"""
HTML Widget classes
"""

import copy
import datetime
import re
from contextlib import contextmanager
from itertools import chain

from django.conf import settings
from django.forms.utils import to_current_timezone
from django.templatetags.static import static
from django.utils import datetime_safe, formats
from django.utils.dates import MONTHS
from django.utils.encoding import force_text
from django.utils.formats import get_format
from django.utils.html import format_html, html_safe
from django.utils.safestring import mark_safe
from django.utils.translation import ugettext_lazy

from .renderers import get_default_renderer

__all__ = (
    'Media', 'MediaDefiningClass', 'Widget', 'TextInput', 'NumberInput',
    'EmailInput', 'URLInput', 'PasswordInput', 'HiddenInput',
    'MultipleHiddenInput', 'FileInput', 'ClearableFileInput', 'Textarea',
    'DateInput', 'DateTimeInput', 'TimeInput', 'CheckboxInput', 'Select',
    'NullBooleanSelect', 'SelectMultiple', 'RadioSelect',
    'CheckboxSelectMultiple', 'MultiWidget', 'SplitDateTimeWidget',
    'SplitHiddenDateTimeWidget', 'SelectDateWidget',
)

MEDIA_TYPES = ('css', 'js')


@html_safe
class Media:
    def __init__(self, media=None, **kwargs):
        if media:
            media_attrs = media.__dict__
        else:
            media_attrs = kwargs

        self._css = {}
        self._js = []

        for name in MEDIA_TYPES:
            getattr(self, 'add_' + name)(media_attrs.get(name))

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

    def render(self):
        return mark_safe('\n'.join(chain(*[getattr(self, 'render_' + name)() for name in MEDIA_TYPES])))

    def render_js(self):
        return [
            format_html(
                '<script type="text/javascript" src="{}"></script>',
                self.absolute_path(path)
            ) for path in self._js
        ]

    def render_css(self):
        # To keep rendering order consistent, we can't just iterate over items().
        # We need to sort the keys, and iterate over the sorted list.
        media = sorted(self._css.keys())
        return chain(*[[
            format_html(
                '<link href="{}" type="text/css" media="{}" rel="stylesheet" />',
                self.absolute_path(path), medium
            ) for path in self._css[medium]
        ] for medium in media])

    def absolute_path(self, path):
        """
        Given a relative or absolute path to a static asset, return an absolute
        path. An absolute path will be returned unchanged while a relative path
        will be passed to django.templatetags.static.static().
        """
        if path.startswith(('http://', 'https://', '/')):
            return path
        return static(path)

    def __getitem__(self, name):
        "Returns a Media object that only contains media of the given type"
        if name in MEDIA_TYPES:
            return Media(**{str(name): getattr(self, '_' + name)})
        raise KeyError('Unknown media type "%s"' % name)

    def add_js(self, data):
        if data:
            for path in data:
                if path not in self._js:
                    self._js.append(path)

    def add_css(self, data):
        if data:
            for medium, paths in data.items():
                for path in paths:
                    if not self._css.get(medium) or path not in self._css[medium]:
                        self._css.setdefault(medium, []).append(path)

    def __add__(self, other):
        combined = Media()
        for name in MEDIA_TYPES:
            getattr(combined, 'add_' + name)(getattr(self, '_' + name, None))
            getattr(combined, 'add_' + name)(getattr(other, '_' + name, None))
        return combined


def media_property(cls):
    def _media(self):
        # Get the media property of the superclass, if it exists
        sup_cls = super(cls, self)
        try:
            base = sup_cls.media
        except AttributeError:
            base = Media()

        # Get the media definition for this class
        definition = getattr(cls, 'Media', None)
        if definition:
            extend = getattr(definition, 'extend', True)
            if extend:
                if extend is True:
                    m = base
                else:
                    m = Media()
                    for medium in extend:
                        m = m + base[medium]
                return m + Media(definition)
            else:
                return Media(definition)
        else:
            return base
    return property(_media)


class MediaDefiningClass(type):
    """
    Metaclass for classes that can have media definitions.
    """
    def __new__(mcs, name, bases, attrs):
        new_class = super(MediaDefiningClass, mcs).__new__(mcs, name, bases, attrs)

        if 'media' not in attrs:
            new_class.media = media_property(new_class)

        return new_class


class Widget(metaclass=MediaDefiningClass):
    needs_multipart_form = False  # Determines does this widget need multipart form
    is_localized = False
    is_required = False
    supports_microseconds = True

    def __init__(self, attrs=None):
        if attrs is not None:
            self.attrs = attrs.copy()
        else:
            self.attrs = {}

    def __deepcopy__(self, memo):
        obj = copy.copy(self)
        obj.attrs = self.attrs.copy()
        memo[id(self)] = obj
        return obj

