--[[
  2djab decode/encode program
  Vague specification:
    - Probably little endian
    - 2djab files start with "2djab1" (the 1 is the version)
    - Then have a 4-byte unsigned integer dictating the number of posters in the file
    - Then, each poster sequentially follows
    - Each poster:
      - Starts with a 2-byte unsigned integer (dictating its length in bytes)
      - Has a UTF-8 label, string starting with a 2-byte unsigned integer for length in bytes
        - (length of 0 is assumed to be no label)
      - Has a UTF-8 tooltip, string starting with a 2-byte unsigned integer for length in bytes
        - (length of 0 is assumed to be no label)
      - Has a palette
        - Starts with a 1-byte unsigned integer, dictating its length in bytes
          - The amount of colors it contains is its length divided by 3
        - Continues with many 3-byte integers, one for each color
      - Has an image data section
        - Starts with a 2-byte unsigned integer, dictating its length in bytes
        - Then has many 1-byte unsigned integers
          - If the 1-byte unsigned integer is within the range 0-63 inclusive:
            - it is a palette index
          - If the 1-byte unsigned integer is within the range 64-127 inclusive:
            - its value minus 64 is a palette index repeated twice
          - If the 1-byte unsigned integer is within the range 128-255 inclusive:
            - its value minus 128 is the amount of times that the previous palette index should be repeated
            - The previous palette index byte is still included
            - This byte must come directly after a byte within the 0-63 range.
  2djabc files are just the 2djab file but compressed with LibDeflate:CompressZlib
]]
local success, LibDeflate = pcall(require, "LibDeflate")

if not success then
  print("Error in requiring LibDeflate. Install? [y/n] ")
  local s = read()
  if s:lower():find("y") then
    shell.run("wget https://raw.githubusercontent.com/MCJack123/CC-Archive/master/LibDeflate.lua")
    LibDeflate = require("LibDeflate")
  else
    return
  end
end

local function decode2djab(str)
  local ver, numPosters = ("c6I4"):unpack(str:sub(1, 10))

  assert(ver == "2djab1")
  local pages = {}
  local out = {
    pages = pages
  }

  local posterStrs = {("s2"):rep(numPosters):unpack(str:sub(11))}
  for i = 1, numPosters do
    local posterStr = posterStrs[i]
    local label, tooltip, palette, data = ("s2s2s1s2"):unpack(posterStr)
    palette = {("I3"):rep(#palette / 3):unpack(palette)}
    palette[#palette] = nil
    data = data:gsub("([\0-\63])([\128-\255])", function(a, b) return a:rep(b:byte() - 127) end)
    data = data:gsub("[\64-\127]", function(a) return string.char(a:byte() - 64):rep(2) end)
    data = {data:byte(1, -1)}
    pages[#pages+1] = {
      label = label, tooltip = tooltip, palette = palette, pixels = data
    }
  end

  return out
end

local function encode2djab(input)
  local pages = input.pages
  local numPages = #pages
  local output = "2djab1" .. ("I4"):pack(numPages)

  for _i, page in ipairs(pages) do
    local data = page.pixels
    data[#data + 1] = -1
    local d2 = ''

    local currentPixel = -1
    local currentPixelCount = 0
    for i, pix in ipairs(data) do
      if pix == currentPixel then
        currentPixelCount = currentPixelCount + 1
        if currentPixelCount == 128 then
          d2 = d2 .. string.char(currentPixel) .. "\255"
          currentPixel, currentPixelCount = -1, 0
        end
      elseif pix ~= currentPixel then
        if currentPixel ~= -1 then
          if currentPixelCount == 1 then
            d2 = d2 .. string.char(currentPixel)
          elseif currentPixelCount == 2 then
            d2 = d2 .. string.char(currentPixel + 64)
          else
            d2 = d2 .. string.char(currentPixel) .. string.char(currentPixelCount + 127)
          end
        end
        currentPixel, currentPixelCount = pix, 1
      end
    end

    output = output .. ("s2"):pack(("s2s2s1s2"):pack(
      page.label or '',
      page.tooltip or '',
      ("I3"):rep(#page.palette):pack(unpack(page.palette)),
      d2
    ))
  end

  return output
end

local function decode2djabc(input)
  return decode2djab(LibDeflate:DecompressZlib(input))
end

local function encode2djabc(input)
  return LibDeflate:CompressZlib(encode2djab(input), {level = 9})
end

local function readfile(name)
	local hn = fs.open(shell.resolve(name), "rb")
  assert(hn, "Input file does not exist")
  local text = hn.readAll()
  hn.close()
  return text
end

local function writefile(name, text)
  local hn = fs.open(shell.resolve(name), "wb")
  hn.write(text)
  hn.close()
end

local mode, inputfile, outputfile = arg[1], arg[2], arg[3]
if not outputfile or not inputfile or (mode ~= "encode" and mode ~= "decode") then
  print("Usage: 2djab <encode|decode> <infile> <outfile>")
end

if mode == "encode" then
  print("Reading file " .. inputfile .. "...")
  local text = readfile(inputfile)
  print("Decoding JSON...")
  local dat = textutils.unserializeJSON(text)
  print("Encoding file...")
  local res = outputfile:find("%.2djabc$") and encode2djabc(dat) or encode2djab(dat)
  print("Writing file...")
  writefile(outputfile, res)
  print("Done!")
elseif mode == "decode" then
  print("Reading file " .. inputfile .. "...")
  local text = readfile(inputfile)
  print("Decoding 2djab...")
  local dat = inputfile:find("%.2djabc$") and decode2djabc(text) or decode2djab(text)
  print("Encoding JSON...")
  local res = textutils.serializeJSON(dat)
  print("Writing file...")
  writefile(outputfile, res)
  print("Done!")
end