/**
 * /api/chunk?doc=<doc-id>&chunk=<c0042>
 *
 * Returns one chunk's payload (page, type, bbox, content_en, content_pt,
 * classification, anomaly flags). Used by client-side InlineCitation
 * component to expand `[[doc/p007#c0042]]` links into rich cards.
 *
 * Tries DB first (with embeddings already indexed), falls back to filesystem
 * (raw/<doc>--subagent/chunks/cXXXX.md) so the UX works even before the
 * indexer has run on a particular doc.
 */
import { NextRequest } from "next/server";
import { getChunk } from "@/lib/retrieval/hybrid";
import { readChunk as readChunkFs } from "@/lib/chunks";

export const runtime = "nodejs";
export const dynamic = "force-dynamic";

function json(data: unknown, status = 200) {
  return new Response(JSON.stringify(data), {
    status,
    headers: {
      "content-type": "application/json",
      "cache-control": "public, max-age=300",
    },
  });
}

export async function GET(req: NextRequest) {
  const u = new URL(req.url);
  const doc = u.searchParams.get("doc")?.trim();
  const chunk = u.searchParams.get("chunk")?.trim();
  if (!doc || !chunk) return json({ error: "doc and chunk required" }, 400);

  // 1. Try DB
  try {
    const c = await getChunk(doc, chunk);
    if (c) {
      return json({
        source: "db",
        chunk_id: c.chunk_id,
        doc_id: c.doc_id,
        page: c.page,
        type: c.type,
        bbox: c.bbox,
        classification: c.classification,
        content_en: c.content_en,
        content_pt: c.content_pt,
      });
    }
  } catch {
    // db unavailable → fall through to fs
  }

  // 2. Filesystem fallback
  const fs = await readChunkFs(doc, chunk);
  if (!fs) return json({ error: "not_found", doc_id: doc, chunk_id: chunk }, 404);
  return json({
    source: "fs",
    chunk_id: fs.fm.chunk_id,
    doc_id: doc,
    page: fs.fm.page,
    type: fs.fm.type,
    bbox: fs.fm.bbox,
    classification: fs.fm.classification,
    content_en: fs.content_en,
    content_pt: fs.content_pt,
  });
}