#!/usr/bin/python
#
# Copyright (C) 2006 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


"""Contains classes representing Atom elements.

  Module objective: provide data classes for Atom constructs. These classes hide
  the XML-ness of Atom and provide a set of native Python classes to interact 
  with.

  Conversions to and from XML should only be necessary when the Atom classes
  "touch the wire" and are sent over HTTP. For this reason this module 
  provides  methods and functions to convert Atom classes to and from strings.

  For more information on the Atom data model, see RFC 4287 
  (http://www.ietf.org/rfc/rfc4287.txt)

  AtomBase: A foundation class on which Atom classes are built. It 
      handles the parsing of attributes and children which are common to all
      Atom classes. By default, the AtomBase class translates all XML child 
      nodes into ExtensionElements.

  ExtensionElement: Atom allows Atom objects to contain XML which is not part 
      of the Atom specification, these are called extension elements. If a 
      classes parser encounters an unexpected XML construct, it is translated
      into an ExtensionElement instance. ExtensionElement is designed to fully
      capture the information in the XML. Child nodes in an XML extension are
      turned into ExtensionElements as well.
"""


__author__ = 'api.jscudder (Jeffrey Scudder)'

try:
  from xml.etree import cElementTree as ElementTree
except ImportError:
  try:
    import cElementTree as ElementTree
  except ImportError:
    try:
      from xml.etree import ElementTree
    except ImportError:
      from elementtree import ElementTree


# XML namespaces which are often used in Atom entities.
ATOM_NAMESPACE = 'http://www.w3.org/2005/Atom'
ELEMENT_TEMPLATE = '{http://www.w3.org/2005/Atom}%s'
APP_NAMESPACE = 'http://purl.org/atom/app#'
APP_TEMPLATE = '{http://purl.org/atom/app#}%s'

# This encoding is used for converting strings before translating the XML
# into an object.
XML_STRING_ENCODING = 'utf-8'
# The desired string encoding for object members. set or monkey-patch to 
# unicode if you want object members to be Python unicode strings, instead of
# encoded strings
MEMBER_STRING_ENCODING = 'utf-8'
#MEMBER_STRING_ENCODING = unicode

def CreateClassFromXMLString(target_class, xml_string, string_encoding=None):
  """Creates an instance of the target class from the string contents.
  
  Args:
    target_class: class The class which will be instantiated and populated
        with the contents of the XML. This class must have a _tag and a
        _namespace class variable.
    xml_string: str A string which contains valid XML. The root element
        of the XML string should match the tag and namespace of the desired
        class.
    string_encoding: str The character encoding which the xml_string should
        be converted to before it is interpreted and translated into 
        objects. The default is None in which case the string encoding
        is not changed.

  Returns:
    An instance of the target class with members assigned according to the
    contents of the XML - or None if the root XML tag and namespace did not
    match those of the target class.
  """
  encoding = string_encoding or XML_STRING_ENCODING
  if encoding and isinstance(xml_string, unicode):
    xml_string = xml_string.encode(encoding)
  tree = ElementTree.fromstring(xml_string)
  return _CreateClassFromElementTree(target_class, tree)


def _CreateClassFromElementTree(target_class, tree, namespace=None, tag=None):
  """Instantiates the class and populates members according to the tree.

  Note: Only use this function with classes that have _namespace and _tag
  class members.

  Args:
    target_class: class The class which will be instantiated and populated
        with the contents of the XML.
    tree: ElementTree An element tree whose contents will be converted into
        members of the new target_class instance.
    namespace: str (optional) The namespace which the XML tree's root node must
        match. If omitted, the namespace defaults to the _namespace of the 
        target class.
    tag: str (optional) The tag which the XML tree's root node must match. If
        omitted, the tag defaults to the _tag class member of the target 
        class.

