server.js

require("dotenv").config();
const express = require("express");
const app = express();
const PORT = 3000;

// ── API keys ──
const RETELL_API_KEY = process.env.RETELL_API_KEY || "";
const GEMINI_API_KEY = process.env.GEMINI_API_KEY || "";

app.use(express.json());
app.use(express.static(__dirname)); // serves index.html, styles.css, main.js

// Endpoint that main.js calls to get an access token
app.post("/api/create-web-call", async (req, res) => {
  try {
    const response = await fetch("https://api.retellai.com/v2/create-web-call", {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        Authorization: `Bearer ${RETELL_API_KEY}`,
      },
      body: JSON.stringify({
        agent_id: req.body.agent_id,
      }),
    });

    if (!response.ok) {
      const text = await response.text();
      console.error("Retell API error:", response.status, text);
      return res.status(response.status).json({ error: text });
    }

    const data = await response.json();
    res.json({ access_token: data.access_token });
  } catch (err) {
    console.error("Server error:", err);
    res.status(500).json({ error: "Failed to create web call" });
  }
});

// Chat endpoint using Gemini API
app.post("/api/chat", async (req, res) => {
  const { message, history } = req.body;

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

  const systemInstruction = `You are Sarah, a friendly and knowledgeable AI assistant for Tertiary Infotech Academy, a Singapore-based training provider offering SkillsFuture and WSQ accredited IT courses for working adults.

Key information you should know:
- Courses offered: Cybersecurity Fundamentals (40hrs), Cloud Computing & AWS (36hrs), Data Analytics with Python (32hrs), AI & Machine Learning (44hrs), Full-Stack Web Development (48hrs), Digital Marketing & SEO (28hrs)
- All courses come with certificates
- Funding: SkillsFuture Credit, subsidies, and absentee payroll support available
- Instructors are industry practitioners with real-world experience
- Flexible scheduling: weekday, evening, and weekend classes
- Over 2,500 graduates, 50+ courses, 95% satisfaction rate, 10+ years experience

Keep responses concise (2-3 sentences max), friendly, and helpful. If asked about something outside the academy's scope, politely redirect to relevant academy topics.`;

  const contents = [];
  if (history && Array.isArray(history)) {
    for (const entry of history) {
      contents.push({
        role: entry.role === "user" ? "user" : "model",
        parts: [{ text: entry.text }],
      });
    }
  }
  contents.push({ role: "user", parts: [{ text: message }] });

  try {
    const response = await fetch(
      `https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent?key=${GEMINI_API_KEY}`,
      {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({
          system_instruction: { parts: [{ text: systemInstruction }] },
          contents,
        }),
      }
    );

    if (!response.ok) {
      const text = await response.text();
      console.error("Gemini API error:", response.status, text);
      return res.status(response.status).json({ error: text });
    }

    const data = await response.json();
    const reply =
      data.candidates?.[0]?.content?.parts?.[0]?.text ||
      "Sorry, I couldn't generate a response. Please try again.";

    res.json({ reply });
  } catch (err) {
    console.error("Gemini error:", err);
    res.status(500).json({ error: "Failed to get response" });
  }
});

app.listen(PORT, () => {
  console.log(`Server running at http://localhost:${PORT}`);
});