Calculate ETag for the index page using last modified date

.gitignore

@@ -12,3 +12,4 @@ stale_outputs_checked
 __pycache__
 *.iml
 *.pages
+/git_commit

thoughts/migrations/0008_thought_last_updated.py

@@ -0,0 +1,19 @@
+# Generated by Django 4.0.3 on 2023-12-12 20:39
+
+from django.db import migrations, models
+import django.utils.timezone
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('thoughts', '0007_thought_html_content_alter_thought_posted'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='thought',
+            name='last_updated',
+            field=models.DateTimeField(default=django.utils.timezone.now),
+        ),
+    ]

thoughts/migrations/0009_thought_thoughts_th_posted_6b4f21_idx_and_more.py

@@ -0,0 +1,21 @@
+# Generated by Django 4.0.3 on 2023-12-12 21:17
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('thoughts', '0008_thought_last_updated'),
+    ]
+
+    operations = [
+        migrations.AddIndex(
+            model_name='thought',
+            index=models.Index(fields=['-posted'], name='thoughts_th_posted_6b4f21_idx'),
+        ),
+        migrations.AddIndex(
+            model_name='thought',
+            index=models.Index(fields=['-last_updated'], name='thoughts_th_last_up_2f98ba_idx'),
+        ),
+    ]

thoughts/models.py

@@ -68,6 +68,12 @@ class Thought(models.Model):
             except cls.DoesNotExist:
                 return None
 
+    class Meta:
+        indexes = [
+            models.Index(fields=["-posted"]),
+            models.Index(fields=["-last_updated"])
+        ]
+
 # Honestly I'm so sick of this problem that writing out a comment here to explain why it is necessary is beyond me.
 # I'm calling this CharField and not MySpecialLineNormalizingCharField
 #   because I think this should be the default behavior and I don't understand why it's not.
@@ -126,7 +132,7 @@ class ThoughtForm(forms.ModelForm):
 
     class Meta:
         model = Thought
-        exclude = ["posted"]
+        exclude = ["posted", "last_updated"]
         widgets = {
             "timezone_offset": forms.NumberInput,
         }

thoughts/views.py

@@ -3,6 +3,7 @@ import uuid
 import subprocess
 import base64
 import collections
+import hashlib
 from itertools import islice
 
 import magic
@@ -10,6 +11,7 @@ import magic
 from django import forms
 from django.shortcuts import render, redirect
 from django.utils.crypto import constant_time_compare
+from django.views.decorators.http import condition
 
 from haystack.views import SearchView, search_view_factory
 from haystack.query import SearchQuerySet
@@ -21,7 +23,7 @@ from .pagination import get_all_pages, get_page_slug
 
 # Python's itertools standard library is bad
 # Instead of providing functions
-# They provide "receipes" that you can copy-paste into your own program
+# They provide "recipes" that you can copy-paste into your own program
 # => https://docs.python.org/3/library/itertools.html#itertools-recipes
 def sliding_window(iterable, n):
     # sliding_window('ABCDEFG', 4) --> ABCD BCDE CDEF DEFG
@@ -43,15 +45,14 @@ def check_authenticated(request):
         pass
     return authenticated
 
-
-def index(request):
-    authenticated = check_authenticated(request)
-
+def get_highlighted_uuid(request):
     try:
-        highlighted_uuid = uuid.UUID(request.GET.get("show", ""))
+        return uuid.UUID(request.GET.get("show", ""))
     except ValueError:
-        highlighted_uuid = ""
+        return ""
 
+# Return the previous, current, and next page
+def get_pages(request):
     ## Figure out what page we're viewing
     pages = get_all_pages()
 
@@ -59,6 +60,7 @@ def index(request):
 
     # If we've passed a valid highlighted thought uuid,
     #  that takes priority over a page= value, so we overwrite requested_slug
+    highlighted_uuid = get_highlighted_uuid(request)
     if highlighted_uuid:
         try:
             requested_slug = get_page_slug(Thought.objects.get(uuid=highlighted_uuid))
@@ -82,8 +84,42 @@ def index(request):
         if nex.slug == requested_slug:
             previous_page, current_page, next_page = curr, nex, None
 
+    return previous_page, current_page, next_page
+
+
+# Takes a Queryset of Thoughts and returns a hash of:
+#   the last-modified time for the most recently modified
+#   the number of thoughts
+#   and the current git commit (read from settings (which reads it from the git_commit file or randomly generates an id))
+# I can't think of any edge cases. It's impossible to change page without changing the query params, the time, or the count
+# I still need to double check that different query params are treated differently
+def get_etag_from_thoughts(thoughts):
+    count = thoughts.count()
+    last_updated = thoughts.order_by("-last_updated").first().last_updated
+    # Do I need to include query params? I'd hope that it was seen as a different URL
+
+    hash_str = f"{count}:{last_updated}:{settings.COMMIT}"
+    return hashlib.sha256(hash_str.encode()).hexdigest()
+
+
+def get_etag(request):
+    previous_page, current_page, next_page = get_pages(request)
+
     thoughts = current_page.get_all_entries()
 
+    return get_etag_from_thoughts(thoughts)
+
+
+@condition(etag_func=get_etag)
+def index(request):
+    authenticated = check_authenticated(request)
+
+    previous_page, current_page, next_page = get_pages(request)
+
+    thoughts = current_page.get_all_entries()
+
+    highlighted_uuid = get_highlighted_uuid(request)
+
     return render(request, "thoughts/index.html", {
         "thoughts": thoughts,
         "highlighted": highlighted_uuid,
@@ -91,8 +127,8 @@ def index(request):
         "page": current_page,
         "previous_page_slug": getattr(previous_page, "slug", None),
         "next_page_slug": getattr(next_page, "slug", None),
-        "is_first_page": current_page.slug == pages[0].slug, # if you're viewing the first page
-        "is_last_page": current_page.slug == pages[-1].slug
+        "is_first_page": previous_page is None, # if you're viewing the first page
+        "is_last_page": next_page is None
     })
 
 

whispermaphone/settings.py

@@ -12,6 +12,7 @@ https://docs.djangoproject.com/en/3.1/ref/settings/
 
 from pathlib import Path
 from decouple import config
+import secrets
 import os
 
 # Build paths inside the project like this: BASE_DIR / "subdir".
@@ -40,6 +41,14 @@ def split_string(string):
 # DO NOT USE THE COLORS I USE. These values right here are black and white, if you're lazy, keep them
 COLORS = config("COLORS", default="#FEFEFE,#222222,#999999", cast=split_string)
 
+# The current git commit if known; used for cache invalidation
+COMMIT = ""
+try:
+    with open(BASE_DIR / "git_commit", "r") as f:
+        COMMIT = f.read().strip()
+except FileNotFoundError:
+    COMMIT = "unknown-" + secrets.token_hex(15)
+
 INSTALLED_APPS = [
     "django.contrib.contenttypes",
     "django.contrib.staticfiles",