Mixin for Wagtail Pages to have custom templates per site domain

site_domain_page_template_mixin.py

# The MIT License (MIT)
# 
# Copyright (c) 2023 Christian Haintz
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from django.template import Engine, TemplateDoesNotExist
from wagtail.core.models import Page, Site


class SiteDomainPageTemplateMixin(Page):
    """
    Mixin for Wagtail Page Class to have different html template files for
    different Wagtail sites. For example you can create multiple templates for a single
    wagtail Page class. In your templates folder just create additional files
    for the Page with the Site hostname added before the extension of the file
    (usually .html) like so:

    my_page.html  <-- default/fallback template
    my_page.example.com.html  <-- is used when the site hostname example.com is called
    my_page.otherdomain.com.html  <-- is used for otherdomain.com site

    Use the mixin for your Template like:

    class MyPage(SiteDomainPageTemplateMixin, Page):
        pass

    """

    class Meta:
        abstract = True

    def get_template(self, request, *args, **kwargs):
        current_site = Site.find_for_request(request)
        try:
            template_path = super().get_template(request, args, kwargs)
            # split the template path in "app/filename" and "fileextension"
            path_segments = template_path.rsplit('.', 1)
            site_template_path = (
                path_segments[0] + '.' + current_site.hostname + '.' + path_segments[1]
            )
            # get the default template engine and try to load the template
            # if no exception happens, the custom site template exists
            # and we return the path
            engine = Engine.get_default()
            engine.get_template(site_template_path)
            return site_template_path
          
        except TemplateDoesNotExist as e:
            # if an exception happens a site template could not be found and we
            # fallback to the default template path
            regular_template_path = super().get_template(request, args, kwargs)
            return regular_template_path