"""
Form classes
"""

import copy
from django.core.exceptions import ValidationError
from django.utils.datastructures import SortedDict
from django.utils.html import conditional_escape
from django.utils.encoding import StrAndUnicode, smart_unicode, force_unicode
from django.utils.safestring import mark_safe

from fields import Field, FileField
from widgets import Media, media_property, TextInput, Textarea
from util import flatatt, ErrorDict, ErrorList

__all__ = ('BaseForm', 'Form')

NON_FIELD_ERRORS = '__all__'

def pretty_name(name):
    """Converts 'first_name' to 'First name'"""
    if not name:
        return u''
    return name.replace('_', ' ').capitalize()

def get_declared_fields(bases, attrs, with_base_fields=True):
    """
    Create a list of form field instances from the passed in 'attrs', plus any
    similar fields on the base classes (in 'bases'). This is used by both the
    Form and ModelForm metclasses.

    If 'with_base_fields' is True, all fields from the bases are used.
    Otherwise, only fields in the 'declared_fields' attribute on the bases are
    used. The distinction is useful in ModelForm subclassing.
    Also integrates any additional media definitions
    """
    fields = [(field_name, attrs.pop(field_name)) for field_name, obj in attrs.items() if isinstance(obj, Field)]
    fields.sort(key=lambda x: x[1].creation_counter)

    # If this class is subclassing another Form, add that Form's fields.
    # Note that we loop over the bases in *reverse*. This is necessary in
    # order to preserve the correct order of fields.
    if with_base_fields:
        for base in bases[::-1]:
            if hasattr(base, 'base_fields'):
                fields = base.base_fields.items() + fields
    else:
        for base in bases[::-1]:
            if hasattr(base, 'declared_fields'):
                fields = base.declared_fields.items() + fields

    return SortedDict(fields)

class DeclarativeFieldsMetaclass(type):
    """
    Metaclass that converts Field attributes to a dictionary called
    'base_fields', taking into account parent class 'base_fields' as well.
    """
    def __new__(cls, name, bases, attrs):
        attrs['base_fields'] = get_declared_fields(bases, attrs)
        new_class = super(DeclarativeFieldsMetaclass,
                     cls).__new__(cls, name, bases, attrs)
        if 'media' not in attrs:
            new_class.media = media_property(new_class)
        return new_class

class BaseForm(StrAndUnicode):
    # This is the main implementation of all the Form logic. Note that this
    # class is different than Form. See the comments by the Form class for more
    # information. Any improvements to the form API should be made to *this*
    # class, not to the Form class.
    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                 initial=None, error_class=ErrorList, label_suffix=':',
                 empty_permitted=False):
        self.is_bound = data is not None or files is not None
        self.data = data or {}
        self.files = files or {}
        self.auto_id = auto_id
        self.prefix = prefix
        self.initial = initial or {}
        self.error_class = error_class
        self.label_suffix = label_suffix
        self.empty_permitted = empty_permitted
        self._errors = None # Stores the errors after clean() has been called.
        self._changed_data = None

        # The base_fields class attribute is the *class-wide* definition of
        # fields. Because a particular *instance* of the class might want to
        # alter self.fields, we create self.fields here by copying base_fields.
        # Instances should always modify self.fields; they should not modify
        # self.base_fields.
        self.fields = copy.deepcopy(self.base_fields)

    def __unicode__(self):
        return self.as_table()

    def __iter__(self):
        for name, field in self.fields.items():
            yield BoundField(self, field, name)

    def __getitem__(self, name):
        "Returns a BoundField with the given name."
        try:
            field = self.fields[name]
        except KeyError:
            raise KeyError('Key %r not found in Form' % name)
        return BoundField(self, field, name)

    def _get_errors(self):
        "Returns an ErrorDict for the data provided for the form"
        if self._errors is None:
            self.full_clean()
        return self._errors
    errors = property(_get_errors)

    def is_valid(self):
        """
        Returns True if the form has no errors. Otherwise, False. If errors are
        being ignored, returns False.
        """
        return self.is_bound and not bool(self.errors)

    def add_prefix(self, field_name):
        """
        Returns the field name with a prefix appended, if this Form has a
        prefix set.

