Merge pull request #2524 from chdorner/feature/tag-support

Initial hashtag support

bookwyrm/activitypub/__init__.py

@@ -3,7 +3,7 @@ import inspect
 import sys
 
 from .base_activity import ActivityEncoder, Signature, naive_parse
-from .base_activity import Link, Mention
+from .base_activity import Link, Mention, Hashtag
 from .base_activity import ActivitySerializerError, resolve_remote_id
 from .image import Document, Image
 from .note import Note, GeneratedNote, Article, Comment, Quotation

bookwyrm/activitypub/base_activity.py

@@ -186,7 +186,7 @@ class ActivityObject:
 
             # add many to many fields, which have to be set post-save
             for field in instance.many_to_many_fields:
-                # mention books/users, for example
+                # mention books/users/hashtags, for example
                 field.set_field_from_activity(
                     instance,
                     self,
@@ -426,3 +426,10 @@ class Mention(Link):
     """a subtype of Link for mentioning an actor"""
 
     type: str = "Mention"
+
+
+@dataclass(init=False)
+class Hashtag(Link):
+    """a subtype of Link for mentioning a hashtag"""
+
+    type: str = "Hashtag"

bookwyrm/activitypub/note.py

@@ -1,9 +1,12 @@
 """ note serializer and children thereof """
 from dataclasses import dataclass, field
 from typing import Dict, List
-from django.apps import apps
+import re
 
-from .base_activity import ActivityObject, Link
+from django.apps import apps
+from django.db import IntegrityError, transaction
+
+from .base_activity import ActivityObject, ActivitySerializerError, Link
 from .image import Document
 
 
@@ -38,6 +41,47 @@ class Note(ActivityObject):
     updated: str = None
     type: str = "Note"
 
+    # pylint: disable=too-many-arguments
+    def to_model(
+        self,
+        model=None,
+        instance=None,
+        allow_create=True,
+        save=True,
+        overwrite=True,
+        allow_external_connections=True,
+    ):
+        instance = super().to_model(
+            model, instance, allow_create, save, overwrite, allow_external_connections
+        )
+
+        if instance is None:
+            return instance
+
+        # Replace links to hashtags in content with local URLs
+        changed_content = False
+        for hashtag in instance.mention_hashtags.all():
+            updated_content = re.sub(
+                rf'(<a href=")[^"]*(" data-mention="hashtag">{hashtag.name}</a>)',
+                rf"\1{hashtag.remote_id}\2",
+                instance.content,
+                flags=re.IGNORECASE,
+            )
+            if instance.content != updated_content:
+                instance.content = updated_content
+                changed_content = True
+
+        if not save or not changed_content:
+            return instance
+
+        with transaction.atomic():
+            try:
+                instance.save(broadcast=False, update_fields=["content"])
+            except IntegrityError as e:
+                raise ActivitySerializerError(e)
+
+        return instance
+
 
 @dataclass(init=False)
 class Article(Note):

bookwyrm/migrations/0176_hashtag_support.py

@@ -0,0 +1,53 @@
+# Generated by Django 3.2.16 on 2022-12-17 19:28
+
+import bookwyrm.models.fields
+import django.contrib.postgres.fields.citext
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bookwyrm", "0174_auto_20230130_1240"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="Hashtag",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("created_date", models.DateTimeField(auto_now_add=True)),
+                ("updated_date", models.DateTimeField(auto_now=True)),
+                (
+                    "remote_id",
+                    bookwyrm.models.fields.RemoteIdField(
+                        max_length=255,
+                        null=True,
+                        validators=[bookwyrm.models.fields.validate_remote_id],
+                    ),
+                ),
+                (
+                    "name",
+                    django.contrib.postgres.fields.citext.CICharField(max_length=256),
+                ),
+            ],
+            options={
+                "abstract": False,
+            },
+        ),
+        migrations.AddField(
+            model_name="status",
+            name="mention_hashtags",
+            field=bookwyrm.models.fields.TagField(
+                related_name="mention_hashtag", to="bookwyrm.Hashtag"
+            ),
+        ),
+    ]

