vcl 4.1;

import vsthrottle;
import std;

backend app {
  .host = "app";
  .port = "${APP_PORT}";
}

acl purge {
  "127.0.0.1";
  "::1";
}

sub vcl_recv {
  # Internal markers can only be set by our own VCL.
  unset req.http.X-RFC9211-State;
  unset req.http.X-RFC9211-Entry;
  unset req.http.X-RFC9211-TTL;
  unset req.http.X-RFC9211-Synthetic;
  unset req.http.Cache-Status;

  if (vsthrottle.is_denied(client.identity, 200, 10s, 60s)) {
    return (synth(429, "Too Many Requests"));
  }

  if (req.method == "PURGE") {
    if (!client.ip ~ purge) {
      return (synth(405, "Not allowed"));
    }
    return (purge);
  }

  if (!req.http.X-Forwarded-Proto) {
    set req.http.X-Forwarded-Proto = "https";
  }

  if (req.url ~ "^/healthcheck(\?.*)?$" || req.http.X-Internal-Check) {
    return (pass);
  }

  # Only WebSocket upgrades use pipe, not Socket.IO polling.
  if (req.http.Upgrade ~ "(?i)websocket") {
    return (pipe);
  }
  if (req.url ~ "^/socket\.io/") {
    return (pass);
  }

  if (req.method != "GET" && req.method != "HEAD") {
    return (pass);
  }
  if (req.http.Authorization) {
    return (pass);
  }

  if (req.http.Accept-Encoding) {
    if (req.http.Accept-Encoding ~ "zstd") {
      set req.http.Accept-Encoding = "zstd";
    } else if (req.http.Accept-Encoding ~ "br") {
      set req.http.Accept-Encoding = "br";
    } else if (req.http.Accept-Encoding ~ "gzip") {
      set req.http.Accept-Encoding = "gzip";
    } else {
      set req.http.Accept-Encoding = "identity";
    }
  }

  # Public static resources do not vary by session cookie.
  if (req.url ~ "^/(static|uploads)/" ||
      req.url ~ "(?i)\.(css|js|png|jpe?g|webp|svg|ico|woff2?)(\?.*)?$") {
    unset req.http.Cookie;
    return (hash);
  }

  return (hash);
}

sub vcl_pipe {
  if (req.http.Upgrade) {
    set bereq.http.Upgrade = req.http.Upgrade;
    set bereq.http.Connection = "Upgrade";
  }
}

sub vcl_hash {
  hash_data(req.url);
  if (req.http.host) {
    hash_data(req.http.host);
  } else {
    hash_data(server.ip);
  }
  if (req.http.Cookie) {
    hash_data(req.http.Cookie);
  }
  if (req.http.Accept-Encoding) {
    hash_data(req.http.Accept-Encoding);
  }
  if (req.http.X-Accept-Image) {
    hash_data(req.http.X-Accept-Image);
  }
}

# Track actual request transitions; leave the final return to builtin VCL.
sub vcl_hit {
  set req.http.X-RFC9211-State = "hit";
}

sub vcl_miss {
  # 'miss' is intentionally generic: we cannot always distinguish
  # uri-miss from vary-miss in this VCL hook.
  set req.http.X-RFC9211-State = "miss";
}

sub vcl_pass {
  if (req.method == "GET" || req.method == "HEAD") {
    set req.http.X-RFC9211-State = "bypass";
  } else {
    set req.http.X-RFC9211-State = "method";
  }
}

sub vcl_backend_fetch {
  # Never forward diagnostic state to the application.
  unset bereq.http.X-RFC9211-State;
  unset bereq.http.X-RFC9211-Entry;
  unset bereq.http.X-RFC9211-TTL;
  unset bereq.http.X-RFC9211-Synthetic;
}

sub vcl_backend_response {
  # Origin must not control our local backend-error marker.
  unset beresp.http.X-RFC9211-Synthetic;

  # Never store backend 5xx responses.
  if (beresp.status >= 500) {
    set beresp.uncacheable = true;
    set beresp.ttl = 0s;
    return (deliver);
  }

  if (beresp.http.Cache-Control ~ "(?i)no-store|private|no-cache" ||
      beresp.http.Surrogate-Control ~ "(?i)no-store" ||
      beresp.http.Vary == "*") {
    set beresp.uncacheable = true;
    set beresp.ttl = 0s;
    return (deliver);
  }

  if (beresp.status >= 300 && beresp.status < 400) {
    set beresp.uncacheable = true;
    set beresp.ttl = 0s;
    return (deliver);
  }

  if (bereq.url ~ "^/(static|uploads)/" ||
      bereq.url ~ "(?i)\.(css|js|png|jpe?g|webp|svg|ico|woff2?)(\?.*)?$") {
    if (beresp.status != 200) {
      set beresp.uncacheable = true;
      set beresp.ttl = 0s;
      return (deliver);
    }
  }

  if (bereq.url ~ "(?i)\.(js|css)(\?.*)?$" &&
      beresp.http.Content-Type ~ "(?i)text/html") {
    set beresp.uncacheable = true;
    set beresp.ttl = 0s;
    return (deliver);
  }

  if (bereq.url ~ "(?i)\.js(\?.*)?$" && !beresp.http.Content-Type) {
    set beresp.http.Content-Type = "application/javascript; charset=utf-8";
  }
  if (bereq.url ~ "(?i)\.css(\?.*)?$" && !beresp.http.Content-Type) {
    set beresp.http.Content-Type = "text/css; charset=utf-8";
  }

  if (bereq.url ~ "^/(static|uploads)/" ||
      bereq.url ~ "(?i)\.(css|js|png|jpe?g|webp|svg|ico|woff2?)(\?.*)?$") {
    unset beresp.http.Set-Cookie;