    Returns:
      An instance of the target class - or None if the tag and namespace of 
      the XML tree's root node did not match the desired namespace and tag.
  """
  if namespace is None:
    namespace = target_class._namespace
  if tag is None:
    tag = target_class._tag
  if tree.tag == '{%s}%s' % (namespace, tag):
    target = target_class()
    target._HarvestElementTree(tree)
    return target
  else:
    return None


class ExtensionContainer(object):
  
  def __init__(self, extension_elements=None, extension_attributes=None,
      text=None):
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}
    self.text = text
 
  # Three methods to create an object from an ElementTree
  def _HarvestElementTree(self, tree):
    # Fill in the instance members from the contents of the XML tree.
    for child in tree:
      self._ConvertElementTreeToMember(child)
    for attribute, value in tree.attrib.iteritems():
      self._ConvertElementAttributeToMember(attribute, value)
    # Encode the text string according to the desired encoding type. (UTF-8)
    if tree.text:
      if MEMBER_STRING_ENCODING is unicode:
        self.text = tree.text
      else:
        self.text = tree.text.encode(MEMBER_STRING_ENCODING)
    
  def _ConvertElementTreeToMember(self, child_tree, current_class=None):
    self.extension_elements.append(_ExtensionElementFromElementTree(
        child_tree))

  def _ConvertElementAttributeToMember(self, attribute, value):
    # Encode the attribute value's string with the desired type Default UTF-8
    if value:
      if MEMBER_STRING_ENCODING is unicode:
        self.extension_attributes[attribute] = value
      else:
        self.extension_attributes[attribute] = value.encode(
          MEMBER_STRING_ENCODING)

  # One method to create an ElementTree from an object
  def _AddMembersToElementTree(self, tree):
    for child in self.extension_elements:
      child._BecomeChildElement(tree)
    for attribute, value in self.extension_attributes.iteritems():
      if value:
        if isinstance(value, unicode) or MEMBER_STRING_ENCODING is unicode:
          tree.attrib[attribute] = value
        else:
          # Decode the value from the desired encoding (default UTF-8).
          tree.attrib[attribute] = value.decode(MEMBER_STRING_ENCODING)
    if self.text:
      if isinstance(self.text, unicode) or MEMBER_STRING_ENCODING is unicode:
        tree.text = self.text 
      else:
        tree.text = self.text.decode(MEMBER_STRING_ENCODING)

  def FindExtensions(self, tag=None, namespace=None):
    """Searches extension elements for child nodes with the desired name.

    Returns a list of extension elements within this object whose tag
    and/or namespace match those passed in. To find all extensions in
    a particular namespace, specify the namespace but not the tag name.
    If you specify only the tag, the result list may contain extension
    elements in multiple namespaces.

    Args:
      tag: str (optional) The desired tag
      namespace: str (optional) The desired namespace

    Returns:
      A list of elements whose tag and/or namespace match the parameters
      values
    """

    results = []

    if tag and namespace:
      for element in self.extension_elements:
        if element.tag == tag and element.namespace == namespace:
          results.append(element)
    elif tag and not namespace:
      for element in self.extension_elements:
        if element.tag == tag:
          results.append(element)
    elif namespace and not tag:
      for element in self.extension_elements:
        if element.namespace == namespace:
          results.append(element)
    else:
      for element in self.extension_elements:
        results.append(element)

    return results
  

class AtomBase(ExtensionContainer):

  _children = {}
  _attributes = {}

  def __init__(self, extension_elements=None, extension_attributes=None,
      text=None):
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}
    self.text = text
      
  def _ConvertElementTreeToMember(self, child_tree):
    # Find the element's tag in this class's list of child members
    if self.__class__._children.has_key(child_tree.tag):
      member_name = self.__class__._children[child_tree.tag][0]
      member_class = self.__class__._children[child_tree.tag][1]
      # If the class member is supposed to contain a list, make sure the
      # matching member is set to a list, then append the new member
      # instance to the list.
      if isinstance(member_class, list):
        if getattr(self, member_name) is None:
          setattr(self, member_name, [])
        getattr(self, member_name).append(_CreateClassFromElementTree(
            member_class[0], child_tree))
      else:
        setattr(self, member_name, 
                _CreateClassFromElementTree(member_class, child_tree))
    else:
      ExtensionContainer._ConvertElementTreeToMember(self, child_tree)      

  def _ConvertElementAttributeToMember(self, attribute, value):
    # Find the attribute in this class's list of attributes. 
    if self.__class__._attributes.has_key(attribute):
      # Find the member of this class which corresponds to the XML attribute
      # (lookup in current_class._attributes) and set this member to the
      # desired value (using self.__dict__).
      if value:
        # Encode the string to capture non-ascii characters (default UTF-8)
        if MEMBER_STRING_ENCODING is unicode:
          setattr(self, self.__class__._attributes[attribute], value)
        else:
          setattr(self, self.__class__._attributes[attribute], 
                value.encode(MEMBER_STRING_ENCODING))
    else:
      ExtensionContainer._ConvertElementAttributeToMember(self, attribute, 
          value)

