"""
Field classes.
"""

import copy
import datetime
import os
import re
import time
# Python 2.3 fallbacks
try:
    from decimal import Decimal, DecimalException
except ImportError:
    from django.utils._decimal import Decimal, DecimalException
try:
    set
except NameError:
    from sets import Set as set

from django.utils.translation import ugettext_lazy as _
from django.utils.encoding import StrAndUnicode, smart_unicode, smart_str

from util import ErrorList, ValidationError
from widgets import TextInput, PasswordInput, HiddenInput, MultipleHiddenInput, FileInput, CheckboxInput, Select, NullBooleanSelect, SelectMultiple, DateTimeInput


__all__ = (
    'Field', 'CharField', 'IntegerField',
    'DEFAULT_DATE_INPUT_FORMATS', 'DateField',
    'DEFAULT_TIME_INPUT_FORMATS', 'TimeField',
    'DEFAULT_DATETIME_INPUT_FORMATS', 'DateTimeField',
    'RegexField', 'EmailField', 'FileField', 'ImageField', 'URLField',
    'BooleanField', 'NullBooleanField', 'ChoiceField', 'MultipleChoiceField',
    'ComboField', 'MultiValueField', 'FloatField', 'DecimalField',
    'SplitDateTimeField', 'IPAddressField', 'FilePathField',
)

# These values, if given to to_python(), will trigger the self.required check.
EMPTY_VALUES = (None, '')


class Field(object):
    widget = TextInput # Default widget to use when rendering this type of Field.
    hidden_widget = HiddenInput # Default widget to use when rendering this as "hidden".
    default_error_messages = {
        'required': _(u'This field is required.'),
        'invalid': _(u'Enter a valid value.'),
    }

    # Tracks each time a Field instance is created. Used to retain order.
    creation_counter = 0

    def __init__(self, required=True, widget=None, label=None, initial=None,
                 help_text=None, error_messages=None):
        # required -- Boolean that specifies whether the field is required.
        #             True by default.
        # widget -- A Widget class, or instance of a Widget class, that should
        #           be used for this Field when displaying it. Each Field has a
        #           default Widget that it'll use if you don't specify this. In
        #           most cases, the default widget is TextInput.
        # label -- A verbose name for this field, for use in displaying this
        #          field in a form. By default, Django will use a "pretty"
        #          version of the form field name, if the Field is part of a
        #          Form.
        # initial -- A value to use in this Field's initial display. This value
        #            is *not* used as a fallback if data isn't given.
        # help_text -- An optional string to use as "help text" for this Field.
        if label is not None:
            label = smart_unicode(label)
        self.required, self.label, self.initial = required, label, initial
        self.help_text = smart_unicode(help_text or '')
        widget = widget or self.widget
        if isinstance(widget, type):
            widget = widget()

        # Hook into self.widget_attrs() for any Field-specific HTML attributes.
        extra_attrs = self.widget_attrs(widget)
        if extra_attrs:
            widget.attrs.update(extra_attrs)

        self.widget = widget

        # Increase the creation counter, and save our local copy.
        self.creation_counter = Field.creation_counter
        Field.creation_counter += 1

        def set_class_error_messages(messages, klass):
            for base_class in klass.__bases__:
                set_class_error_messages(messages, base_class)
            messages.update(getattr(klass, 'default_error_messages', {}))

        messages = {}
        set_class_error_messages(messages, self.__class__)
        messages.update(error_messages or {})
        self.error_messages = messages

    def clean(self, value):
        """
        Validates the given value and returns its "cleaned" value as an
        appropriate Python object.

