#
#
#            Nim's Runtime Library
#        (c) Copyright 2010 Andreas Rumpf
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

## This module implements a base64 encoder and decoder.
##
## Encoding data
## -------------
##
## In order to encode some text simply call the ``encode`` procedure:
##
##   .. code-block::nim
##      import base64
##      let encoded = encode("Hello World")
##      echo(encoded) # SGVsbG8gV29ybGQ=
##
## Apart from strings you can also encode lists of integers or characters:
##
##   .. code-block::nim
##      import base64
##      let encodedInts = encode([1,2,3])
##      echo(encodedInts) # AQID
##      let encodedChars = encode(['h','e','y'])
##      echo(encodedChars) # aGV5
##
## The ``encode`` procedure takes an ``openarray`` so both arrays and sequences
## can be passed as parameters.
##
## Decoding data
## -------------
##
## To decode a base64 encoded data string simply call the ``decode``
## procedure:
##
##   .. code-block::nim
##      import base64
##      echo(decode("SGVsbG8gV29ybGQ=")) # Hello World

const
  cb64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

template encodeInternal(s: typed, lineLen: int, newLine: string): untyped =
  ## encodes `s` into base64 representation. After `lineLen` characters, a
  ## `newline` is added.
  var total = ((len(s) + 2) div 3) * 4
  let numLines = (total + lineLen - 1) div lineLen
  if numLines > 0: inc(total, (numLines - 1) * newLine.len)

  result = newString(total)
  var 
    i = 0
    r = 0
    currLine = 0
  while i < s.len - 2:
    let
      a = ord(s[i])
      b = ord(s[i+1])
      c = ord(s[i+2])
    result[r] = cb64[a shr 2]
    result[r+1] = cb64[((a and 3) shl 4) or ((b and 0xF0) shr 4)]
    result[r+2] = cb64[((b and 0x0F) shl 2) or ((c and 0xC0) shr 6)]
    result[r+3] = cb64[c and 0x3F]
    inc(r, 4)
    inc(i, 3)
    inc(currLine, 4)
    # avoid index out of bounds when lineLen == encoded length
    if