next-ai-draw-io/app/api/log-save/route.ts

import { getLangfuseClient } from '@/lib/langfuse';
import { randomUUID } from 'crypto';
import { z } from 'zod';

const saveSchema = z.object({
  filename: z.string().min(1).max(255),
  format: z.enum(['drawio', 'png', 'svg']),
  sessionId: z.string().min(1).max(200).optional(),
});

export async function POST(req: Request) {
  const langfuse = getLangfuseClient();
  if (!langfuse) {
    return Response.json({ success: true, logged: false });
  }

  // Validate input
  let data;
  try {
    data = saveSchema.parse(await req.json());
  } catch {
    return Response.json({ success: false, error: 'Invalid input' }, { status: 400 });
  }

  const { filename, format, sessionId } = data;

  try {
    const timestamp = new Date().toISOString();

    // Find the most recent chat trace for this session to attach the save flag
    const tracesResponse = await langfuse.api.trace.list({
      sessionId,
      limit: 1,
    });

    const traces = tracesResponse.data || [];
    const latestTrace = traces[0];

    if (latestTrace) {
      // Add a score to the existing trace to flag that user saved
      await langfuse.api.ingestion.batch({
        batch: [
          {
            type: 'score-create',
            id: randomUUID(),
            timestamp,
            body: {
              id: randomUUID(),
              traceId: latestTrace.id,
              name: 'diagram-saved',
              value: 1,
              comment: `User saved diagram as ${filename}.${format}`,
            },
          },
        ],
      });
    }
    // If no trace found, skip logging (user hasn't chatted yet)

    return Response.json({ success: true, logged: !!latestTrace });
  } catch (error) {
    console.error('Langfuse save error:', error);
    return Response.json({ success: false, error: 'Failed to log save' }, { status: 500 });
  }
}