from __future__ import absolute_import, unicode_literals

import logging
import os

from django.apps import apps
from django.db import models, transaction
from django.template import Context, Template
from django.urls import reverse
from django.utils.encoding import force_text, python_2_unicode_compatible
from django.utils.functional import cached_property
from django.utils.translation import ugettext_lazy as _

from mayan.apps.converter import TransformationRotate, converter_class
from mayan.apps.converter.exceptions import InvalidOfficeFormat, PageCountError
from mayan.apps.converter.models import Transformation
from mayan.apps.mimetype.api import get_mimetype

from ..events import event_document_new_version, event_document_version_revert
from ..literals import DOCUMENT_IMAGES_CACHE_NAME
from ..managers import DocumentVersionManager
from ..settings import setting_fix_orientation
from ..signals import post_document_created, post_version_upload
from ..storages import storage_documentversion_wrapper
from ..utils import document_hash_function, document_uuid_function

from .document_models import Document

__all__ = ('DocumentVersion',)
logger = logging.getLogger(__name__)


@python_2_unicode_compatible
class DocumentVersion(models.Model):
    """
    Model that describes a document version and its properties
    Fields:
    * mimetype - File mimetype. MIME types are a standard way to describe the
    format of a file, in this case the file format of the document.
    Some examples: "text/plain" or "image/jpeg". Mayan uses this to determine
    how to render a document's file. More information:
    http://www.freeformatter.com/mime-types-list.html
    * encoding - File Encoding. The filesystem encoding of the document's
    file: binary 7-bit, binary 8-bit, text, base64, etc.
    * checksum - A hash/checkdigit/fingerprint generated from the document's
    binary data. Only identical documents will have the same checksum. If a
    document is modified after upload it's checksum will not match, used for
    detecting file tampering among other things.
    """
    _pre_open_hooks = {}
    _post_save_hooks = {}

    document = models.ForeignKey(
        on_delete=models.CASCADE, related_name='versions', to=Document,
        verbose_name=_('Document')
    )
    timestamp = models.DateTimeField(
        auto_now_add=True, db_index=True, help_text=_(
            'The server date and time when the document version was processed.'
        ), verbose_name=_('Timestamp')
    )
    comment = models.TextField(
        blank=True, default='', help_text=_(
            'An optional short text describing the document version.'
        ), verbose_name=_('Comment')
    )

    # File related fields
    file = models.FileField(
        storage=storage_documentversion_wrapper, upload_to=document_uuid_function,
        verbose_name=_('File')
    )
    mimetype = models.CharField(
        blank=True, editable=False, help_text=_(
            'The document version\'s file mimetype. MIME types are a '
            'standard way to describe the format of a file, in this case '
            'the file format of the document. Some examples: "text/plain" '
            'or "image/jpeg". '
        ), max_length=255, null=True, verbose_name=_('MIME type')
    )
    encoding = models.CharField(
        blank=True, editable=False, help_text=_(
            'The document version file encoding. binary 7-bit, binary 8-bit, '
            'text, base64, etc.'
        ), max_length=64, null=True, verbose_name=_('Encoding')
    )
    checksum = models.CharField(
        blank=True, db_index=True, editable=False, help_text=(
            'A hash/checkdigit/fingerprint generated from the document\'s '
            'binary data. Only identical documents will have the same '
            'checksum.'
        ), max_length=64, null=True, verbose_name=_('Checksum')
    )

    class Meta:
        ordering = ('timestamp',)
        verbose_name = _('Document version')
        verbose_name_plural = _('Document version')

    objects = DocumentVersionManager()

    def __str__(self):
        return self.get_rendered_string()

    @classmethod
    def register_pre_open_hook(cls, order, func):
        cls._pre_open_hooks[order] = func

    @classmethod
    def register_post_save_hook(cls, order, func):
        cls._post_save_hooks[order] = func

    @cached_property
    def cache(self):
        Cache = apps.get_model(app_label='file_caching', model_name='Cache')
        return Cache.objects.get(name=DOCUMENT_IMAGES_CACHE_NAME)

    @cached_property
    def cache_partition(self):
        partition, created = self.cache.partitions.get_or_create(
            name='version-{}'.format(self.uuid)
        )
        return partition

    def delete(self, *args, **kwargs):
        for page in self.pages.all():
            page.delete()

        self.file.storage.delete(self.file.name)

        return super(DocumentVersion, self).delete(*args, **kwargs)

    def exists(self):
        """
        Returns a boolean value that indicates if the document's file
        exists in storage. Returns True if the document's file is verified to
        be in the document storage. This is a diagnostic flag to help users
        detect if the storage has desynchronized (ie: Amazon's S3).
        """
        return self.file.storage().exists(self.file.name)

    def fix_orientation(self):
        for page in self.pages.all():
            degrees = page.detect_orientation()
            if degrees:
                Transformation.objects.add_for_model(
                    obj=page, transformation=TransformationRotate,
                    arguments='{{"degrees": {}}}'.format(360 - degrees)
                )

    def get_absolute_url(self):
        return reverse('documents:document_version_view', args=(self.pk,))

    def get_api_image_url(self, *args, **kwargs):
        first_page = self.pages.first()
        if first_page:
            return first_page.get_api_image_url(*args, **kwargs)

    def get_intermidiate_file(self):
        cache_file = self.cache_partition.get_file(filename='intermediate_file')
        if cache_file:
            logger.debug('Intermidiate file found.')
            return cache_file.open()
        else:
            logger.debug('Intermidiate file not found.')

