/**
 * @file @see https://github.com/parshap/truncate-utf8-bytes
 */
function isHighSurrogate(codePoint) {
  return codePoint >= 0xd800 && codePoint <= 0xdbff
}

function isLowSurrogate(codePoint) {
  return codePoint >= 0xdc00 && codePoint <= 0xdfff
}

// Truncate string by size in bytes
function truncate(getLength, string, byteLength) {
  if (typeof string !== 'string') {
    throw new Error('Input must be string')
  }

  const charLength = string.length
  let curByteLength = 0
  let codePoint
  let segment

  for (let i = 0; i < charLength; i += 1) {
    codePoint = string.charCodeAt(i)
    segment = string[i]

    if (
      isHighSurrogate(codePoint) &&
      isLowSurrogate(string.charCodeAt(i + 1))
    ) {
      i += 1
      segment += string[i]
    }

    curByteLength += getLength(segment)

    if (curByteLength === byteLength) {
      return string.slice(0, i + 1)
    } else if (curByteLength > byteLength) {
      return string.slice(0, i - segment.length + 1)
    }
  }

  return string
}

const getLength = Buffer.byteLength.bind(Buffer)
const fromStringToTruncatedUtf8 = truncate.bind(undefined, getLength)
export { fromStringToTruncatedUtf8 }