import { NextRequest, NextResponse } from 'next/server';
import { getStalwartCredentials } from '@/lib/stalwart/credentials';
import { serverSearchMail, hydrateMailRefs } from '@/lib/ai/retrieval/mail-embeddings';
import { logger } from '@/lib/logger';

export const runtime = 'nodejs';

const MAX_QUERY_CHARS = 512;
const DEFAULT_LIMIT = 6;

/**
 * POST /api/ai/retrieve — the server embedding leg (docs/AI-ASSISTANT-CONCEPT.md
 * §7 step 2). Real JMAP fetch + real Ollama embeddings + real cosine ranking
 * (lib/ai/retrieval/mail-embeddings.ts), not a mock.
 *
 * ACL note (§7 step 2b): this only ever embeds/searches the *authenticated
 * session's own* JMAP account — there is no shared-mailbox fan-out to
 * pre-filter yet, since group accounts are still deferred entirely (matches
 * the doc's own "shared-mailbox retrieval ships server-only" decision, which
 * itself hasn't been reached because there's no group account to retrieve
 * from). Nothing here can leak across accounts because nothing crosses the
 * account boundary in the first place.
 */
export async function POST(request: NextRequest) {
  const auth = await getStalwartCredentials(request);
  if (!auth) {
    return NextResponse.json({ error: 'not authenticated' }, { status: 401 });
  }

  if (!process.env.AI_SERVER_BASE_URL) {
    return new NextResponse(null, { status: 404 });
  }

  let body: { query?: unknown; limit?: unknown };
  try {
    body = await request.json();
  } catch {
    return NextResponse.json({ error: 'invalid JSON body' }, { status: 400 });
  }

  const query = typeof body.query === 'string' ? body.query.trim() : '';
  if (!query) {
    return NextResponse.json({ error: 'query is required' }, { status: 400 });
  }
  if (query.length > MAX_QUERY_CHARS) {
    return NextResponse.json({ error: 'query too long' }, { status: 400 });
  }
  const limit = typeof body.limit === 'number' ? Math.min(Math.max(Math.trunc(body.limit), 1), 20) : DEFAULT_LIMIT;

  try {
    const scored = await serverSearchMail(auth.serverUrl, auth.authHeader, query, limit);
    const chunks = await hydrateMailRefs(auth.serverUrl, auth.authHeader, scored.map((s) => s.ref));

    const contextBlock = chunks
      .map((c, i) => `[${i + 1}] Subject: ${c.title}\n${c.text}`)
      .join('\n\n');

    return NextResponse.json({
      ok: true,
      hits: chunks.map((c, i) => ({ ref: c.ref, title: c.title, snippet: c.text.slice(0, 200), rank: i + 1 })),
      contextBlock,
    }, { headers: { 'Cache-Control': 'no-store' } });
  } catch (cause) {
    logger.error('ai retrieve failed', { error: cause instanceof Error ? cause.message : String(cause) });
    return NextResponse.json({ error: 'retrieval unavailable' }, { status: 502 });
  }
}