  # Three methods to create an ElementTree from an object
  def _AddMembersToElementTree(self, tree):
    # Convert the members of this class which are XML child nodes. 
    # This uses the class's _children dictionary to find the members which
    # should become XML child nodes.
    member_node_names = [values[0] for tag, values in 
                                       self.__class__._children.iteritems()]
    for member_name in member_node_names:
      member = getattr(self, member_name)
      if member is None:
        pass
      elif isinstance(member, list):
        for instance in member:
          instance._BecomeChildElement(tree)
      else:
        member._BecomeChildElement(tree)
    # Convert the members of this class which are XML attributes.
    for xml_attribute, member_name in self.__class__._attributes.iteritems():
      member = getattr(self, member_name)
      if member is not None:
        if isinstance(member, unicode) or MEMBER_STRING_ENCODING is unicode:
          tree.attrib[xml_attribute] = member
        else:
          tree.attrib[xml_attribute] = member.decode(MEMBER_STRING_ENCODING)
    # Lastly, call the ExtensionContainers's _AddMembersToElementTree to 
    # convert any extension attributes.
    ExtensionContainer._AddMembersToElementTree(self, tree)
    
  
  def _BecomeChildElement(self, tree):
    """

    Note: Only for use with classes that have a _tag and _namespace class 
    member. It is in AtomBase so that it can be inherited but it should
    not be called on instances of AtomBase.
    
    """
    new_child = ElementTree.Element('')
    tree.append(new_child)
    new_child.tag = '{%s}%s' % (self.__class__._namespace, 
                                self.__class__._tag)
    self._AddMembersToElementTree(new_child)

  def _ToElementTree(self):
    """

    Note, this method is designed to be used only with classes that have a 
    _tag and _namespace. It is placed in AtomBase for inheritance but should
    not be called on this class.

    """
    new_tree = ElementTree.Element('{%s}%s' % (self.__class__._namespace,
                                               self.__class__._tag))
    self._AddMembersToElementTree(new_tree)
    return new_tree

  def ToString(self, string_encoding='UTF-8'):
    """Converts the Atom object to a string containing XML."""
    return ElementTree.tostring(self._ToElementTree(), encoding=string_encoding)

  def __str__(self):
    return self.ToString()

    
class Name(AtomBase):
  """The atom:name element"""

  _tag = 'name'
  _namespace = ATOM_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()

  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Name

    Args:
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def NameFromString(xml_string):
  return CreateClassFromXMLString(Name, xml_string)


class Email(AtomBase):
  """The atom:email element"""

  _tag = 'email'
  _namespace = ATOM_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()
  
  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Email

    Args:
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
      text: str The text data in the this element
    """

    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def EmailFromString(xml_string):
  return CreateClassFromXMLString(Email, xml_string)


class Uri(AtomBase):
  """The atom:uri element"""

  _tag = 'uri'
  _namespace = ATOM_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()

  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Uri

    Args:
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
      text: str The text data in the this element
    """

    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def UriFromString(xml_string):
  return CreateClassFromXMLString(Uri, xml_string)

  
class Person(AtomBase):
  """A foundation class from which atom:author and atom:contributor extend.
  
  A person contains information like name, email address, and web page URI for
  an author or contributor to an Atom feed. 
  """

  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()
  _children['{%s}name' % (ATOM_NAMESPACE)] = ('name', Name)
  _children['{%s}email' % (ATOM_NAMESPACE)] = ('email', Email)
  _children['{%s}uri' % (ATOM_NAMESPACE)] = ('uri', Uri)

  def __init__(self, name=None, email=None, uri=None,
      extension_elements=None, extension_attributes=None, text=None):
    """Foundation from which author and contributor are derived.

    The constructor is provided for illustrative purposes, you should not
    need to instantiate a Person.

