decompress

local inFN, outFN

local args = {...}
if #args ~= 2 then
    error("Usage: "..shell.getRunningProgram().." <input file> <output file>")
end
inFN = args[1]
outFN = args[2]

local f = fs.open(inFN, "r")
local inText = f.readAll()
f.close()

local inPos = 1

local huffmanCompression = true

if huffmanCompression then
    -- convert characters to bits
    local inBits = {}
    for k = 1, #inText do
        local byte = inText:sub(k, k):byte() - 32
        for i = 0, 5 do
            local testBit = 2 ^ i
            inBits[#inBits + 1] = (byte % (2 * testBit)) >= testBit
        end
    end

    -- remove padding
    local padbit = inBits[#inBits]
    while inBits[#inBits] == padbit do
        inBits[#inBits] = nil
    end

    local pos = 1
    local function readBit()
        if pos > #inBits then error("end of stream", 2) end
        pos = pos + 1
        return inBits[pos - 1]
    end

    -- read huffman tree
    local function readTree()
        if readBit() then
            local byte = 0
            for i = 0, 7 do
                if readBit() then
                    byte = byte + 2 ^ i
                end
            end
            --write(string.char(byte))
            return string.char(byte)
        else
            local subtree_0 = readTree()
            local subtree_1 = readTree()
            return {[false]=subtree_0, [true]=subtree_1}
        end
    end
    local tree = readTree()

    inText = ""

    local treePos = tree
    while pos <= #inBits do
        local bit = readBit()
        treePos = treePos[bit]
        if type(treePos) ~= "table" then
            inText = inText .. treePos
            treePos = tree
        end
    end
    if treePos ~= tree then
        error("unexpected end of stream")
    end
end

local function readTo(delim)
    local start = inPos
    local nextCaret = inText:find(delim, inPos, true)
    if not nextCaret then
        inPos = #inText + 1
        return inText:sub(start)
    end
    inPos = nextCaret + 1
    return inText:sub(start, nextCaret - 1)
end

-- returns iterator
local function splitString(str, delim)
    local pos = 1
    return function()
        if pos > #str then return end
        local start = pos
        local nextDelim = str:find(delim, pos, true)
        if not nextDelim then
            pos = #str + 1
            return str:sub(start)
        end
        pos = nextDelim + 1
        return str:sub(start, nextDelim - 1)
    end
end

local nameTable = {}

local idents = "abcdefghijklmnopqrstvuwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_"
local nextCompressed
do
    local validchars = idents:gsub("_","")

    local function encode(n)
        local s = ""
        while n > 0 do
            local digit = (n % #validchars) + 1
            s = s .. validchars:sub(digit, digit)
            n = math.floor(n / #validchars)
        end
        return s
    end

    local next = 0
    function nextCompressed()
        next = next + 1
        return encode(next)
    end
end

for k = 1, tonumber(readTo("^")) do
    local key = nextCompressed()
    local value = readTo("^")
    --print(key," -> ",value)
    nameTable[key] = value
    --assert(readTo("^") == tostring(k), "mismatch at "..k)
end

local out = ""

local function onFinishSegment(isIdent, segment)
    if isIdent then
        if segment:sub(1, 1) == "_" then
            out = out .. segment:sub(2)
        else
            out = out .. tostring(nameTable[segment])
        end
    else
        out = out .. segment
    end
end

local parsed = {}
local idents = "abcdefghijklmnopqrstvuwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_"
local lastIdent = nil

for k = inPos, #inText do
    local ch = inText:sub(k, k)
    local isIdent = idents:find(ch, 1, true) ~= nil
    if isIdent ~= lastIdent then
        if #parsed > 0 then
            onFinishSegment(lastIdent, parsed[#parsed])
        end
        parsed[#parsed+1] = ""
    end
    lastIdent = isIdent
    parsed[#parsed] = parsed[#parsed]..ch
end
if #parsed > 0 then
    onFinishSegment(isIdent, parsed[#parsed])
end

-- convert indentation back
local out2 = ""
local lastIndent = ""
for line in splitString(out, "\n") do
    while line:sub(1,2) == "&+" do
        lastIndent = lastIndent .. "\t"
        line = line:sub(3)
    end
    while line:sub(1,2) == "&-" do
        lastIndent = lastIndent:sub(1, #lastIndent - 1)
        line = line:sub(3)
    end
    if line:sub(1,2) == "&&" then
        line = line:sub(2)
    end

    out2 = out2 .. lastIndent .. line .. "\n"
end

--print(out2)

local f = fs.open(outFN, "w")
f.write(out2)
f.close()