        Raises ValidationError for any errors.
        """
        if self.required and value in EMPTY_VALUES:
            raise ValidationError(self.error_messages['required'])
        return value

    def widget_attrs(self, widget):
        """
        Given a Widget instance (*not* a Widget class), returns a dictionary of
        any HTML attributes that should be added to the Widget, based on this
        Field.
        """
        return {}

    def __deepcopy__(self, memo):
        result = copy.copy(self)
        memo[id(self)] = result
        result.widget = copy.deepcopy(self.widget, memo)
        return result

class CharField(Field):
    default_error_messages = {
        'max_length': _(u'Ensure this value has at most %(max)d characters (it has %(length)d).'),
        'min_length': _(u'Ensure this value has at least %(min)d characters (it has %(length)d).'),
    }

    def __init__(self, max_length=None, min_length=None, *args, **kwargs):
        self.max_length, self.min_length = max_length, min_length
        super(CharField, self).__init__(*args, **kwargs)

    def clean(self, value):
        "Validates max_length and min_length. Returns a Unicode object."
        super(CharField, self).clean(value)
        if value in EMPTY_VALUES:
            return u''
        value = smart_unicode(value)
        value_length = len(value)
        if self.max_length is not None and value_length > self.max_length:
            raise ValidationError(self.error_messages['max_length'] % {'max': self.max_length, 'length': value_length})
        if self.min_length is not None and value_length < self.min_length:
            raise ValidationError(self.error_messages['min_length'] % {'min': self.min_length, 'length': value_length})
        return value

    def widget_attrs(self, widget):
        if self.max_length is not None and isinstance(widget, (TextInput, PasswordInput)):
            # The HTML attribute is maxlength, not max_length.
            return {'maxlength': str(self.max_length)}

class IntegerField(Field):
    default_error_messages = {
        'invalid': _(u'Enter a whole number.'),
        'max_value': _(u'Ensure this value is less than or equal to %s.'),
        'min_value': _(u'Ensure this value is greater than or equal to %s.'),
    }

    def __init__(self, max_value=None, min_value=None, *args, **kwargs):
        self.max_value, self.min_value = max_value, min_value
        super(IntegerField, self).__init__(*args, **kwargs)

    def clean(self, value):
        """
        Validates that int() can be called on the input. Returns the result
        of int(). Returns None for empty values.
        """
        super(IntegerField, self).clean(value)
        if value in EMPTY_VALUES:
            return None
        try:
            value = int(str(value))
        except (ValueError, TypeError):
            raise ValidationError(self.error_messages['invalid'])
        if self.max_value is not None and value > self.max_value:
            raise ValidationError(self.error_messages['max_value'] % self.max_value)
        if self.min_value is not None and value < self.min_value:
            raise ValidationError(self.error_messages['min_value'] % self.min_value)
        return value

class FloatField(Field):
    default_error_messages = {
        'invalid': _(u'Enter a number.'),
        'max_value': _(u'Ensure this value is less than or equal to %s.'),
        'min_value': _(u'Ensure this value is greater than or equal to %s.'),
    }

    def __init__(self, max_value=None, min_value=None, *args, **kwargs):
        self.max_value, self.min_value = max_value, min_value
        Field.__init__(self, *args, **kwargs)

    def clean(self, value):
        """
        Validates that float() can be called on the input. Returns a float.
        Returns None for empty values.
        """
        super(FloatField, self).clean(value)
        if not self.required and value in EMPTY_VALUES:
            return None
        try:
            value = float(value)
        except (ValueError, TypeError):
            raise ValidationError(self.error_messages['invalid'])
        if self.max_value is not None and value > self.max_value:
            raise ValidationError(self.error_messages['max_value'] % self.max_value)
        if self.min_value is not None and value < self.min_value:
            raise ValidationError(self.error_messages['min_value'] % self.min_value)
        return value

class DecimalField(Field):
    default_error_messages = {
        'invalid': _(u'Enter a number.'),
        'max_value': _(u'Ensure this value is less than or equal to %s.'),
        'min_value': _(u'Ensure this value is greater than or equal to %s.'),
        'max_digits': _('Ensure that there are no more than %s digits in total.'),
        'max_decimal_places': _('Ensure that there are no more than %s decimal places.'),
        'max_whole_digits': _('Ensure that there are no more than %s digits before the decimal point.')
    }

    def __init__(self, max_value=None, min_value=None, max_digits=None, decimal_places=None, *args, **kwargs):
        self.max_value, self.min_value = max_value, min_value
        self.max_digits, self.decimal_places = max_digits, decimal_places
        Field.__init__(self, *args, **kwargs)