    Args:
      name: Name The person's name
      email: Email The person's email address
      uri: Uri The URI of the person's webpage
      extension_elements: list A list of ExtensionElement instances which are
          children of this element.
      extension_attributes: dict A dictionary of strings which are the values
          for additional XML attributes of this element.
      text: String The text contents of the element. This is the contents
          of the Entry's XML text node. (Example: <foo>This is the text</foo>)
    """

    self.name = name
    self.email = email
    self.uri = uri
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}
    self.text = text


class Author(Person):
  """The atom:author element
  
  An author is a required element in Feed. 
  """

  _tag = 'author'
  _namespace = ATOM_NAMESPACE
  _children = Person._children.copy()
  _attributes = Person._attributes.copy()
  #_children = {}
  #_attributes = {}

  def __init__(self, name=None, email=None, uri=None, 
      extension_elements=None, extension_attributes=None, text=None):
    """Constructor for Author
    
    Args:
      name: Name
      email: Email
      uri: Uri
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
      text: str The text data in the this element
    """
    
    self.name = name
    self.email = email
    self.uri = uri
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}
    self.text = text

    
def AuthorFromString(xml_string):
  return CreateClassFromXMLString(Author, xml_string)
  

class Contributor(Person):
  """The atom:contributor element"""

  _tag = 'contributor'
  _namespace = ATOM_NAMESPACE
  _children = Person._children.copy()
  _attributes = Person._attributes.copy()

  def __init__(self, name=None, email=None, uri=None,
      extension_elements=None, extension_attributes=None, text=None):
    """Constructor for Contributor
    
    Args:
      name: Name
      email: Email
      uri: Uri
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
      text: str The text data in the this element
    """

    self.name = name
    self.email = email
    self.uri = uri
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}
    self.text = text


def ContributorFromString(xml_string):
  return CreateClassFromXMLString(Contributor, xml_string)
  
  
class Link(AtomBase):
  """The atom:link element"""

  _tag = 'link'
  _namespace = ATOM_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()
  _attributes['rel'] = 'rel'
  _attributes['href'] = 'href'
  _attributes['type'] = 'type'
  _attributes['title'] = 'title'
  _attributes['length'] = 'length'
  _attributes['hreflang'] = 'hreflang'
  
  def __init__(self, href=None, rel=None, link_type=None, hreflang=None, 
      title=None, length=None, text=None, extension_elements=None, 
      extension_attributes=None):
    """Constructor for Link
    
    Args:
      href: string The href attribute of the link
      rel: string
      type: string
      hreflang: string The language for the href
      title: string
      length: string The length of the href's destination
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
      text: str The text data in the this element
    """

    self.href = href
    self.rel = rel
    self.type = link_type
    self.hreflang = hreflang
    self.title = title
    self.length = length
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def LinkFromString(xml_string):
  return CreateClassFromXMLString(Link, xml_string)
  

class Generator(AtomBase):
  """The atom:generator element"""

  _tag = 'generator'
  _namespace = ATOM_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()
  _attributes['uri'] = 'uri'
  _attributes['version'] = 'version'

  def __init__(self, uri=None, version=None, text=None, 
      extension_elements=None, extension_attributes=None):
    """Constructor for Generator
    
    Args:
      uri: string
      version: string
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.uri = uri
    self.version = version
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}

def GeneratorFromString(xml_string):
  return CreateClassFromXMLString(Generator, xml_string)


class Text(AtomBase):
  """A foundation class from which atom:title, summary, etc. extend.
  
  This class should never be instantiated.
  """

  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()
  _attributes['type'] = 'type'

  def __init__(self, text_type=None, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Text
    
    Args:
      text_type: string
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """
    
    self.type = text_type
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


class Title(Text):
  """The atom:title element"""

  _tag = 'title'
  _namespace = ATOM_NAMESPACE
  _children = Text._children.copy()
  _attributes = Text._attributes.copy()

  def __init__(self, title_type=None, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Title
    
    Args:
      title_type: string
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.type = title_type
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def TitleFromString(xml_string):
  return CreateClassFromXMLString(Title, xml_string)


class Subtitle(Text):
  """The atom:subtitle element"""

  _tag = 'subtitle'
  _namespace = ATOM_NAMESPACE
  _children = Text._children.copy()
  _attributes = Text._attributes.copy()

  def __init__(self, subtitle_type=None, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Subtitle
    
