boards/models/attachment/viewers.py

from django.template.defaultfilters import filesizeformat
from django.templatetags.static import static


class AbstractViewer:
    def __init__(self, file, file_type):
        self.file = file
        self.file_type = file_type

    @staticmethod
    def get_viewer(file_type, file):
        for viewer in VIEWERS:
            if viewer.supports(file_type):
                return viewer(file)
        return AbstractViewer(file)

    @staticmethod
    def supports(file_type):
        return true

    def get_view(self):
        return '<div class="image"><a href="{}">'\
               '<img src="{}" width="200" height="150"/>'\
               '</a>'\
               '<div class="image-metadata">{}, {}</div>'\
               '</div>'.format(self.file.url, static('images/file.png'), self.file_type,
                       filesizeformat(self.file.size))


class WebmViewer(AbstractViewer):
    @staticmethod
    def supports(file_type):
        return file_type == 'webm'

    def get_view(self):
        return '<div class="image">'\
               '<video width="200" height="150" controls/>'\
               '<source src="{}">'\
               '</div>'.format(self.file.url)