 1);
  const reader = readerFor(origin);
  const ch = channelRef(channelSlug, origin);
  const manifest = await reader.transcriptsManifest(ch);
  const pageIndex = manifest.slugToPage[videoId];
  if (pageIndex === undefined)
    throw new Error(`Unknown transcript slug: ${slug}`);
  const page = await reader.transcriptPage(ch, pageIndex);
  let found: TranscriptDetail | undefined;
  for (const entry of page) {
    // Re-key warmed entries by their OriginId so a cross-origin
    // channelSlug/videoId can't shadow a same-origin one with the same slug.
    const entryId = makeId(origin, entry.slug);
    if (entry.slug === slug) found = entry;
    // Opportunistically warm the per-id memory + IDB caches so subsequent
    // fetches for other videos in this page hit without a network round-trip.
    // Huge win for searchPipeline which iterates many slugs from the same
    // channel/page.
    resolved.set(entryId, entry);
    idbPutBatch(entryId, entry);
  }
  if (!found)
    throw new Error(`Transcript ${slug} missing from page ${pageIndex}`);
  return found;
}