import operator
# look at snippets 59, 148, 99 for newforms helpers

# http://www.djangosnippets.org/snippets/59/
def form_decorator(fields = {}, attrs = {}, widgets = {}, 
    labels = {}, choices = {}):
    
    """
    This function helps to add overrides when creating forms from models/instances.
    Pass in dictionary of fields to override certain fields altogether, otherwise
    add widgets or labels as desired.
    
    For example:
    
    class Project(models.Model):
    
        name = models.CharField(maxlength = 100)
        description = models.TextField()
        owner = models.ForeignKey(User)
   
    project_fields = dict(
        owner = None
    )
    
    project_widgets = dict(
        name = forms.TextInput({"size":40}),
        description = forms.Textarea({"rows":5, "cols":40}))
    
    project_labels = dict(
        name = "Enter your project name here"
    )
    
    callback = form_decorator(project_fields, project_widgets, project_labels)
    project_form = forms.form_for_model(Project, formfield_callback = callback)
    
    This saves having to redefine whole fields for example just to change a widget
    setting or label.
    """
    
    def formfields_callback(f, **kw):
    
        if f.name in fields:
            
            # replace field altogether
            field = fields[f.name]
            f.initial = kw.pop("initial", None)
            return field
        
        if f.name in widgets:
            
            kw["widget"] = widgets[f.name]

        if f.name in attrs:
            
            widget = kw.pop("widget", f.formfield().widget)
            if widget :
                widget.attrs.update(attrs[f.name])
                kw["widget"] = widget

        if f.name in labels:
        
            kw["label"] = labels[f.name]
        
        if f.name in choices:
        
            choice_set = choices[f.name]
            if callable(choice_set) : choice_set = choice_set()
            kw["choices"] = choice_set
            
                
        return f.formfield(**kw)
    
    return formfields_callback


# Caching accessor for the reverse of a ForeignKey relatinoship
# Started by axiak on #django
class FKAsOneToOne(object):
    def __init__(self, field, reverse = False, query = None):
        self.field = field
        self.reverse = reverse
	self.query = query
    
    def __get_attr(self, instance):
        if self.reverse:
            field_name = '%s_set' % self.field
        else:
            field_name = self.field
        return getattr(instance, field_name)

    def __get__(self, instance, Model):
        if not hasattr(instance, '_field_values'):
            instance._field_values = {}
        try:
            return instance._field_values[self.field]
	except KeyError:
	    pass

        if self.reverse:
            value_set = self.__get_attr(instance).all()
	    if self.query:
		value_set = value_set.filter(self.query)
	    try:
                instance._field_values[self.field] = value_set[0]
	    except IndexError:
                instance._field_values[self.field] = None
        else:
            instance._field_values[self.field] = self.__get_attr(instance)

        return instance._field_values[self.field]

    def __set__(self, instance, value):
        if self.reverse:
            # this is dangerous
            #other_instance = self.__get_attr(instance).all()[0]
            #setattr(other_instance, self.field, value)
            #other_instance.save()
	    raise NotImplemented
        else:
            setattr(instance, self.field, value)


def orl(list):
    """ Return the "or" of every element in a list.
    Used to generate "or" queries with a list of Q objects. """
    return reduce(operator.__or__, list)

def flattenl(list):
    """ Flatten a list one level, e.g., turn
	[ ['a'], ['b'], ['c', 'd'] ] into
	[ 'a', 'b', 'c', 'd' ]
    """
    return reduce(operator.__concat__, list)