bookwyrm/models/__init__.py

@@ -34,6 +34,8 @@ from .antispam import EmailBlocklist, IPBlocklist, AutoMod, automod_task
 
 from .notification import Notification
 
+from .hashtag import Hashtag
+
 cls_members = inspect.getmembers(sys.modules[__name__], inspect.isclass)
 activity_models = {
     c[1].activity_serializer.__name__: c[1]

bookwyrm/models/fields.py

@@ -7,6 +7,7 @@ from urllib.parse import urljoin
 import dateutil.parser
 from dateutil.parser import ParserError
 from django.contrib.postgres.fields import ArrayField as DjangoArrayField
+from django.contrib.postgres.fields import CICharField as DjangoCICharField
 from django.core.exceptions import ValidationError
 from django.db import models
 from django.forms import ClearableFileInput, ImageField as DjangoImageField
@@ -388,6 +389,15 @@ class TagField(ManyToManyField):
             if tag_type != self.related_model.activity_serializer.type:
                 # tags can contain multiple types
                 continue
+
+            if tag_type == "Hashtag":
+                # we already have all data to create hashtags,
+                # no need to fetch from remote
+                item = self.related_model.activity_serializer(**link_json)
+                hashtag = item.to_model(model=self.related_model, save=True)
+                items.append(hashtag)
+            else:
+                # for other tag types we fetch them remotely
                 items.append(
                     activitypub.resolve_remote_id(
                         link.href,
@@ -546,6 +556,10 @@ class CharField(ActivitypubFieldMixin, models.CharField):
     """activitypub-aware char field"""
 
 
+class CICharField(ActivitypubFieldMixin, DjangoCICharField):
+    """activitypub-aware cichar field"""
+
+
 class URLField(ActivitypubFieldMixin, models.URLField):
     """activitypub-aware url field"""
 

bookwyrm/models/hashtag.py

@@ -0,0 +1,23 @@
+""" model for tags """
+from bookwyrm import activitypub
+from .activitypub_mixin import ActivitypubMixin
+from .base_model import BookWyrmModel
+from .fields import CICharField
+
+
+class Hashtag(ActivitypubMixin, BookWyrmModel):
+    "a hashtag which can be used in statuses"
+
+    name = CICharField(
+        max_length=256,
+        blank=False,
+        null=False,
+        activitypub_field="name",
+        deduplication_field=True,
+    )
+
+    name_field = "name"
+    activity_serializer = activitypub.Hashtag
+
+    def __repr__(self):
+        return f"<{self.__class__} id={self.id} name={self.name}>"

bookwyrm/models/status.py

@@ -34,6 +34,7 @@ class Status(OrderedCollectionPageMixin, BookWyrmModel):
     raw_content = models.TextField(blank=True, null=True)
     mention_users = fields.TagField("User", related_name="mention_user")
     mention_books = fields.TagField("Edition", related_name="mention_book")
+    mention_hashtags = fields.TagField("Hashtag", related_name="mention_hashtag")
     local = models.BooleanField(default=True)
     content_warning = fields.CharField(
         max_length=500, blank=True, null=True, activitypub_field="summary"

bookwyrm/templates/hashtag.html

@@ -0,0 +1,32 @@
+{% extends "layout.html" %}
+{% load i18n %}
+
+{% block title %}{{ hashtag }}{% endblock %}
+
+{% block content %}
+<div class="container is-max-desktop">
+    <section class="block">
+        <header class="block content has-text-centered">
+            <h1 class="title">{{ hashtag }}</h1>
+            <p class="subtitle">
+                {% blocktrans trimmed with site_name=site.name %}
+                See tagged statuses in the local {{ site_name }} community
+                {% endblocktrans %}
+            </p>
+        </header>
+
+        {% for activity in activities %}
+        <div class="block">
+            {% include 'snippets/status/status.html' with status=activity %}
+        </div>
+        {% endfor %}
+        {% if not activities %}
+        <div class="block">
+            <p>{% trans "No activities for this hashtag yet!" %}</p>
+        </div>
+        {% endif %}
+
+        {% include 'snippets/pagination.html' with page=activities path=path %}
+    </section>
+</div>
+{% endblock %}

bookwyrm/tests/activitypub/test_base_activity.py

@@ -183,12 +183,21 @@ class BaseActivity(TestCase):
                     "name": "gerald j. books",
                     "href": "http://book.com/book",
                 },
+                {
+                    "type": "Hashtag",
+                    "name": "#BookClub",
+                    "href": "http://example.com/tags/BookClub",
+                },
             ],
         )
         update_data.to_model(model=models.Status, instance=status)
         self.assertEqual(status.mention_users.first(), self.user)
         self.assertEqual(status.mention_books.first(), book)
 
