// SRC-06: Backend-for-Frontend-Route für Facettenzählungen. Spiegelt
// mail/internal/search/facets.go (Client.Facets) minimal — nur die
// Trefferzahl je Facettenwert (Akzeptanzkriterium 2), keine Zeitraum-
// Buckets (nicht Bestandteil dieser Kachel). Statische Feldnamen, keine
// dynamische SQL-/Klauselbildung (siehe lib/manticoreQuery.ts).
import { NextRequest, NextResponse } from "next/server";
import { FACET_FIELDS } from "../../../lib/facetFields";
import { buildMust, parseFilterParams } from "../../../lib/manticoreQuery";

const INDEX_NAME = "mail_documents";

function manticoreURL(): string {
  const base = process.env.MANTICORE_URL;
  if (!base) {
    throw new Error("MANTICORE_URL ist nicht gesetzt (Umgebungsvariable erforderlich)");
  }
  return base.replace(/\/$/, "");
}

interface ManticoreFacetResponse {
  aggregations?: Record<string, { buckets?: { key: string; doc_count: number }[] }>;
  error?: string;
}

export async function GET(request: NextRequest) {
  const tenantSlug = request.nextUrl.searchParams.get("tenant");
  const query = request.nextUrl.searchParams.get("q") ?? "";
  if (!tenantSlug) {
    return NextResponse.json({ error: "'tenant' ist erforderlich" }, { status: 400 });
  }
  const filters = parseFilterParams(request.nextUrl.searchParams.getAll("filter"));

  const aggs: Record<string, unknown> = {};
  for (const field of FACET_FIELDS) {
    aggs[field] = { terms: { field, size: 100 } };
  }

  const manticorePayload = {
    index: INDEX_NAME,
    query: { bool: { must: buildMust(tenantSlug, query, filters) } },
    aggs,
    limit: 0,
  };

  let manticoreResponse: Response;
  try {
    manticoreResponse = await fetch(`${manticoreURL()}/search`, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify(manticorePayload),
    });
  } catch (err) {
    return NextResponse.json({ error: `Facetten nicht erreichbar: ${(err as Error).message}` }, { status: 502 });
  }

  const parsed: ManticoreFacetResponse = await manticoreResponse.json().catch(() => ({}));
  if (!manticoreResponse.ok || parsed.error) {
    return NextResponse.json({ error: parsed.error ?? "Facetten fehlgeschlagen" }, { status: 502 });
  }

  const values: Record<string, { value: string; count: number }[]> = {};
  for (const field of FACET_FIELDS) {
    const buckets = parsed.aggregations?.[field]?.buckets ?? [];
    values[field] = buckets.filter((b) => b.key !== "").map((b) => ({ value: b.key, count: b.doc_count }));
  }

  return NextResponse.json({ values });
}