        Subclasses may wish to override.
        """
        return self.prefix and ('%s-%s' % (self.prefix, field_name)) or field_name

    def add_initial_prefix(self, field_name):
        """
        Add a 'initial' prefix for checking dynamic initial values
        """
        return u'initial-%s' % self.add_prefix(field_name)

    def _html_output(self, normal_row, error_row, row_ender, help_text_html, errors_on_separate_row):
        "Helper function for outputting HTML. Used by as_table(), as_ul(), as_p()."
        top_errors = self.non_field_errors() # Errors that should be displayed above all fields.
        output, hidden_fields = [], []

        for name, field in self.fields.items():
            html_class_attr = ''
            bf = BoundField(self, field, name)
            bf_errors = self.error_class([conditional_escape(error) for error in bf.errors]) # Escape and cache in local variable.
            if bf.is_hidden:
                if bf_errors:
                    top_errors.extend([u'(Hidden field %s) %s' % (name, force_unicode(e)) for e in bf_errors])
                hidden_fields.append(unicode(bf))
            else:
                # Create a 'class="..."' atribute if the row should have any
                # CSS classes applied.
                css_classes = bf.css_classes()
                if css_classes:
                    html_class_attr = ' class="%s"' % css_classes

                if errors_on_separate_row and bf_errors:
                    output.append(error_row % force_unicode(bf_errors))

                if bf.label:
                    label = conditional_escape(force_unicode(bf.label))
                    # Only add the suffix if the label does not end in
                    # punctuation.
                    if self.label_suffix:
                        if label[-1] not in ':?.!':
                            label += self.label_suffix
                    label = bf.label_tag(label) or ''
                else:
                    label = ''

                if field.help_text:
                    help_text = help_text_html % force_unicode(field.help_text)
                else:
                    help_text = u''

                output.append(normal_row % {
                    'errors': force_unicode(bf_errors),
                    'label': force_unicode(label),
                    'field': unicode(bf),
                    'help_text': help_text,
                    'html_class_attr': html_class_attr
                })

        if top_errors:
            output.insert(0, error_row % force_unicode(top_errors))

        if hidden_fields: # Insert any hidden fields in the last row.
            str_hidden = u''.join(hidden_fields)
            if output:
                last_row = output[-1]
                # Chop off the trailing row_ender (e.g. '</td></tr>') and
                # insert the hidden fields.
                if not last_row.endswith(row_ender):
                    # This can happen in the as_p() case (and possibly others
                    # that users write): if there are only top errors, we may
                    # not be able to conscript the last row for our purposes,
                    # so insert a new, empty row.
                    last_row = (normal_row % {'errors': '', 'label': '',
                                              'field': '', 'help_text':'',
                                              'html_class_attr': html_class_attr})
                    output.append(last_row)
                output[-1] = last_row[:-len(row_ender)] + str_hidden + row_ender
            else:
                # If there aren't any rows in the output, just append the
                # hidden fields.
                output.append(str_hidden)
        return mark_safe(u'\n'.join(output))

    def as_table(self):
        "Returns this form rendered as HTML <tr>s -- excluding the <table></table>."
        return self._html_output(
            normal_row = u'<tr%(html_class_attr)s><th>%(label)s</th><td>%(errors)s%(field)s%(help_text)s</td></tr>',
            error_row = u'<tr><td colspan="2">%s</td></tr>',
            row_ender = u'</td></tr>',
            help_text_html = u'<br /><span class="helptext">%s</span>',
            errors_on_separate_row = False)

    def as_ul(self):
        "Returns this form rendered as HTML <li>s -- excluding the <ul></ul>."
        return self._html_output(
            normal_row = u'<li%(html_class_attr)s>%(errors)s%(label)s %(field)s%(help_text)s</li>',
            error_row = u'<li>%s</li>',
            row_ender = '</li>',
            help_text_html = u' <span class="helptext">%s</span>',
            errors_on_separate_row = False)

    def as_p(self):
        "Returns this form rendered as HTML <p>s."
        return self._html_output(
            normal_row = u'<p%(html_class_attr)s>%(label)s %(field)s%(help_text)s</p>',
            error_row = u'%s',
            row_ender = '</p>',
            help_text_html = u' <span class="helptext">%s</span>',
            errors_on_separate_row = True)

    def non_field_errors(self):
        """
        Returns an ErrorList of errors that aren't associated with a particular
        field -- i.e., from Form.clean(). Returns an empty ErrorList if there
        are none.
        """
        return self.errors.get(NON_FIELD_ERRORS, self.error_class())

    def _raw_value(self, fieldname):
        """
        Returns the raw_value for a particular field name. This is just a
        convenient wrapper around widget.value_from_datadict.
        """
        field = self.fields[fieldname]
        prefix = self.add_prefix(fieldname)
        return field.widget.value_from_datadict(self.data, self.files, prefix)