    @property
    def is_hidden(self):
        return self.input_type == 'hidden' if hasattr(self, 'input_type') else False

    def subwidgets(self, name, value, attrs=None):
        context = self.get_context(name, value, attrs)
        yield context['widget']

    def format_value(self, value):
        """
        Return a value as it should appear when rendered in a template.
        """
        if value is None:
            value = ''
        if self.is_localized:
            return formats.localize_input(value)
        return force_text(value)

    def get_context(self, name, value, attrs=None):
        context = {}
        context['widget'] = {
            'name': name,
            'is_hidden': self.is_hidden,
            'required': self.is_required,
            'value': self.format_value(value),
            'attrs': self.build_attrs(self.attrs, attrs),
            'template_name': self.template_name,
        }
        return context

    def render(self, name, value, attrs=None, renderer=None):
        """Render the widget as an HTML string."""
        context = self.get_context(name, value, attrs)
        return self._render(self.template_name, context, renderer)

    def _render(self, template_name, context, renderer=None):
        if renderer is None:
            renderer = get_default_renderer()
        return mark_safe(renderer.render(template_name, context))

    def build_attrs(self, base_attrs, extra_attrs=None):
        "Helper function for building an attribute dictionary."
        attrs = base_attrs.copy()
        if extra_attrs is not None:
            attrs.update(extra_attrs)
        return attrs

    def value_from_datadict(self, data, files, name):
        """
        Given a dictionary of data and this widget's name, returns the value
        of this widget. Returns None if it's not provided.
        """
        return data.get(name)

    def value_omitted_from_data(self, data, files, name):
        return name not in data

    def id_for_label(self, id_):
        """
        Returns the HTML ID attribute of this Widget for use by a <label>,
        given the ID of the field. Returns None if no ID is available.

        This hook is necessary because some widgets have multiple HTML
        elements and, thus, multiple IDs. In that case, this method should
        return an ID value that corresponds to the first ID in the widget's
        tags.
        """
        return id_

    def use_required_attribute(self, initial):
        return not self.is_hidden


class Input(Widget):
    """
    Base class for all <input> widgets.
    """
    input_type = None  # Subclasses must define this.
    template_name = 'django/forms/widgets/input.html'

    def __init__(self, attrs=None):
        if attrs is not None:
            attrs = attrs.copy()
            self.input_type = attrs.pop('type', self.input_type)
        super().__init__(attrs)

    def get_context(self, name, value, attrs=None):
        context = super().get_context(name, value, attrs)
        context['widget']['type'] = self.input_type
        return context


class TextInput(Input):
    input_type = 'text'
    template_name = 'django/forms/widgets/text.html'


class NumberInput(Input):
    input_type = 'number'
    template_name = 'django/forms/widgets/number.html'


class EmailInput(Input):
    input_type = 'email'
    template_name = 'django/forms/widgets/email.html'


class URLInput(Input):
    input_type = 'url'
    template_name = 'django/forms/widgets/url.html'


class PasswordInput(Input):
    input_type = 'password'
    template_name = 'django/forms/widgets/password.html'

    def __init__(self, attrs=None, render_value=False):
        super().__init__(attrs)
        self.render_value = render_value

    def get_context(self, name, value, attrs):
        if not self.render_value:
            value = None
        return super().get_context(name, value, attrs)


class HiddenInput(Input):
    input_type = 'hidden'
    template_name = 'django/forms/widgets/hidden.html'


class MultipleHiddenInput(HiddenInput):
    """
    A widget that handles <input type="hidden"> for fields that have a list
    of values.
    """
    template_name = 'django/forms/widgets/multiple_hidden.html'

    def get_context(self, name, value, attrs=None):
        context = super().get_context(name, value, attrs)
        final_attrs = context['widget']['attrs']
        id_ = context['widget']['attrs'].get('id')

