src/app/api/chat/route.ts

import { NextRequest, NextResponse } from 'next/server';
import { db } from '@/lib/db';
import { getCookieToken, getSessionUser } from '@/lib/auth';
import { chatSchema } from '@/lib/validation';
import { chatRateLimit } from '@/lib/rate-limit';

function buildInvoiceContext(userId: string): string {
  // Intentionally synchronous placeholder — actual query runs async
  return '';
}

export async function POST(request: NextRequest) {
  try {
    // ── Auth ──────────────────────────────────────────────────────────
    const token = getCookieToken(request);
    if (!token) {
      return NextResponse.json({ error: 'Not authenticated' }, { status: 401 });
    }
    const user = await getSessionUser(token);
    if (!user) {
      return NextResponse.json({ error: 'Not authenticated' }, { status: 401 });
    }

    // ── Plan Check (Pro / Enterprise only) ───────────────────────────
    if (user.plan !== 'pro' && user.plan !== 'enterprise') {
      return NextResponse.json(
        { error: 'AI Chat is available on Pro and Enterprise plans. Please upgrade your plan.' },
        { status: 403 }
      );
    }

    // ── Rate Limit ────────────────────────────────────────────────────
    const { allowed, retryAfterMs } = await chatRateLimit(`chat:${user.id}`);
    if (!allowed) {
      return NextResponse.json(
        { error: 'Chat rate limit exceeded. Please try again later.' },
        {
          status: 429,
          headers: { 'Retry-After': String(Math.ceil(retryAfterMs / 1000)) },
        }
      );
    }

    // ── Validate Body ─────────────────────────────────────────────────
    const body = await request.json();
    const parsed = chatSchema.safeParse(body);
    if (!parsed.success) {
      return NextResponse.json(
        { error: parsed.error.issues[0].message },
        { status: 400 }
      );
    }

    const { message, history = [] } = parsed.data;

    // ── Fetch User's Invoices for Context ─────────────────────────────
    const recentInvoices = await db.invoice.findMany({
      where: { userId: user.id },
      orderBy: { createdAt: 'desc' },
      take: 20,
    });

    const invoiceSummary = recentInvoices.length > 0
      ? recentInvoices
          .map(
            (inv) =>
              `- Invoice ${inv.invNumber || 'N/A'} from ${inv.vendor || 'Unknown'}: ${inv.currency} ${inv.total ?? 0} (${inv.status}, ${inv.isDuplicate ? 'duplicate' : 'unique'}, confidence: ${inv.confidence ? (inv.confidence * 100).toFixed(0) + '%' : 'N/A'})`
          )
          .join('\n')
      : 'No invoices found.';

    const totalAmount = recentInvoices.reduce((sum, inv) => sum + (inv.total ?? 0), 0);
    const duplicateCount = recentInvoices.filter((inv) => inv.isDuplicate).length;

    const systemPrompt = `You are OmniParse AI, an intelligent invoice processing assistant. You help users understand, analyze, and manage their invoices. Be concise, helpful, and professional.

Here is the user's recent invoice data:
Total invoices (recent 20): ${recentInvoices.length}
Total amount: USD ${totalAmount.toFixed(2)}
Duplicates found: ${duplicateCount}

${invoiceSummary}

The user is on the "${user.plan}" plan. Answer questions about their invoices, provide spending insights, flag potential duplicates, and help with invoice management. Keep responses concise and actionable.`;

    // ── Try AI SDK, Fall Back to Demo Response ────────────────────────
    let aiResponse: string;

    try {
      // Attempt to use z-ai-web-dev-sdk for real AI responses
      const { default: ZAI } = await import('z-ai-web-dev-sdk');
      const zai = await ZAI.create();

      const messages: Array<{ role: string; content: string }> = [
        { role: 'system', content: systemPrompt },
        ...history.map((h) => ({ role: h.role, content: h.content })),
        { role: 'user', content: message },
      ];

      const result = await zai.chat.completions.create({
        model: 'default',
        messages: messages as never,
      });

      const completion = result as Record<string, unknown>;
      const choices = completion.choices as Array<{ message: { content: string } }>;
      aiResponse = choices?.[0]?.message?.content ?? 'I was unable to generate a response. Please try again.';
    } catch {
      // Fallback: Generate a helpful context-aware demo response
      aiResponse = generateDemoResponse(message, recentInvoices, totalAmount, duplicateCount, user.plan);
    }

    return NextResponse.json({ reply: aiResponse });
  } catch (error) {
    console.error('[CHAT_ERROR]', error);
    return NextResponse.json(
      { error: 'Internal server error' },
      { status: 500 }
    );
  }
}

