Custom HTML email renderers and new email style (#991)

* Custom HTML email renderers

* Move inline_css call

* Small fixes

* New HTML mail style for pretix

* Thumbs

* Inlinestyle for notifications

* Documentation

* Set line-height

src/pretix/base/email.py

@@ -1,7 +1,18 @@
 import logging
 from smtplib import SMTPRecipientsRefused, SMTPSenderRefused
 
+import bleach
+import markdown
+from django.conf import settings
 from django.core.mail.backends.smtp import EmailBackend
+from django.dispatch import receiver
+from django.template.loader import get_template
+from django.utils.translation import ugettext_lazy as _
+from inlinestyler.utils import inline_css
+
+from pretix.base.models import Event, Order
+from pretix.base.signals import register_html_mail_renderers
+from pretix.base.templatetags.rich_text import markdown_compile
 
 logger = logging.getLogger('pretix.base.email')
 
@@ -24,3 +35,103 @@ class CustomSMTPBackend(EmailBackend):
                 raise SMTPRecipientsRefused(senderrs)
         finally:
             self.close()
+
+
+class BaseHTMLMailRenderer:
+    """
+    This is the base class for all HTML e-mail renderers.
+    """
+
+    def __init__(self, event: Event):
+        self.event = event
+
+    def __str__(self):
+        return self.identifier
+
+    def render(self, plain_body: str, plain_signature: str, subject: str, order: Order=None) -> str:
+        """
+        This method should generate the HTML part of the email.
+
+        :param plain_body: The body of the email in plain text.
+        :param plain_signature: The signature with event organizer contact details in plain text.
+        :param subject: The email subject.
+        :param order: The order if this email is connected to one, otherwise ``None``.
+        :return: An HTML string
+        """
+        raise NotImplementedError()
+
+    @property
+    def verbose_name(self) -> str:
+        """
+        A human-readable name for this renderer. This should be short but self-explanatory.
+        """
+        raise NotImplementedError()  # NOQA
+
+    @property
+    def identifier(self) -> str:
+        """
+        A short and unique identifier for this renderer.
+        This should only contain lowercase letters and in most cases will be the same as your package name or prefixed
+        with your package name.
+        """
+        raise NotImplementedError()  # NOQA
+
+    @property
+    def thumbnail_filename(self) -> str:
+        """
+        A file name discoverable in the static file storage that contains a preview of your renderer. This should
+        be with aspect resolution 4:3.
+        """
+        raise NotImplementedError()  # NOQA
+
+    @property
+    def is_available(self) -> bool:
+        """
+        This renderer will only be available if this returns ``True``. You can use this to limit this renderer
+        to certain events. Defaults to ``True``.
+        """
+        return True
+
+
+class TemplateBasedMailRenderer(BaseHTMLMailRenderer):
+
+    @property
+    def template_name(self):
+        raise NotImplemented
+
+    def render(self, plain_body: str, plain_signature: str, subject: str, order: Order) -> str:
+        body_md = bleach.linkify(markdown_compile(plain_body))
+        htmlctx = {
+            'site': settings.PRETIX_INSTANCE_NAME,
+            'site_url': settings.SITE_URL,
+            'body': body_md,
+            'subject': str(subject),
+            'color': '#8E44B3'
+        }
+        if self.event:
+            htmlctx['event'] = self.event
+            htmlctx['color'] = self.event.settings.primary_color
+
+        if plain_signature:
+            signature_md = plain_signature.replace('\n', '<br>\n')
+            signature_md = bleach.linkify(bleach.clean(markdown.markdown(signature_md), tags=bleach.ALLOWED_TAGS + ['p', 'br']))
+            htmlctx['signature'] = signature_md
+
+        if order:
+            htmlctx['order'] = order
+
+        tpl = get_template(self.template_name)
+        body_html = inline_css(tpl.render(htmlctx))
+        return body_html
+
+
+class ClassicMailRenderer(TemplateBasedMailRenderer):
+    verbose_name = _('pretix default')
+    identifier = 'classic'
+    thumbnail_filename = 'pretixbase/email/thumb.png'
+    template_name = 'pretixbase/email/plainwrapper.html'
+
+
+@receiver(register_html_mail_renderers, dispatch_uid="pretixbase_email_renderers")
+def base_renderers(sender, **kwargs):
+    return [ClassicMailRenderer]