    def clean(self, value):
        """
        Validates that the input is a decimal number. Returns a Decimal
        instance. Returns None for empty values. Ensures that there are no more
        than max_digits in the number, and no more than decimal_places digits
        after the decimal point.
        """
        super(DecimalField, self).clean(value)
        if not self.required and value in EMPTY_VALUES:
            return None
        value = smart_str(value).strip()
        try:
            value = Decimal(value)
        except DecimalException:
            raise ValidationError(self.error_messages['invalid'])
        pieces = str(value).lstrip("-").split('.')
        decimals = (len(pieces) == 2) and len(pieces[1]) or 0
        digits = len(pieces[0])
        if self.max_value is not None and value > self.max_value:
            raise ValidationError(self.error_messages['max_value'] % self.max_value)
        if self.min_value is not None and value < self.min_value:
            raise ValidationError(self.error_messages['min_value'] % self.min_value)
        if self.max_digits is not None and (digits + decimals) > self.max_digits:
            raise ValidationError(self.error_messages['max_digits'] % self.max_digits)
        if self.decimal_places is not None and decimals > self.decimal_places:
            raise ValidationError(self.error_messages['max_decimal_places'] % self.decimal_places)
        if self.max_digits is not None and self.decimal_places is not None and digits > (self.max_digits - self.decimal_places):
            raise ValidationError(self.error_messages['max_whole_digits'] % (self.max_digits - self.decimal_places))
        return value

DEFAULT_DATE_INPUT_FORMATS = (
    '%Y-%m-%d', '%m/%d/%Y', '%m/%d/%y', # '2006-10-25', '10/25/2006', '10/25/06'
    '%b %d %Y', '%b %d, %Y',            # 'Oct 25 2006', 'Oct 25, 2006'
    '%d %b %Y', '%d %b, %Y',            # '25 Oct 2006', '25 Oct, 2006'
    '%B %d %Y', '%B %d, %Y',            # 'October 25 2006', 'October 25, 2006'
    '%d %B %Y', '%d %B, %Y',            # '25 October 2006', '25 October, 2006'
)

class DateField(Field):
    default_error_messages = {
        'invalid': _(u'Enter a valid date.'),
    }

    def __init__(self, input_formats=None, *args, **kwargs):
        super(DateField, self).__init__(*args, **kwargs)
        self.input_formats = input_formats or DEFAULT_DATE_INPUT_FORMATS

    def clean(self, value):
        """
        Validates that the input can be converted to a date. Returns a Python
        datetime.date object.
        """
        super(DateField, self).clean(value)
        if value in EMPTY_VALUES:
            return None
        if isinstance(value, datetime.datetime):
            return value.date()
        if isinstance(value, datetime.date):
            return value
        for format in self.input_formats:
            try:
                return datetime.date(*time.strptime(value, format)[:3])
            except ValueError:
                continue
        raise ValidationError(self.error_messages['invalid'])

DEFAULT_TIME_INPUT_FORMATS = (
    '%H:%M:%S',     # '14:30:59'
    '%H:%M',        # '14:30'
)

class TimeField(Field):
    default_error_messages = {
        'invalid': _(u'Enter a valid time.')
    }

    def __init__(self, input_formats=None, *args, **kwargs):
        super(TimeField, self).__init__(*args, **kwargs)
        self.input_formats = input_formats or DEFAULT_TIME_INPUT_FORMATS

    def clean(self, value):
        """
        Validates that the input can be converted to a time. Returns a Python
        datetime.time object.
        """
        super(TimeField, self).clean(value)
        if value in EMPTY_VALUES:
            return None
        if isinstance(value, datetime.time):
            return value
        for format in self.input_formats:
            try:
                return datetime.time(*time.strptime(value, format)[3:6])
            except ValueError:
                continue
        raise ValidationError(self.error_messages['invalid'])

