export function utf16to8(str) {
  let out = ``
  const len = str.length

  for (let i = 0; i < len; i++) {
    const c = str.charCodeAt(i)

    if (c >= 0x0001 && c <= 0x007F) {
      out += str.charAt(i)
    }
    else if (c > 0x07FF) {
      out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F))
      out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F))
      out += String.fromCharCode(0x80 | (c & 0x3F))
    }
    else {
      out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F))
      out += String.fromCharCode(0x80 | (c & 0x3F))
    }
  }

  return out
}

export function utf8to16(str) {
  let out = ``
  let i = 0
  const len = str.length

  while (i < len) {
    const c = str.charCodeAt(i++)
    let char2, char3

    switch (c >> 4) {
      case 0:
      case 1:
      case 2:
      case 3:
      case 4:
      case 5:
      case 6:
      case 7:
        // 0xxxxxxx
        out += str.charAt(i - 1)
        break
      case 12:
      case 13:
        // 110x xxxx 10xx xxxx
        char2 = str.charCodeAt(i++)
        out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F))
        break
      case 14:
        // 1110 xxxx 10xx xxxx 10xx xxxx
        char2 = str.charCodeAt(i++)
        char3 = str.charCodeAt(i++)
        out += String.fromCharCode(
          ((c & 0x0F) << 12) | ((char2 & 0x3F) << 6) | (char3 & 0x3F),
        )
        break
    }
  }

  return out
}

const base64EncodeChars = `ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_`

const base64DecodeChars = [
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  62,
  -1,
  -1,
  -1,
  63,
  52,
  53,
  54,
  55,
  56,
  57,
  58,
  59,
  60,
  61,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  0,
  1,
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9,
  10,
  11,
  12,
  13,
  14,
  15,
  16,
  17,
  18,
  19,
  20,
  21,
  22,
  23,
  24,
  25,
  -1,
  -1,
  -1,
  -1,
  -1,
  -1,
  26,
  27,
  28,
  29,
  30,
  31,
  32,
  33,
  34,
  35,
  36,
  37,
  38,
  39,
  40,
  41,
  42,
  43,
  44,
  45,
  46,
  47,
  48,
  49,
  50,
  51,
  -1,
  -1,
  -1,
  -1,
  -1,
]

export function base64encode(str) {
  let out = ``
  let i = 0
  const len = str.length

  while (i < len) {
    const c1 = str.charCodeAt(i++) & 0xFF

    if (i === len) {
      out += base64EncodeChars.charAt(c1 >> 2)
      out += base64EncodeChars.charAt((c1 & 0x3) << 4)
      out += `==`
      break
    }

    const c2 = str.charCodeAt(i++)

    if (i === len) {
      out += base64EncodeChars.charAt(c1 >> 2)
      out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4))
      out += base64EncodeChars.charAt((c2 & 0xF) << 2)
      out += `=`
      break
    }

    const c3 = str.charCodeAt(i++)

    out += base64EncodeChars.charAt(c1 >> 2)
    out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4))
    out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6))
    out += base64EncodeChars.charAt(c3 & 0x3F)
  }

  return out
}

export function base64decode(str) {
  let c1, c2, c3, c4
  let i = 0
  const len = str.length
  let out = ``

  while (i < len) {
    /* c1 */
    do {
      c1 = base64DecodeChars[str.charCodeAt(i++) & 0xFF]
    } while (i < len && c1 === -1)
    if (c1 === -1)
      break

    /* c2 */
    do {
      c2 = base64DecodeChars[str.charCodeAt(i++) & 0xFF]
    } while (i < len && c2 === -1)
    if (c2 === -1)
      break

    out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4))

    /* c3 */
    do {
      c3 = str.charCodeAt(i++) & 0xFF
      if (c3 === 61)
        return out
      c3 = base64DecodeChars[c3]
    } while (i < len && c3 === -1)
    if (c3 === -1)
      break

    out += String.fromCharCode(((c2 & 0xF) << 4) | ((c3 & 0x3C) >> 2))

    /* c4 */
    do {
      c4 = str.charCodeAt(i++) & 0xFF
      if (c4 === 61)
        return out
      c4 = base64DecodeChars[c4]
    } while (i < len && c4 === -1)
    if (c4 === -1)
      break

    out += String.fromCharCode(((c3 & 0x03) << 6) | c4)
  }

  return out
}

export function safe64(base64) {
  base64 = base64.replace(/\+/g, `-`)
  base64 = base64.replace(/\//g, `_`)
  return base64
}