        subwidgets = []
        for index, value_ in enumerate(context['widget']['value']):
            widget_attrs = final_attrs.copy()
            if id_:
                # An ID attribute was given. Add a numeric index as a suffix
                # so that the inputs don't all have the same ID attribute.
                widget_attrs['id'] = '%s_%s' % (id_, index)
            widget = HiddenInput()
            widget.is_required = self.is_required
            subwidgets.append(widget.get_context(name, value_, widget_attrs)['widget'])

        context['widget']['subwidgets'] = subwidgets
        return context

    def value_from_datadict(self, data, files, name):
        try:
            getter = data.getlist
        except AttributeError:
            getter = data.get
        return getter(name)

    def format_value(self, value):
        return [] if value is None else value


class FileInput(Input):
    input_type = 'file'
    needs_multipart_form = True
    template_name = 'django/forms/widgets/file.html'

    def format_value(self, value):
        """File input never renders a value."""
        return

    def value_from_datadict(self, data, files, name):
        "File widgets take data from FILES, not POST"
        return files.get(name)

    def value_omitted_from_data(self, data, files, name):
        return name not in files


FILE_INPUT_CONTRADICTION = object()


class ClearableFileInput(FileInput):
    clear_checkbox_label = ugettext_lazy('Clear')
    initial_text = ugettext_lazy('Currently')
    input_text = ugettext_lazy('Change')
    template_name = 'django/forms/widgets/clearable_file_input.html'

    def clear_checkbox_name(self, name):
        """
        Given the name of the file input, return the name of the clear checkbox
        input.
        """
        return name + '-clear'

    def clear_checkbox_id(self, name):
        """
        Given the name of the clear checkbox input, return the HTML id for it.
        """
        return name + '_id'

    def is_initial(self, value):
        """
        Return whether value is considered to be initial value.
        """
        return bool(value and getattr(value, 'url', False))

    def format_value(self, value):
        """
        Return the file object if it has a defined url attribute.
        """
        if self.is_initial(value):
            return value

    def get_context(self, name, value, attrs=None):
        context = super().get_context(name, value, attrs)
        checkbox_name = self.clear_checkbox_name(name)
        checkbox_id = self.clear_checkbox_id(checkbox_name)
        context.update({
            'checkbox_name': checkbox_name,
            'checkbox_id': checkbox_id,
            'is_initial': self.is_initial(value),
            'input_text': self.input_text,
            'initial_text': self.initial_text,
            'clear_checkbox_label': self.clear_checkbox_label,
        })
        return context

    def value_from_datadict(self, data, files, name):
        upload = super().value_from_datadict(data, files, name)
        if not self.is_required and CheckboxInput().value_from_datadict(
                data, files, self.clear_checkbox_name(name)):

            if upload:
                # If the user contradicts themselves (uploads a new file AND
                # checks the "clear" checkbox), we return a unique marker
                # object that FileField will turn into a ValidationError.
                return FILE_INPUT_CONTRADICTION
            # False signals to clear any existing value, as opposed to just None
            return False
        return upload

    def use_required_attribute(self, initial):
        return super().use_required_attribute(initial) and not initial


class Textarea(Widget):
    template_name = 'django/forms/widgets/textarea.html'

    def __init__(self, attrs=None):
        # Use slightly better defaults than HTML's 20x2 box
        default_attrs = {'cols': '40', 'rows': '10'}
        if attrs:
            default_attrs.update(attrs)
        super().__init__(default_attrs)


class DateTimeBaseInput(TextInput):
    format_key = ''
    supports_microseconds = False

    def __init__(self, attrs=None, format=None):
        super().__init__(attrs)
        self.format = format if format else None

    def format_value(self, value):
        return formats.localize_input(value, self.format or formats.get_format(self.format_key)[0])


class DateInput(DateTimeBaseInput):
    format_key = 'DATE_INPUT_FORMATS'
    template_name = 'django/forms/widgets/date.html'


class DateTimeInput(DateTimeBaseInput):
    format_key = 'DATETIME_INPUT_FORMATS'
    template_name = 'django/forms/widgets/datetime.html'


class TimeInput(DateTimeBaseInput):
    format_key = 'TIME_INPUT_FORMATS'
    template_name = 'django/forms/widgets/time.html'


