import { concat } from '@utils/concat.js'
import { assert, isString } from '@blackglory/prelude'

const UNORDERED_NODE_ITERATOR_TYPE =
  'XPathResult' in globalThis
  ? XPathResult.UNORDERED_NODE_ITERATOR_TYPE
  : 4

export function xpath<T extends Node>(
  strings: TemplateStringsArray
, ...values: string[]
): (this: Document, node: Node) => Iterable<T>
export function xpath<T extends Node>(
  expression: string
): (this: Document, node: Node) => Iterable<T>
export function xpath<T extends Node>(...args:
| [expression: string]
| [strings: TemplateStringsArray, ...values: string[]]
): (this: Document, node: Node) => Iterable<T> {
  if (isString(args[0])) {
    const [expression] = args
    assert(expression.startsWith('.'), 'XPath expressions must start with "."')

    return function* (this: Document, node: Node) {
      const iterator = this.evaluate(
        expression
      , node
      , null
      , UNORDERED_NODE_ITERATOR_TYPE
      , null
      )

      let value
      while ((value = iterator.iterateNext()) !== null) {
        yield value as T
      }
    }
  } else {
    const [strings, ...values] = args
    const expression = concat(strings, values).join('')

    return xpath(expression)
  }
}