Auto slug, auto summary/SEO, and deterministic tag colours

Issue #61: Strengthen auto-generation for slug, summary, and SEO fields.
- ArticlePage.save() now auto-generates slug from title when empty
- ArticlePage.save() auto-populates search_description from summary
- Admin form also auto-populates search_description from summary

Issue #63: Replace manual TagMetadata colour assignment with deterministic
hash-based auto-colour. Tags get a consistent colour from a 12-entry
palette without needing a TagMetadata snippet. TagMetadata still works
as an explicit override.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/blog/models.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import hashlib
 import re
 from math import ceil
 from typing import Any
@@ -174,20 +175,87 @@ class Category(models.Model):
         return self.name
 
 
+# ── Tag colour palette ────────────────────────────────────────────────────────
+# Deterministic hash-based colour assignment for tags.  Each entry is a dict
+# with Tailwind CSS class strings for bg, text, and border.
+
+TAG_COLOUR_PALETTE: list[dict[str, str]] = [
+    {
+        "bg": "bg-brand-cyan/10",
+        "text": "text-brand-cyan",
+        "border": "border-brand-cyan/20",
+    },
+    {
+        "bg": "bg-brand-pink/10",
+        "text": "text-brand-pink",
+        "border": "border-brand-pink/20",
+    },
+    {
+        "bg": "bg-amber-500/10",
+        "text": "text-amber-400",
+        "border": "border-amber-500/20",
+    },
+    {
+        "bg": "bg-emerald-500/10",
+        "text": "text-emerald-400",
+        "border": "border-emerald-500/20",
+    },
+    {
+        "bg": "bg-violet-500/10",
+        "text": "text-violet-400",
+        "border": "border-violet-500/20",
+    },
+    {
+        "bg": "bg-rose-500/10",
+        "text": "text-rose-400",
+        "border": "border-rose-500/20",
+    },
+    {
+        "bg": "bg-sky-500/10",
+        "text": "text-sky-400",
+        "border": "border-sky-500/20",
+    },
+    {
+        "bg": "bg-lime-500/10",
+        "text": "text-lime-400",
+        "border": "border-lime-500/20",
+    },
+    {
+        "bg": "bg-orange-500/10",
+        "text": "text-orange-400",
+        "border": "border-orange-500/20",
+    },
+    {
+        "bg": "bg-fuchsia-500/10",
+        "text": "text-fuchsia-400",
+        "border": "border-fuchsia-500/20",
+    },
+    {
+        "bg": "bg-teal-500/10",
+        "text": "text-teal-400",
+        "border": "border-teal-500/20",
+    },
+    {
+        "bg": "bg-indigo-500/10",
+        "text": "text-indigo-400",
+        "border": "border-indigo-500/20",
+    },
+]
+
+
+def get_auto_tag_colour_css(tag_name: str) -> dict[str, str]:
+    """Deterministically assign a colour from the palette based on tag name."""
+    digest = hashlib.md5(tag_name.lower().encode(), usedforsecurity=False).hexdigest()  # noqa: S324
+    index = int(digest, 16) % len(TAG_COLOUR_PALETTE)
+    return TAG_COLOUR_PALETTE[index]
+
+
 class TagMetadata(models.Model):
     COLOUR_CHOICES = [("cyan", "Cyan"), ("pink", "Pink"), ("neutral", "Neutral")]
 
     tag = models.OneToOneField("taggit.Tag", on_delete=CASCADE, related_name="metadata")
     colour = models.CharField(max_length=20, choices=COLOUR_CHOICES, default="neutral")
 
-    @classmethod
-    def get_fallback_css(cls) -> dict[str, str]:
-        return {
-            "bg": "bg-zinc-800 dark:bg-zinc-100",
-            "text": "text-white dark:text-black",
-            "border": "border-zinc-600/20 dark:border-zinc-400/20",
-        }
-
     def get_css_classes(self) -> dict[str, str]:
         mapping = {
             "cyan": {
@@ -200,9 +268,13 @@ class TagMetadata(models.Model):
                 "text": "text-brand-pink",
                 "border": "border-brand-pink/20",
             },
-            "neutral": self.get_fallback_css(),
+            "neutral": {
+                "bg": "bg-zinc-800 dark:bg-zinc-100",
+                "text": "text-white dark:text-black",
+                "border": "border-zinc-600/20 dark:border-zinc-400/20",
+            },
         }
-        return mapping.get(self.colour, self.get_fallback_css())
+        return mapping.get(self.colour, get_auto_tag_colour_css(self.tag.name))
 
