local format = string.format
local gsub = string.gsub
local byte = string.byte
local pack = string.pack
local error = error
local pairs = pairs
local setmetatable = setmetatable
local assigned = {}
local delayed = {}
-- slightly tricky interface: No/nil return means that the objects content
-- isn't known yet, while false indicates a delayed object.
local function written(pdf, num)
  num = pdf[num]
  if not num or num == assigned then return end
  return num ~= delayed
end
-- raw: Pass on preencoded stream. Currently ignored.
local function stream(pdf, num, dict, content, isfile, raw)
  if not num then num = pdf:getobj() end
  if pdf[num] ~= assigned then
    error[[Invalid object]]
  end
  pdf[num] = {offset = pdf.file:seek()}
  if isfile then
    local f = io.open(content)
    content = f:read'a'
    f:close()
  end
  pdf.file:write(format('%i 0 obj\n<<%s/Length %i>>stream\n', num, dict, #content))
  pdf.file:write(content)
  pdf.file:write'\nendstream\nendobj\n'
  return num
end
local function delayedstream(pdf, num, dict, content, isfile)
  if not num then num = pdf:getobj() end
  if pdf[num] ~= assigned then
    error[[Invalid object]]
  end
  pdf[num] = delayed
  pdf[-num] = {stream, dict, content, isfile}
  return num
end
local function indirect(pdf, num, content, isfile)
  if not num then num = pdf:getobj() end
  if pdf[num] ~= assigned then
    error[[Invalid object]]
  end
  pdf[num] = {offset = pdf.file:seek()}
  pdf.file:write(format('%i 0 obj\n', num))
  if isfile then
    local f = io.open(content)
    content = f:read'a'
    f:close()
  end
  pdf.file:write(content)
  pdf.file:write'\nendobj\n'
  return num
end
local function delay(pdf, num, content, isfile)
  if not num then num = pdf:getobj() end
  if pdf[num] ~= assigned then
    error[[Invalid object]]
  end
  pdf[num] = delayed
  pdf[-num] = {indirect, content, isfile}
  return num
end
local function reference(pdf, num)
  local status = pdf[num]
  if status == delayed then
    local saved = pdf[-num]
    pdf[-num] = nil
    pdf[num] = assigned
    return saved[1](pdf, num, table.unpack(saved, 2))
  elseif status == assigned or not status then
    error[[Invalid object]]
  -- else -- Already written
  end
end
local function getid(pdf)
  local id = pdf[0] + 1
  pdf[0] = id
  pdf[id] = assigned
  return id
end
local function trailer(pdf)
  local nextid = getid(pdf)
  local myoff = pdf.file:seek()
  pdf[nextid] = {offset = myoff}
  local linked = 0
  local offsets = {}
  for i=1,nextid do
    local off = pdf[i].offset
    if off then
      offsets[i+1] = pack(">I1I3I1", 1, off, 0)
    else
      offsets[linked+1] = pack(">I1I3I1", 0, i, 255)
      linked = i
    end
  end
  offsets[linked+1] = '\0\0\0\0\255'
  pdf[nextid] = assigned
  -- TODO: Add an /ID according to 14.4
  local info = pdf.info and string.format("/Info %i 0 R", pdf.info) or ""
  stream(pdf, nextid, format([[/Type/XRef/Size %i/W[1 3 1]/Root %i 0 R%s]], nextid+1, pdf.root, info), table.concat(offsets))
  pdf.file:write('startxref\n', myoff, '\n%%EOF')
end
local function close(pdf)
  trailer(pdf)
  local size = pdf.file:seek()
  if #pdf.version ~= 3 then
    error[[Invalid PDF version]]
  end
  pdf.file:seek('set', 5)
  pdf.file:write(pdf.version)
  pdf.file:close()
  return size
end
local pagetree = require'luametalatex-pdf-pagetree'
local pdfmeta = {
  close = close,
  getobj = getid,
  indirect = indirect,
  stream = stream,
  newpage = pagetree.newpage,
  writepages = pagetree.write,
  delayed = delay,
  delayedstream = delayedstream,
  reference = reference,
  written = written,
}
pdfmeta.__index = pdfmeta
local function open(filename)
  local file = io.open(filename, 'w')
  file:write"%PDF-X.X\n%🖋\n"
  return setmetatable({file = file, version = '1.7', [0] = 0, pages = {}}, pdfmeta)
end
return {
  open = open,
}