    def full_clean(self):
        """
        Cleans all of self.data and populates self._errors and
        self.cleaned_data.
        """
        self._errors = ErrorDict()
        if not self.is_bound: # Stop further processing.
            return
        self.cleaned_data = {}
        # If the form is permitted to be empty, and none of the form data has
        # changed from the initial data, short circuit any validation.
        if self.empty_permitted and not self.has_changed():
            return
        self._clean_fields()
        self._clean_form()
        self._post_clean()
        if self._errors:
            del self.cleaned_data

    def _clean_fields(self):
        for name, field in self.fields.items():
            # value_from_datadict() gets the data from the data dictionaries.
            # Each widget type knows how to retrieve its own data, because some
            # widgets split data over several HTML fields.
            value = field.widget.value_from_datadict(self.data, self.files, self.add_prefix(name))
            try:
                if isinstance(field, FileField):
                    initial = self.initial.get(name, field.initial)
                    value = field.clean(value, initial)
                else:
                    value = field.clean(value)
                self.cleaned_data[name] = value
                if hasattr(self, 'clean_%s' % name):
                    value = getattr(self, 'clean_%s' % name)()
                    self.cleaned_data[name] = value
            except ValidationError, e:
                self._errors[name] = self.error_class(e.messages)
                if name in self.cleaned_data:
                    del self.cleaned_data[name]

    def _clean_form(self):
        try:
            self.cleaned_data = self.clean()
        except ValidationError, e:
            self._errors[NON_FIELD_ERRORS] = self.error_class(e.messages)

    def _post_clean(self):
        """
        An internal hook for performing additional cleaning after form cleaning
        is complete. Used for model validation in model forms.
        """
        pass

    def clean(self):
        """
        Hook for doing any extra form-wide cleaning after Field.clean() been
        called on every field. Any ValidationError raised by this method will
        not be associated with a particular field; it will have a special-case
        association with the field named '__all__'.
        """
        return self.cleaned_data

    def has_changed(self):
        """
        Returns True if data differs from initial.
        """
        return bool(self.changed_data)

    def _get_changed_data(self):
        if self._changed_data is None:
            self._changed_data = []
            # XXX: For now we're asking the individual widgets whether or not the
            # data has changed. It would probably be more efficient to hash the
            # initial data, store it in a hidden field, and compare a hash of the
            # submitted data, but we'd need a way to easily get the string value
            # for a given field. Right now, that logic is embedded in the render
            # method of each widget.
            for name, field in self.fields.items():
                prefixed_name = self.add_prefix(name)
                data_value = field.widget.value_from_datadict(self.data, self.files, prefixed_name)
                if not field.show_hidden_initial:
                    initial_value = self.initial.get(name, field.initial)
                else:
                    initial_prefixed_name = self.add_initial_prefix(name)
                    hidden_widget = field.hidden_widget()
                    initial_value = hidden_widget.value_from_datadict(
                        self.data, self.files, initial_prefixed_name)
                if field.widget._has_changed(initial_value, data_value):
                    self._changed_data.append(name)
        return self._changed_data
    changed_data = property(_get_changed_data)

    def _get_media(self):
        """
        Provide a description of all media required to render the widgets on this form
        """
        media = Media()
        for field in self.fields.values():
            media = media + field.widget.media
        return media
    media = property(_get_media)

    def is_multipart(self):
        """
        Returns True if the form needs to be multipart-encrypted, i.e. it has
        FileInput. Otherwise, False.
        """
        for field in self.fields.values():
            if field.widget.needs_multipart_form:
                return True
        return False

    def hidden_fields(self):
        """
        Returns a list of all the BoundField objects that are hidden fields.
        Useful for manual form layout in templates.
        """
        return [field for field in self if field.is_hidden]

    def visible_fields(self):
        """
        Returns a list of BoundField objects that aren't hidden fields.
        The opposite of the hidden_fields() method.
        """
        return [field for field in self if not field.is_hidden]

class Form(BaseForm):
    "A collection of Fields, plus their associated data."
    # This is a separate class from BaseForm in order to abstract the way
    # self.fields is specified. This class (Form) is the one that does the
    # fancy metaclass stuff purely for the semantic sugar -- it allows one
    # to define a form using declarative syntax.
    # BaseForm itself has no way of designating self.fields.
    __metaclass__ = DeclarativeFieldsMetaclass

class BoundField(StrAndUnicode):
    "A Field plus data"
    def __init__(self, form, field, name):
        self.form = form
        self.field = field
        self.name = name
        self.html_name = form.add_prefix(name)
        self.html_initial_name = form.add_initial_prefix(name)
        self.html_initial_id = form.add_initial_prefix(self.auto_id)
        if self.field.label is None:
            self.label = pretty_name(name)
        else:
            self.label = self.field.label
        self.help_text = field.help_text or ''