+        hashtag = models.Hashtag.objects.filter(name="#BookClub").first()
+        self.assertIsNotNone(hashtag)
+        self.assertEqual(status.mention_hashtags.first(), hashtag)
+
     @responses.activate
     def test_to_model_one_to_many(self, *_):
         """these are reversed relationships, where the secondary object

bookwyrm/tests/activitypub/test_note.py

@@ -0,0 +1,64 @@
+""" tests functionality specifically for the Note ActivityPub dataclass"""
+from unittest.mock import patch
+
+from django.test import TestCase
+
+from bookwyrm import activitypub
+from bookwyrm import models
+
+
+class Note(TestCase):
+    """the model-linked ActivityPub dataclass for Note-based types"""
+
+    # pylint: disable=invalid-name
+    def setUp(self):
+        """create a shared user"""
+        with patch("bookwyrm.suggested_users.rerank_suggestions_task.delay"), patch(
+            "bookwyrm.activitystreams.populate_stream_task.delay"
+        ), patch("bookwyrm.lists_stream.populate_lists_task.delay"):
+            self.user = models.User.objects.create_user(
+                "mouse", "mouse@mouse.mouse", "mouseword", local=True, localname="mouse"
+            )
+        self.user.remote_id = "https://test-instance.org/user/critic"
+        self.user.save(broadcast=False, update_fields=["remote_id"])
+
+        self.book = models.Edition.objects.create(
+            title="Test Edition", remote_id="http://book.com/book"
+        )
+
+    def test_to_model_hashtag_postprocess_content(self):
+        """test that hashtag links are post-processed and link to local URLs"""
+        update_data = activitypub.Comment(
+            id="https://test-instance.org/user/critic/comment/42",
+            attributedTo=self.user.remote_id,
+            inReplyToBook=self.book.remote_id,
+            content="<p>This is interesting "
+            + '<a href="https://test-instance.org/hashtag/2" data-mention="hashtag">'
+            + "#bookclub</a></p>",
+            published="2023-02-17T23:12:59.398030+00:00",
+            to=[],
+            cc=[],
+            tag=[
+                {
+                    "type": "Edition",
+                    "name": "gerald j. books",
+                    "href": "http://book.com/book",
+                },
+                {
+                    "type": "Hashtag",
+                    "name": "#BookClub",
+                    "href": "https://test-instance.org/hashtag/2",
+                },
+            ],
+        )
+
+        instance = update_data.to_model(model=models.Status)
+        self.assertIsNotNone(instance)
+        hashtag = models.Hashtag.objects.filter(name="#BookClub").first()
+        self.assertIsNotNone(hashtag)
+        self.assertEqual(
+            instance.content,
+            "<p>This is interesting "
+            + f'<a href="{hashtag.remote_id}" data-mention="hashtag">'
+            + "#bookclub</a></p>",
+        )

bookwyrm/tests/models/test_status_model.py

@@ -265,7 +265,7 @@ class Status(TestCase):
         self.assertEqual(activity["attachment"][0]["type"], "Document")
         self.assertTrue(
             re.match(
-                r"https:\/\/your.domain.here\/images\/covers\/test_[A-z0-9]+.jpg",
+                r"https:\/\/your.domain.here\/images\/covers\/test(_[A-z0-9]+)?.jpg",
                 activity["attachment"][0]["url"],
             )
         )