    Args:
      subtitle_type: string
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.type = subtitle_type
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def SubtitleFromString(xml_string):
  return CreateClassFromXMLString(Subtitle, xml_string)


class Rights(Text):
  """The atom:rights element"""

  _tag = 'rights'
  _namespace = ATOM_NAMESPACE
  _children = Text._children.copy()
  _attributes = Text._attributes.copy()

  def __init__(self, rights_type=None, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Rights
    
    Args:
      rights_type: string
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.type = rights_type
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def RightsFromString(xml_string):
  return CreateClassFromXMLString(Rights, xml_string)


class Summary(Text):
  """The atom:summary element"""

  _tag = 'summary'
  _namespace = ATOM_NAMESPACE
  _children = Text._children.copy()
  _attributes = Text._attributes.copy()

  def __init__(self, summary_type=None, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Summary
    
    Args:
      summary_type: string
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.type = summary_type
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def SummaryFromString(xml_string):
  return CreateClassFromXMLString(Summary, xml_string)


class Content(Text):
  """The atom:content element"""

  _tag = 'content'
  _namespace = ATOM_NAMESPACE
  _children = Text._children.copy()
  _attributes = Text._attributes.copy()
  _attributes['src'] = 'src'

  def __init__(self, content_type=None, src=None, text=None, 
      extension_elements=None, extension_attributes=None):
    """Constructor for Content
    
    Args:
      content_type: string
      src: string
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """
    
    self.type = content_type
    self.src = src
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}

def ContentFromString(xml_string):
  return CreateClassFromXMLString(Content, xml_string)


class Category(AtomBase):
  """The atom:category element"""

  _tag = 'category'
  _namespace = ATOM_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()
  _attributes['term'] = 'term'
  _attributes['scheme'] = 'scheme'
  _attributes['label'] = 'label'

  def __init__(self, term=None, scheme=None, label=None, text=None, 
      extension_elements=None, extension_attributes=None):
    """Constructor for Category
    
    Args:
      term: str
      scheme: str
      label: str
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """
    
    self.term = term
    self.scheme = scheme
    self.label = label
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def CategoryFromString(xml_string):
  return CreateClassFromXMLString(Category, xml_string)


class Id(AtomBase):
  """The atom:id element."""

  _tag = 'id'
  _namespace = ATOM_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()

  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Id
    
    Args:
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def IdFromString(xml_string):
  return CreateClassFromXMLString(Id, xml_string)


class Icon(AtomBase):
  """The atom:icon element."""
  
  _tag = 'icon'
  _namespace = ATOM_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()

  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Icon
    
    Args:
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def IconFromString(xml_string):
  return CreateClassFromXMLString(Icon, xml_string)


class Logo(AtomBase):
  """The atom:logo element."""

  _tag = 'logo'
  _namespace = ATOM_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()

  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Logo
    
    Args:
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """
    
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def LogoFromString(xml_string):
  return CreateClassFromXMLString(Logo, xml_string)


class Draft(AtomBase):
  """The app:draft element which indicates if this entry should be public."""

  _tag = 'draft'
  _namespace = APP_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()

  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for app:draft

    Args:
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def DraftFromString(xml_string):
  return CreateClassFromXMLString(Draft, xml_string)


class Control(AtomBase):
  """The app:control element indicating restrictions on publication.
  
  The APP control element may contain a draft element indicating whether or
  not this entry should be publicly available.
  """

  _tag = 'control'
  _namespace = APP_NAMESPACE
  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()
  _children['{%s}draft' % APP_NAMESPACE] = ('draft', Draft)

  def __init__(self, draft=None, text=None, extension_elements=None,
        extension_attributes=None):
    """Constructor for app:control"""
    
    self.draft = draft
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def ControlFromString(xml_string):
  return CreateClassFromXMLString(Control, xml_string)


class Date(AtomBase):
  """A parent class for atom:updated, published, etc."""

  #TODO Add text to and from time conversion methods to allow users to set
  # the contents of a Date to a python DateTime object.

  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()

  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


class Updated(Date):
  """The atom:updated element."""

  _tag = 'updated'
  _namespace = ATOM_NAMESPACE
  _children = Date._children.copy()
  _attributes = Date._attributes.copy()

  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Updated
    
    Args:
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def UpdatedFromString(xml_string):
  return CreateClassFromXMLString(Updated, xml_string)


class Published(Date):
  """The atom:published element."""