DEFAULT_DATETIME_INPUT_FORMATS = (
    '%Y-%m-%d %H:%M:%S',     # '2006-10-25 14:30:59'
    '%Y-%m-%d %H:%M',        # '2006-10-25 14:30'
    '%Y-%m-%d',              # '2006-10-25'
    '%m/%d/%Y %H:%M:%S',     # '10/25/2006 14:30:59'
    '%m/%d/%Y %H:%M',        # '10/25/2006 14:30'
    '%m/%d/%Y',              # '10/25/2006'
    '%m/%d/%y %H:%M:%S',     # '10/25/06 14:30:59'
    '%m/%d/%y %H:%M',        # '10/25/06 14:30'
    '%m/%d/%y',              # '10/25/06'
)

class DateTimeField(Field):
    widget = DateTimeInput
    default_error_messages = {
        'invalid': _(u'Enter a valid date/time.'),
    }

    def __init__(self, input_formats=None, *args, **kwargs):
        super(DateTimeField, self).__init__(*args, **kwargs)
        self.input_formats = input_formats or DEFAULT_DATETIME_INPUT_FORMATS

    def clean(self, value):
        """
        Validates that the input can be converted to a datetime. Returns a
        Python datetime.datetime object.
        """
        super(DateTimeField, self).clean(value)
        if value in EMPTY_VALUES:
            return None
        if isinstance(value, datetime.datetime):
            return value
        if isinstance(value, datetime.date):
            return datetime.datetime(value.year, value.month, value.day)
        if isinstance(value, list):
            # Input comes from a SplitDateTimeWidget, for example. So, it's two
            # components: date and time.
            if len(value) != 2:
                raise ValidationError(self.error_messages['invalid'])
            value = '%s %s' % tuple(value)
        for format in self.input_formats:
            try:
                return datetime.datetime(*time.strptime(value, format)[:6])
            except ValueError:
                continue
        raise ValidationError(self.error_messages['invalid'])

class RegexField(CharField):
    def __init__(self, regex, max_length=None, min_length=None, error_message=None, *args, **kwargs):
        """
        regex can be either a string or a compiled regular expression object.
        error_message is an optional error message to use, if
        'Enter a valid value' is too generic for you.
        """
        # error_message is just kept for backwards compatibility:
        if error_message:
            error_messages = kwargs.get('error_messages') or {}
            error_messages['invalid'] = error_message
            kwargs['error_messages'] = error_messages
        super(RegexField, self).__init__(max_length, min_length, *args, **kwargs)
        if isinstance(regex, basestring):
            regex = re.compile(regex)
        self.regex = regex

    def clean(self, value):
        """
        Validates that the input matches the regular expression. Returns a
        Unicode object.
        """
        value = super(RegexField, self).clean(value)
        if value == u'':
            return value
        if not self.regex.search(value):
            raise ValidationError(self.error_messages['invalid'])
        return value

email_re = re.compile(
    r"(^[-!#$%&'*+/=?^_`{}|~0-9A-Z]+(\.[-!#$%&'*+/=?^_`{}|~0-9A-Z]+)*"  # dot-atom
    r'|^"([\001-\010\013\014\016-\037!#-\[\]-\177]|\\[\001-011\013\014\016-\177])*"' # quoted-string
    r')@(?:[A-Z0-9-]+\.)+[A-Z]{2,6}$', re.IGNORECASE)  # domain

class EmailField(RegexField):
    default_error_messages = {
        'invalid': _(u'Enter a valid e-mail address.'),
    }

    def __init__(self, max_length=None, min_length=None, *args, **kwargs):
        RegexField.__init__(self, email_re, max_length, min_length, *args,
                            **kwargs)

try:
    from django.conf import settings
    URL_VALIDATOR_USER_AGENT = settings.URL_VALIDATOR_USER_AGENT
except ImportError:
    # It's OK if Django settings aren't configured.
    URL_VALIDATOR_USER_AGENT = 'Django (http://www.djangoproject.com/)'

class UploadedFile(StrAndUnicode):
    "A wrapper for files uploaded in a FileField"
    def __init__(self, filename, content):
        self.filename = filename
        self.content = content

