lwz.lua

--Port of LWZ Compression
--Original: https://github.com/Magiczvn/LWZCompression/blob/master/LZW/LZWAlgorithm.lua

function InitDictionary(isEncode)
    mDictionary = {}
    local s = " !#$%&'\"()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~"
    local len = string.len(s)

    for i = 1, len do
        if isEncode then
            mDictionary[string.sub(s, i, i)] = i
        else
            mDictionary[i] = string.sub(s, i, i)
        end
    end

    mDictionaryLen = len
end

function Encode(sInput)
    InitDictionary(true)

    local s = ""
    local ch

    local len = string.len(sInput)
    local result = {}

    local dic = mDictionary
    local temp

    for i = 1, len do
        ch = string.sub(sInput, i, i)
        temp = s..ch
        if dic[temp] then
            s = temp
        else
            result[#result + 1] = dic[s]
            mDictionaryLen = mDictionaryLen + 1
            dic[temp] = mDictionaryLen
            s = ch
        end
    end
    result[#result + 1] = dic[s]

    return result
end

function Decode(data)
    InitDictionary(false)

    local dic = mDictionary

    local entry
    local ch
    local prevCode, currCode

    local result = {}

    prevCode = data[1]
    result[#result + 1] = dic[prevCode]

    for i = 2, #data do
        currCode = data[i]
        entry = dic[currCode]
        if entry then--exists in dictionary
            ch = string.sub(entry, 1, 1)
            result[#result + 1] = entry
        else
            ch = string.sub(dic[prevCode], 1, 1)
            result[#result + 1] = dic[prevCode]..ch
        end

        dic[#dic + 1] = dic[prevCode]..ch

        prevCode = currCode
    end

    return table.concat(result)
end