local ZZBase64 = {}
local string = string

ZZBase64.__code = {
           \'A\', \'B\', \'C\', \'D\', \'E\', \'F\', \'G\', \'H\', \'I\', \'J\', \'K\', \'L\', \'M\', \'N\', \'O\', \'P\',
           \'Q\', \'R\', \'S\', \'T\', \'U\', \'V\', \'W\', \'X\', \'Y\', \'Z\', \'a\', \'b\', \'c\', \'d\', \'e\', \'f\',
           \'g\', \'h\', \'i\', \'j\', \'k\', \'l\', \'m\', \'n\', \'o\', \'p\', \'q\', \'r\', \'s\', \'t\', \'u\', \'v\',
           \'w\', \'x\', \'y\', \'z\', \'0\', \'1\', \'2\', \'3\', \'4\', \'5\', \'6\', \'7\', \'8\', \'9\', \'+\', \'/\',
       };
ZZBase64.__decode = {}
for k,v in pairs(ZZBase64.__code) do
   ZZBase64.__decode[string.byte(v,1)] = k - 1
end

function ZZBase64.encode(text)
    local len = string.len(text)
    local left = len % 3
    len = len - left
    local res = {}
    local index  = 1
    for i = 1, len, 3 do
       local a = string.byte(text, i )
       local b = string.byte(text, i + 1)
       local c = string.byte(text, i + 2)
       -- num = a<<16 + b<<8 + c
       local num = a * 65536 + b * 256 + c 
       for j = 1, 4 do
           --tmp = num >> ((4 -j) * 6)
           local tmp = math.floor(num / (2 ^ ((4-j) * 6)))
           --curPos = tmp&0x3f
           local curPos = tmp % 64 + 1
           res[index] = ZZBase64.__code[curPos]
           index = index + 1
       end
    end

    if left == 1 then
       ZZBase64.__left1(res, index, text, len)
    elseif left == 2 then
       ZZBase64.__left2(res, index, text, len)       
    end
    return table.concat(res)
end

function ZZBase64.__left2(res, index, text, len)
    local num1 = string.byte(text, len + 1)
    num1 = num1 * 1024 --lshift 10 
    local num2 = string.byte(text, len + 2)
    num2 = num2 * 4 --lshift 2 
    local num = num1 + num2
   
    local tmp1 = math.floor(num / 4096) --rShift 12
    local curPos = tmp1 % 64 + 1
    res[index] = ZZBase64.__code[curPos]
    
    local tmp2 = math.floor(num / 64)
    curPos = tmp2 % 64 + 1
    res[index + 1] = ZZBase64.__code[curPos]

    curPos = num % 64 + 1
    res[index + 2] = ZZBase64.__code[curPos]
    
    res[index + 3] = "=" 
end

function ZZBase64.__left1(res, index,text, len)
    local num = string.byte(text, len + 1)
    num = num * 16 
    
    tmp = math.floor(num / 64)
    local curPos = tmp % 64 + 1
    res[index ] = ZZBase64.__code[curPos]
    
    curPos = num % 64 + 1
    res[index + 1] = ZZBase64.__code[curPos]
    
    res[index + 2] = "=" 
    res[index + 3] = "=" 
end

function ZZBase64.decode(text)
    local len = string.len(text)
    local left = 0 
    if string.sub(text, len - 1) == "==" then
       left = 2 
       len = len - 4
    elseif string.sub(text, len) == "=" then
       left = 1
       len = len - 4
    end

    local res = {}
    local index = 1
    local decode = ZZBase64.__decode
    for i =1, len, 4 do
       local a = decode[string.byte(text,i    )] 
       local b = decode[string.byte(text,i + 1)] 
       local c = decode[string.byte(text,i + 2)] 
       local d = decode[string.byte(text,i + 3)]

       --num = a<<18 + b<<12 + c<<6 + d
       local num = a * 262144 + b * 4096 + c * 64 + d
       
       local e = string.char(num % 256)
       num = math.floor(num / 256)
       local f = string.char(num % 256)
       num = math.floor(num / 256)
       res[index ] = string.char(num % 256)
       res[index + 1] = f
       res[index + 2] = e
       index = index + 3
    end

    if left == 1 then
       ZZBase64.__decodeLeft1(res, index, text, len)
    elseif left == 2 then
       ZZBase64.__decodeLeft2(res, index, text, len)
    end
    return table.concat(res)
end

function ZZBase64.__decodeLeft1(res, index, text, len)
    local decode = ZZBase64.__decode
    local a = decode[string.byte(text, len + 1)] 
    local b = decode[string.byte(text, len + 2)] 
    local c = decode[string.byte(text, len + 3)] 
    local num = a * 4096 + b * 64 + c
    
    local num1 = math.floor(num / 1024) % 256
    local num2 = math.floor(num / 4) % 256
    res[index] = string.char(num1)
    res[index + 1] = string.char(num2)
end

function ZZBase64.__decodeLeft2(res, index, text, len)
    local decode = ZZBase64.__decode
    local a = decode[string.byte(text, len + 1)] 
    local b = decode[string.byte(text, len + 2)]
    local num = a * 64 + b
    num = math.floor(num / 16)
    res[index] = string.char(num)
end

function ZZBase64.test()
    local data = "a\193\207="
    local abc = ZZBase64.encode(data)
    print(abc)

    def = ZZBase64.decode(abc)
    if def == data then
       print("yes")
    end
end

return ZZBase64