  _tag = 'published'
  _namespace = ATOM_NAMESPACE
  _children = Date._children.copy()
  _attributes = Date._attributes.copy()

  def __init__(self, text=None, extension_elements=None,
      extension_attributes=None):
    """Constructor for Published
    
    Args:
      text: str The text data in the this element
      extension_elements: list A  list of ExtensionElement instances
      extension_attributes: dict A dictionary of attribute value string pairs
    """

    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def PublishedFromString(xml_string):
  return CreateClassFromXMLString(Published, xml_string)


class LinkFinder(object):
  """An "interface" providing methods to find link elements

  Entry elements often contain multiple links which differ in the rel
  attribute or content type. Often, developers are interested in a specific
  type of link so this class provides methods to find specific classes of
  links.

  This class is used as a mixin in Atom entries and feeds.
  """

  def GetSelfLink(self):
    """Find the first link with rel set to 'self'

    Returns:
      An atom.Link or none if none of the links had rel equal to 'self'
    """

    for a_link in self.link:
      if a_link.rel == 'self':
        return a_link
    return None

  def GetEditLink(self):
    for a_link in self.link:
      if a_link.rel == 'edit':
        return a_link
    return None

  def GetNextLink(self):
    for a_link in self.link:
      if a_link.rel == 'next':
        return a_link
    return None

  def GetLicenseLink(self):
    for a_link in self.link:
      if a_link.rel == 'license':
        return a_link
    return None

  def GetAlternateLink(self):
    for a_link in self.link:
      if a_link.rel == 'alternate':
        return a_link
    return None
    
 
class FeedEntryParent(AtomBase, LinkFinder):
  """A super class for atom:feed and entry, contains shared attributes"""

  _children = AtomBase._children.copy()
  _attributes = AtomBase._attributes.copy()
  _children['{%s}author' % ATOM_NAMESPACE] = ('author', [Author])
  _children['{%s}category' % ATOM_NAMESPACE] = ('category', [Category])
  _children['{%s}contributor' % ATOM_NAMESPACE] = ('contributor', [Contributor])
  _children['{%s}id' % ATOM_NAMESPACE] = ('id', Id)
  _children['{%s}link' % ATOM_NAMESPACE] = ('link', [Link])
  _children['{%s}rights' % ATOM_NAMESPACE] = ('rights', Rights)
  _children['{%s}title' % ATOM_NAMESPACE] = ('title', Title)
  _children['{%s}updated' % ATOM_NAMESPACE] = ('updated', Updated)

  def __init__(self, author=None, category=None, contributor=None, 
      atom_id=None, link=None, rights=None, title=None, updated=None, 
      text=None, extension_elements=None, extension_attributes=None):
    self.author = author or []
    self.category = category or []
    self.contributor = contributor or []
    self.id = atom_id
    self.link = link or []
    self.rights = rights
    self.title = title
    self.updated = updated
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


class Source(FeedEntryParent):
  """The atom:source element"""

  _tag = 'source'
  _namespace = ATOM_NAMESPACE
  _children = FeedEntryParent._children.copy()
  _attributes = FeedEntryParent._attributes.copy()
  _children['{%s}generator' % ATOM_NAMESPACE] = ('generator', Generator)
  _children['{%s}icon' % ATOM_NAMESPACE] = ('icon', Icon)
  _children['{%s}logo' % ATOM_NAMESPACE] = ('logo', Logo)
  _children['{%s}subtitle' % ATOM_NAMESPACE] = ('subtitle', Subtitle)

  def __init__(self, author=None, category=None, contributor=None,
      generator=None, icon=None, atom_id=None, link=None, logo=None, 
      rights=None, subtitle=None, title=None, updated=None, text=None,
      extension_elements=None, extension_attributes=None):
    """Constructor for Source

