-- http/nego.wo — framework v1 slice 2: response-side content negotiation
-- and ETag / conditional requests (the crypto slice's first ledger
-- consumer beyond the WS handshake).

-- Does the request accept this media type? Absent Accept = yes (RFC 9110
-- §12.5.1: no header means anything goes). Matching is exact, type/*,
-- or */*; q-values are stripped, not ranked — v1 answers CAN I send
-- this, not WHICH ONE is best (a ranking negotiation waits for an app
-- that serves alternates).
pub fn accepts(req: Req, mtype: Text) -> Bool {
  let acc = req.headers["accept"];
  if acc == nil { return true; }
  let slash = index_of(mtype, "/");
  let major = mtype;
  if slash >= 0 { major = substr(mtype, 0, slash); }
  for part in split(to_lower("${acc}"), ",") {
    let item = trim(part);
    let semi = index_of(item, ";");
    if semi >= 0 { item = trim(substr(item, 0, semi)); }
    if item == mtype { return true; }
    if item == "*/*" { return true; }
    if item == "${major}/*" { return true; }
  }
  return false;
}

-- A strong ETag for a body: quoted base64 of its SHA-256. Deterministic,
-- content-addressed — two identical bodies share one tag across
-- restarts and shards.
pub fn etag_for(body: Text) -> Text {
  return "\"${base64_encode(sha256(bytes_of_text(body)))}\"";
}

-- Stamp the response's ETag and collapse it to 304 when the request's
-- If-None-Match already has it. The 304 keeps the etag header and
-- drops the body (RFC 9110 §15.4.5). Call it last in a handler:
--   return with_etag(req, ok_json(body));
pub fn with_etag(req: Req, take r: Resp) -> Resp {
  let tag = etag_for(r.body);
  r.headers["etag"] = tag;
  let inm = req.headers["if-none-match"];
  if inm != nil {
    if trim(inm) == tag {
      r.status = 304;
      r.body = "";
    }
  }
  return r;
}