# attrs_node.ludic — @Node(model): a string naming a node inside the glTF another field of the same
# record names. That field is @Asset("gltf") itself, or an @Ref(R) whose record has exactly one
# @Asset("gltf") field (the model is found through the row). Anything else is an error naming it.

# the field of record d called name, or null
function at_field_of(d: Node, name: pointer) -> Node {
  var k = 0
  while k < len(d.kids) {
    if d.kids[k].s != null and vis_plain(d.kids[k].s) == name { return d.kids[k] }
    k += 1
  }
  return null
}
# field f's argument to attribute a as written, or null when f does not carry it
function at_arg_of(f: Node, a: pointer) -> pointer {
  if f.at < 0 { return null }
  var j = g_at_start[f.at]
  while j < g_at_start[f.at] + g_at_count[f.at] {
    if g_at_name[j] == a { return g_at_first[j] }
    j += 1
  }
  return null
}
function at_is_gltf(f: Node) -> bool {
  let a = at_arg_of(f, "Asset")
  return a != null and a == "gltf"
}
# the record called name (a property or record), or null
function at_record(name: pointer) -> Node {
  let plain = vis_plain(name)
  var i = 0
  while i < len(prog) {
    if prog[i].kind == N_COMP and prog[i].s != null and vis_plain(prog[i].s) == plain { return prog[i] }
    i += 1
  }
  return null
}
# how many @Asset("gltf") fields record r carries
function at_gltf_count(r: Node) -> int {
  var n = 0
  var k = 0
  while k < len(r.kids) {
    if at_is_gltf(r.kids[k]) { n += 1 }
    k += 1
  }
  return n
}
function at_check_node(d: Node, f: Node, target: pointer) -> void {
  let where = `field {d.s}.{f.s}: @Node({target})`
  let t = at_field_of(d, target)
  if t == null {
    perr_at(f.file, f.line, f.col, `{where} names no field - {d.s} has no field {target}`)
    return
  }
  if at_is_gltf(t) { return }
  let reg = at_arg_of(t, "Ref")
  if reg == null {
    perr_at(f.file, f.line, f.col, `{where}: {target} is neither @Asset("gltf") nor an @Ref to a registry of models`)
    return
  }
  let r = reg_find(reg)
  if r < 0 { return }                                  # @Ref's own check says so
  let rec = at_record(g_rg_type[r])
  var n = 0
  if rec != null { n = at_gltf_count(rec) }
  if n != 1 {
    perr_at(f.file, f.line, f.col, `{where}: {target} is an @Ref({reg}), and its record {g_rg_type[r]} has {n} @Asset("gltf") fields, not one`)
  }
}