# Defined at module level so that CheckboxInput is picklable (#17976)
def boolean_check(v):
    return not (v is False or v is None or v == '')


class CheckboxInput(Input):
    input_type = 'checkbox'
    template_name = 'django/forms/widgets/checkbox.html'

    def __init__(self, attrs=None, check_test=None):
        super().__init__(attrs)
        # check_test is a callable that takes a value and returns True
        # if the checkbox should be checked for that value.
        self.check_test = boolean_check if check_test is None else check_test

    def format_value(self, value):
        """Only return the 'value' attribute if value isn't empty."""
        if value is True or value is False or value is None or value == '':
            return
        return force_text(value)

    def get_context(self, name, value, attrs=None):
        if self.check_test(value):
            if attrs is None:
                attrs = {}
            attrs['checked'] = True
        return super().get_context(name, value, attrs)

    def value_from_datadict(self, data, files, name):
        if name not in data:
            # A missing value means False because HTML form submission does not
            # send results for unselected checkboxes.
            return False
        value = data.get(name)
        # Translate true and false strings to boolean values.
        values = {'true': True, 'false': False}
        if isinstance(value, str):
            value = values.get(value.lower(), value)
        return bool(value)

    def value_omitted_from_data(self, data, files, name):
        # HTML checkboxes don't appear in POST data if not checked, so it's
        # never known if the value is actually omitted.
        return False


class ChoiceWidget(Widget):
    allow_multiple_selected = False
    input_type = None
    template_name = None
    option_template_name = None
    add_id_index = True
    checked_attribute = {'checked': True}
    option_inherits_attrs = True

    def __init__(self, attrs=None, choices=()):
        super().__init__(attrs)
        # choices can be any iterable, but we may need to render this widget
        # multiple times. Thus, collapse it into a list so it can be consumed
        # more than once.
        self.choices = list(choices)

    def __deepcopy__(self, memo):
        obj = copy.copy(self)
        obj.attrs = self.attrs.copy()
        obj.choices = copy.copy(self.choices)
        memo[id(self)] = obj
        return obj

    def subwidgets(self, name, value, attrs=None):
        """
        Yield all "subwidgets" of this widget. Used to enable iterating
        options from a BoundField for choice widgets.
        """
        value = self.format_value(value)
        for option in self.options(name, value, attrs):
            yield option

    def options(self, name, value, attrs=None):
        """Yield a flat list of options for this widgets."""
        for group in self.optgroups(name, value, attrs):
            for option in group[1]:
                yield option

    def optgroups(self, name, value, attrs=None):
        """Return a list of optgroups for this widget."""
        default = (None, [], 0)
        groups = [default]
        has_selected = False

        for option_value, option_label in chain(self.choices):
            if option_value is None:
                option_value = ''
            else:
                option_value = force_text(option_value)

            if isinstance(option_label, (list, tuple)):
                index = groups[-1][2] + 1
                subindex = 0
                subgroup = []
                groups.append((option_value, subgroup, index))
                choices = option_label
            else:
                index = len(default[1])
                subgroup = default[1]
                subindex = None
                choices = [(option_value, option_label)]

            for subvalue, sublabel in choices:
                selected = (
                    subvalue in value and
                    (has_selected is False or self.allow_multiple_selected)
                )
                if selected is True and has_selected is False:
                    has_selected = True
                subgroup.append(self.create_option(
                    name, subvalue, sublabel, selected, index, subindex,
                    attrs=attrs,
                ))
                if subindex is not None:
                    subindex += 1
        return groups

    def create_option(self, name, value, label, selected, index, subindex=None, attrs=None):
        index = str(index) if subindex is None else "%s_%s" % (index, subindex)
        if attrs is None:
            attrs = {}
        option_attrs = self.build_attrs(self.attrs, attrs) if self.option_inherits_attrs else {}
        if selected:
            option_attrs.update(self.checked_attribute)
        if 'id' in option_attrs:
            option_attrs['id'] = self.id_for_label(option_attrs['id'], index)
        return {
            'name': name,
            'value': value,
            'label': label,
            'selected': selected,
            'index': index,
            'attrs': option_attrs,
            'type': self.input_type,
            'template_name': self.option_template_name,
        }

    def get_context(self, name, value, attrs=None):
        context = super().get_context(name, value, attrs)
        context['widget']['optgroups'] = self.optgroups(name, context['widget']['value'], attrs)
        context['wrap_label'] = True
        return context

    def id_for_label(self, id_, index='0'):
        """
        Use an incremented id for each option where the main widget
        references the zero index.
        """
        if id_ and self.add_id_index:
            id_ = '%s_%s' % (id_, index)
        return id_

    def value_from_datadict(self, data, files, name):
        getter = data.get
        if self.allow_multiple_selected:
            try:
                getter = data.getlist
            except AttributeError:
                pass
        return getter(name)