 
 class ArticlePageAdminForm(WagtailAdminPageForm):
@@ -254,6 +326,8 @@ class ArticlePageAdminForm(WagtailAdminPageForm):
                 cleaned_data.get("body"),
                 max_chars=self.SUMMARY_MAX_CHARS,
             ) or title
+        if not cleaned_data.get("search_description") and cleaned_data.get("summary"):
+            cleaned_data["search_description"] = cleaned_data["summary"]
 
         return cleaned_data
 
@@ -375,6 +449,8 @@ class ArticlePage(SeoMixin, Page):
         return " ".join(parts)
 
     def save(self, *args: Any, **kwargs: Any) -> None:
+        if not getattr(self, "slug", "") and self.title:
+            self.slug = self._auto_slug_from_title()
         if not self.category_id:
             self.category, _ = Category.objects.get_or_create(
                 slug="general",
@@ -382,12 +458,27 @@ class ArticlePage(SeoMixin, Page):
             )
         if not (self.summary or "").strip():
             self.summary = _generate_summary_from_stream(self.body) or self.title
+        if not getattr(self, "search_description", "") and self.summary:
+            self.search_description = self.summary
         if not self.published_date and self.first_published_at:
             self.published_date = self.first_published_at
         if self._should_refresh_read_time():
             self.read_time_mins = self._compute_read_time()
         return super().save(*args, **kwargs)
 
+    def _auto_slug_from_title(self) -> str:
+        base_slug = slugify(self.title) or "article"
+        parent = self.get_parent() if self.pk else None
+        if parent is None:
+            return base_slug
+        sibling_pages = parent.get_children().exclude(pk=self.pk)
+        slug = base_slug
+        suffix = 2
+        while sibling_pages.filter(slug=slug).exists():
+            slug = f"{base_slug}-{suffix}"
+            suffix += 1
+        return slug
+
     def _should_refresh_read_time(self) -> bool:
         if not self.pk:
             return True

apps/blog/tests/test_admin_experience.py

@@ -411,6 +411,73 @@ def test_snippet_category_listing_shows_categories(client, django_user_model):
     assert "Tutorials" in content
 
 
+@pytest.mark.django_db
+def test_article_admin_form_clean_auto_populates_search_description(article_index, django_user_model, monkeypatch):
+    """Form clean should auto-populate search_description from summary."""
+    user = django_user_model.objects.create_user(
+        username="writer",
+        email="writer@example.com",
+        password="writer-pass",
+        first_name="Writer",
+        last_name="User",
+    )
+    form_class = ArticlePage.get_edit_handler().get_form_class()
+    form = form_class(parent_page=article_index, for_user=user)
+
+    body = [
+        SimpleNamespace(block_type="rich_text", value=SimpleNamespace(source="<p>Article body text.</p>")),
+    ]
+    form.cleaned_data = {
+        "title": "SEO Test",
+        "slug": "",
+        "author": None,
+        "category": None,
+        "summary": "",
+        "search_description": "",
+        "body": body,
+    }
+
+    mro = form.__class__.__mro__
+    super_form_class = mro[mro.index(ArticlePageAdminForm) + 1]
+    monkeypatch.setattr(super_form_class, "clean", lambda _self: _self.cleaned_data)
+    cleaned = form.clean()
+
+    assert cleaned["summary"] == "Article body text."
+    assert cleaned["search_description"] == "Article body text."
+
+
+@pytest.mark.django_db
+def test_article_admin_form_preserves_explicit_search_description(article_index, django_user_model, monkeypatch):
+    """Form clean should not overwrite an explicit search_description."""
+    user = django_user_model.objects.create_user(
+        username="writer2",
+        email="writer2@example.com",
+        password="writer-pass",
+    )
+    form_class = ArticlePage.get_edit_handler().get_form_class()
+    form = form_class(parent_page=article_index, for_user=user)
+
+    body = [
+        SimpleNamespace(block_type="rich_text", value=SimpleNamespace(source="<p>Body.</p>")),
+    ]
+    form.cleaned_data = {
+        "title": "SEO Explicit Test",
+        "slug": "seo-explicit-test",
+        "author": None,
+        "category": None,
+        "summary": "My summary.",
+        "search_description": "Custom SEO text.",
+        "body": body,
+    }
+
+    mro = form.__class__.__mro__
+    super_form_class = mro[mro.index(ArticlePageAdminForm) + 1]
+    monkeypatch.setattr(super_form_class, "clean", lambda _self: _self.cleaned_data)
+    cleaned = form.clean()
+
+    assert cleaned["search_description"] == "Custom SEO text."
+
+
 @pytest.mark.django_db
 def test_article_page_omits_admin_messages_on_frontend(article_page, rf):
     """Frontend templates should not render admin session messages."""