    Args:
      author: list (optional) A list of Author instances which belong to this
          class.
      category: list (optional) A list of Category instances
      contributor: list (optional) A list on Contributor instances
      generator: Generator (optional)
      icon: Icon (optional)
      id: Id (optional) The entry's Id element
      link: list (optional) A list of Link instances
      logo: Logo (optional)
      rights: Rights (optional) The entry's Rights element
      subtitle: Subtitle (optional) The entry's subtitle element
      title: Title (optional) the entry's title element
      updated: Updated (optional) the entry's updated element
      text: String (optional) The text contents of the element. This is the
          contents of the Entry's XML text node.
          (Example: <foo>This is the text</foo>)
      extension_elements: list (optional) A list of ExtensionElement instances
          which are children of this element.
      extension_attributes: dict (optional) A dictionary of strings which are
          the values for additional XML attributes of this element.
    """

    self.author = author or []
    self.category = category or []
    self.contributor = contributor or []
    self.generator = generator
    self.icon = icon
    self.id = atom_id
    self.link = link or []
    self.logo = logo
    self.rights = rights
    self.subtitle = subtitle
    self.title = title
    self.updated = updated
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def SourceFromString(xml_string):
  return CreateClassFromXMLString(Source, xml_string)


class Entry(FeedEntryParent):
  """The atom:entry element"""

  _tag = 'entry'
  _namespace = ATOM_NAMESPACE
  _children = FeedEntryParent._children.copy()
  _attributes = FeedEntryParent._attributes.copy()
  _children['{%s}content' % ATOM_NAMESPACE] = ('content', Content)
  _children['{%s}published' % ATOM_NAMESPACE] = ('published', Published)
  _children['{%s}source' % ATOM_NAMESPACE] = ('source', Source)
  _children['{%s}summary' % ATOM_NAMESPACE] = ('summary', Summary)
  _children['{%s}control' % APP_NAMESPACE] = ('control', Control)

  def __init__(self, author=None, category=None, content=None, 
      contributor=None, atom_id=None, link=None, published=None, rights=None,
      source=None, summary=None, control=None, title=None, updated=None,
      extension_elements=None, extension_attributes=None, text=None):
    """Constructor for atom:entry

    Args:
      author: list A list of Author instances which belong to this class.
      category: list A list of Category instances
      content: Content The entry's Content
      contributor: list A list on Contributor instances
      id: Id The entry's Id element
      link: list A list of Link instances
      published: Published The entry's Published element
      rights: Rights The entry's Rights element
      source: Source the entry's source element
      summary: Summary the entry's summary element
      title: Title the entry's title element
      updated: Updated the entry's updated element
      control: The entry's app:control element which can be used to mark an 
          entry as a draft which should not be publicly viewable.
      text: String The text contents of the element. This is the contents
          of the Entry's XML text node. (Example: <foo>This is the text</foo>)
      extension_elements: list A list of ExtensionElement instances which are
          children of this element.
      extension_attributes: dict A dictionary of strings which are the values
          for additional XML attributes of this element.
    """

    self.author = author or []
    self.category = category or []
    self.content = content
    self.contributor = contributor or []
    self.id = atom_id
    self.link = link or []
    self.published = published
    self.rights = rights
    self.source = source
    self.summary = summary
    self.title = title
    self.updated = updated
    self.control = control
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def EntryFromString(xml_string):
  return CreateClassFromXMLString(Entry, xml_string)


class Feed(Source):
  """The atom:feed element"""

  _tag = 'feed'
  _namespace = ATOM_NAMESPACE
  _children = Source._children.copy()
  _attributes = Source._attributes.copy()
  _children['{%s}entry' % ATOM_NAMESPACE] = ('entry', [Entry])

  def __init__(self, author=None, category=None, contributor=None,
      generator=None, icon=None, atom_id=None, link=None, logo=None, 
      rights=None, subtitle=None, title=None, updated=None, entry=None, 
      text=None, extension_elements=None, extension_attributes=None):
    """Constructor for Source
    
    Args:
      author: list (optional) A list of Author instances which belong to this
          class.
      category: list (optional) A list of Category instances
      contributor: list (optional) A list on Contributor instances
      generator: Generator (optional) 
      icon: Icon (optional) 
      id: Id (optional) The entry's Id element
      link: list (optional) A list of Link instances
      logo: Logo (optional) 
      rights: Rights (optional) The entry's Rights element
      subtitle: Subtitle (optional) The entry's subtitle element
      title: Title (optional) the entry's title element
      updated: Updated (optional) the entry's updated element
      entry: list (optional) A list of the Entry instances contained in the 
          feed.
      text: String (optional) The text contents of the element. This is the 
          contents of the Entry's XML text node. 
          (Example: <foo>This is the text</foo>)
      extension_elements: list (optional) A list of ExtensionElement instances
          which are children of this element.
      extension_attributes: dict (optional) A dictionary of strings which are 
          the values for additional XML attributes of this element.
    """