    @contextmanager
    def override_choices(self, choices):
        old = self.choices
        self.choices = choices
        yield
        self.choices = old

    def format_value(self, value):
        """Return selected values as a set."""
        if not isinstance(value, (tuple, list)):
            value = [value]
        values = set()
        for v in value:
            if v is None:
                values.add('')
            else:
                values.add(force_text(v))
        return values


class Select(ChoiceWidget):
    input_type = 'select'
    template_name = 'django/forms/widgets/select.html'
    option_template_name = 'django/forms/widgets/select_option.html'
    add_id_index = False
    checked_attribute = {'selected': True}
    option_inherits_attrs = False

    def get_context(self, name, value, attrs=None):
        context = super().get_context(name, value, attrs)
        if self.allow_multiple_selected:
            context['widget']['attrs']['multiple'] = 'multiple'
        return context

    @staticmethod
    def _choice_has_empty_value(choice):
        """Return True if the choice's value is empty string or None."""
        value, _ = choice
        return (isinstance(value, str) and not bool(value)) or value is None

    def use_required_attribute(self, initial):
        """
        Don't render 'required' if the first <option> has a value, as that's
        invalid HTML.
        """
        use_required_attribute = super().use_required_attribute(initial)
        # 'required' is always okay for <select multiple>.
        if self.allow_multiple_selected:
            return use_required_attribute

        first_choice = next(iter(self.choices), None)
        return use_required_attribute and first_choice is not None and self._choice_has_empty_value(first_choice)


class NullBooleanSelect(Select):
    """
    A Select Widget intended to be used with NullBooleanField.
    """
    def __init__(self, attrs=None):
        choices = (
            ('1', ugettext_lazy('Unknown')),
            ('2', ugettext_lazy('Yes')),
            ('3', ugettext_lazy('No')),
        )
        super().__init__(attrs, choices)

    def format_value(self, value):
        try:
            return {True: '2', False: '3', '2': '2', '3': '3'}[value]
        except KeyError:
            return '1'

    def value_from_datadict(self, data, files, name):
        value = data.get(name)
        return {
            '2': True,
            True: True,
            'True': True,
            '3': False,
            'False': False,
            False: False,
        }.get(value)


class SelectMultiple(Select):
    allow_multiple_selected = True

    def value_from_datadict(self, data, files, name):
        try:
            getter = data.getlist
        except AttributeError:
            getter = data.get
        return getter(name)


class RadioSelect(ChoiceWidget):
    input_type = 'radio'
    template_name = 'django/forms/widgets/radio.html'
    option_template_name = 'django/forms/widgets/radio_option.html'


class CheckboxSelectMultiple(ChoiceWidget):
    allow_multiple_selected = True
    input_type = 'checkbox'
    template_name = 'django/forms/widgets/checkbox_select.html'
    option_template_name = 'django/forms/widgets/checkbox_option.html'

    def use_required_attribute(self, initial):
        # Don't use the 'required' attribute because browser validation would
        # require all checkboxes to be checked instead of at least one.
        return False

    def value_omitted_from_data(self, data, files, name):
        # HTML checkboxes don't appear in POST data if not checked, so it's
        # never known if the value is actually omitted.
        return False

    def id_for_label(self, id_, index=None):
        """"
        Don't include for="field_0" in <label> because clicking such a label
        would toggle the first checkbox.
        """
        if index is None:
            return ''
        return super().id_for_label(id_, index)


class MultiWidget(Widget):
    """
    A widget that is composed of multiple widgets.

    In addition to the values added by Widget.get_context(), this widget
    adds a list of subwidgets to the context as widget['subwidgets'].
    These can be looped over and rendered like normal widgets.

