boards/models/attachment/viewers.py

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

FILE_STUB_IMAGE = 'images/file.png'

FILE_TYPES_VIDEO = (
    'webm',
    'mp4',
    'mpeg',
    'ogv',
)
FILE_TYPE_SVG = 'svg'
FILE_TYPES_AUDIO = (
    'ogg',
    'mp3',
    'opus',
)

PLAIN_FILE_FORMATS = {
    'pdf': 'pdf',
    'djvu': 'djvu',
    'txt': 'txt',
}


def get_viewers():
    return AbstractViewer.__subclasses__()


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

    @staticmethod
    def supports(file_type):
        return True

    def get_view(self):
        return '<div class="image">'\
               '{}'\
               '<div class="image-metadata"><a href="{}" download >{}, {}</a></div>'\
               '</div>'.format(self.get_format_view(), self.file.url,
                               self.file_type, filesizeformat(self.file.size))

    def get_format_view(self):
        if self.file_type in PLAIN_FILE_FORMATS:
            image = 'images/fileformats/{}.png'.format(
                    PLAIN_FILE_FORMATS[self.file_type])
        else:
            image = FILE_STUB_IMAGE

        return '<a href="{}">'\
               '<img src="{}" width="200" height="150"/>'\
               '</a>'.format(self.file.url, static(image))


class VideoViewer(AbstractViewer):
    @staticmethod
    def supports(file_type):
        return file_type in FILE_TYPES_VIDEO

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


class AudioViewer(AbstractViewer):
    @staticmethod
    def supports(file_type):
        return file_type in FILE_TYPES_AUDIO

    def get_format_view(self):
        return '<audio controls src="{}"></audio>'.format(self.file.url)


class SvgViewer(AbstractViewer):
    @staticmethod
    def supports(file_type):
        return file_type == FILE_TYPE_SVG

    def get_format_view(self):
        return '<a class="thumb" href="{}">'\
               '<img class="post-image-preview" width="200" height="150" src="{}" />'\
               '</a>'.format(self.file.url, self.file.url)