lua-filters.md: use pandoc.system module in TikZ example

Showcase temporary directory handling with `with_temporary_directory`
and `with_working_directory`.

1 files changed, 48 insertions, 39 deletions

diff --git a/doc/lua-filters.md b/doc/lua-filters.md
index 7cae8c186..c5f7d2713 100644
--- a/doc/lua-filters.md
+++ b/doc/lua-filters.md
@@ -653,59 +653,68 @@ document is built. (A more sophisticated version of this might
 put these in a special cache directory.)
 
 ``` lua
+local system = require 'pandoc.system'
+
+local tikz_doc_template = [[
+\documentclass{standalone}
+\usepackage{xcolor}
+\usepackage{tikz}
+\begin{document}
+\nopagecolor
+%s
+\end{document}
+]]
+
 local function tikz2image(src, filetype, outfile)
-    local tmp = os.tmpname()
-    local tmpdir = string.match(tmp, "^(.*[\\/])") or "."
-    local f = io.open(tmp .. ".tex", 'w')
-    f:write("\\documentclass{standalone}\n\\usepackage{xcolor}\n\\usepackage{tikz}\n\\begin{document}\n\\nopagecolor\n")
-    f:write(src)
-    f:write("\n\\end{document}\n")
-    f:close()
-    os.execute("pdflatex -output-directory " .. tmpdir  .. " " .. tmp)
-    if filetype == 'pdf' then
-        os.rename(tmp .. ".pdf", outfile)
-    else
-        os.execute("pdf2svg " .. tmp .. ".pdf " .. outfile)
-    end
-    os.remove(tmp .. ".tex")
-    os.remove(tmp .. ".pdf")
-    os.remove(tmp .. ".log")
-    os.remove(tmp .. ".aux")
+  system.with_temporary_directory('tikz2image', function (tmpdir)
+    system.with_working_directory(tmpdir, function()
+      local f = io.open('tikz.tex', 'w')
+      f:write(tikz_doc_template:format(src))
+      f:close()
+      os.execute('pdflatex tikz.tex')
+      if filetype == 'pdf' then
+        os.rename('tikz.pdf', outfile)
+      else
+        os.execute('pdf2svg tikz.pdf ' .. outfile)
+      end
+    end)
+  end)
 end
 
 extension_for = {
-    html = 'svg',
-    html4 = 'svg',
-    html5 = 'svg',
-    latex = 'pdf',
-    beamer = 'pdf' }
+  html = 'svg',
+  html4 = 'svg',
+  html5 = 'svg',
+  latex = 'pdf',
+  beamer = 'pdf' }
 
 local function file_exists(name)
-    local f = io.open(name, 'r')
-    if f ~= nil then
-        io.close(f)
-        return true
-    else
-        return false
-    end
+  local f = io.open(name, 'r')
+  if f ~= nil then
+    io.close(f)
+    return true
+  else
+    return false
+  end
 end
 
 local function starts_with(start, str)
-   return str:sub(1, #start) == start
+  return str:sub(1, #start) == start
 end
 
 
 function RawBlock(el)
-    if starts_with("\\begin{tikzpicture}", el.text) then
-        local filetype = extension_for[FORMAT] or "svg"
-        local fname = pandoc.sha1(el.text) .. "." .. filetype
-        if not file_exists(fname) then
-            tikz2image(el.text, filetype, fname)
-        end
-        return pandoc.Para({pandoc.Image({}, fname)})
-    else
-       return el
+  if starts_with('\\begin{tikzpicture}', el.text) then
+    local filetype = extension_for[FORMAT] or 'svg'
+    local fname = system.get_working_directory() .. '/' ..
+        pandoc.sha1(el.text) .. '.' .. filetype
+    if not file_exists(fname) then
+      tikz2image(el.text, filetype, fname)
     end
+    return pandoc.Para({pandoc.Image({}, fname)})
+  else
+   return el
+  end
 end
 ```