bookwyrm/tests/views/test_hashtag.py

@@ -0,0 +1,197 @@
+""" tests for hashtag view """
+from unittest.mock import patch
+
+from django.contrib.auth.models import AnonymousUser
+from django.http import Http404
+from django.template.response import TemplateResponse
+from django.test import TestCase
+from django.test.client import RequestFactory
+
+from bookwyrm import models, views
+from bookwyrm.tests.validate_html import validate_html
+
+
+class HashtagView(TestCase):
+    """hashtag view"""
+
+    def setUp(self):
+        self.factory = RequestFactory()
+        with patch("bookwyrm.suggested_users.rerank_suggestions_task.delay"), patch(
+            "bookwyrm.activitystreams.populate_stream_task.delay"
+        ), patch("bookwyrm.lists_stream.populate_lists_task.delay"):
+            self.local_user = models.User.objects.create_user(
+                "mouse@local.com",
+                "mouse@mouse.com",
+                "mouseword",
+                local=True,
+                localname="mouse",
+                remote_id="https://example.com/users/mouse",
+            )
+            self.follower_user = models.User.objects.create_user(
+                "follower@local.com",
+                "follower@email.com",
+                "followerword",
+                local=True,
+                localname="follower",
+                remote_id="https://example.com/users/follower",
+            )
+            self.local_user.followers.add(self.follower_user)
+            self.other_user = models.User.objects.create_user(
+                "other@local.com",
+                "other@email.com",
+                "otherword",
+                local=True,
+                localname="other",
+                remote_id="https://example.com/users/other",
+            )
+
+        self.work = models.Work.objects.create(title="Test Work")
+        self.book = models.Edition.objects.create(
+            title="Example Edition",
+            remote_id="https://example.com/book/1",
+            parent_work=self.work,
+        )
+
+        self.hashtag_bookclub = models.Hashtag.objects.create(name="#BookClub")
+        with patch(
+            "bookwyrm.models.activitypub_mixin.broadcast_task.apply_async"
+        ), patch("bookwyrm.activitystreams.add_status_task.delay"):
+            self.statuses_bookclub = [
+                models.Comment.objects.create(
+                    book=self.book, user=self.local_user, content="#BookClub"
+                ),
+            ]
+        for status in self.statuses_bookclub:
+            status.mention_hashtags.add(self.hashtag_bookclub)
+
+        self.anonymous_user = AnonymousUser
+        self.anonymous_user.is_authenticated = False
+        models.SiteSettings.objects.create()
+
+    def test_hashtag_page(self):
+        """just make sure it loads"""
+        view = views.Hashtag.as_view()
+        request = self.factory.get("")
+        request.user = self.local_user
+
+        result = view(request, self.hashtag_bookclub.id)
+
+        self.assertIsInstance(result, TemplateResponse)
+        validate_html(result.render())
+        self.assertEqual(result.status_code, 200)
+        self.assertEqual(len(result.context_data["activities"]), 1)
+
+    def test_privacy_direct(self):
+        """ensure statuses with privacy set to direct are always filtered out"""
+        view = views.Hashtag.as_view()
+        request = self.factory.get("")
+
+        hashtag = models.Hashtag.objects.create(name="#test")
+        with patch(
+            "bookwyrm.models.activitypub_mixin.broadcast_task.apply_async"
+        ), patch("bookwyrm.activitystreams.add_status_task.delay"):
+            status = models.Comment.objects.create(
+                user=self.local_user, book=self.book, content="#test", privacy="direct"
+            )
