// fixtures/frames.mjs — the updates wire's framing (spec plan, Global
// Constraints: "each update framed as a 4-byte big-endian length then
// the bytes, in seq order"). live.go's updatesGet writes it; this reads
// it back into the individual Yjs updates Y.applyUpdate takes one at a
// time.
//
// Docs' endpoint concatenates updates with no framing and its client
// loops Y.readUpdate over one decoder; Slides frames them so the
// client never has to know how a Yjs update finds its own end, and so
// a snapshot (one large update) and a tail (many small ones) travel the
// same way. Pure bytes in, bytes out, so it is tested under plain Node.

/** The frames a body carries, in order. Throws on a body that does not divide cleanly. */
export function parseFrames (bytes) {
  const out = []
  let at = 0
  while (at < bytes.length) {
    if (bytes.length - at < 4) throw new Error(`frame: ${bytes.length - at} trailing bytes with no length prefix`)
    const n = ((bytes[at] << 24) >>> 0) + (bytes[at + 1] << 16) + (bytes[at + 2] << 8) + bytes[at + 3]
    at += 4
    if (bytes.length - at < n) throw new Error(`frame: a frame claims ${n} bytes and ${bytes.length - at} remain`)
    out.push(bytes.subarray(at, at + n))
    at += n
  }
  return out
}

/** One frame: the length prefix then the bytes (what a test or a beacon builds). */
export function frame (update) {
  const out = new Uint8Array(4 + update.length)
  out[0] = (update.length >>> 24) & 255
  out[1] = (update.length >>> 16) & 255
  out[2] = (update.length >>> 8) & 255
  out[3] = update.length & 255
  out.set(update, 4)
  return out
}