export type Attrs = {[name: string]: string}

export function combineAttrs(source: Attrs, target: Attrs) {
  for (let name in source) {
    if (name == "class" && target.class) target.class += " " + source.class
    else if (name == "style" && target.style) target.style += ";" + source.style
    else target[name] = source[name]
  }
  return target
}

export function attrsEq(a: Attrs | null, b: Attrs | null): boolean {
  if (a == b) return true
  if (!a || !b) return false
  let keysA = Object.keys(a), keysB = Object.keys(b)
  if (keysA.length != keysB.length) return false
  for (let key of keysA) {
    if (keysB.indexOf(key) == -1 || a[key] !== b[key]) return false
  }
  return true
}

export function updateAttrs(dom: HTMLElement, prev: Attrs | null, attrs: Attrs | null) {
  if (prev) for (let name in prev) if (!(attrs && name in attrs)) dom.removeAttribute(name)
  if (attrs) for (let name in attrs) if (!(prev && prev[name] == attrs[name])) dom.setAttribute(name, attrs[name])
}