    def __unicode__(self):
        """
        The unicode representation is the filename, so that the pre-database-insertion
        logic can use UploadedFile objects
        """
        return self.filename

class FileField(Field):
    widget = FileInput
    default_error_messages = {
        'invalid': _(u"No file was submitted. Check the encoding type on the form."),
        'missing': _(u"No file was submitted."),
        'empty': _(u"The submitted file is empty."),
    }

    def __init__(self, *args, **kwargs):
        super(FileField, self).__init__(*args, **kwargs)

    def clean(self, data, initial=None):
        super(FileField, self).clean(initial or data)
        if not self.required and data in EMPTY_VALUES:
            return None
        elif not data and initial:
            return initial
        try:
            f = UploadedFile(data['filename'], data['content'])
        except TypeError:
            raise ValidationError(self.error_messages['invalid'])
        except KeyError:
            raise ValidationError(self.error_messages['missing'])
        if not f.content:
            raise ValidationError(self.error_messages['empty'])
        return f

class ImageField(FileField):
    default_error_messages = {
        'invalid_image': _(u"Upload a valid image. The file you uploaded was either not an image or a corrupted image."),
    }

    def clean(self, data, initial=None):
        """
        Checks that the file-upload field data contains a valid image (GIF, JPG,
        PNG, possibly others -- whatever the Python Imaging Library supports).
        """
        f = super(ImageField, self).clean(data, initial)
        if f is None:
            return None
        elif not data and initial:
            return initial
        from PIL import Image
        from cStringIO import StringIO
        try:
            # load() is the only method that can spot a truncated JPEG,
            #  but it cannot be called sanely after verify()
            trial_image = Image.open(StringIO(f.content))
            trial_image.load()
            # verify() is the only method that can spot a corrupt PNG,
            #  but it must be called immediately after the constructor
            trial_image = Image.open(StringIO(f.content))
            trial_image.verify()
        except Exception: # Python Imaging Library doesn't recognize it as an image
            raise ValidationError(self.error_messages['invalid_image'])
        return f

url_re = re.compile(
    r'^https?://' # http:// or https://
    r'(?:(?:[A-Z0-9-]+\.)+[A-Z]{2,6}|' #domain...
    r'localhost|' #localhost...
    r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})' # ...or ip
    r'(?::\d+)?' # optional port
    r'(?:/?|/\S+)$', re.IGNORECASE)

class URLField(RegexField):
    default_error_messages = {
        'invalid': _(u'Enter a valid URL.'),
        'invalid_link': _(u'This URL appears to be a broken link.'),
    }

    def __init__(self, max_length=None, min_length=None, verify_exists=False,
            validator_user_agent=URL_VALIDATOR_USER_AGENT, *args, **kwargs):
        super(URLField, self).__init__(url_re, max_length, min_length, *args,
                                       **kwargs)
        self.verify_exists = verify_exists
        self.user_agent = validator_user_agent

    def clean(self, value):
        # If no URL scheme given, assume http://
        if value and '://' not in value:
            value = u'http://%s' % value
        value = super(URLField, self).clean(value)
        if value == u'':
            return value
        if self.verify_exists:
            import urllib2
            from django.conf import settings
            headers = {
                "Accept": "text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5",
                "Accept-Language": "en-us,en;q=0.5",
                "Accept-Charset": "ISO-8859-1,utf-8;q=0.7,*;q=0.7",
                "Connection": "close",
                "User-Agent": self.user_agent,
            }
            try:
                req = urllib2.Request(value, None, headers)
                u = urllib2.urlopen(req)
            except ValueError:
                raise ValidationError(self.error_messages['invalid'])
            except: # urllib2.URLError, httplib.InvalidURL, etc.
                raise ValidationError(self.error_messages['invalid_link'])
        return value

class BooleanField(Field):
    widget = CheckboxInput

    def clean(self, value):
        """Returns a Python boolean object."""
        super(BooleanField, self).clean(value)
        # Explicitly check for the string 'False', which is what a hidden field
        # will submit for False. Because bool("True") == True, we don't need to
        # handle that explicitly.
        if value == 'False':
            return False
        return bool(value)

