'use strict'

module.exports = encode

// Encode special characters in `value`.
function encode(value, options) {
  value = value.replace(
    options.subset ? charactersToExpression(options.subset) : /["&'<>`]/g,
    basic
  )

  if (options.subset || options.escapeOnly) {
    return value
  }

  return (
    value
      // Surrogate pairs.
      .replace(/[\uD800-\uDBFF][\uDC00-\uDFFF]/g, surrogate)
      // BMP control characters (C0 except for LF, CR, SP; DEL; and some more
      // non-ASCII ones).
      .replace(
        // eslint-disable-next-line no-control-regex, unicorn/no-hex-escape
        /[\x01-\t\v\f\x0E-\x1F\x7F\x81\x8D\x8F\x90\x9D\xA0-\uFFFF]/g,
        basic
      )
  )

  function surrogate(pair, index, all) {
    return options.format(
      (pair.charCodeAt(0) - 0xd800) * 0x400 +
        pair.charCodeAt(1) -
        0xdc00 +
        0x10000,
      all.charCodeAt(index + 2),
      options
    )
  }

  function basic(character, index, all) {
    return options.format(
      character.charCodeAt(0),
      all.charCodeAt(index + 1),
      options
    )
  }
}

function charactersToExpression(subset) {
  var groups = []
  var index = -1

  while (++index < subset.length) {
    groups.push(subset[index].replace(/[|\\{}()[\]^$+*?.]/g, '\\$&'))
  }

  return new RegExp('(?:' + groups.join('|') + ')', 'g')
}