+            status.mention_hashtags.add(hashtag)
+
+        for user in [
+            self.local_user,
+            self.follower_user,
+            self.other_user,
+            self.anonymous_user,
+        ]:
+            request.user = user
+            result = view(request, hashtag.id)
+            self.assertNotIn(status, result.context_data["activities"])
+
+    def test_privacy_unlisted(self):
+        """ensure statuses with privacy set to unlisted are always filtered out"""
+        view = views.Hashtag.as_view()
+        request = self.factory.get("")
+
+        hashtag = models.Hashtag.objects.create(name="#test")
+        with patch(
+            "bookwyrm.models.activitypub_mixin.broadcast_task.apply_async"
+        ), patch("bookwyrm.activitystreams.add_status_task.delay"):
+            status = models.Comment.objects.create(
+                user=self.local_user,
+                book=self.book,
+                content="#test",
+                privacy="unlisted",
+            )
+            status.mention_hashtags.add(hashtag)
+
+        for user in [
+            self.local_user,
+            self.follower_user,
+            self.other_user,
+            self.anonymous_user,
+        ]:
+            request.user = user
+            result = view(request, hashtag.id)
+            self.assertNotIn(status, result.context_data["activities"])
+
+    def test_privacy_following(self):
+        """ensure only creator and followers can see statuses with privacy
+        set to followers"""
+        view = views.Hashtag.as_view()
+        request = self.factory.get("")
+
+        hashtag = models.Hashtag.objects.create(name="#test")
+        with patch(
+            "bookwyrm.models.activitypub_mixin.broadcast_task.apply_async"
+        ), patch("bookwyrm.activitystreams.add_status_task.delay"):
+            status = models.Comment.objects.create(
+                user=self.local_user,
+                book=self.book,
+                content="#test",
+                privacy="followers",
+            )
+            status.mention_hashtags.add(hashtag)
+
+        for user in [self.local_user, self.follower_user]:
+            request.user = user
+            result = view(request, hashtag.id)
+            self.assertIn(status, result.context_data["activities"])
+
+        for user in [self.other_user, self.anonymous_user]:
+            request.user = user
+            result = view(request, hashtag.id)
+            self.assertNotIn(status, result.context_data["activities"])
+
+    def test_not_found(self):
+        """make sure 404 is rendered"""
+        view = views.Hashtag.as_view()
+        request = self.factory.get("")
+        request.user = self.local_user
+
+        with self.assertRaises(Http404):
+            view(request, 42)
+
+    def test_empty(self):
+        """hashtag without any statuses should still render"""
+        view = views.Hashtag.as_view()
+        request = self.factory.get("")
+        request.user = self.local_user
+
+        hashtag_empty = models.Hashtag.objects.create(name="#empty")
+        result = view(request, hashtag_empty.id)
+
+        self.assertIsInstance(result, TemplateResponse)
+        validate_html(result.render())
+        self.assertEqual(result.status_code, 200)
+        self.assertEqual(len(result.context_data["activities"]), 0)
+
+    def test_logged_out(self):
+        """make sure it loads all activities"""
+        view = views.Hashtag.as_view()
+        request = self.factory.get("")
+        request.user = self.anonymous_user
+
+        result = view(request, self.hashtag_bookclub.id)
+
+        self.assertIsInstance(result, TemplateResponse)
+        validate_html(result.render())
+        self.assertEqual(result.status_code, 200)
+        self.assertEqual(len(result.context_data["activities"]), 1)