class NullBooleanField(BooleanField):
    """
    A field whose valid values are None, True and False. Invalid values are
    cleaned to None.
    """
    widget = NullBooleanSelect

    def clean(self, value):
        return {True: True, False: False}.get(value, None)

class ChoiceField(Field):
    widget = Select
    default_error_messages = {
        'invalid_choice': _(u'Select a valid choice. That choice is not one of the available choices.'),
    }

    def __init__(self, choices=(), required=True, widget=None, label=None,
                 initial=None, help_text=None, *args, **kwargs):
        super(ChoiceField, self).__init__(required, widget, label, initial,
                                          help_text, *args, **kwargs)
        self.choices = choices

    def _get_choices(self):
        return self._choices

    def _set_choices(self, value):
        # Setting choices also sets the choices on the widget.
        # choices can be any iterable, but we call list() on it because
        # it will be consumed more than once.
        self._choices = self.widget.choices = list(value)

    choices = property(_get_choices, _set_choices)

    def clean(self, value):
        """
        Validates that the input is in self.choices.
        """
        value = super(ChoiceField, self).clean(value)
        if value in EMPTY_VALUES:
            value = u''
        value = smart_unicode(value)
        if value == u'':
            return value
        valid_values = set([smart_unicode(k) for k, v in self.choices])
        if value not in valid_values:
            raise ValidationError(self.error_messages['invalid_choice'] % {'value': value})
        return value

class MultipleChoiceField(ChoiceField):
    hidden_widget = MultipleHiddenInput
    widget = SelectMultiple
    default_error_messages = {
        'invalid_choice': _(u'Select a valid choice. %(value)s is not one of the available choices.'),
        'invalid_list': _(u'Enter a list of values.'),
    }

    def clean(self, value):
        """
        Validates that the input is a list or tuple.
        """
        if self.required and not value:
            raise ValidationError(self.error_messages['required'])
        elif not self.required and not value:
            return []
        if not isinstance(value, (list, tuple)):
            raise ValidationError(self.error_messages['invalid_list'])
        new_value = [smart_unicode(val) for val in value]
        # Validate that each value in the value list is in self.choices.
        valid_values = set([smart_unicode(k) for k, v in self.choices])
        for val in new_value:
            if val not in valid_values:
                raise ValidationError(self.error_messages['invalid_choice'] % {'value': val})
        return new_value

class ComboField(Field):
    """
    A Field whose clean() method calls multiple Field clean() methods.
    """
    def __init__(self, fields=(), *args, **kwargs):
        super(ComboField, self).__init__(*args, **kwargs)
        # Set 'required' to False on the individual fields, because the
        # required validation will be handled by ComboField, not by those
        # individual fields.
        for f in fields:
            f.required = False
        self.fields = fields

    def clean(self, value):
        """
        Validates the given value against all of self.fields, which is a
        list of Field instances.
        """
        super(ComboField, self).clean(value)
        for field in self.fields:
            value = field.clean(value)
        return value

class MultiValueField(Field):
    """
    A Field that aggregates the logic of multiple Fields.

    Its clean() method takes a "decompressed" list of values, which are then
    cleaned into a single value according to self.fields. Each value in
    this list is cleaned by the corresponding field -- the first value is
    cleaned by the first field, the second value is cleaned by the second
    field, etc. Once all fields are cleaned, the list of clean values is
    "compressed" into a single value.

    Subclasses should not have to implement clean(). Instead, they must
    implement compress(), which takes a list of valid values and returns a
    "compressed" version of those values -- a single value.

    You'll probably want to use this with MultiWidget.
    """
    default_error_messages = {
        'invalid': _(u'Enter a list of values.'),
    }

    def __init__(self, fields=(), *args, **kwargs):
        super(MultiValueField, self).__init__(*args, **kwargs)
        # Set 'required' to False on the individual fields, because the
        # required validation will be handled by MultiValueField, not by those
        # individual fields.
        for f in fields:
            f.required = False
        self.fields = fields

    def clean(self, value):
        """
        Validates every value in the given list. A value is validated against
        the corresponding Field in self.fields.

