import xml.etree.ElementTree as et
from django.db import transaction
from boards.models import KeyPair, GlobalId, Signature, Post

ENCODING_UNICODE = 'unicode'

TAG_MODEL = 'model'
TAG_REQUEST = 'request'
TAG_RESPONSE = 'response'
TAG_ID = 'id'
TAG_STATUS = 'status'
TAG_MODELS = 'models'
TAG_TITLE = 'title'
TAG_TEXT = 'text'
TAG_THREAD = 'thread'
TAG_PUB_TIME = 'pub-time'
TAG_SIGNATURES = 'signatures'
TAG_SIGNATURE = 'signature'
TAG_CONTENT = 'content'
TAG_ATTACHMENTS = 'attachments'
TAG_ATTACHMENT = 'attachment'

TYPE_GET = 'get'

ATTR_VERSION = 'version'
ATTR_TYPE = 'type'
ATTR_NAME = 'name'
ATTR_VALUE = 'value'
ATTR_MIMETYPE = 'mimetype'
ATTR_KEY = 'key'

STATUS_SUCCESS = 'success'


class SyncManager:
    @staticmethod
    def generate_response_get(model_list: list):
        response = et.Element(TAG_RESPONSE)

        status = et.SubElement(response, TAG_STATUS)
        status.text = STATUS_SUCCESS

        models = et.SubElement(response, TAG_MODELS)

        for post in model_list:
            model = et.SubElement(models, TAG_MODEL)
            model.set(ATTR_NAME, 'post')

            content_tag = et.SubElement(model, TAG_CONTENT)

            tag_id = et.SubElement(content_tag, TAG_ID)
            post.global_id.to_xml_element(tag_id)

            title = et.SubElement(content_tag, TAG_TITLE)
            title.text = post.title

            text = et.SubElement(content_tag, TAG_TEXT)
            text.text = post.get_sync_text()

            if not post.is_opening():
                thread = et.SubElement(content_tag, TAG_THREAD)
                thread_id = et.SubElement(thread, TAG_ID)
                post.get_thread().get_opening_post().global_id.to_xml_element(thread_id)
            else:
                # TODO Output tags here
                pass

            pub_time = et.SubElement(content_tag, TAG_PUB_TIME)
            pub_time.text = str(post.get_pub_time_str())

            signatures_tag = et.SubElement(model, TAG_SIGNATURES)
            post_signatures = post.signature.all()
            if post_signatures:
                signatures = post_signatures
                # TODO Adding signature to a post is not yet added. For now this
                # block is useless
            else:
                # TODO Maybe the signature can be computed only once after
                # the post is added? Need to add some on_save signal queue
                # and add this there.
                key = KeyPair.objects.get(public_key=post.global_id.key)
                signatures = [Signature(
                    key_type=key.key_type,
                    key=key.public_key,
                    signature=key.sign(et.tostring(content_tag, ENCODING_UNICODE)),
                )]
            for signature in signatures:
                signature_tag = et.SubElement(signatures_tag, TAG_SIGNATURE)
                signature_tag.set(ATTR_TYPE, signature.key_type)
                signature_tag.set(ATTR_VALUE, signature.signature)
                signature_tag.set(ATTR_KEY, signature.key)

        return et.tostring(response, ENCODING_UNICODE)

    @staticmethod
    @transaction.atomic
    def parse_response_get(response_xml):
        tag_root = et.fromstring(response_xml)
        tag_status = tag_root.find(TAG_STATUS)
        if STATUS_SUCCESS == tag_status.text:
            tag_models = tag_root.find(TAG_MODELS)
            for tag_model in tag_models:
                tag_content = tag_model.find(TAG_CONTENT)

                valid = SyncManager._verify_model(tag_content, tag_model)

                if not valid:
                    raise Exception('Invalid model signature')

                tag_id = tag_content.find(TAG_ID)
                global_id, exists = GlobalId.from_xml_element(tag_id)

                if exists:
                    print('Post with same ID already exists')
                else:
                    global_id.save()

                    title = tag_content.find(TAG_TITLE).text
                    text = tag_content.find(TAG_TEXT).text
                    pub_time = tag_content.find(TAG_PUB_TIME).text

                    thread = tag_content.find(TAG_THREAD)
                    if thread:
                        opening_post = Post.objects.get(
                            id=thread.find(TAG_ID).text)
                    else:
                        opening_post = None
                        # TODO Get tags here

                    # TODO Check that the replied posts are already present
                    # before adding new ones

                    # TODO Get images

                    post = Post.objects.import_post(
                        title=title, text=text, pub_time=pub_time,
                        opening_post=opening_post)
                    post.global_id = global_id
        else:
            # TODO Throw an exception?
            pass

    @staticmethod
    def _verify_model(tag_content, tag_model):
        """
        Verifies all signatures for a single model.
        """

        valid = True

        tag_signatures = tag_model.find(TAG_SIGNATURES)
        for tag_signature in tag_signatures:
            signature_type = tag_signature.get(ATTR_TYPE)
            signature_value = tag_signature.get(ATTR_VALUE)
            signature_key = tag_signature.get(ATTR_KEY)

            if not KeyPair.objects.verify(
                    signature_key,
                    et.tostring(tag_content, ENCODING_UNICODE),
                    signature_value, signature_type):
                valid = False
                break

        return valid