bookwyrm/tests/views/test_status.py

@@ -6,7 +6,7 @@ from django.test import TestCase, TransactionTestCase
 from django.test.client import RequestFactory
 
 from bookwyrm import forms, models, views
-from bookwyrm.views.status import find_mentions
+from bookwyrm.views.status import find_mentions, find_or_create_hashtags
 from bookwyrm.settings import DOMAIN
 
 from bookwyrm.tests.validate_html import validate_html
@@ -95,6 +95,7 @@ class StatusViews(TestCase):
                 local=True,
                 localname="nutria",
             )
+            self.existing_hashtag = models.Hashtag.objects.create(name="#existing")
         with patch("bookwyrm.models.user.set_remote_server"):
             self.remote_user = models.User.objects.create_user(
                 "rat",
@@ -333,6 +334,71 @@ class StatusViews(TestCase):
             result = find_mentions(self.local_user, "@beep@beep.com")
             self.assertEqual(result, {})
 
+    def test_create_status_hashtags(self, *_):
+        """#mention a hashtag in a post"""
+        view = views.CreateStatus.as_view()
+        form = forms.CommentForm(
+            {
+                "content": "this is an #EXISTING hashtag but all uppercase, "
+                + "this one is #NewTag.",
+                "user": self.local_user.id,
+                "book": self.book.id,
+                "privacy": "public",
+            }
+        )
+        request = self.factory.post("", form.data)
+        request.user = self.local_user
+
+        view(request, "comment")
+        status = models.Status.objects.get()
+
+        hashtags = models.Hashtag.objects.all()
+        self.assertEqual(len(hashtags), 2)
+        self.assertEqual(list(status.mention_hashtags.all()), list(hashtags))
+
+        hashtag_exising = models.Hashtag.objects.filter(name="#existing").first()
+        hashtag_new = models.Hashtag.objects.filter(name="#NewTag").first()
+        self.assertEqual(
+            status.content,
+            "<p>this is an "
+            + f'<a href="{hashtag_exising.remote_id}" data-mention="hashtag">'
+            + "#EXISTING</a> hashtag but all uppercase, this one is "
+            + f'<a href="{hashtag_new.remote_id}" data-mention="hashtag">'
+            + "#NewTag</a>.</p>",
+        )
+
+    def test_find_or_create_hashtags(self, *_):
+        """detect and look up #hashtags"""
+        result = find_or_create_hashtags("no hashtag to be found here")
+        self.assertEqual(result, {})
+
+        result = find_or_create_hashtags("#existing")
+        self.assertEqual(result["#existing"], self.existing_hashtag)
+
+        result = find_or_create_hashtags("leading text #existing")
+        self.assertEqual(result["#existing"], self.existing_hashtag)
+
+        result = find_or_create_hashtags("leading #existing trailing")
+        self.assertEqual(result["#existing"], self.existing_hashtag)
+
+        self.assertIsNone(models.Hashtag.objects.filter(name="new").first())
+        result = find_or_create_hashtags("leading #new trailing")
+        new_hashtag = models.Hashtag.objects.filter(name="#new").first()
+        self.assertIsNotNone(new_hashtag)
+        self.assertEqual(result["#new"], new_hashtag)
+
+        result = find_or_create_hashtags("leading #existing #new trailing")
+        self.assertEqual(result["#existing"], self.existing_hashtag)
+        self.assertEqual(result["#new"], new_hashtag)
+
+        result = find_or_create_hashtags("#Braunbär")
+        hashtag = models.Hashtag.objects.filter(name="#Braunbär").first()
+        self.assertEqual(result["#Braunbär"], hashtag)
+
+        result = find_or_create_hashtags("#ひぐま")
+        hashtag = models.Hashtag.objects.filter(name="#ひぐま").first()
+        self.assertEqual(result["#ひぐま"], hashtag)
+
     def test_format_links_simple_url(self, *_):
         """find and format urls into a tags"""
         url = "http://www.fish.com/"

bookwyrm/urls.py

@@ -356,6 +356,15 @@ urlpatterns = [
         name="notifications",
     ),
     re_path(r"^directory/?", views.Directory.as_view(), name="directory"),
+    # hashtag
+    re_path(
+        r"^hashtag/(?P<hashtag_id>\d+)/?$", views.Hashtag.as_view(), name="hashtag"
+    ),
+    re_path(
+        rf"^hashtag/(?P<hashtag_id>\d+){regex.SLUG}/?$",
+        views.Hashtag.as_view(),
+        name="hashtag",
+    ),
     # Get started
     re_path(
         r"^get-started/profile/?$",

bookwyrm/utils/regex.py

@@ -7,5 +7,6 @@ USERNAME = rf"{LOCALNAME}(@{DOMAIN})?"
 STRICT_USERNAME = rf"(\B{STRICT_LOCALNAME}(@{DOMAIN})?\b)"
 FULL_USERNAME = rf"{LOCALNAME}@{DOMAIN}\b"
 SLUG = r"/s/(?P<slug>[-_a-z0-9]*)"
+HASHTAG = r"(#[^!@#$%^&*(),.?\":{}|<>\s]+)"
 # should match (BookWyrm/1.0.0; or (BookWyrm/99.1.2;
 BOOKWYRM_USER_AGENT = r"\(BookWyrm/[0-9]+\.[0-9]+\.[0-9]+;"

bookwyrm/utils/sanitizer.py

@@ -21,6 +21,6 @@ def clean(input_text):
             "ol",
             "li",
         ],
-        attributes=["href", "rel", "src", "alt"],
+        attributes=["href", "rel", "src", "alt", "data-mention"],
         strip=True,
     )

