#!/usr/bin/luajit
-- Construct a simple PDF, cargo-culted from Dave Long’s code.
-- Try with input of '100 100 m 100 200 l 200 100 l h f'.
-- By Kragen Javier Sitaker, 02025.  Public domain, CC0.

-- Keeps track of the byte offset in the accumulating output.
local function spew(maker, data)
   maker.offset = maker.offset + #data
   table.insert(maker.chunks, data)
end

local function pdfmaker(objs)
   local maker = {offset = 0, chunks = {}, output = output, offsets = {}}
   spew(maker, '%PDF-1.1\n%\xa5\xa5\xa5\xa5\n')
   for i, data in ipairs(objs) do
      maker.offsets[i] = maker.offset
      spew(maker, ('%d 0 obj\n%s\nendobj\n'):format(i, data))
   end

   local startxref = maker.offset

   -- PDF reserves object index 0 for the head of the free object ID list
   spew(maker, ('xref\n0 %d\n0000000000 65535 f \n'):format(#maker.offsets+1))

   for i, offset in ipairs(maker.offsets) do
      spew(maker, ('%010d 00000 n \n'):format(offset))
   end

   spew(maker, ([[trailer
<</Size %d /Root 1 0 R>>
startxref
%d
%%%%EOF
]]):format(#maker.offsets+1, startxref))

   return table.concat(maker.chunks)
end

      

local input = io.read('*a') -- read a page of drawing operators from input

-- The PDF objects are indexed by their PDF object index in this
-- table, so, for example, /Pages 2 0 R refers to object “[2]”, and
-- /Contents 3 0 R refers to object “[3]”.  But pdfmaker depends on
-- there being no gaps in the sequence.
io.write(pdfmaker {
   [1] = '<</Type /Catalog /Pages 2 0 R>>',
   [2] = '<</Type /Pages /Count 1 /Kids [3 0 R]>>',
   [3] = [[<</Parent 2 0 R /Contents 4 0 R
             /Type /Page /MediaBox [0 0 612 792]
             /Resources <</Font <</F1
                 <</Type /Font /BaseFont /Courier /Subtype /Type1>>
          >> >> >>
   ]],
   [4] = ('<</Length %d>>\nstream\n%s\nendstream'):format(#input, input),
})