-- Copyright (c) 2026 Marc Wäckerlin. SPDX-License-Identifier: MIT
-- Every drawing a document shows, converted while pandoc reads the document.
--
-- graphicx cannot read an SVG, and pandoc's own answer to one is the svg
-- package, which calls inkscape from inside the LaTeX run and therefore needs
-- shell escape — a document could then run any command it likes. So the drawing
-- is converted here, before a single line of LaTeX exists, and the picture in
-- the document points at the PDF that comes out.
--
-- The two directories arrive in the environment, from the converter: where the
-- document lies, and where the build may write.

local build = os.getenv('MD2PDF_BUILD')
local source = os.getenv('MD2PDF_SOURCE_DIR')

local function absolute(file)
  return file:sub(1, 1) == '/' and file or source .. '/' .. file
end

function Image(image)
  if not image.src:lower():match('%.svg$') then return nil end
  local name = image.src:gsub('.*/', ''):gsub('%.[Ss][Vv][Gg]$', '') .. '.pdf'
  local target = build .. '/' .. name
  local converted, message = pcall(pandoc.pipe, 'inkscape',
    {'--export-type=pdf', '--export-filename=' .. target,
     absolute(image.src)}, '')
  if not converted then
    error('the drawing ' .. image.src .. ' could not be converted: '
          .. tostring(message))
  end
  image.src = target
  return image
end