    def __unicode__(self):
        """Renders this field as an HTML widget."""
        if self.field.show_hidden_initial:
            return self.as_widget() + self.as_hidden(only_initial=True)
        return self.as_widget()

    def _errors(self):
        """
        Returns an ErrorList for this field. Returns an empty ErrorList
        if there are none.
        """
        return self.form.errors.get(self.name, self.form.error_class())
    errors = property(_errors)

    def as_widget(self, widget=None, attrs=None, only_initial=False):
        """
        Renders the field by rendering the passed widget, adding any HTML
        attributes passed as attrs.  If no widget is specified, then the
        field's default widget will be used.
        """
        if not widget:
            widget = self.field.widget

        attrs = attrs or {}
        auto_id = self.auto_id
        if auto_id and 'id' not in attrs and 'id' not in widget.attrs:
            if not only_initial:
                attrs['id'] = auto_id
            else:
                attrs['id'] = self.html_initial_id

        if not only_initial:
            name = self.html_name
        else:
            name = self.html_initial_name
        return widget.render(name, self.value(), attrs=attrs)

    def as_text(self, attrs=None, **kwargs):
        """
        Returns a string of HTML for representing this as an <input type="text">.
        """
        return self.as_widget(TextInput(), attrs, **kwargs)

    def as_textarea(self, attrs=None, **kwargs):
        "Returns a string of HTML for representing this as a <textarea>."
        return self.as_widget(Textarea(), attrs, **kwargs)

    def as_hidden(self, attrs=None, **kwargs):
        """
        Returns a string of HTML for representing this as an <input type="hidden">.
        """
        return self.as_widget(self.field.hidden_widget(), attrs, **kwargs)

    def _data(self):
        """
        Returns the data for this BoundField, or None if it wasn't given.
        """
        return self.field.widget.value_from_datadict(self.form.data, self.form.files, self.html_name)
    data = property(_data)

    def value(self):
        """
        Returns the value for this BoundField, using the initial value if
        the form is not bound or the data otherwise.
        """
        if not self.form.is_bound:
            data = self.form.initial.get(self.name, self.field.initial)
            if callable(data):
                data = data()
        else:
            data = self.field.bound_data(
                self.data, self.form.initial.get(self.name, self.field.initial)
            )
        return self.field.prepare_value(data)

    def label_tag(self, contents=None, attrs=None):
        """
        Wraps the given contents in a <label>, if the field has an ID attribute.
        Does not HTML-escape the contents. If contents aren't given, uses the
        field's HTML-escaped label.

        If attrs are given, they're used as HTML attributes on the <label> tag.
        """
        contents = contents or conditional_escape(self.label)
        widget = self.field.widget
        id_ = widget.attrs.get('id') or self.auto_id
        if id_:
            attrs = attrs and flatatt(attrs) or ''
            contents = u'<label for="%s"%s>%s</label>' % (widget.id_for_label(id_), attrs, unicode(contents))
        return mark_safe(contents)

    def css_classes(self, extra_classes=None):
        """
        Returns a string of space-separated CSS classes for this field.
        """
        if hasattr(extra_classes, 'split'):
            extra_classes = extra_classes.split()
        extra_classes = set(extra_classes or [])
        if self.errors and hasattr(self.form, 'error_css_class'):
            extra_classes.add(self.form.error_css_class)
        if self.field.required and hasattr(self.form, 'required_css_class'):
            extra_classes.add(self.form.required_css_class)
        return ' '.join(extra_classes)

    def _is_hidden(self):
        "Returns True if this BoundField's widget is hidden."
        return self.field.widget.is_hidden
    is_hidden = property(_is_hidden)

    def _auto_id(self):
        """
        Calculates and returns the ID attribute for this BoundField, if the
        associated Form has specified auto_id. Returns an empty string otherwise.
        """
        auto_id = self.form.auto_id
        if auto_id and '%s' in smart_unicode(auto_id):
            return smart_unicode(auto_id) % self.html_name
        elif auto_id:
            return self.html_name
        return ''
    auto_id = property(_auto_id)

    def _id_for_label(self):
        """
        Wrapper around the field widget's `id_for_label` class method.
        Useful, for example, for focusing on this field regardless of whether
        it has a single widget or a MutiWidget.
        """
        widget = self.field.widget
        id_ = widget.attrs.get('id') or self.auto_id
        return widget.id_for_label(id_)
    id_for_label = property(_id_for_label)
