Add /user_actions page.

Add a /user_actions page. This page shows you a global timeline of
(almost) all activity on the site, including uploads, comments, votes,
edits, forum posts, and so on.

The main things it doesn't include are post edits, pool edits, and
favorites (posts and pools live in a separate database, and favorites
don't have the timestamps we need for ordering).

This page is useful for moderation purposes because it lets you see a
history of almost all of a user's activity on a single page.

Currently this page is mod-only. In the future it will be open to all
users, so you can view the history of your own site activity, or the
activity of others.

app/models/user_action.rb

@@ -0,0 +1,122 @@
+# frozen_string_literal: true
+
+class UserAction < ApplicationRecord
+  belongs_to :model, polymorphic: true
+  belongs_to :user
+
+  attribute :model_type, :string
+  attribute :model_id, :integer
+  attribute :user_id, :integer
+  attribute :event_type, :string
+  attribute :event_at, :time
+
+  def self.model_types
+    %w[ArtistVersion ArtistCommentaryVersion Ban BulkUpdateRequest Comment
+    CommentVote Dmail FavoriteGroup ForumPost ForumPostVote ForumTopic
+    ModAction ModerationReport NoteVersion Post PostAppeal PostApproval
+    PostDisapproval PostFlag PostReplacement PostVote SavedSearch TagAlias
+    TagImplication TagVersion Upload User UserEvent UserFeedback UserUpgrade
+    UserNameChangeRequest WikiPageVersion]
+  end
+
+  def self.for_user(user)
+    sql = <<~SQL.squish
+      (#{ArtistVersion.visible(user).select("'ArtistVersion'::character varying AS model_type, id AS model_id, updater_id AS user_id, 'create'::character varying AS event_type, created_at AS event_at").to_sql})
+    UNION ALL
+      (#{ArtistCommentaryVersion.visible(user).select("'ArtistCommentaryVersion', id, updater_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{Ban.visible(user).select("'Ban', id, user_id, 'subject', created_at").to_sql})
+    UNION ALL
+      (#{BulkUpdateRequest.visible(user).select("'BulkUpdateRequest', id, user_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{Comment.visible(user).select("'Comment', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{CommentVote.visible(user).select("'CommentVote', id, user_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{Dmail.visible(user).sent.select("'Dmail', id, from_id, 'create', created_at").order(created_at: :desc).to_sql})
+    UNION ALL
+      (#{FavoriteGroup.visible(user).select("'FavoriteGroup', id, creator_id, 'create', created_at").order(created_at: :desc).to_sql})
+    UNION ALL
+      (#{ForumPost.visible(user).select("'ForumPost', id, creator_id, 'create', created_at").order(created_at: :desc).to_sql})
+    UNION ALL
+      (#{ForumPostVote.visible(user).select("'ForumPostVote', id, creator_id, 'create', created_at").order(created_at: :desc).to_sql})
+    UNION ALL
+      (#{ForumTopic.visible(user).select("'ForumTopic', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{ModAction.visible(user).select("'ModAction', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{ModerationReport.visible(user).select("'ModerationReport', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{NoteVersion.visible(user).select("'NoteVersion', id, updater_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{Post.visible(user).select("'Post', id, uploader_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{PostAppeal.visible(user).select("'PostAppeal', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{PostApproval.visible(user).select("'PostApproval', id, user_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{PostDisapproval.visible(user).select("'PostDisapproval', id, user_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{PostFlag.visible(user).select("'PostFlag', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{PostReplacement.visible(user).select("'PostReplacement', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{PostVote.visible(user).select("'PostVote', id, user_id, 'create', created_at").order(created_at: :desc).to_sql})
+    UNION ALL
+      (#{SavedSearch.visible(user).select("'SavedSearch', id, user_id, 'create', created_at").order(created_at: :desc).to_sql})
+    UNION ALL
+      (#{TagAlias.visible(user).select("'TagAlias', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{TagImplication.visible(user).select("'TagImplication', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{TagVersion.visible(user).select("'TagVersion', id, updater_id, 'create', created_at").where("updater_id IS NOT NULL").order(created_at: :desc).to_sql})
+    UNION ALL
+      (#{Upload.visible(user).select("'Upload', id, uploader_id, 'create', created_at").order(created_at: :desc).to_sql})
+    UNION ALL
+      (#{User.visible(user).select("'User', id, id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{UserEvent.visible(user).select("'UserEvent', id, user_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{UserFeedback.visible(user).select("'UserFeedback', id, creator_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{UserFeedback.visible(user).select("'UserFeedback', id, user_id, 'subject', created_at").to_sql})
+    UNION ALL (
+      (#{UserUpgrade.visible(user).select("'UserUpgrade', id, purchaser_id, 'create', created_at").where(status: [:complete, :refunded]).order(created_at: :desc).to_sql})
+    ) UNION ALL
+      (#{UserNameChangeRequest.visible(user).select("'UserNameChangeRequest', id, user_id, 'create', created_at").to_sql})
+    UNION ALL
+      (#{WikiPageVersion.visible(user).select("'WikiPageVersion', id, updater_id, 'create', created_at").to_sql})
+    SQL
+
+    from("(#{sql}) user_actions")
+  end
+
+  def self.visible(user)
+    all
+  end
+
+  def self.search(params)
+    q = search_attributes(params, :event_type, :user, :model)
+
+    case params[:order]
+    when "event_at_asc"
+      q = q.order(event_at: :asc, model_id: :asc)
+    else
+      q = q.apply_default_order(params)
+    end
+
+    q
+  end
+
+  def self.default_order
+    order(event_at: :desc, model_id: :desc)
+  end
+
+  def self.available_includes
+    [:user, :model]
+  end
+
+  def readonly?
+    true
+  end
+end