    self.author = author or []
    self.category = category or []
    self.contributor = contributor or []
    self.generator = generator
    self.icon = icon
    self.id = atom_id
    self.link = link or []
    self.logo = logo
    self.rights = rights
    self.subtitle = subtitle
    self.title = title
    self.updated = updated
    self.entry = entry or []
    self.text = text
    self.extension_elements = extension_elements or []
    self.extension_attributes = extension_attributes or {}


def FeedFromString(xml_string):
  return CreateClassFromXMLString(Feed, xml_string)
  
  
class ExtensionElement(object):
  """Represents extra XML elements contained in Atom classes."""
  
  def __init__(self, tag, namespace=None, attributes=None, 
      children=None, text=None):
    """Constructor for EtensionElement

    Args:
      namespace: string (optional) The XML namespace for this element.
      tag: string (optional) The tag (without the namespace qualifier) for
          this element. To reconstruct the full qualified name of the element,
          combine this tag with the namespace.
      attributes: dict (optinal) The attribute value string pairs for the XML 
          attributes of this element.
      children: list (optional) A list of ExtensionElements which represent 
          the XML child nodes of this element.
    """

    self.namespace = namespace
    self.tag = tag
    self.attributes = attributes or {}
    self.children = children or []
    self.text = text
    
  def ToString(self):
    element_tree = self._TransferToElementTree(ElementTree.Element(''))
    return ElementTree.tostring(element_tree, encoding="UTF-8")
    
  def _TransferToElementTree(self, element_tree):
    if self.tag is None:
      return None
      
    if self.namespace is not None:
      element_tree.tag = '{%s}%s' % (self.namespace, self.tag)
    else:
      element_tree.tag = self.tag
      
    for key, value in self.attributes.iteritems():
      element_tree.attrib[key] = value
      
    for child in self.children:
      child._BecomeChildElement(element_tree)
      
    element_tree.text = self.text
      
    return element_tree

  def _BecomeChildElement(self, element_tree):
    """Converts this object into an etree element and adds it as a child node.

    Adds self to the ElementTree. This method is required to avoid verbose XML
    which constantly redefines the namespace.

    Args:
      element_tree: ElementTree._Element The element to which this object's XML
          will be added.
    """
    new_element = ElementTree.Element('')
    element_tree.append(new_element)
    self._TransferToElementTree(new_element)

  def FindChildren(self, tag=None, namespace=None):
    """Searches child nodes for objects with the desired tag/namespace.

    Returns a list of extension elements within this object whose tag
    and/or namespace match those passed in. To find all children in
    a particular namespace, specify the namespace but not the tag name.
    If you specify only the tag, the result list may contain extension
    elements in multiple namespaces.

    Args:
      tag: str (optional) The desired tag
      namespace: str (optional) The desired namespace

    Returns:
      A list of elements whose tag and/or namespace match the parameters
      values
    """

    results = []

    if tag and namespace:
      for element in self.children:
        if element.tag == tag and element.namespace == namespace:
          results.append(element)
    elif tag and not namespace:
      for element in self.children:
        if element.tag == tag:
          results.append(element)
    elif namespace and not tag:
      for element in self.children:
        if element.namespace == namespace:
          results.append(element)
    else:
      for element in self.children:
        results.append(element)

    return results
 
    
def ExtensionElementFromString(xml_string):
  element_tree = ElementTree.fromstring(xml_string)
  return _ExtensionElementFromElementTree(element_tree)


def _ExtensionElementFromElementTree(element_tree):
  element_tag = element_tree.tag
  if '}' in element_tag:
    namespace = element_tag[1:element_tag.index('}')]
    tag = element_tag[element_tag.index('}')+1:]
  else: 
    namespace = None
    tag = element_tag
  extension = ExtensionElement(namespace=namespace, tag=tag)
  for key, value in element_tree.attrib.iteritems():
    extension.attributes[key] = value
  for child in element_tree:
    extension.children.append(_ExtensionElementFromElementTree(child))
  extension.text = element_tree.text
  return extension