apps/blog/tests/test_models.py

@@ -2,7 +2,15 @@ import pytest
 from django.db import IntegrityError
 from taggit.models import Tag
 
-from apps.blog.models import ArticleIndexPage, ArticlePage, Category, HomePage, TagMetadata
+from apps.blog.models import (
+    TAG_COLOUR_PALETTE,
+    ArticleIndexPage,
+    ArticlePage,
+    Category,
+    HomePage,
+    TagMetadata,
+    get_auto_tag_colour_css,
+)
 from apps.blog.tests.factories import AuthorFactory
 
 
@@ -92,3 +100,108 @@ def test_category_ordering():
     Category.objects.create(name="A", slug="a", sort_order=1)
     names = list(Category.objects.values_list("name", flat=True))
     assert names == ["General", "A", "Z"]
+
+
+# ── Auto tag colour tests ────────────────────────────────────────────────────
+
+
+def test_auto_tag_colour_is_deterministic():
+    """Same tag name always produces the same colour."""
+    css1 = get_auto_tag_colour_css("python")
+    css2 = get_auto_tag_colour_css("python")
+    assert css1 == css2
+
+
+def test_auto_tag_colour_is_case_insensitive():
+    """Tag colour assignment is case-insensitive."""
+    assert get_auto_tag_colour_css("Python") == get_auto_tag_colour_css("python")
+
+
+def test_auto_tag_colour_returns_valid_palette_entry():
+    """Returned CSS dict must be from the palette."""
+    css = get_auto_tag_colour_css("llms")
+    assert css in TAG_COLOUR_PALETTE
+
+
+def test_auto_tag_colour_distributes_across_palette():
+    """Different tag names should map to multiple palette entries."""
+    sample_tags = ["python", "javascript", "rust", "go", "ruby", "java",
+                   "typescript", "css", "html", "sql", "llms", "mlops"]
+    colours = {get_auto_tag_colour_css(t)["text"] for t in sample_tags}
+    assert len(colours) >= 3, "Tags should spread across at least 3 palette colours"
+
+
+@pytest.mark.django_db
+def test_tag_without_metadata_uses_auto_colour():
+    """Tags without TagMetadata should get auto-assigned colour, not neutral."""
+    tag = Tag.objects.create(name="fastapi", slug="fastapi")
+    expected = get_auto_tag_colour_css("fastapi")
+    # Verify no metadata exists
+    assert not TagMetadata.objects.filter(tag=tag).exists()
+    # The template tag helper should fall back to auto colour
+    from apps.core.templatetags.core_tags import _resolve_tag_css
+    assert _resolve_tag_css(tag) == expected
+
+
+@pytest.mark.django_db
+def test_tag_with_metadata_overrides_auto_colour():
+    """Tags with explicit TagMetadata should use that colour."""
+    tag = Tag.objects.create(name="django", slug="django")
+    TagMetadata.objects.create(tag=tag, colour="pink")
+    from apps.core.templatetags.core_tags import _resolve_tag_css
+    css = _resolve_tag_css(tag)
+    assert css["text"] == "text-brand-pink"
+
+
+# ── Auto slug tests ──────────────────────────────────────────────────────────
+
+
+@pytest.mark.django_db
+def test_article_save_auto_generates_slug_from_title(home_page):
+    """Model save should auto-generate slug from title when slug is empty."""
+    index = ArticleIndexPage(title="Articles", slug="articles")
+    home_page.add_child(instance=index)
+    author = AuthorFactory()
+    article = ArticlePage(
+        title="My Great Article",
+        slug="my-great-article",
+        author=author,
+        summary="summary",
+        body=[("rich_text", "<p>body</p>")],
+    )
+    index.add_child(instance=article)
+    article.save()
+    assert article.slug == "my-great-article"
+
+
+@pytest.mark.django_db
+def test_article_save_auto_generates_search_description(article_index):
+    """Model save should populate search_description from summary."""
+    author = AuthorFactory()
+    article = ArticlePage(
+        title="SEO Auto",
+        slug="seo-auto",
+        author=author,
+        summary="This is the article summary.",
+        body=[("rich_text", "<p>body</p>")],
+    )
+    article_index.add_child(instance=article)
+    article.save()
+    assert article.search_description == "This is the article summary."
+
+
+@pytest.mark.django_db
+def test_article_save_preserves_explicit_search_description(article_index):
+    """Explicit search_description should not be overwritten."""
+    author = AuthorFactory()
+    article = ArticlePage(
+        title="SEO Explicit",
+        slug="seo-explicit",
+        author=author,
+        summary="Generated summary.",
+        search_description="Custom SEO description.",
+        body=[("rich_text", "<p>body</p>")],
+    )
+    article_index.add_child(instance=article)
+    article.save()
+    assert article.search_description == "Custom SEO description."

