local mtar = {}

-- detect OS hopefully
if _OSVERSION then
 if _OSVERSION:sub(1,8) == "OpenOS" then
  OPENOS = true
 elseif _OSVERSION:sub(1,9) == "PsychOS" then
  PSYCHOS = true
 end
else
 LINUX = true
end

local function mkdir(dir)
 if OPENOS or LINUX then
  os.execute("mkdir "..dest.."/"..dir.." &> /dev/null")
 elseif PSYCHOS then
  -- todo: write PsychOS support
 end
end

local function toint(s)
 local n = 0
 local i = 1
 for p in s:gmatch(".") do
  n = n << 8
  n = n | string.byte(p)
  i=i+1
 end
 return n
end

local function cint(n,l)
 local t={}
 for i = 0, 7 do
  t[i+1] = (n >> (i * 8)) & 0xFF
 end
 return string.reverse(string.char(table.unpack(t)):sub(1,l))
end

local function cleanPath(path)
 local pt = {}
 for segment in path:gmatch("[^/]+") do
  if segment == ".." then
   pt[#pt] = nil
  elseif segment ~= "." then
   pt[#pt+1] = segment
  end
 end
 return table.concat(pt,"/")
end

function mtar.genHeader(fname,len) -- generate a header for file *fname* when provided with file length *len*
 return string.format("%s%s%s",cint(fname:len(),2),fname,cint(len,2))
end

function mtar.iter(stream) -- table -- function -- Given buffer *stream*, returns an iterator suitable for use with *for* that returns, for each iteration, the file name, a function to read from the file, and the length of the file.
 local remain = 0
 local function read(n)
  local rb = stream:read(math.min(n,remain))
  remain = remain - rb:len()
  return rb
 end
 return function()
  stream:read(remain)
  local nlen = toint(stream:read(2) or "\0\0")
  if nlen == 0 then
   return
  end
  local name = cleanPath(stream:read(nlen))
  local fsize = toint(stream:read(2))
  remain = fsize
  return name, read, fsize
 end
end

function mtar.unarchive(stream,dest,verbose) -- Extract mtar archive read from *stream* to *dest*. If *verbose*, print status.
 dest = dest or "."
 while true do
  local nlen = toint(stream:read(2) or "\0\0")
  if nlen == 0 then
   break
  end
  local name = cleanPath(stream:read(nlen))
  local fsize = toint(stream:read(2))
  if verbose then
   io.write(name.." "..tostring(fsize).."... ")
  end
  local dir = name:match("(.+)/.*%.?.+")
  if (dir) then
   mkdir(dir)
  end
  local f = io.open(dest.."/"..name,"wb")
  local rsize,buf = fsize, ""
  if f then
   repeat
    buf = stream:read(math.min(rsize,2048))
    f:write(buf)
    rsize = rsize - buf:len()
    if verbose then
     io.write(tostring(rsize).." ")
    end
   until rsize <= 1
   f:close()
  end
  if verbose then
   print("done.")
  end
 end
end

return mtar