from django.db import models
from django.contrib.auth.models import User
from django.utils.encoding import python_2_unicode_compatible
from django.utils.timezone import now

#In order to run the database queries, there’s a manager for every model.
# Unless it’s otherwise defined, the attribute objects holds a reference to the default manager.
# The queries can be altered by overriding the default manager or adding another one.
class PublicBookmarkManager(models.Manager):
    def get_queryset(self):
        qs = super(PublicBookmarkManager, self).get_queryset()
        return qs.filter(is_public=True)

# Create your models here.
# Models define how data is saved. Usually a model represents a table in the database, and has fields, metadata and methods
@python_2_unicode_compatible
class Tag(models.Model):
    name = models.CharField(max_length=50, unique=True)

    # Models can contain Metadata, that can influence how they are displayed or how they behave
    class Meta:
        verbose_name = 'tag'
        verbose_name_plural = 'tagS'
        ordering = ['name']

    # You can now add Model functionality Methods for actions that apply to a single record.
    # For instance, it is usual to create a human readable form of the record with the method __str__.
    def __str__(self):
        return self.name

@python_2_unicode_compatible
class Bookmark(models.Model):
    url = models.URLField()
    title = models.CharField('title', max_length=255)
    description = models.TextField('description', blank=True)
    is_public = models.BooleanField('public', default=True)
    date_created = models.DateTimeField('date created')
    date_updated = models.DateTimeField('date updated')
    owner = models.ForeignKey(User, verbose_name='owner', related_name='bookmarks', on_delete=models.DO_NOTHING)
    tags = models.ManyToManyField(Tag, blank=True)

    # In our example we’ll often show only public bookmarks so we add a second manager to the Bookmark model that will only return the public bookmarks.
    # We’ll assign it to the attribute public. In order to keep a reference to the default manager, we have to explicitely assign it to the objects
    object = models.Manager()
    public = PublicBookmarkManager()

    class Meta:
        verbose_name = 'bookmark'
        verbose_name_plural = 'bookmarkS'
        ordering = ['-date_created']

    def __str__(self):
        return '%s (%s)' % (self.title, self.url)

    #In the bookmark model, we’ll also override the method save() to set the right creation or last-changed date.
    # The state of the id field will be used, in order to decide if the model has already been saved or not.
    def save(self, *args, **kwargs):
        if not self.id:
            self.date_created =now()
        self.date_updated = now()
        super(Bookmark, self).save(*args, **kwargs)