    You'll probably want to use this class with MultiValueField.
    """
    template_name = 'django/forms/widgets/multiwidget.html'

    def __init__(self, widgets, attrs=None):
        self.widgets = [w() if isinstance(w, type) else w for w in widgets]
        super().__init__(attrs)

    @property
    def is_hidden(self):
        return all(w.is_hidden for w in self.widgets)

    def get_context(self, name, value, attrs=None):
        context = super().get_context(name, value, attrs)
        if self.is_localized:
            for widget in self.widgets:
                widget.is_localized = self.is_localized
        # value is a list of values, each corresponding to a widget
        # in self.widgets.
        if not isinstance(value, list):
            value = self.decompress(value)

        final_attrs = context['widget']['attrs']
        input_type = final_attrs.pop('type', None)
        id_ = final_attrs.get('id')
        subwidgets = []
        for i, widget in enumerate(self.widgets):
            if input_type is not None:
                widget.input_type = input_type
            widget_name = '%s_%s' % (name, i)
            try:
                widget_value = value[i]
            except IndexError:
                widget_value = None
            if id_:
                widget_attrs = final_attrs.copy()
                widget_attrs['id'] = '%s_%s' % (id_, i)
            else:
                widget_attrs = final_attrs
            subwidgets.append(widget.get_context(widget_name, widget_value, widget_attrs)['widget'])
        context['widget']['subwidgets'] = subwidgets
        return context

    def id_for_label(self, id_):
        if id_:
            id_ += '_0'
        return id_

    def value_from_datadict(self, data, files, name):
        return [widget.value_from_datadict(data, files, name + '_%s' % i) for i, widget in enumerate(self.widgets)]

    def value_omitted_from_data(self, data, files, name):
        return all(
            widget.value_omitted_from_data(data, files, name + '_%s' % i)
            for i, widget in enumerate(self.widgets)
        )

    def decompress(self, value):
        """
        Returns a list of decompressed values for the given compressed value.
        The given value can be assumed to be valid, but not necessarily
        non-empty.
        """
        raise NotImplementedError('Subclasses must implement this method.')

    def _get_media(self):
        "Media for a multiwidget is the combination of all media of the subwidgets"
        media = Media()
        for w in self.widgets:
            media = media + w.media
        return media
    media = property(_get_media)

    def __deepcopy__(self, memo):
        obj = super().__deepcopy__(memo)
        obj.widgets = copy.deepcopy(self.widgets)
        return obj

    @property
    def needs_multipart_form(self):
        return any(w.needs_multipart_form for w in self.widgets)


class SplitDateTimeWidget(MultiWidget):
    """
    A Widget that splits datetime input into two <input type="text"> boxes.
    """
    supports_microseconds = False
    template_name = 'django/forms/widgets/splitdatetime.html'

    def __init__(self, attrs=None, date_format=None, time_format=None):
        widgets = (
            DateInput(attrs=attrs, format=date_format),
            TimeInput(attrs=attrs, format=time_format),
        )
        super().__init__(widgets, attrs)

    def decompress(self, value):
        if value:
            value = to_current_timezone(value)
            return [value.date(), value.time().replace(microsecond=0)]
        return [None, None]


class SplitHiddenDateTimeWidget(SplitDateTimeWidget):
    """
    A Widget that splits datetime input into two <input type="hidden"> inputs.
    """
    template_name = 'django/forms/widgets/splithiddendatetime.html'

    def __init__(self, attrs=None, date_format=None, time_format=None):
        super().__init__(attrs, date_format, time_format)
        for widget in self.widgets:
            widget.input_type = 'hidden'


class SelectDateWidget(Widget):
    """
    A Widget that splits date input into three <select> boxes.

    This also serves as an example of a Widget that has more than one HTML
    element and hence implements value_from_datadict.
    """
    none_value = (0, '---')
    month_field = '%s_month'
    day_field = '%s_day'
    year_field = '%s_year'
    template_name = 'django/forms/widgets/select_date.html'
    input_type = 'select'
    select_widget = Select
    date_re = re.compile(r'(\d{4})-(\d\d?)-(\d\d?)$')

    def __init__(self, attrs=None, years=None, months=None, empty_label=None):
        self.attrs = attrs or {}

        # Optional list or tuple of years to use in the "year" select box.
        if years:
            self.years = years
        else:
            this_year = datetime.date.today().year
            self.years = range(this_year, this_year + 10)

        # Optional dict of months to use in the "month" select box.
        if months:
            self.months = months
        else:
            self.months = MONTHS

