from bs4 import BeautifulSoup, Tag, NavigableString

_NEWLINE_INDICATOR = '<<<newline>>>'

def _bold(elem):
  elem.replace_with('*%s*' % elem.text)

def _unordered_list(elem):
  constructed = ''
  for child in elem.children:
    if child.name == 'li':
      constructed += '* %s\n' % child.text
  elem.replace_with(constructed)

def _horizontal_rule(elem):
  elem.replace_with('%s\n' % ('-' * 80))

def _anchor(elem):
  elem.replace_with('[%s](%s)' % (elem.text, elem['href']))

def _table(elem):
  elem.replace_with('%s%s' % (elem.text, _NEWLINE_INDICATOR))


_ELEMENT_REPLACER = {
  'b': _bold,
  'strong': _bold,
  'ul': _unordered_list,
  'hr': _horizontal_rule,
  'a': _anchor,
  'table': _table,
}

def _collapse_whitespace(text):
  new_lines = []
  lines = text.split('\n')
  for line in lines:
    if not line.strip():
      continue

    new_lines.append(line.strip().replace(_NEWLINE_INDICATOR, '\n'))

  return '\n'.join(new_lines)

def html2text(html):
  soup = BeautifulSoup(html, 'html5lib')
  _html2text(soup)
  return _collapse_whitespace(soup.text)

def _html2text(elem):
  for child in elem.children:
    if isinstance(child, Tag):
      _html2text(child)
    elif isinstance(child, NavigableString):
      # No changes necessary
      continue

  if elem.parent:
    if elem.name in _ELEMENT_REPLACER:
      _ELEMENT_REPLACER[elem.name](elem)