docs/graphviz.py: pandoc filter to build dot graphs in SVG format

Licensed BSD-3-Clause: https://spdx.org/licenses/BSD-3-Clause.html
Based on https://github.com/jgm/pandocfilters/blob/master/examples/graphviz.pySigned-off-by: Tim Janik <timj@gnu.org>

docs/graphviz.py

+#!/usr/bin/env python3
+# Licensed BSD-3-Clause: https://spdx.org/licenses/BSD-3-Clause.html
+"""
+Pandoc filter to process code blocks with class "graphviz" into
+SVG based graphviz-generated images.
+
+Needs pygraphviz
+"""
+# Based on https://github.com/jgm/pandocfilters/blob/master/examples/graphviz.py
+
+import sys, os, pygraphviz
+from pandocfilters import toJSONFilter, Para, Image, RawBlock, get_filename4code, get_caption, get_extension, get_value
+
+# https://pandoc.org/lua-filters.html
+
+def graphviz (key, value, frmat, _):
+  if key == 'CodeBlock':
+    [[ident, classes, keyvals], code] = value
+    if "graphviz" in classes:
+      # sys.stderr.write ('Debug: ' + str (value) + '\n')
+      caption, typef, keyvals = get_caption (keyvals)
+      prog, keyvals = get_value (keyvals, u"prog", u"dot")
+      force, keyvals = get_value (keyvals, u"force", u"false")
+
+      filetype = get_extension (frmat, "svg", html ="svg", latex ="pdf")
+      dest = get_filename4code ("graphviz", str (value), filetype)
+
+      if force != u"false" or not os.path.isfile (dest):
+        g = pygraphviz.AGraph (string = code)
+        g.layout ()
+        g.draw (dest, prog = prog)
+        sys.stderr.write ('Create image: ' + dest + '\n')
+      if dest.endswith ('.svg'):
+        return RawBlock (u'html', '<object type="image/svg+xml" data="%s"></object>' % dest)
+      return Para ([Image ([ident, [], keyvals], caption, [dest, typef])])
+
+if __name__ == "__main__":
+  toJSONFilter (graphviz)