        For example, if this MultiValueField was instantiated with
        fields=(DateField(), TimeField()), clean() would call
        DateField.clean(value[0]) and TimeField.clean(value[1]).
        """
        clean_data = []
        errors = ErrorList()
        if not value or isinstance(value, (list, tuple)):
            if not value or not [v for v in value if v not in EMPTY_VALUES]:
                if self.required:
                    raise ValidationError(self.error_messages['required'])
                else:
                    return self.compress([])
        else:
            raise ValidationError(self.error_messages['invalid'])
        for i, field in enumerate(self.fields):
            try:
                field_value = value[i]
            except IndexError:
                field_value = None
            if self.required and field_value in EMPTY_VALUES:
                raise ValidationError(self.error_messages['required'])
            try:
                clean_data.append(field.clean(field_value))
            except ValidationError, e:
                # Collect all validation errors in a single list, which we'll
                # raise at the end of clean(), rather than raising a single
                # exception for the first error we encounter.
                errors.extend(e.messages)
        if errors:
            raise ValidationError(errors)
        return self.compress(clean_data)

    def compress(self, data_list):
        """
        Returns a single value for the given list of values. The values can be
        assumed to be valid.

        For example, if this MultiValueField was instantiated with
        fields=(DateField(), TimeField()), this might return a datetime
        object created by combining the date and time in data_list.
        """
        raise NotImplementedError('Subclasses must implement this method.')

class FilePathField(ChoiceField):
    def __init__(self, path, match=None, recursive=False, required=True,
                 widget=Select, label=None, initial=None, help_text=None,
                 *args, **kwargs):
        self.path, self.match, self.recursive = path, match, recursive
        super(FilePathField, self).__init__(choices=(), required=required,
            widget=widget, label=label, initial=initial, help_text=help_text,
            *args, **kwargs)
        self.choices = []
        if self.match is not None:
            self.match_re = re.compile(self.match)
        if recursive:
            for root, dirs, files in os.walk(self.path):
                for f in files:
                    if self.match is None or self.match_re.search(f):
                        f = os.path.join(root, f)
                        self.choices.append((f, f.replace(path, "", 1)))
        else:
            try:
                for f in os.listdir(self.path):
                    full_file = os.path.join(self.path, f)
                    if os.path.isfile(full_file) and (self.match is None or self.match_re.search(f)):
                        self.choices.append((full_file, f))
            except OSError:
                pass
        self.widget.choices = self.choices

class SplitDateTimeField(MultiValueField):
    default_error_messages = {
        'invalid_date': _(u'Enter a valid date.'),
        'invalid_time': _(u'Enter a valid time.'),
    }

    def __init__(self, *args, **kwargs):
        errors = self.default_error_messages.copy()
        if 'error_messages' in kwargs:
            errors.update(kwargs['error_messages'])
        fields = (
            DateField(error_messages={'invalid': errors['invalid_date']}),
            TimeField(error_messages={'invalid': errors['invalid_time']}),
        )
        super(SplitDateTimeField, self).__init__(fields, *args, **kwargs)

    def compress(self, data_list):
        if data_list:
            # Raise a validation error if time or date is empty
            # (possible if SplitDateTimeField has required=False).
            if data_list[0] in EMPTY_VALUES:
                raise ValidationError(self.error_messages['invalid_date'])
            if data_list[1] in EMPTY_VALUES:
                raise ValidationError(self.error_messages['invalid_time'])
            return datetime.datetime.combine(*data_list)
        return None

ipv4_re = re.compile(r'^(25[0-5]|2[0-4]\d|[0-1]?\d?\d)(\.(25[0-5]|2[0-4]\d|[0-1]?\d?\d)){3}$')

class IPAddressField(RegexField):
    default_error_messages = {
        'invalid': _(u'Enter a valid IPv4 address.'),
    }

    def __init__(self, *args, **kwargs):
        super(IPAddressField, self).__init__(ipv4_re, *args, **kwargs)
