import xml.etree.ElementTree as et

from django.db import models

from boards.models import KeyPair

TAG_MODEL = 'model'
TAG_REQUEST = 'request'
TAG_ID = 'id'

TYPE_GET = 'get'
TYPE_LIST = 'list'

ATTR_VERSION = 'version'
ATTR_TYPE = 'type'
ATTR_NAME = 'name'

ATTR_KEY = 'key'
ATTR_KEY_TYPE = 'type'
ATTR_LOCAL_ID = 'local-id'


class GlobalIdManager(models.Manager):
    def global_id_exists(self, global_id):
        """
        Checks if the same global id already exists in the system.
        """

        return self.filter(key=global_id.key,
                           key_type=global_id.key_type,
                           local_id=global_id.local_id).exists()


class GlobalId(models.Model):
    """
    Global model ID and cache.
    Key, key type and local ID make a single global identificator of the model.
    Content is an XML cache of the model that can be passed along between nodes
    without manual serialization each time.
    """
    class Meta:
        app_label = 'boards'

    objects = GlobalIdManager()

    def __init__(self, *args, **kwargs):
        models.Model.__init__(self, *args, **kwargs)

        if 'key' in kwargs and 'key_type' in kwargs and 'local_id' in kwargs:
            self.key = kwargs['key']
            self.key_type = kwargs['key_type']
            self.local_id = kwargs['local_id']

    key = models.TextField()
    key_type = models.TextField()
    local_id = models.IntegerField()
    content = models.TextField(blank=True, null=True)

    def __str__(self):
        return '%s::%s::%d' % (self.key_type, self.key, self.local_id)

    def to_xml_element(self, element: et.Element):
        """
        Exports global id to an XML element.
        """

        element.set(ATTR_KEY, self.key)
        element.set(ATTR_KEY_TYPE, self.key_type)
        element.set(ATTR_LOCAL_ID, str(self.local_id))

    @staticmethod
    def from_xml_element(element: et.Element):
        """
        Parses XML id tag and gets global id from it.

        Arguments:
        element -- the XML 'id' element

        Returns:
        global_id -- id itself
        exists -- True if the global id was taken from database, False if it
        did not exist and was created.
        """

        try:
            return GlobalId.objects.get(key=element.get(ATTR_KEY),
                                        key_type=element.get(ATTR_KEY_TYPE),
                                        local_id=int(element.get(
                                            ATTR_LOCAL_ID))), True
        except GlobalId.DoesNotExist:
            return GlobalId(key=element.get(ATTR_KEY),
                            key_type=element.get(ATTR_KEY_TYPE),
                            local_id=int(element.get(ATTR_LOCAL_ID))), False

    def is_local(self):
        """Checks fo the ID is local model's"""
        return KeyPair.objects.filter(
                key_type=self.key_type, public_key=self.key).exists()

    def clear_cache(self):
        """
        Removes content cache and signatures.
        """
        self.content = None
        self.save()
        self.signature_set.all().delete()


class Signature(models.Model):
    class Meta:
        app_label = 'boards'

    def __init__(self, *args, **kwargs):
        models.Model.__init__(self, *args, **kwargs)

        if 'key' in kwargs and 'key_type' in kwargs and 'signature' in kwargs:
            self.key_type = kwargs['key_type']
            self.key = kwargs['key']
            self.signature = kwargs['signature']

    key_type = models.TextField()
    key = models.TextField()
    signature = models.TextField()

    global_id = models.ForeignKey('GlobalId', on_delete=models.CASCADE)