            try:
                converter = converter_class(file_object=self.open())
                pdf_file_object = converter.to_pdf()

                with self.cache_partition.create_file(filename='intermediate_file') as file_object:
                    for chunk in pdf_file_object:
                        file_object.write(chunk)

                return self.cache_partition.get_file(filename='intermediate_file').open()
            except InvalidOfficeFormat:
                return self.open()
            except Exception as exception:
                logger.error(
                    'Error creating intermediate file; %s.', exception
                )
                raise

    def get_page_count(self):
        return self.pages.count()
    get_page_count.short_description = _('Pages')

    def get_rendered_string(self, preserve_extension=False):
        if preserve_extension:
            filename, extension = os.path.splitext(self.document.label)
            return '{} ({}){}'.format(
                filename, self.get_rendered_timestamp(), extension
            )
        else:
            return Template(
                '{{ instance.document }} - {{ instance.timestamp }}'
            ).render(context=Context({'instance': self}))

    def get_rendered_timestamp(self):
        return Template('{{ instance.timestamp }}').render(
            context=Context({'instance': self})
        )
    get_rendered_timestamp.short_description = _('Date and time')

    def natural_key(self):
        return (self.checksum, self.document.natural_key())
    natural_key.dependencies = ['documents.Document']

    def invalidate_cache(self):
        self.cache_partition.purge()
        for page in self.pages.all():
            page.invalidate_cache()

    @property
    def is_in_trash(self):
        return self.document.is_in_trash

    def open(self, raw=False):
        """
        Return a file descriptor to a document version's file irrespective of
        the storage backend
        """
        if raw:
            return self.file.storage.open(self.file.name)
        else:
            result = self.file.storage.open(self.file.name)
            for key in sorted(DocumentVersion._pre_open_hooks):
                result = DocumentVersion._pre_open_hooks[key](
                    file_object=result, document_version=self
                )

            return result

    @property
    def page_count(self):
        """
        The number of pages that the document posses.
        """
        return self.pages.count()

    def revert(self, _user=None):
        """
        Delete the subsequent versions after this one
        """
        logger.info(
            'Reverting to document document: %s to version: %s',
            self.document, self
        )

        event_document_version_revert.commit(actor=_user, target=self.document)
        for version in self.document.versions.filter(timestamp__gt=self.timestamp):
            version.delete()

    def save(self, *args, **kwargs):
        """
        Overloaded save method that updates the document version's checksum,
        mimetype, and page count when created
        """
        user = kwargs.pop('_user', None)
        new_document_version = not self.pk

        if new_document_version:
            logger.info('Creating new version for document: %s', self.document)

        try:
            with transaction.atomic():
                super(DocumentVersion, self).save(*args, **kwargs)

                for key in sorted(DocumentVersion._post_save_hooks):
                    DocumentVersion._post_save_hooks[key](
                        document_version=self
                    )

                if new_document_version:
                    # Only do this for new documents
                    self.update_checksum(save=False)
                    self.update_mimetype(save=False)
                    self.save()
                    self.update_page_count(save=False)
                    if setting_fix_orientation.value:
                        self.fix_orientation()

                    logger.info(
                        'New document version "%s" created for document: %s',
                        self, self.document
                    )

                    self.document.is_stub = False
                    if not self.document.label:
                        self.document.label = force_text(self.file)

                    self.document.save(_commit_events=False)
        except Exception as exception:
            logger.error(
                'Error creating new document version for document "%s"; %s',
                self.document, exception
            )
            raise
        else:
            if new_document_version:
                event_document_new_version.commit(
                    actor=user, target=self, action_object=self.document
                )
                post_version_upload.send(sender=DocumentVersion, instance=self)

                if tuple(self.document.versions.all()) == (self,):
                    post_document_created.send(
                        sender=Document, instance=self.document
                    )

    def save_to_file(self, filepath, buffer_size=1024 * 1024):
        """
        Save a copy of the document from the document storage backend
        to the local filesystem
        """
        input_descriptor = self.open()
        output_descriptor = open(filepath, 'wb')
        while True:
            copy_buffer = input_descriptor.read(buffer_size)
            if copy_buffer:
                output_descriptor.write(copy_buffer)
            else:
                break

        output_descriptor.close()
        input_descriptor.close()
        return filepath

    @property
    def size(self):
        if self.exists():
            return self.file.storage().size(self.file.name)
        else:
            return None

    def update_checksum(self, save=True):
        """
        Open a document version's file and update the checksum field using
        the user provided checksum function
        """
        if self.exists():
            source = self.open()
            self.checksum = force_text(document_hash_function(source.read()))
            source.close()
            if save:
                self.save()

    def update_mimetype(self, save=True):
        """
        Read a document verions's file and determine the mimetype by calling
        the get_mimetype wrapper
        """
        if self.exists():
            try:
                with self.open() as file_object:
                    self.mimetype, self.encoding = get_mimetype(
                        file_object=file_object
                    )
            except Exception:
                self.mimetype = ''
                self.encoding = ''
            finally:
                if save:
                    self.save()

    def update_page_count(self, save=True):
        try:
            with self.open() as file_object:
                converter = converter_class(
                    file_object=file_object, mime_type=self.mimetype
                )
                detected_pages = converter.get_page_count()
        except PageCountError:
            # If converter backend doesn't understand the format,
            # use 1 as the total page count
            pass
        else:
            with transaction.atomic():
                self.pages.all().delete()

                for page_number in range(detected_pages):
                    self.pages.create(page_number=page_number + 1)

            if save:
                self.save()

            return detected_pages

    @cached_property
    def uuid(self):
        # Make cache UUID a mix of document UUID, version ID
        return '{}-{}'.format(self.document.uuid, self.pk)