const markerRunLength = (characters, start, marker) => {
  let length = 0
  while (characters[start + length] === marker) length += 1
  return length
}

export const renderChatMarkdownCharacters = (value) => {
  const characters = Array.isArray(value) ? value : Array.from(String(value || ''))
  const output = []
  let bold = false
  let italic = false
  let code = false
  let heading = false
  let lineStart = true

  const push = (text, key) => {
    output.push({
      text,
      key,
      bold,
      italic,
      code,
      heading,
      newline: text === '\n',
    })
  }

  for (let index = 0; index < characters.length; index += 1) {
    const character = characters[index]

    if (lineStart && character === '#') {
      const length = markerRunLength(characters, index, '#')
      if (characters[index + length] === ' ') {
        heading = true
        index += length
        continue
      }
    }

    if (lineStart && (character === '-' || character === '*') && characters[index + 1] === ' ') {
      push('•', `${index}-bullet`)
      push(' ', `${index}-space`)
      index += 1
      lineStart = false
      continue
    }

    if (!code && (character === '*' || character === '_')) {
      const length = markerRunLength(characters, index, character)
      if (length >= 2) {
        bold = !bold
        index += length - 1
        continue
      }
      italic = !italic
      continue
    }

    if (character === '`') {
      code = !code
      continue
    }

    push(character, index)
    if (character === '\n') {
      heading = false
      lineStart = true
    } else {
      lineStart = false
    }
  }

  return output
}