        # Optional string, list, or tuple to use as empty_label.
        if isinstance(empty_label, (list, tuple)):
            if not len(empty_label) == 3:
                raise ValueError('empty_label list/tuple must have 3 elements.')

            self.year_none_value = (0, empty_label[0])
            self.month_none_value = (0, empty_label[1])
            self.day_none_value = (0, empty_label[2])
        else:
            if empty_label is not None:
                self.none_value = (0, empty_label)

            self.year_none_value = self.none_value
            self.month_none_value = self.none_value
            self.day_none_value = self.none_value

    def get_context(self, name, value, attrs=None):
        context = super().get_context(name, value, attrs)
        date_context = {}
        year_choices = [(i, i) for i in self.years]
        if self.is_required is False:
            year_choices.insert(0, self.year_none_value)
        year_attrs = context['widget']['attrs'].copy()
        year_name = self.year_field % name
        year_attrs['id'] = 'id_%s' % year_name
        date_context['year'] = self.select_widget(attrs, choices=year_choices).get_context(
            name=year_name,
            value=context['widget']['value']['year'],
            attrs=year_attrs,
        )
        month_choices = list(self.months.items())
        if self.is_required is False:
            month_choices.insert(0, self.month_none_value)
        month_attrs = context['widget']['attrs'].copy()
        month_name = self.month_field % name
        month_attrs['id'] = 'id_%s' % month_name
        date_context['month'] = self.select_widget(attrs, choices=month_choices).get_context(
            name=month_name,
            value=context['widget']['value']['month'],
            attrs=month_attrs,
        )
        day_choices = [(i, i) for i in range(1, 32)]
        if self.is_required is False:
            day_choices.insert(0, self.day_none_value)
        day_attrs = context['widget']['attrs'].copy()
        day_name = self.day_field % name
        day_attrs['id'] = 'id_%s' % day_name
        date_context['day'] = self.select_widget(attrs, choices=day_choices,).get_context(
            name=day_name,
            value=context['widget']['value']['day'],
            attrs=day_attrs,
        )
        subwidgets = []
        for field in self._parse_date_fmt():
            subwidgets.append(date_context[field]['widget'])
        context['widget']['subwidgets'] = subwidgets
        return context

    def format_value(self, value):
        """
        Return a dict containing the year, month, and day of the current value.
        Use dict instead of a datetime to allow invalid dates such as February
        31 to display correctly.
        """
        year, month, day = None, None, None
        if isinstance(value, (datetime.date, datetime.datetime)):
            year, month, day = value.year, value.month, value.day
        elif isinstance(value, str):
            if settings.USE_L10N:
                try:
                    input_format = get_format('DATE_INPUT_FORMATS')[0]
                    d = datetime.datetime.strptime(value, input_format)
                    year, month, day = d.year, d.month, d.day
                except ValueError:
                    pass
            match = self.date_re.match(value)
            if match:
                year, month, day = [int(val) for val in match.groups()]
        return {'year': year, 'month': month, 'day': day}

    @staticmethod
    def _parse_date_fmt():
        fmt = get_format('DATE_FORMAT')
        escaped = False
        for char in fmt:
            if escaped:
                escaped = False
            elif char == '\\':
                escaped = True
            elif char in 'Yy':
                yield 'year'
            elif char in 'bEFMmNn':
                yield 'month'
            elif char in 'dj':
                yield 'day'

    def id_for_label(self, id_):
        for first_select in self._parse_date_fmt():
            return '%s_%s' % (id_, first_select)
        else:
            return '%s_month' % id_

    def value_from_datadict(self, data, files, name):
        y = data.get(self.year_field % name)
        m = data.get(self.month_field % name)
        d = data.get(self.day_field % name)
        if y == m == d == "0":
            return None
        if y and m and d:
            if settings.USE_L10N:
                input_format = get_format('DATE_INPUT_FORMATS')[0]
                try:
                    date_value = datetime.date(int(y), int(m), int(d))
                except ValueError:
                    return '%s-%s-%s' % (y, m, d)
                else:
                    date_value = datetime_safe.new_date(date_value)
                    return date_value.strftime(input_format)
            else:
                return '%s-%s-%s' % (y, m, d)
        return data.get(name)

    def value_omitted_from_data(self, data, files, name):
        return not any(
            ('{}_{}'.format(name, interval) in data)
            for interval in ('year', 'month', 'day')
        )