import { NextResponse } from "next/server";
import { randomUUID } from "node:crypto";
import type { SendMessageResponse } from "@duoc-thu/shared-types";
import { buildAssistantMessage, type RagAnswerRaw } from "../_lib/ragResponse";

export const runtime = "nodejs";

// RAG never goes through api-gateway. The gateway proxies `/auth/*` only --
// apps/api-gateway/src/proxy/ holds a single AuthProxyController -- so
// preferring AI_SERVICE_URL here pointed every RAG call at a service with no
// such route the moment apiGateway was enabled, breaking chat, suggest,
// history, sections, section-text and feedback at once. Resolve ai-service
// directly and let AI_SERVICE_URL mean what its name says: auth only.
const AI_SERVICE_URL = process.env.AI_SERVICE_URL ?? "http://localhost:8000";

interface RagResponse extends RagAnswerRaw {
  trace_id: string;
  correlation_id?: string;
  otel_trace_id?: string | null;
}

export async function POST(request: Request) {
  let content: string;
  let conversationId: string | null = null;
  let responseMode: "ai" | "monograph" = "ai";
  try {
    const body = await request.json();
    content = typeof body?.content === "string" ? body.content.trim() : "";
    conversationId =
      typeof body?.conversationId === "string" ? body.conversationId : null;
    responseMode = body?.responseMode === "monograph" ? "monograph" : "ai";
  } catch {
    return NextResponse.json({ error: "invalid_body" }, { status: 400 });
  }
  if (!content) {
    return NextResponse.json({ error: "empty_query" }, { status: 400 });
  }
  if (content.length > 4000) {
    return NextResponse.json({ error: "query_too_long" }, { status: 400 });
  }
  if (conversationId && conversationId.length > 128) {
    return NextResponse.json({ error: "conversation_id_too_long" }, { status: 400 });
  }

  const incomingCorrelationId = request.headers.get("x-correlation-id")?.trim();
  const correlationId =
    incomingCorrelationId && /^[A-Za-z0-9][A-Za-z0-9._:-]{0,127}$/.test(incomingCorrelationId)
      ? incomingCorrelationId
      : randomUUID();
  let responseCorrelationId = correlationId;
  let responseTraceId: string | null = null;

  let rag: RagResponse;
  try {
    const targetUrl = AI_SERVICE_URL.includes("/v1/rag")
      ? AI_SERVICE_URL
      : `${AI_SERVICE_URL}/v1/rag/query`;

    const upstreamHeaders: Record<string, string> = {
      "Content-Type": "application/json",
      "X-Correlation-ID": correlationId,
      "X-Client-Version": "1.0.0",
    };
    const traceparent = request.headers.get("traceparent");
    const tracestate = request.headers.get("tracestate");
    if (traceparent) upstreamHeaders.traceparent = traceparent;
    if (tracestate) upstreamHeaders.tracestate = tracestate;

    const upstream = await fetch(targetUrl, {
      method: "POST",
      headers: upstreamHeaders,
      body: JSON.stringify({
        query: content,
        subject_scope: "human",
        intent: "fact_lookup",
        conversation_id: conversationId,
        response_mode: responseMode,
      }),
      cache: "no-store",
      // Propagate a browser disconnect/Stop action to the upstream fetch.
      // The synchronous Bedrock call already in flight may finish, but this
      // prevents the BFF itself from keeping an orphaned HTTP request open.
      signal: request.signal,
    });
    responseCorrelationId = upstream.headers.get("x-correlation-id") ?? correlationId;
    responseTraceId = upstream.headers.get("x-trace-id");
    if (!upstream.ok) {
      rag = {
        trace_id: `fallback-${Date.now()}`,
        decision: "abstain",
        reason: "upstream_error",
        answer: "Dịch vụ AI Service đang khởi động hoặc gặp sự cố tạm thời. Vui lòng thử lại trong giây lát.",
        resolved_drug_id: null,
        citations: [],
      };
    } else {
      rag = (await upstream.json()) as RagResponse;
    }
  } catch {
    rag = {
      trace_id: `fallback-${Date.now()}`,
      decision: "abstain",
      reason: "upstream_unreachable",
      answer: `Không thể kết nối đến AI Service (${AI_SERVICE_URL}). Vui lòng đảm bảo AI Service đã được bật.`,
      resolved_drug_id: null,
      citations: [],
    };
  }

  // The RagAgent orchestrator (F-03) puts a specific, already-Vietnamese
  // message into `answer` for most abstain cases too (e.g. "Không tìm thấy
  // X trong Dược thư Quốc gia Việt Nam") — prefer it over the static
  // REFUSALS lookup, which only covers the retired resolver's reason codes
  // and would otherwise discard a good message in favor of a generic one.
  // REFUSALS/GENERIC_REFUSAL (in `_lib/ragResponse`) are now purely the
  // fallback for the genuinely answer-less case (retrieval abstained with
  // no message to show).
  const message: SendMessageResponse["message"] = buildAssistantMessage(
    rag,
    rag.trace_id || `msg-${Date.now()}`,
    new Date().toISOString()
  );

  const responseHeaders = new Headers({
    "X-Correlation-ID": responseCorrelationId,
  });
  if (responseTraceId) responseHeaders.set("X-Trace-ID", responseTraceId);

  return NextResponse.json(
    { message, sessionId: conversationId ?? undefined } satisfies SendMessageResponse,
    {
      headers: responseHeaders,
    }
  );
}