import os

class Tags(object):
  """file (e.g. .ini) based tagging scheme"""

  def __init__(self, path):
    """
    - path: path to file
    """
    self.path = path
    if not os.path.exists(path):
      f = file(path, 'w')
      f.close()
    self.tags = {}
    self.urls = {}
    self.read(path)
    

  def read(self):
    for line in file(path).readlines():
      line = line.strip()
      if not line:
        continue
      tag, urls = line.split('=', 1) # asserts '=' in line
      tag = tag.strip()
      urls = urls.strip()
      self.tags[tag] = set([urls])
      for url in urls:
        self.urls.setdefault(url, set()).add(tag)

  def write(self):
    f = file(self.path, 'w')
    for tag in sorted(self.tags.keys()):
      print >> f, '%s = %s' % (tag, ' '.join(self.tags[tag]))
    f.close()

  def add(self, tag, url):
    if url in self.tags[tag]:
      return
    self.tags[tag].add(url)
    self.urls[url].add(tag)
    self.write()

  def remove(self, tag, url):
    if url not in self.tags[tag]:
      return
    self.tags[tag].remove(url)
    self.urls[url].remove(tag)
    self.write()