bookwyrm/views/__init__.py

@@ -130,6 +130,7 @@ from .group import (
     accept_membership,
     reject_membership,
 )
+from .hashtag import Hashtag
 from .inbox import Inbox
 from .interaction import Favorite, Unfavorite, Boost, Unboost
 from .isbn import Isbn

bookwyrm/views/hashtag.py

@@ -0,0 +1,54 @@
+""" listing statuses for a given hashtag """
+from django.core.paginator import Paginator
+from django.db.models import Q
+from django.views import View
+from django.shortcuts import get_object_or_404
+from django.template.response import TemplateResponse
+
+from bookwyrm import models
+from bookwyrm.settings import PAGE_LENGTH
+from bookwyrm.views.helpers import maybe_redirect_local_path
+
+
+# pylint: disable= no-self-use
+class Hashtag(View):
+    """listing statuses for a given hashtag"""
+
+    # pylint: disable=unused-argument
+    def get(self, request, hashtag_id, slug=None):
+        """show hashtag with related statuses"""
+        hashtag = get_object_or_404(models.Hashtag, id=hashtag_id)
+
+        if redirect_local_path := maybe_redirect_local_path(request, hashtag):
+            return redirect_local_path
+
+        activities = (
+            models.Status.privacy_filter(
+                request.user,
+            )
+            .filter(
+                Q(mention_hashtags=hashtag),
+            )
+            .exclude(
+                privacy__in=["direct", "unlisted"],
+            )
+            .select_related(
+                "user",
+                "reply_parent",
+                "review__book",
+                "comment__book",
+                "quotation__book",
+            )
+            .prefetch_related(
+                "mention_books",
+                "mention_users",
+                "attachments",
+            )
+        )
+        paginated = Paginator(activities, PAGE_LENGTH)
+
+        data = {
+            "hashtag": hashtag.name,
+            "activities": paginated.get_page(request.GET.get("page", 1)),
+        }
+        return TemplateResponse(request, "hashtag.html", data)

bookwyrm/views/status.py

@@ -115,6 +115,19 @@ class CreateStatus(View):
         if status.reply_parent:
             status.mention_users.add(status.reply_parent.user)
 
+        # inspect the text for hashtags
+        for (mention_text, mention_hashtag) in find_or_create_hashtags(content).items():
+            # add them to status mentions fk
+            status.mention_hashtags.add(mention_hashtag)
+
+            # turn the mention into a link
+            content = re.sub(
+                rf"{mention_text}\b(?!@)",
+                rf'<a href="{mention_hashtag.remote_id}" data-mention="hashtag">'
+                + rf"{mention_text}</a>",
+                content,
+            )
+
         # deduplicate mentions
         status.mention_users.set(set(status.mention_users.all()))
 
@@ -237,6 +250,38 @@ def find_mentions(user, content):
     return username_dict
 
 
+def find_or_create_hashtags(content):
+    """detect #hashtags in raw status content
+
+    it stores hashtags case-sensitive, but ensures that an existing
+    hashtag with different case are found and re-used. for example,
+    an existing #BookWyrm hashtag will be found and used even if the
+    status content is using #bookwyrm.
+    """
+    if not content:
+        return {}
+
+    found_hashtags = {t.lower(): t for t in re.findall(regex.HASHTAG, content)}
+    if len(found_hashtags) == 0:
+        return {}
+
+    known_hashtags = {
+        t.name.lower(): t
+        for t in models.Hashtag.objects.filter(
+            Q(name__in=found_hashtags.keys())
+        ).distinct()
+    }
+
+    not_found = found_hashtags.keys() - known_hashtags.keys()
+    for lower_name in not_found:
+        tag_name = found_hashtags[lower_name]
+        mention_hashtag = models.Hashtag(name=tag_name)
+        mention_hashtag.save()
+        known_hashtags[lower_name] = mention_hashtag
+
+    return {found_hashtags[k]: v for k, v in known_hashtags.items()}
+
+
 def format_links(content):
     """detect and format links"""
     validator = URLValidator()