import re

LINE_CONTINUATION_REGEX = re.compile(r'(\s)*\\(\s)*\n')
COMMAND_REGEX = re.compile('([A-Za-z]+)\s(.*)')

COMMENT_CHARACTER = '#'
LATEST_TAG = 'latest'

class ParsedDockerfile(object):
  def __init__(self, commands):
    self.commands = commands

  def _get_commands_of_kind(self, kind):
    return [command for command in self.commands if command['command'] == kind]

  def _get_from_image_identifier(self):
    from_commands = self._get_commands_of_kind('FROM')
    if not from_commands:
      return None

    return from_commands[-1]['parameters']

  @staticmethod
  def parse_image_identifier(image_identifier):
    """ Parses a docker image identifier, and returns a tuple of image name and tag, where the tag
        is filled in with "latest" if left unspecified.
    """
    # Note:
    # Dockerfile images references can be of multiple forms:
    #   server:port/some/path
    #   somepath
    #   server/some/path
    #   server/some/path:tag
    #   server:port/some/path:tag
    parts = image_identifier.strip().split(':')

    if len(parts) == 1:
      # somepath
      return (parts[0], LATEST_TAG)

    # Otherwise, determine if the last part is a port
    # or a tag.
    if parts[-1].find('/') >= 0:
      # Last part is part of the hostname.
      return (image_identifier, LATEST_TAG)

    # Remaining cases:
    #   server/some/path:tag
    #   server:port/some/path:tag    
    return (':'.join(parts[0:-1]), parts[-1])    

  def get_base_image(self):
    """ Return the base image without the tag name. """
    return self.get_image_and_tag()[0]

  def get_image_and_tag(self):
    """ Returns the image and tag from the FROM line of the dockerfile. """
    image_identifier = self._get_from_image_identifier()
    if image_identifier is None:
      return (None, None)

    return self.parse_image_identifier(image_identifier)


def strip_comments(contents):
  lines = [line for line in contents.split('\n') if not line.startswith(COMMENT_CHARACTER)]
  return '\n'.join(lines)


def join_continued_lines(contents):
  return LINE_CONTINUATION_REGEX.sub('', contents)


def parse_dockerfile(contents):
  contents = join_continued_lines(strip_comments(contents))
  lines = [line for line in contents.split('\n') if len(line) > 0]

  commands = []
  for line in lines:
    match_command = COMMAND_REGEX.match(line)
    if match_command:
      command = match_command.group(1).upper()
      parameters = match_command.group(2)

      commands.append({
        'command': command,
        'parameters': parameters
      })

  return ParsedDockerfile(commands)


def serialize_dockerfile(parsed_dockerfile):
  return '\n'.join([' '.join([command['command'], command['parameters']])
                    for command in parsed_dockerfile.commands])
