Add announcements (#12662)

* Add announcements

Fix #11006

* Add reactions to announcements

* Add admin UI for announcements

* Add unit tests

* Fix issues

- Add `with_dismissed` param to announcements API
- Fix end date not being formatted when time range is given
- Fix announcement delete causing reactions to send streaming updates
- Fix announcements container growing too wide and mascot too small
- Fix `all_day` being settable when no time range is given
- Change text "Update" to "Announcement"

* Fix scheduler unpublishing announcements before they are due

* Fix filter params not being passed to announcements filter

app/controllers/admin/announcements_controller.rb

@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+class Admin::AnnouncementsController < Admin::BaseController
+  before_action :set_announcements, only: :index
+  before_action :set_announcement, except: [:index, :new, :create]
+
+  def index
+    authorize :announcement, :index?
+  end
+
+  def new
+    authorize :announcement, :create?
+
+    @announcement = Announcement.new
+  end
+
+  def create
+    authorize :announcement, :create?
+
+    @announcement = Announcement.new(resource_params)
+
+    if @announcement.save
+      log_action :create, @announcement
+      redirect_to admin_announcements_path
+    else
+      render :new
+    end
+  end
+
+  def edit
+    authorize :announcement, :update?
+  end
+
+  def update
+    authorize :announcement, :update?
+
+    if @announcement.update(resource_params)
+      log_action :update, @announcement
+      redirect_to admin_announcements_path
+    else
+      render :edit
+    end
+  end
+
+  def destroy
+    authorize :announcement, :destroy?
+    @announcement.destroy!
+    log_action :destroy, @announcement
+    redirect_to admin_announcements_path
+  end
+
+  private
+
+  def set_announcements
+    @announcements = AnnouncementFilter.new(filter_params).results.page(params[:page])
+  end
+
+  def set_announcement
+    @announcement = Announcement.find(params[:id])
+  end
+
+  def filter_params
+    params.slice(*AnnouncementFilter::KEYS).permit(*AnnouncementFilter::KEYS)
+  end
+
+  def resource_params
+    params.require(:announcement).permit(:text, :scheduled_at, :starts_at, :ends_at, :all_day)
+  end
+end