boards/models/attachment/__init__.py

from django.db import models

from boards import utils
from boards.models.attachment.viewers import get_viewers, AbstractViewer
from boards.utils import get_upload_filename, get_file_mimetype


class AttachmentManager(models.Manager):
    def create_with_hash(self, file):
        file_hash = utils.get_file_hash(file)
        existing = self.filter(hash=file_hash)
        if len(existing) > 0:
            attachment = existing[0]
        else:
            file_type = get_file_mimetype(file)
            attachment = self.create(file=file, mimetype=file_type,
                                     hash=file_hash)

        return attachment


class Attachment(models.Model):
    objects = AttachmentManager()

    file = models.FileField(upload_to=get_upload_filename)
    mimetype = models.CharField(max_length=50)
    hash = models.CharField(max_length=36)

    def get_view(self):
        file_viewer = None
        for viewer in get_viewers():
            if viewer.supports(self.mimetype):
                file_viewer = viewer
                break
        if file_viewer is None:
            file_viewer = AbstractViewer

        return file_viewer(self.file, self.mimetype).get_view()