class Base64

# Base64 provides the base64/Base64 standard library API.
class Base64
  private ALPHABET: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

  # Base64.decode provides the base64/Base64 standard library operation.
  # @param text String text value.
  # @return String the resulting value.
  static decode: text ->
    cleaned = ""
    n = text.byte_len()
    cr = chr(13)
    i = 0
    while i < n
      c = text[i]
      if c != " " and c != "\n" and c != cr and c != "\t" and c != "="
        cleaned = cleaned + c
      i = i + 1
    m = cleaned.byte_len()
    if m % 4 == 1
      raise error("base64.decode: invalid length")
    arr = []
    j = 0
    while j + 4 <= m
      v1 = Self.decode_value(cleaned[j])
      v2 = Self.decode_value(cleaned[j + 1])
      v3 = Self.decode_value(cleaned[j + 2])
      v4 = Self.decode_value(cleaned[j + 3])
      arr.push(v1 * 4 + v2 / 16)
      arr.push(v2 % 16 * 16 + v3 / 4)
      arr.push(v3 % 4 * 64 + v4)
      j = j + 4
    rem = m - j
    if rem == 2
      v1 = Self.decode_value(cleaned[j])
      v2 = Self.decode_value(cleaned[j + 1])
      arr.push(v1 * 4 + v2 / 16)
    elseif rem == 3
      v1 = Self.decode_value(cleaned[j])
      v2 = Self.decode_value(cleaned[j + 1])
      v3 = Self.decode_value(cleaned[j + 2])
      arr.push(v1 * 4 + v2 / 16)
      arr.push(v2 % 16 * 16 + v3 / 4)
    bytes(arr)

  # Base64.encode provides the base64/Base64 standard library operation.
  # @param value String value value.
  # @return String the resulting value.
  static encode: value ->
    data = nil
    if value.class == String
      data = bytes_array(bytes_of(value))
    else
      data = bytes_array(value)
    n = data.len()
    out = ""
    i = 0
    while i + 3 <= n
      b1 = data[i]
      b2 = data[i + 1]
      b3 = data[i + 2]
      g1 = b1 / 4
      g2 = b1 % 4 * 16 + b2 / 16
      g3 = b2 % 16 * 4 + b3 / 64
      g4 = b3 % 64
      out = out
        + Self.ALPHABET[g1]
        + Self.ALPHABET[g2]
        + Self.ALPHABET[g3]
        + Self.ALPHABET[g4]
      i = i + 3
    rem = n - i
    if rem == 1
      b1 = data[i]
      g1 = b1 / 4
      g2 = b1 % 4 * 16
      out = out + Self.ALPHABET[g1] + Self.ALPHABET[g2] + "=="
    elseif rem == 2
      b1 = data[i]
      b2 = data[i + 1]
      g1 = b1 / 4
      g2 = b1 % 4 * 16 + b2 / 16
      g3 = b2 % 16 * 4
      out = out
        + Self.ALPHABET[g1]
        + Self.ALPHABET[g2]
        + Self.ALPHABET[g3]
        + "="
    out

  # Base64.decode_value returns the Base64 alphabet index for a character.
  private static decode_value: c ->
    alphabet = bytes_array(bytes_of(Self.ALPHABET))
    target = bytes_array(bytes_of(c))[0]
    i = 0
    while i < alphabet.len()
      if alphabet[i] == target
        return i
      i = i + 1
    raise error("base64.decode: invalid character")