-- https://github.com/PixelToast/ComputerCraft/blob/master/apis/enc

local Crypto = { }

local function serialize(t) 
  local sType = type(t)
  if sType == "table" then
    local lstcnt=0
    for k,v in pairs(t) do
      lstcnt = lstcnt + 1
    end
    local result = "{"
    local aset=1
    for k,v in pairs(t) do
      if k==aset then
        result = result..serialize(v)..","
        aset=aset+1
      else
        result = result..("["..serialize(k).."]="..serialize(v)..",")
      end
    end
    result = result.."}"
    return result
  elseif sType == "string" then
    return string.format("%q",t)
  elseif sType == "number" or sType == "boolean" or sType == "nil" then
    return tostring(t)
  elseif sType == "function" then
    local status,data=pcall(string.dump,t)
    if status then
      data2=""
      for char in string.gmatch(data,".") do
        data2=data2..zfill(string.byte(char))
      end
      return 'f("'..data2..'")'
    else
      error("Invalid function: "..data)
    end
  else
    error("Could not serialize type "..sType..".")
  end
end

local function unserialize( s )
  local func, e = loadstring( "return "..s, "serialize" )
  if not func then
    return s,e
  else
    setfenv( func, {
      f=function(S)
        return loadstring(splitnum(S))
      end,
    })
    return func()
  end
end

local function splitnum(S)
  local Out=""
  for l1=1,#S,2 do
    local l2=(#S-l1)+1
    local function sure(N,n)
      if (l2-n)<1 then N="0" end
      return N
    end
    local CNum=tonumber("0x"..sure(string.sub(S,l2-1,l2-1),1) .. sure(string.sub(S,l2,l2),0))
    Out=string.char(CNum)..Out
  end
  return Out
end

local function zfill(N)
  N=string.format("%X",N)
  Zs=""
  if #N==1 then
    Zs="0"
  end
  return Zs..N
end

local function wrap(N)
  return N-(math.floor(N/256)*256)
end

local function checksum(S)
  local sum=0
  for char in string.gmatch(S,".") do
    math.randomseed(string.byte(char)+sum)
    sum=sum+math.random(0,9999)
  end
  math.randomseed(sum)
  return sum
end

local function genkey(len,psw)
  checksum(psw)
  local key={}
  local tKeys={}
  for l1=1,len do
    local num=math.random(1,len)
    while tKeys[num] do
      num=math.random(1,len)
    end
    tKeys[num]=true
    key[l1]={num,math.random(0,255)}
  end
  return key
end

function Crypto.encrypt(data,psw)
  data=serialize(data)
  local chs=checksum(data)
  local key=genkey(#data,psw)
  local out={}
  local cnt=1
  for char in string.gmatch(data,".") do
    table.insert(out,key[cnt][1],zfill(wrap(string.byte(char)+key[cnt][2])),chars)
    cnt=cnt+1
  end
  return string.sub(serialize({chs,table.concat(out)}),2,-3)
end

function Crypto.decrypt(data,psw)
  local oData=data
  data=unserialize("{"..data.."}")
  if type(data)~="table" then
    return oData
  end
  local chs=data[1]
  data=data[2]
  local key=genkey((#data)/2,psw)
  local sKey={}
  for k,v in pairs(key) do
    sKey[v[1]]={k,v[2]}
  end
  local str=splitnum(data)
  local cnt=1
  local out={}
  for char in string.gmatch(str,".") do
    table.insert(out,sKey[cnt][1],string.char(wrap(string.byte(char)-sKey[cnt][2])))
    cnt=cnt+1
  end
  out=table.concat(out)
  if checksum(out or "")==chs then
    return unserialize(out)
  end
  return oData,out,chs
end

return Crypto