Error Handling

// Express identifies error middleware by the 4-argument signature
app.use((err, req, res, next) => {
  console.error(err);

  // Different responses for different error types
  if (err.name === "ValidationError") {
    return res.status(400).json({
      error: "Validation failed",
      details: err.message,
    });
  }

  if (err.name === "UnauthorizedError") {
    return res.status(401).json({ error: "Invalid token" });
  }

  // Default: internal server error
  res.status(err.status || 500).json({
    error: process.env.NODE_ENV === "production"
      ? "Something went wrong"
      : err.message,
  });
});

// Catch-all 404
app.use((req, res) => {
  res.status(404).json({ error: `Route not found: ${req.method} ${req.path}` });
});

// Pass errors to the error handler from route handlers
app.get("/courses/:id", async (req, res, next) => {
  try {
    const course = await getCourse(req.params.id);
    if (!course) return res.status(404).json({ error: "Not found" });
    res.json(course);
  } catch (err) {
    next(err);  // pass to error handler
  }
});