#!/usr/bin/env python

"""
Pandoc filter to process code blocks with class "graphviz" into
graphviz-generated images.
"""

import pygraphviz
import hashlib
import os
import sys
from pandoc import toJSONFilter

def sha1(x):
  return hashlib.sha1(x).hexdigest()

imagedir = "graphviz-images"

def graphviz(key, value, format):
  if key == 'CodeBlock':
    [[ident,classes,keyvals], code] = value
    caption = "caption"
    if "graphviz" in classes:
      G = pygraphviz.AGraph(string = code)
      G.layout()
      filename = sha1(code)
      if format == "html":
        filetype = "png"
      elif format == "latex":
        filetype = "pdf"
      else:
        filetype = "png"
      alt = [{'Str': caption}]
      src = imagedir + '/' + filename + '.' + filetype
      if not os.path.isfile(src):
        try:
          os.mkdir(imagedir)
          sys.stderr.write('Created directory ' + imagedir + '\n')
        except OSError:
          pass
        G.draw(src)
        sys.stderr.write('Created image ' + src + '\n')
      tit = ""
      return {'Para': [{'Image': [alt, [src,tit]]}]}

if __name__ == "__main__":
  toJSONFilter(graphviz)