/**
 * @typedef {import('nlcst').Sentence} Sentence
 */

import {toString} from 'nlcst-to-string'
import {modifyChildren} from 'unist-util-modify-children'

// Merge certain punctuation marks into their following words.
export const mergeInitialWordSymbol = modifyChildren(
  /**
   * @type {import('unist-util-modify-children').Modifier<Sentence>}
   */
  function (child, index, parent) {
    if (
      (child.type !== 'SymbolNode' && child.type !== 'PunctuationNode') ||
      toString(child) !== '&'
    ) {
      return
    }

    const children = parent.children
    const next = children[index + 1]

    // If either a previous word, or no following word, exists, exit early.
    if (
      (index > 0 && children[index - 1].type === 'WordNode') ||
      !(next && next.type === 'WordNode')
    ) {
      return
    }

    // Remove `child` from parent.
    children.splice(index, 1)

    // Add the punctuation mark at the start of the next node.
    next.children.unshift(child)

    // Update position.
    if (next.position && child.position) {
      next.position.start = child.position.start
    }

    // Next, iterate over the node at the previous position, as it's now adjacent
    // to a following word.
    return index - 1
  }
)