web/app/api/chat/route.ts

import { NextRequest, NextResponse } from "next/server";
import { createClient } from "@/lib/supabase/server";

const GRADIO_URL = process.env.CLAUSEGUARD_GRADIO_URL || "https://gaurv007-clauseguard.hf.space";

/**
 * FIX v4.1: The chat endpoint now properly documents its limitations.
 *
 * ARCHITECTURE NOTE:
 * The Gradio ChatInterface uses gr.State to store RAG embeddings per-session.
 * This state is NOT accessible via the Gradio API from an external caller —
 * each API call creates a new session with empty state.
 *
 * For the Next.js web app, chat should either:
 * 1. Use the FastAPI backend (/api/chat) which manages its own RAG sessions, OR
 * 2. Embed the Gradio Space in an iframe for direct interaction
 *
 * This route attempts to use the Gradio API as a best-effort fallback,
 * but will clearly communicate to the user if the session is unavailable.
 */
export async function POST(req: NextRequest) {
  try {
    const supabase = await createClient();
    const { data: { user } } = await supabase.auth.getUser();

    if (!user) {
      return NextResponse.json({ error: "Unauthorized. Please log in." }, { status: 401 });
    }

    const body = await req.json();
    const { message, history, session_id } = body;

    if (!message) {
      return NextResponse.json(
        { error: "message is required" },
        { status: 400 }
      );
    }

    // FIX v4.1: Input validation
    if (message.length > 2000) {
      return NextResponse.json(
        { error: "Message too long (max 2000 characters)" },
        { status: 400 }
      );
    }

    // Try the FastAPI backend first (it has proper RAG session management)
    const apiUrl = process.env.CLAUSEGUARD_API_URL || "";
    if (apiUrl && session_id) {
      try {
        const apiRes = await fetch(`${apiUrl}/api/chat`, {
          method: "POST",
          headers: { "Content-Type": "application/json" },
          body: JSON.stringify({ message, session_id, history: history || [] }),
        });
        if (apiRes.ok) {
          const data = await apiRes.json();
          return NextResponse.json({ response: data.response });
        }
      } catch {
        // Fall through to Gradio attempt
      }
    }

    // Fallback: Try the Gradio API
    const submitRes = await fetch(`${GRADIO_URL}/gradio_api/call/chat`, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({ data: [message] }),
    });

    if (!submitRes.ok) {
      const errText = await submitRes.text().catch(() => "");
      throw new Error(`Chat submit failed (${submitRes.status}): ${errText}`);
    }

    const { event_id } = await submitRes.json();
    if (!event_id) throw new Error("No event_id from Gradio chat");

    // Poll for result with timeout
    let resultText = "";
    let attempts = 0;
    const maxAttempts = 30;

    while (attempts < maxAttempts) {
      const resultRes = await fetch(
        `${GRADIO_URL}/gradio_api/call/chat/${event_id}`,
        { headers: { Accept: "text/event-stream" } }
      );

      if (!resultRes.ok) {
        throw new Error(`Chat result failed: ${resultRes.status}`);
      }

      resultText = await resultRes.text();

      if (resultText.includes("event: complete")) break;
      if (resultText.includes("event: error")) {
        const errMatch = resultText.match(/event:\s*error\s*\ndata:\s*(.+)/);
        if (errMatch) throw new Error(`Chat error: ${errMatch[1]}`);
        throw new Error("Chat error from backend");
      }

      await new Promise(r => setTimeout(r, 1000));
      attempts++;
    }

    // Find the complete event data
    const dataMatch = resultText.match(/event:\s*complete\s*\ndata:\s*(.+)/);
    if (!dataMatch) {
      return NextResponse.json({
        response: "⚠️ Chat is unavailable. The contract needs to be analyzed in the same session. " +
          "Please analyze a contract first in the Gradio Space, then use the chat tab there directly."
      });
    }

    const responseData = JSON.parse(dataMatch[1]);
    const responseText = typeof responseData === "string" ? responseData : responseData[0] || "";

    return NextResponse.json({ response: responseText });
  } catch (error: any) {
    console.error("Chat error:", error.message);
    return NextResponse.json(
      { error: error.message || "Chat failed. Make sure you analyzed a contract first." },
      { status: 500 }
    );
  }
}