    if (beresp.http.Vary) {
      set beresp.http.Vary = regsuball(beresp.http.Vary, "(?i)(^|,)[[:space:]]*Cookie[[:space:]]*(,|$)", "\1");
      set beresp.http.Vary = regsuball(beresp.http.Vary, ",[[:space:]]*,", ",");
      set beresp.http.Vary = regsub(beresp.http.Vary, "^[[:space:]]*,[[:space:]]*", "");
      set beresp.http.Vary = regsub(beresp.http.Vary, "[[:space:]]*,[[:space:]]*$", "");
      if (beresp.http.Vary ~ "^[[:space:]]*$") {
        unset beresp.http.Vary;
      }
    }

    if (!(beresp.http.Cache-Control ~ "(?i)(s-maxage|max-age)")) {
      set beresp.ttl = 24h;
      set beresp.http.Cache-Control = "public, max-age=86400, immutable";
    }

    set beresp.grace = 1h;
    set beresp.keep = 24h;
  }

  if (beresp.http.Cache-Control ~ "(?i)s-maxage=([0-9]+)") {
    set beresp.ttl = std.duration(regsub(beresp.http.Cache-Control, "(?i).*s-maxage=([0-9]+).*", "\1") + "s", 0s);
  } else if (beresp.http.Cache-Control ~ "(?i)max-age=([0-9]+)") {
    set beresp.ttl = std.duration(regsub(beresp.http.Cache-Control, "(?i).*max-age=([0-9]+).*", "\1") + "s", 0s);
  } else if (beresp.http.Expires) {
    set beresp.ttl = std.time(beresp.http.Expires, now) - now;
    if (beresp.ttl < 0s) {
      set beresp.ttl = 0s;
    }
  } else if (beresp.ttl <= 0s) {
    set beresp.ttl = 60s;
  }

  if (beresp.http.Cache-Control ~ "(?i)immutable") {
    set beresp.grace = 1h;
    set beresp.keep = 24h;
  }

  if (!beresp.http.Content-Encoding && bereq.http.Accept-Encoding ~ "gzip") {
    if (beresp.http.Content-Type ~ "(?i)text/|application/(javascript|json|xml)") {
      set beresp.do_gzip = true;
    }
  }

  if (beresp.http.Content-Length &&
      std.integer(beresp.http.Content-Length, 0) > 1048576) {
    set beresp.do_stream = true;
  }
}

sub vcl_backend_error {
  # Synthetic fetch errors were not served from cache.
  set beresp.uncacheable = true;
  set beresp.ttl = 0s;
  set beresp.http.X-RFC9211-Synthetic = "1";
  return (deliver);
}

sub vcl_deliver {
  # Cache-Status MUST be calculated per request, not cached as an origin header.
  # Synthetic backend errors do not receive a local Cache-Status member.
  if (resp.http.X-RFC9211-Synthetic) {
    unset resp.http.Cache-Status;
  } else {
    if (req.http.X-RFC9211-State == "hit") {
      # VCL DURATION -> STRING produces seconds with 3 decimal places.
      # RFC 9211 ttl is an integer; negative subsecond TTL is rounded to -1.
      set req.http.X-RFC9211-TTL = obj.ttl;
      if (obj.ttl < 0s && obj.ttl > -1s) {
        set req.http.X-RFC9211-TTL = "-1";
      } else {
        set req.http.X-RFC9211-TTL = regsub(req.http.X-RFC9211-TTL, "\.[0-9]+$", "");
      }
      set req.http.X-RFC9211-Entry = "varnish; hit; ttl=" + req.http.X-RFC9211-TTL;
    } else if (req.http.X-RFC9211-State == "miss") {
      set req.http.X-RFC9211-Entry = "varnish; fwd=miss";
      if (obj.uncacheable) {
        set req.http.X-RFC9211-Entry = req.http.X-RFC9211-Entry + "; stored=?0";
      } else {
        set req.http.X-RFC9211-Entry = req.http.X-RFC9211-Entry + "; stored";
      }
    } else if (req.http.X-RFC9211-State == "method") {
      set req.http.X-RFC9211-Entry = "varnish; fwd=method; stored=?0";
    } else if (req.http.X-RFC9211-State == "bypass") {
      set req.http.X-RFC9211-Entry = "varnish; fwd=bypass; stored=?0";
    }

    # Preserve the existing upstream cache chain, append Varnish LAST.
    # If the request path is unknown, avoid fabricating a bypass.
    if (req.http.X-RFC9211-Entry) {
      if (resp.http.Cache-Status) {
        set resp.http.Cache-Status = resp.http.Cache-Status + ", " + req.http.X-RFC9211-Entry;
      } else {
        set resp.http.Cache-Status = req.http.X-RFC9211-Entry;
      }
    }
  }

  unset resp.http.X-RFC9211-Synthetic;
  unset resp.http.X-Cache;
  unset resp.http.X-Pass-Reason;
  unset resp.http.Via;
  unset resp.http.X-Varnish;
  unset resp.http.Server;
  unset resp.http.Content-Disposition;
  # Preserve Age (it is standard HTTP cache metadata).
}

sub vcl_synth {
  set resp.http.Cache-Control = "private, no-store, no-cache";
  unset resp.http.Cache-Status;
  unset resp.http.X-Cache;
  unset resp.http.X-Pass-Reason;
  unset resp.http.Via;
  unset resp.http.X-Varnish;
  unset resp.http.Server;
  unset resp.http.Content-Disposition;
}

sub vcl_purge {
  return (synth(200, "Purged"));
}