Revamp post filtering system (#18058)

* Add model for custom filter keywords

* Use CustomFilterKeyword internally

Does not change the API

* Fix /filters/edit and /filters/new

* Add migration tests

* Remove whole_word column from custom_filters (covered by custom_filter_keywords)

* Redesign /filters

Instead of a list, present a card that displays more information and handles
multiple keywords per filter.

* Redesign /filters/new and /filters/edit to add and remove keywords

This adds a new gem dependency: cocoon, as well as a npm dependency:
cocoon-js-vanilla. Those are used to easily populate and remove form fields
from the user interface when manipulating multiple keyword filters at once.

* Add /api/v2/filters to edit filter with multiple keywords

Entities:
- `Filter`: `id`, `title`, `filter_action` (either `hide` or `warn`), `context`
  `keywords`
- `FilterKeyword`: `id`, `keyword`, `whole_word`

API endpoits:
- `GET /api/v2/filters` to list filters (including keywords)
- `POST /api/v2/filters` to create a new filter
  `keywords_attributes` can also be passed to create keywords in one request
- `GET /api/v2/filters/:id` to read a particular filter
- `PUT /api/v2/filters/:id` to update a new filter
  `keywords_attributes` can also be passed to edit, delete or add keywords in
   one request
- `DELETE /api/v2/filters/:id` to delete a particular filter
- `GET /api/v2/filters/:id/keywords` to list keywords for a filter
- `POST /api/v2/filters/:filter_id/keywords/:id` to add a new keyword to a
   filter
- `GET /api/v2/filter_keywords/:id` to read a particular keyword
- `PUT /api/v2/filter_keywords/:id` to edit a particular keyword
- `DELETE /api/v2/filter_keywords/:id` to delete a particular keyword

* Change from `irreversible` boolean to `action` enum

* Remove irrelevent `irreversible_must_be_within_context` check

* Fix /filters/new and /filters/edit with update for filter_action

* Fix Rubocop/Codeclimate complaining about task names

* Refactor FeedManager#phrase_filtered?

This moves regexp building and filter caching to the `CustomFilter` class.

This does not change the functional behavior yet, but this changes how the
cache is built, doing per-custom_filter regexps so that filters can be matched
independently, while still offering caching.

* Perform server-side filtering and output result in REST API

* Fix numerous filters_changed events being sent when editing multiple keywords at once

* Add some tests

* Use the new API in the WebUI

- use client-side logic for filters we have fetched rules for.
  This is so that filter changes can be retroactively applied without
  reloading the UI.
- use server-side logic for filters we haven't fetched rules for yet
  (e.g. network error, or initial timeline loading)

* Minor optimizations and refactoring

* Perform server-side filtering on the streaming server

* Change the wording of filter action labels

* Fix issues pointed out by linter

* Change design of “Show anyway” link in accordence to review comments

* Drop “irreversible” filtering behavior

* Move /api/v2/filter_keywords to /api/v1/filters/keywords

* Rename `filter_results` attribute to `filtered`

* Rename REST::LegacyFilterSerializer to REST::V1::FilterSerializer

* Fix systemChannelId value in streaming server

* Simplify code by removing client-side filtering code

The simplifcation comes at a cost though: filters aren't retroactively
applied anymore.

3 files changed, 67 insertions, 0 deletions

diff --git a/db/migrate/20220613110628_create_custom_filter_keywords.rb b/db/migrate/20220613110628_create_custom_filter_keywords.rb
new file mode 100644
index 000000000..353fc334f
--- /dev/null
+++ b/db/migrate/20220613110628_create_custom_filter_keywords.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class CreateCustomFilterKeywords < ActiveRecord::Migration[6.1]
+  def change
+    create_table :custom_filter_keywords do |t|
+      t.belongs_to :custom_filter, foreign_key: { on_delete: :cascade }, null: false
+      t.text :keyword, null: false, default: ''
+      t.boolean :whole_word, null: false, default: true
+
+      t.timestamps
+    end
+  end
+end
diff --git a/db/migrate/20220613110711_migrate_custom_filters.rb b/db/migrate/20220613110711_migrate_custom_filters.rb
new file mode 100644
index 000000000..ea6a9b8c6
--- /dev/null
+++ b/db/migrate/20220613110711_migrate_custom_filters.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+class MigrateCustomFilters < ActiveRecord::Migration[6.1]
+  def up
+    # Preserve IDs as much as possible to not confuse existing clients.
+    # As long as this migration is irreversible, we do not have to deal with conflicts.
+    safety_assured do
+      execute <<-SQL.squish
+        INSERT INTO custom_filter_keywords (id, custom_filter_id, keyword, whole_word, created_at, updated_at)
+        SELECT id, id, phrase, whole_word, created_at, updated_at
+        FROM custom_filters
+      SQL
+    end
+  end
+
+  def down
+    # Copy back changes from custom filters guaranteed to be from the old API
+    safety_assured do
+      execute <<-SQL.squish
+        UPDATE custom_filters
+        SET phrase = custom_filter_keywords.keyword, whole_word = custom_filter_keywords.whole_word
+        FROM custom_filter_keywords
+        WHERE custom_filters.id = custom_filter_keywords.id AND custom_filters.id = custom_filter_keywords.custom_filter_id
+      SQL
+    end
+
+    # Drop every keyword as we can't safely provide a 1:1 mapping
+    safety_assured do
+      execute <<-SQL.squish
+        TRUNCATE custom_filter_keywords RESTART IDENTITY
+      SQL
+    end
+  end
+end
diff --git a/db/migrate/20220613110834_add_action_to_custom_filters.rb b/db/migrate/20220613110834_add_action_to_custom_filters.rb
new file mode 100644
index 000000000..9427a66fc
--- /dev/null
+++ b/db/migrate/20220613110834_add_action_to_custom_filters.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+require Rails.root.join('lib', 'mastodon', 'migration_helpers')
+
+class AddActionToCustomFilters < ActiveRecord::Migration[6.1]
+  include Mastodon::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def up
+    safety_assured do
+      add_column_with_default :custom_filters, :action, :integer, allow_null: false, default: 0
+      execute 'UPDATE custom_filters SET action = 1 WHERE irreversible IS TRUE'
+    end
+  end
+
+  def down
+    execute 'UPDATE custom_filters SET irreversible = (action = 1)'
+    remove_column :custom_filters, :action
+  end
+end