apps/blog/tests/test_more_models.py

@@ -1,7 +1,5 @@
 import pytest
 
-from apps.blog.models import TagMetadata
-
 
 @pytest.mark.django_db
 def test_home_context_lists_articles(home_page, article_page):
@@ -22,6 +20,7 @@ def test_get_related_articles_fallback(article_page, article_index):
     assert isinstance(related, list)
 
 
-def test_tag_metadata_fallback_classes():
-    css = TagMetadata.get_fallback_css()
+def test_auto_tag_colour_returns_valid_css():
+    from apps.blog.models import get_auto_tag_colour_css
+    css = get_auto_tag_colour_css("test-tag")
     assert css["bg"].startswith("bg-")

apps/core/templatetags/core_tags.py

@@ -4,7 +4,7 @@ from django import template
 from django.utils.safestring import mark_safe
 from wagtail.models import Site
 
-from apps.blog.models import ArticleIndexPage, Category, TagMetadata
+from apps.blog.models import ArticleIndexPage, Category, TagMetadata, get_auto_tag_colour_css
 from apps.core.models import SiteSettings
 from apps.legal.models import LegalPage
 
@@ -70,20 +70,24 @@ def get_categories_nav(context):
     ]
 
 
-@register.simple_tag
-@register.filter
-def get_tag_css(tag):
+def _resolve_tag_css(tag) -> dict[str, str]:
+    """Return CSS classes for a tag, using TagMetadata if set, else auto-colour."""
     meta = getattr(tag, "metadata", None)
     if meta is None:
         meta = TagMetadata.objects.filter(tag=tag).first()
-    classes = meta.get_css_classes() if meta else TagMetadata.get_fallback_css()
+    if meta:
+        return meta.get_css_classes()
+    return get_auto_tag_colour_css(tag.name)
+
+
+@register.simple_tag
+@register.filter
+def get_tag_css(tag):
+    classes = _resolve_tag_css(tag)
     return mark_safe(f"{classes['bg']} {classes['text']}")
 
 
 @register.filter
 def get_tag_border_css(tag):
-    meta = getattr(tag, "metadata", None)
-    if meta is None:
-        meta = TagMetadata.objects.filter(tag=tag).first()
-    classes = meta.get_css_classes() if meta else TagMetadata.get_fallback_css()
+    classes = _resolve_tag_css(tag)
     return mark_safe(classes.get("border", ""))

apps/core/tests/test_more.py

@@ -21,17 +21,20 @@ def test_context_processor_returns_sitesettings(home_page):
 
 
 @pytest.mark.django_db
-def test_get_tag_css_fallback():
+def test_get_tag_css_auto_colour():
+    """Tags without metadata get a deterministic auto-assigned colour."""
     tag = Tag.objects.create(name="x", slug="x")
     value = core_tags.get_tag_css(tag)
-    assert "bg-zinc" in value
+    assert "bg-" in value
+    assert "text-" in value
 
 
 @pytest.mark.django_db
-def test_get_tag_border_css_fallback():
+def test_get_tag_border_css_auto_colour():
+    """Tags without metadata get a deterministic auto-assigned border colour."""
     tag = Tag.objects.create(name="y", slug="y")
     value = core_tags.get_tag_border_css(tag)
-    assert "border-zinc" in value
+    assert "border-" in value
 
 
 @pytest.mark.django_db