PaintEncode

local function chars(str)
    local pos = 1
    return function()
        if pos <= #str  then
            local pos_was = pos
            pos = pos + 1
            return str:sub(pos_was, pos_was), pos_was
        end
    end
end

local function nybbles(byte)
    return bit.brshift(bit.band(0xF0, byte), 4), bit.band(0x0F, byte)
end

local function from_nybbles(hi, lo)
    return bit.bor(bit.blshift(hi, 4), lo)
end

local hexToColor = {}
for n = 0, 15 do
    hexToColor[string.format("%x", n)] = 2 ^ n
end

local function log2(x)
    return math.log10(x) / math.log10(2)
end

local function decode_col(c)
    return log2(hexToColor[c] or 1)
end

local function split_pair(pair)
    return pair:sub(1, 1), pair:sub(2, 2)
end

local paint_encode = {}

local function groups(str, l)
    local out, current = {}
    local pos = 1
    repeat
        current = str:sub(pos, pos + l - 1)
        pos = pos + l
        table.insert(out, current)
    until current == ""
    return out
end

function paint_encode.encode(str)
    local cols = ""
    for c in chars(str) do
        cols = cols .. string.format("%02x", string.byte(c))
    end
    local line_qty = math.sqrt(#cols)
    return table.concat(groups(cols, line_qty), "\n")
end

function paint_encode.decode(str)
    local outstr = ""
    for pair in str:gsub("\n", ""):gmatch("..") do
        local fst, snd = split_pair(pair)
        outstr = outstr .. string.char(from_nybbles(decode_col(fst), decode_col(snd)))
    end
    return outstr
end

function paint_encode.read(file)
    local f = fs.open(file, "r")
    local out = paint_encode.decode(f.readAll())
    f.close()
    return out
end

function paint_encode.write(file, str)
    local f = fs.open(file, "w")
    f.write(paint_encode.encode(str))
    f.close()
end

return paint_encode