-- Copyright (c) 2026 Marc Wäckerlin. SPDX-License-Identifier: MIT
-- A link to a Markdown file of the same set points at the PDF of that file.
--
-- The documents reference each other, `[ARCHITECTURE.md](ARCHITECTURE.md)`, and
-- that is right in the repository, where the reader opens the Markdown. In the
-- PDF the same target opens nothing: the reader holds a PDF, the file beside it
-- is a PDF, and the link reaches for a source he does not have.
--
-- So a target that names a local Markdown file is rewritten to the PDF that the
-- same converter produces from it, with its anchor kept. An address with a
-- scheme (https:, mailto:) and an anchor inside the same document stay as they
-- are.
local function rewritten(target)
  if target:match('^%a[%w+.-]*:') or target:match('^#') then
    return nil
  end
  local file, anchor = target:match('^([^#]+)(#?.*)$')
  if not file or not file:lower():match('%.md$') then
    return nil
  end
  return file:sub(1, #file - 3) .. '.pdf' .. anchor
end

function Link(link)
  local target = rewritten(link.target)
  if not target then return nil end
  link.target = target
  return link
end