Implement configurable default values for the subject and preheader

docs/usage.md

@@ -354,6 +354,23 @@ with translation.override(language_code):
 
 ## Edge Cases and Considerations
 
+### Default Subject and Preheader
+
+- **Providing Defaults**: If the `subject` and `preheader` blocks are not defined in the template, the default values are used.
+- **Customizing Defaults**: You can set default values for the subject and preheader in the context when sending the email.
+
+#### Settings
+
+You can also set default values for the subject and preheader in your Django settings. These are used if a value is not provided
+in the template or context, or if you have set `fail_silently` to `True` and an error occurs.
+
+```python
+TEMPLATED_EMAIL_DEFAULT_SUBJECT = 'Default Subject'
+TEMPLATED_EMAIL_DEFAULT_PREHEADER = 'Default Preheader'
+```
+
+If not set, the default value for subject is `'Hello!'` and for preheader is `''`.
+
 ### Subject Overriding
 
 - **From Context**: You can override the subject by providing a `subject` key in the context.

example_project/example/templates/templated_email/test_no_subject_preheader.md

@@ -0,0 +1,6 @@
+{% block content %}
+
+# Hello {{ name }}!
+
+This is a test message.
+{% endblock %}

example_project/example/templates/templated_email/test_subject_preheader_provided.md

@@ -0,0 +1,9 @@
+{% block subject %}Subject from Template{% endblock %}
+{% block preheader %}Preheader from Template{% endblock %}
+
+{% block content %}
+
+# Hello {{ name }}!
+
+This is a test message.
+{% endblock %}

example_project/test_django_templated_email_md.py

@@ -5,6 +5,7 @@
 from django.core import mail
 from django.template import TemplateDoesNotExist
 from django.utils import translation
+from django.utils.translation import gettext as _
 from templated_email import send_templated_mail
 
 from templated_email_md.backend import MarkdownTemplateBackend
@@ -137,7 +138,7 @@ def test_fail_silently():
     # Should get a fallback response instead of an exception
     assert "Email template rendering failed" in response["html"]
     assert "Email template rendering failed" in response["plain"]
-    assert response["subject"] == "No Subject"
+    assert response["subject"] == "Hello!"
 
 
 def test_subject_from_context(backend):
@@ -379,3 +380,79 @@ def test_remove_comments():
     assert "HTML Comment" not in cleaned_html
     assert "CSS Comment" not in cleaned_html
     assert "JavaScript Comment" not in cleaned_html
+
+
+def test_default_subject_and_preheader():
+    """
+    Test that the default subject and preheader are used when
+    not provided in the template or context.
+    """
+    # Send an email without subject or preheader in template or context
+    send_templated_mail(
+        template_name="test_no_subject_preheader",
+        from_email="[email protected]",
+        recipient_list=["[email protected]"],
+        context={"name": "Test User"},
+    )
+
+    assert len(mail.outbox) == 1
+    email = mail.outbox[0]
+
+    # Default subject should be 'Hello!' as per the default in the backend
+    assert email.subject == _("Hello!")
+    # Preheader should be empty string by default
+    # Since preheader may not be directly visible, check in the HTML content
+    html_content = email.alternatives[0][0]
+    assert "Hello!" in email.subject
+    assert '<span class="preheader"' in html_content
+    # Assuming the preheader is included even if empty, check that it's empty
+    assert "></span>" in html_content
+
+
+def test_custom_default_subject_and_preheader():
+    """
+    Test that the custom default subject and preheader from settings
+    are used when not provided in the template or context.
+    """
+    settings.TEMPLATED_EMAIL_DEFAULT_SUBJECT = "Default Subject from Settings"
+    settings.TEMPLATED_EMAIL_DEFAULT_PREHEADER = "Default Preheader from Settings"
+    # Send an email without subject or preheader in template or context
+    send_templated_mail(
+        template_name="test_no_subject_preheader",
+        from_email="[email protected]",
+        recipient_list=["[email protected]"],
+        context={"name": "Test User"},
+    )
+
+    assert len(mail.outbox) == 1
+    email = mail.outbox[0]
+
+    # Subject should be the custom default from settings
+    assert email.subject == "Default Subject from Settings"
+    # Preheader should be the custom default from settings
+    html_content = email.alternatives[0][0]
+    assert '<span class="preheader"' in html_content
+    assert ">Default Preheader from Settings</span>" in html_content
+
+
+def test_subject_and_preheader_provided():
+    """
+    Test that when subject and preheader are provided in the template,
+    they override the default values.
+    """
+    # Send an email with subject and preheader in the template
+    send_templated_mail(
+        template_name="test_subject_preheader_provided",
+        from_email="[email protected]",
+        recipient_list=["[email protected]"],
+        context={"name": "Test User"},
+    )
+
+    assert len(mail.outbox) == 1
+    email = mail.outbox[0]
+
+    # Subject and preheader should be as provided in the template
+    assert email.subject == "Subject from Template"
+    html_content = email.alternatives[0][0]
+    assert '<span class="preheader"' in html_content
+    assert ">Preheader from Template</span>" in html_content

src/templated_email_md/backend.py

@@ -73,6 +73,8 @@ def __init__(
             ],
         )
         self.html2text_settings = getattr(settings, "TEMPLATED_EMAIL_HTML2TEXT_SETTINGS", {})
+        self.default_subject = getattr(settings, "TEMPLATED_EMAIL_DEFAULT_SUBJECT", _("Hello!"))
+        self.default_preheader = getattr(settings, "TEMPLATED_EMAIL_DEFAULT_PREHEADER", _(""))
 
     def _render_markdown(self, content: str) -> str:
         """Convert Markdown content to HTML.
@@ -241,8 +243,8 @@ def _render_email(
                 return {
                     "html": fallback_content,
                     "plain": fallback_content,
-                    "subject": _("No Subject"),
-                    "preheader": _("No Preheader"),
+                    "subject": self.default_subject,
+                    "preheader": self.default_preheader,
                 }
             raise
 
@@ -259,7 +261,7 @@ def _get_subject_from_template(self, template_path: str, context: Dict[str, Any]
         try:
             subject = render_block_to_string(template_path, "subject", context).strip()
         except BlockNotFound:
-            subject = _("No Subject")
+            subject = self.default_subject
 
         # Override subject if 'subject' is in context
         subject = context.get("subject", subject)
@@ -279,7 +281,7 @@ def _get_preheader_from_template(self, template_path: str, context: Dict[str, An
         try:
             preheader = render_block_to_string(template_path, "preheader", context).strip()
         except BlockNotFound:
-            preheader = _("No Preheader")
+            preheader = self.default_preheader
 
         # Override preheader if 'preheader' is in context
         preheader = context.get("preheader", preheader)