// ─── Demo Response Generator (fallback when AI SDK unavailable) ────────────────

function generateDemoResponse(
  message: string,
  invoices: Array<{
    vendor: string | null;
    invNumber: string | null;
    total: number | null;
    currency: string;
    status: string;
    isDuplicate: boolean;
    confidence: number | null;
    invDate: string | null;
    dueDate: string | null;
  }>,
  totalAmount: number,
  duplicateCount: number,
  plan: string
): string {
  const msgLower = message.toLowerCase();

  // Summary / overview queries
  if (msgLower.includes('summary') || msgLower.includes('overview') || msgLower.includes('how many')) {
    if (invoices.length === 0) {
      return "You don't have any invoices yet. Upload some invoices to get started, and I'll help you analyze them!";
    }
    const vendors = [...new Set(invoices.map((i) => i.vendor).filter(Boolean))];
    const avgAmount = totalAmount / invoices.length;
    return `Here's a quick overview of your invoices:\n\n` +
      `📊 **Total invoices:** ${invoices.length}\n` +
      `💰 **Total amount:** $${totalAmount.toFixed(2)}\n` +
      `📈 **Average invoice:** $${avgAmount.toFixed(2)}\n` +
      `🏢 **Unique vendors:** ${vendors.length} (${vendors.slice(0, 5).join(', ')}${vendors.length > 5 ? '...' : ''})\n` +
      `🔄 **Duplicates:** ${duplicateCount}\n\n` +
      `Would you like me to break this down by vendor or time period?`;
  }

  // Duplicate queries
  if (msgLower.includes('duplicate') || msgLower.includes('repeat')) {
    if (duplicateCount === 0) {
      return "Great news! No duplicates were detected in your invoices. The system automatically flags potential duplicates during upload based on vendor and amount matching.";
    }
    const dups = invoices.filter((i) => i.isDuplicate);
    const dupSummary = dups
      .map((i) => `• ${i.invNumber || 'N/A'} from ${i.vendor || 'Unknown'} — $${i.total ?? 0}`)
      .join('\n');
    return `⚠️ **${duplicateCount} potential duplicate(s) found:**\n\n${dupSummary}\n\n` +
      `These were flagged because they share the same vendor and a similar amount with another invoice. You can review them in the "Duplicates" tab or delete any that are truly repeated.`;
  }

  // Vendor queries
  if (msgLower.includes('vendor') || msgLower.includes('supplier') || msgLower.includes('company')) {
    const vendorMap = new Map<string, { count: number; total: number }>();
    for (const inv of invoices) {
      const v = inv.vendor || 'Unknown';
      const existing = vendorMap.get(v) ?? { count: 0, total: 0 };
      vendorMap.set(v, {
        count: existing.count + 1,
        total: existing.total + (inv.total ?? 0),
      });
    }
    const lines = [...vendorMap.entries()]
      .sort((a, b) => b[1].total - a[1].total)
      .map(([v, data]) => `• **${v}**: ${data.count} invoice(s), totaling $${data.total.toFixed(2)}`)
      .join('\n');
    return `Here's a breakdown by vendor:\n\n${lines || 'No vendor data available.'}`;
  }

  // Spending / amount queries
  if (msgLower.includes('spend') || msgLower.includes('cost') || msgLower.includes('total') || msgLower.includes('amount')) {
    if (invoices.length === 0) return "No invoices to analyze yet.";
    const avgAmount = totalAmount / invoices.length;
    const maxInv = invoices.reduce((a, b) => (b.total ?? 0) > (a.total ?? 0) ? b : a);
    const minInv = invoices.reduce((a, b) => (b.total ?? 0) < (a.total ?? 0) ? b : a);
    return `💰 **Spending Analysis:**\n\n` +
      `• Total: $${totalAmount.toFixed(2)} across ${invoices.length} invoices\n` +
      `• Average: $${avgAmount.toFixed(2)} per invoice\n` +
      `• Largest: $${maxInv.total ?? 0} from ${maxInv.vendor || 'Unknown'} (${maxInv.invNumber || 'N/A'})\n` +
      `• Smallest: $${minInv.total ?? 0} from ${minInv.vendor || 'Unknown'} (${minInv.invNumber || 'N/A'})\n\n` +
      `Want me to analyze spending trends or identify cost-saving opportunities?`;
  }

  // Default helpful response
  return `I can help you with your invoices! Here are some things you can ask me:\n\n` +
    `• **"Give me a summary"** — Overview of all your invoices\n` +
    `• **"Show duplicates"** — Find potential duplicate invoices\n` +
    `• **"Breakdown by vendor"** — Spending per vendor\n` +
    `• **"Spending analysis"** — Cost insights and trends\n\n` +
    `You currently have **${invoices.length} invoice(s)** totaling **$${totalAmount.toFixed(2)}** on the **${plan}** plan. How can I help?`;
}

// Suppress unused import warning
void buildInvoiceContext;