vcl 4.1;

# Minimal, safe Varnish config for a Next.js-style app.
# - Cache static assets aggressively
# - Avoid caching HTML/auth/api by default
# - Preserve websockets / upgrade

backend default {
  .host = "app";
  .port = "3000";
}

sub vcl_recv {
  # Health endpoint should always work.
  if (req.url == "/health") {
    return (pass);
  }

  # Websocket / Upgrade should not be cached.
  if (req.http.Upgrade ~ "(?i)websocket") {
    return (pipe);
  }

  # Only cache GET/HEAD.
  if (req.method != "GET" && req.method != "HEAD") {
    return (pass);
  }

  # If cookies are present, do not cache (safe default).
  if (req.http.Cookie) {
    return (pass);
  }

  # Never cache Next.js data requests (often personalized) unless you explicitly want to.
  if (req.url ~ "^/_next/data/") {
    return (pass);
  }

  # Cache immutable build assets.
  if (req.url ~ "^/_next/static/") {
    unset req.http.Cookie;
    return (hash);
  }

  # Cache common static files.
  if (req.url ~ "\.(?:css|js|mjs|map|png|jpg|jpeg|gif|webp|svg|ico|woff2?|ttf|otf)$") {
    unset req.http.Cookie;
    return (hash);
  }

  # Default: don't cache HTML.
  return (pass);
}

sub vcl_backend_response {
  # Cache immutable Next build assets for a long time.
  if (bereq.url ~ "^/_next/static/") {
    set beresp.ttl = 365d;
    set beresp.grace = 1h;
    set beresp.http.Cache-Control = "public, max-age=31536000, immutable";
    unset beresp.http.Set-Cookie;
    return (deliver);
  }

  # Cache static files for 7 days (safe default).
  if (bereq.url ~ "\.(?:css|js|mjs|map|png|jpg|jpeg|gif|webp|svg|ico|woff2?|ttf|otf)$") {
    set beresp.ttl = 7d;
    set beresp.grace = 1h;
    if (!beresp.http.Cache-Control) {
      set beresp.http.Cache-Control = "public, max-age=604800";
    }
    unset beresp.http.Set-Cookie;
    return (deliver);
  }

  # Everything else: don't cache by default.
  set beresp.ttl = 0s;
  set beresp.uncacheable = true;
  return (deliver);
}

sub vcl_deliver {
  # Helpful debug header; remove if you don't want this visible.
  if (obj.hits > 0) {
    set resp.http.X-Cache = "HIT";
  } else {
    set resp.http.X-Cache = "MISS";
  }
}