"""
Helper functions for creating Form classes from Django models
and database field objects.
"""

from forms import BaseForm, DeclarativeFieldsMetaclass, SortedDictFromList

__all__ = ('form_for_model', 'form_for_instance', 'form_for_fields')

def create(self, save=True):
    """
    Creates and returns model instance according to self.clean_data.

    This method is created for any form_for_model Form.
    """
    if self.errors:
        raise ValueError("The %s could not be created because the data didn't validate." % self._model._meta.object_name)
    obj = self._model(**self.clean_data)
    if save:
        obj.save()
    return obj

def make_apply_changes(opts, instance):
    "Returns the apply_changes() method for a form_for_instance Form."
    from django.db import models
    def apply_changes(self, save=True):
        if self.errors:
            raise ValueError("The %s could not be changed because the data didn't validate." % opts.object_name)
        clean_data = self.clean_data
        for f in opts.fields + opts.many_to_many:
            if isinstance(f, models.AutoField):
                continue
            setattr(instance, f.attname, clean_data[f.name])
        if save:
            instance.save()
        return instance
    return apply_changes

def form_for_model(model, form=BaseForm):
    """
    Returns a Form class for the given Django model class.

    Provide 'form' if you want to use a custom BaseForm subclass.
    """
    opts = model._meta
    field_list = []
    for f in opts.fields + opts.many_to_many:
        formfield = f.formfield()
        if formfield:
            field_list.append((f.name, formfield))
    fields = SortedDictFromList(field_list)
    return type(opts.object_name + 'Form', (form,), {'fields': fields, '_model': model, 'create': create})

def form_for_instance(instance, form=BaseForm):
    """
    Returns a Form class for the given Django model instance.

    Provide 'form' if you want to use a custom BaseForm subclass.
    """
    model = instance.__class__
    opts = model._meta
    field_list = []
    for f in opts.fields + opts.many_to_many:
        current_value = f.value_from_object(instance)
        formfield = f.formfield(initial=current_value)
        if formfield:
            field_list.append((f.name, formfield))
    fields = SortedDictFromList(field_list)
    return type(opts.object_name + 'InstanceForm', (form,),
        {'fields': fields, '_model': model, 'apply_changes': make_apply_changes(opts, instance)})

def form_for_fields(field_list):
    "Returns a Form class for the given list of Django database field instances."
    fields = SortedDictFromList([(f.name, f.formfield()) for f in field_list])
    return type('FormForFields', (BaseForm,), {'fields': fields})