import { isWordCharacter } from '@admin/utils/editor/is-word-character'

export function matchMarkdownMarkSyntax(markdown: string, index: number): number | null {
  const character = markdown[index]
  const nextCharacter = markdown[index + 1]
  const previousCharacter = markdown[index - 1]

  if (character === '`') {
    const match = /^`+/.exec(markdown.slice(index))
    return match ? index + match[0].length : null
  }

  if (character === '*' || character === '~') {
    const match = new RegExp(`^\\${character}+`).exec(markdown.slice(index))
    return match ? index + Math.min(match[0].length, 2) : null
  }

  if (
    character === '_' &&
    !(isWordCharacter(previousCharacter) && isWordCharacter(nextCharacter))
  ) {
    const match = /^_+/.exec(markdown.slice(index))
    return match ? index + Math.min(match[0].length, 2) : null
  }

  return null
}