Segment value types

def clone(self):
    """
    Clones this segment. Must be overridden in subclass.
    """
    raise NotImplementedError

def unwrap(self):
    """
    Pops a component from the beginning of the path. Reversing .wrap().

    For example:

    >>> s = StringSegmentValue('wrapped.field', 'foo')
    >>> s.unwrap()
    'wrapped', StringSegmentValue('field', 'foo')
    """
    first_component, *remaining_components = self.path.split(".")
    new_path = ".".join(remaining_components)

    clone = self.clone()
    clone.path = new_path
    return first_component, clone

def with_order(self, order):
    """
    Sets the order of this segment.
    """
    clone = self.clone()
    clone.order = order
    return clone

def wrap(self, base_path):
    """
    Appends a component to the beginning of the path.

    For example:

    >>> s = StringSegmentValue('field', 'foo')
    >>> s.wrap('wrapped')
    StringSegmentValue('wrapped.field', 'foo')
    """
    new_path = base_path

    if self.path:
        new_path += "." + self.path

    clone = self.clone()
    clone.path = new_path
    return clone

def __init__(self, path, data, **kwargs):
    """
    Initialises a new RelatedObjectSegmentValue.

    Args:
        path (str): The content path of the segment.
        data (any): The value of the field in the source. Must be JSON-serializable.
        order (int, optional): The index that this segment appears on a page.
    """
    self.data = data

    super().__init__(path, **kwargs)

def clone(self):
    """
    Makes an exact copy of this OverridableSegmentValue.

    Instead of mutating SegmentValue classes in place, it's recommended to clone them first.

    Returns:
        OverridableSegmentValue: The new segment value that's a copy of this one.
    """
    return OverridableSegmentValue(self.path, self.data, order=self.order)

def is_empty(self):
    """
    Returns True if the data is empty.

    Returns:
        boolean: True if the data is empty.
    """
    return self.data in ["", None]

def __init__(self, path, content_type, translation_key, **kwargs):
    """
    Initialises a new RelatedObjectSegmentValue.

    Args:
        path (str): The content path of the segment.
        content_type (ContentType): The content type of the base model of the foreign object.
        translation_key (UUID): The value of the foreign object's `translation_key` field.
        order (int, optional): The index that this segment appears on a page.
    """
    self.content_type = content_type
    self.translation_key = translation_key

    super().__init__(path, **kwargs)

def clone(self):
    """
    Makes an exact copy of this RelatedObjectSegmentValue.

    Instead of mutating SegmentValue classes in place, it's recommended to clone them first.

    Returns:
        RelatedObjectSegmentValue: The new segment value that's a copy of this one.
    """
    return RelatedObjectSegmentValue(
        self.path, self.content_type, self.translation_key, order=self.order
    )

@classmethod
def from_instance(cls, path, instance):
    """
    Initialises a new RelatedObjectSegmentValue from a model instance.

    Note: This class only records the type and translation key of the instance. So you will need to save the
    locale separately if you need to get this same instance back later.

    Args:
        path (str): The content path of the segment.
        instance (Model): An instance of the translatable object that needs to be referenced.

    Raises:
        AttributeError: If the instance is not translatable.

    Returns:
        RelatedObjectSegmentValue: The new segment value.
    """
    model = instance.get_translation_model()
    return cls(
        path, ContentType.objects.get_for_model(model), instance.translation_key
    )

def get_instance(self, locale):
    """
    Gets an instance of the referenced translatable object for the given locale.

    Raises:
        Model.DoesNotExist: If there isn't an instance of the translatable object in the given locale.

    Returns:
        Model: The instance.
    """
    from ..models import pk

    return self.content_type.get_object_for_this_type(
        translation_key=self.translation_key, locale_id=pk(locale)
    )

def is_empty(self):
    """
    Returns True if the related object is null.

    Returns:
        boolean: True if the related object is null.
    """
    return self.content_type is None and self.translation_key is None

def __init__(self, path, string, attrs=None, **kwargs):
    """
    Initialises a new StringSegmentValue.

    Args:
        path (str): The content path of the segment.
        string (StringValue): the value of the segment.
        attrs (dict, optional): A dict of HTML attributes that were stripped out of the string.
        order (int, optional): The index that this segment appears on a page.
    """
    if isinstance(string, str):
        string = StringValue.from_plaintext(string)

    elif isinstance(string, StringValue):
        pass

    else:
        raise TypeError(
            "`string` must be either a `StringValue` or a `str`. Got `{}`".format(
                type(string).__name__
            )
        )

    self.string = string
    self.attrs = attrs or None

    super().__init__(path, **kwargs)

def clone(self):
    """
    Makes an exact copy of this StringSegmentValue.

    Instead of mutating SegmentValue classes in place, it's recommended to clone them first.

    Returns:
        StringSegmentValue: The new segment value that's a copy of this one.
    """
    return StringSegmentValue(
        self.path, self.string, attrs=self.attrs, order=self.order
    )

@classmethod
def from_source_html(cls, path, html, **kwargs):
    """
    Initialises a StringSegmentValue from a HTML string.

    Args:
        path (str): The content path of the segment.
        html (str): The HTML value of the segment.
        order (int, optional): The index that this segment appears on a page.
    """
    string, attrs = StringValue.from_source_html(html)
    return cls(path, string, attrs=attrs, **kwargs)

def is_empty(self):
    """
    Returns True if the StringValue is blank.

    Returns:
        boolean: True if the StringValue is blank.
    """
    return self.string.data in ["", None]

def render_html(self):
    """
    Returns a HTML representation of the segment value.

    Note: If the segment value was created from plain text, this escapes special characters.

    Returns:
        str: The HTML representation of the segment value.
    """
    return self.string.render_html(self.attrs)

def render_text(self):
    """
    Returns a plain text representation of the segment value.

    Note: If the segment value was created from HTML, this strips out HTML tags.

    Returns:
        str: The text representation of the segment value.
    """
    return self.string.render_text()

def __init__(self, path, format, template, string_count, **kwargs):
    """
    Initialises a new TemplateSegmentValue.

    Args:
        path (str): The content path of the segment.
        format (str): The format of the template (eg, 'html').
        template (str): The template.
        string_count (int): The number of translatablle string segments that were extracted from the template.
        order (int, optional): The index that this segment appears on a page.
    """
    self.format = format
    self.template = template
    self.string_count = string_count

    super().__init__(path, **kwargs)

def clone(self):
    """
    Makes an exact copy of this TemplateSegmentValue.

    Instead of mutating SegmentValue classes in place, it's recommended to clone them first.

    Returns:
        TemplateSegmentValue: The new segment value that's a copy of this one.
    """
    return TemplateSegmentValue(
        self.path, self.format, self.template, self.string_count, order=self.order
    )

def is_empty(self):
    """
    Returns True if the template is blank.

    Returns:
        boolean: True if the template is blank.
    """
    return self.template in ["", None]