server.js

import express from 'express';
import cors from 'cors';
import Anthropic from '@anthropic-ai/sdk';
import { config } from 'dotenv';
import { fileURLToPath } from 'url';
import { dirname, join } from 'path';

config();

const __dirname = dirname(fileURLToPath(import.meta.url));
const app = express();
const PORT = process.env.PORT || 3001;

app.use(cors());
app.use(express.json());

const ALLOWED_MODELS = ['claude-haiku-4-5-20251001', 'claude-sonnet-4-6', 'claude-opus-4-6'];
const DEFAULT_MODEL = 'claude-haiku-4-5-20251001';
function getModel(body) {
  return ALLOWED_MODELS.includes(body?.model) ? body.model : DEFAULT_MODEL;
}

app.post('/api/validate-key', async (req, res) => {
  const apiKey = req.headers['x-api-key'];
  if (!apiKey) {
    return res.status(401).json({ error: 'API key required.' });
  }
  try {
    const anthropic = new Anthropic({ apiKey });
    await anthropic.messages.create({
      model: 'claude-haiku-4-5-20251001',
      max_tokens: 1,
      messages: [{ role: 'user', content: 'hi' }],
    });
    res.json({ valid: true });
  } catch (error) {
    if (error?.status === 401) {
      return res.status(401).json({ error: 'Invalid API key.' });
    }
    res.status(500).json({ error: 'Failed to validate key.' });
  }
});

app.post('/api/explain', async (req, res) => {
  const apiKey = req.headers['x-api-key'];
  if (!apiKey) {
    return res.status(401).json({ error: 'API key required.' });
  }
  const anthropic = new Anthropic({ apiKey });

  const { concept, parentConcept, rootConcept, existingConcepts } = req.body;

  try {
    const contextLine = parentConcept
      ? `The learner is exploring "${rootConcept}" and clicked on "${concept}" within the explanation of "${parentConcept}". Already explored concepts: ${existingConcepts?.join(', ') || 'none'}.`
      : `The learner wants to learn about "${concept}".`;

    const message = await anthropic.messages.create({
      model: getModel(req.body),
      max_tokens: 1024,
      messages: [{
        role: 'user',
        content: `${contextLine}

Explain "${concept}" concisely for an interactive learning tool. Return ONLY valid JSON with no markdown formatting:

{
  "title": "Short title (2-5 words)",
  "summary": "20-word max definition of what this is",
  "bullets": ["Detail point 1", "Detail point 2"],
  "keyTerms": ["term1", "term2", "term3"]
}

Rules:
- The summary is a single sentence, 20 words MAX. It answers "what is this?" clearly and names 1-2 specific concepts.${parentConcept ? ` Connect it to "${parentConcept}".` : ''} Example: "Mitochondria are organelles that produce ATP through cellular respiration, powering nearly every cell in your body."
- Write 2-5 bullet points that teach the concept in more detail. Each bullet is 1-2 sentences max. Pack each bullet with specific named concepts (proper nouns, named mechanisms, structures, domain terms) — the more clickable terms per bullet, the better.
- IMPORTANT: Identify 10-15 key terms/concepts that appear in your summary AND bullet text. Be very generous — include every distinct concept, proper noun, named mechanism, specific structure, or domain-specific term.
- Key terms must be specific, meaningful concepts (not generic words like "process" or "system")
- Key terms should be standalone concepts someone might want to learn about
- Prefer naming things precisely over describing them generically
- Make explanations engaging and easy to understand
- Return ONLY the JSON object, no other text`
      }],
    });

    const text = message.content[0].type === 'text' ? message.content[0].text : '';
    // Try to extract JSON from the response
    const jsonMatch = text.match(/\{[\s\S]*\}/);
    if (!jsonMatch) {
      throw new Error('No JSON found in response');
    }
    const json = JSON.parse(jsonMatch[0]);
    res.json(json);
  } catch (error) {
    console.error('API error:', error);
    if (error?.status === 401) {
      return res.status(401).json({ error: 'Invalid API key.' });
    }
    res.status(500).json({ error: 'Failed to generate explanation' });
  }
});

app.post('/api/ask', async (req, res) => {
  const apiKey = req.headers['x-api-key'];
  if (!apiKey) {
    return res.status(401).json({ error: 'API key required.' });
  }
  const anthropic = new Anthropic({ apiKey });

  const { question, nodes } = req.body;

  try {
    const nodesContext = nodes.map(n =>
      `[ID: ${n.id}] "${n.concept}": ${n.summary} | Key points: ${n.bullets.join(' | ')}`
    ).join('\n');

    const message = await anthropic.messages.create({
      model: getModel(req.body),
      max_tokens: 1024,
      messages: [{
        role: 'user',
        content: `A learner is viewing these concept cards:\n\n${nodesContext}\n\nThey ask: "${question}"\n\nAnswer using the same format as a concept card. Return ONLY valid JSON:\n{"summary": "20-word max direct answer to their question, mentioning specific named concepts", "bullets": ["Detail point 1", "Detail point 2"], "keyTerms": ["term1", "term2"], "targetNodeId": "the ID of the most relevant concept node"}\n\nRules:\n- summary: 20 words max, direct answer with specific named concepts\n- bullets: 2-4 points expanding on the answer with explorable terms\n- keyTerms: 8-12 specific terms from your summary and bullets\n- targetNodeId: the ID of the most relevant concept card`
      }],
    });

    const text = message.content[0].type === 'text' ? message.content[0].text : '';
    const jsonMatch = text.match(/\{[\s\S]*\}/);
    if (!jsonMatch) {
      throw new Error('No JSON found in response');
    }
    const json = JSON.parse(jsonMatch[0]);
    res.json(json);
  } catch (error) {
    console.error('API error:', error);
    if (error?.status === 401) {
      return res.status(401).json({ error: 'Invalid API key.' });
    }
    res.status(500).json({ error: 'Failed to answer question' });
  }
});

// Serve static files in production
app.use(express.static(join(__dirname, 'dist')));
app.get('*', (req, res) => {
  res.sendFile(join(__dirname, 'dist', 'index.html'));
});

app.listen(PORT, () => {
  console.log(`Rabbit Hole server running on http://localhost:${PORT}`);
});