Add NodeAction: an append-only log of who did what to a nodeHEADmaster

node_id/page_id/user_id are lookup and ordering only -- all three
nullify on delete, so an entry outlives its actor and its subject.
Everything that must survive those deletions lives in a mandatory
metadata jsonb written once at creation: the actor's username, the
node's human-readable name (pinned to the default locale), and
action-specific extras such as publish's title from/to.

NodeAction.record! is the single constructor, so every entry gets
the same baseline metadata without each call site re-implementing
it. occurred_at is one field for live and backfilled entries alike;
inferred_from distinguishes them -- nil means witnessed at the
moment it happened, populated names how a backfilled entry was
estimated.

Instrumented so far: publish (crediting the actual publisher,
threaded through from the controller -- previously nobody had the
act of publishing recorded anywhere), revert's discard_autosave and
destroy_draft branches, and translation destroy. publish_draft! now
runs in a transaction so the promotion and its log entry land
together. The remaining verbs follow once this mechanism has proven
itself.

2 files changed, 70 insertions, 28 deletions

diff --git a/app/models/node.rb b/app/models/node.rb
index 311c5c0..b41df06 100644
--- a/app/models/node.rb
+++ b/app/models/node.rb
@@ -170,10 +170,12 @@ class Node < ApplicationRecord
       self.autosave.destroy
       self.autosave_id = nil
       self.save!
+      NodeAction.record!(:node => self, :user => current_user, :action => "discard_autosave")
     elsif self.draft && self.head
       self.draft.destroy
       self.draft_id = nil
       self.save!
+      NodeAction.record!(:node => self, :user => current_user, :action => "destroy_draft")
     end
 
     self.unlock! unless self.draft
@@ -188,43 +190,50 @@ class Node < ApplicationRecord
     end
   end
 
-  def publish_draft!
+  def publish_draft! current_user = nil
     # Return nil if nothing to publish and no staged changes
     return nil unless self.draft || staged_slug || staged_parent_id
 
-    if self.draft
-      self.head = self.draft
-      self.head.published_at ||= Time.now
-      self.head.save!
-      self.draft = nil
-    end
-
-    if staged_slug && (staged_slug != slug)
-      self.slug = staged_slug
-      self.staged_slug = nil
-    end
+    ActiveRecord::Base.transaction do
+      if self.draft
+        previous_title = self.head ? Globalize.with_locale(I18n.default_locale) { self.head.title } : nil
+        self.head = self.draft
+        self.head.published_at ||= Time.now
+        self.head.save!
+        self.draft = nil
 
-    if staged_parent_id && (staged_parent_id != parent_id)
-      new_parent = Node.find(staged_parent_id)
+        new_title = Globalize.with_locale(I18n.default_locale) { self.head.title }
+        NodeAction.record!(:node => self, :page => self.head, :user => current_user,
+                            :action => "publish", :from => previous_title, :to => new_title)
+      end
 
-      if new_parent == self || self.descendants.include?(new_parent)
-        raise ActiveRecord::RecordInvalid.new(self), "Cannot move a node under itself or one of its own descendants"
+      if staged_slug && (staged_slug != slug)
+        self.slug = staged_slug
+        self.staged_slug = nil
       end
 
-      self.staged_parent_id = nil
-      self.save!
-      self.move_to_child_of(new_parent)
-    else
-      unless self.save
-        raise ActiveRecord::RecordInvalid.new(self)
+      if staged_parent_id && (staged_parent_id != parent_id)
+        new_parent = Node.find(staged_parent_id)
+
+        if new_parent == self || self.descendants.include?(new_parent)
+          raise ActiveRecord::RecordInvalid.new(self), "Cannot move a node under itself or one of its own descendants"
+        end
+
+        self.staged_parent_id = nil
+        self.save!
+        self.move_to_child_of(new_parent)
+      else
+        unless self.save
+          raise ActiveRecord::RecordInvalid.new(self)
+        end
       end
-    end
 
-    self.reload
-    self.update_unique_name
-    self.send(:update_unique_names_of_children)
-    self.unlock!
-    self
+      self.reload
+      self.update_unique_name
+      self.send(:update_unique_names_of_children)
+      self.unlock!
+      self
+    end
   end
 
   def restore_revision! revision
diff --git a/app/models/node_action.rb b/app/models/node_action.rb
new file mode 100644
index 0000000..f32b5b7
--- /dev/null
+++ b/app/models/node_action.rb
@@ -0,0 +1,33 @@
+class NodeAction < ApplicationRecord
+  belongs_to :node, optional: true
+  belongs_to :page, optional: true
+  belongs_to :user, optional: true
+
+  validates :action, presence: true
+  validates :occurred_at, presence: true
+
+  def self.record!(node:, action:, user: nil, page: nil, locale: nil, **extra)
+    create!(
+      :node        => node,
+      :page        => page,
+      :user        => user,
+      :action      => action,
+      :locale      => locale,
+      :occurred_at => Time.now,
+      :metadata    => {
+        "username"                 => user&.login,
+        "human_readable_node_name" => Globalize.with_locale(I18n.default_locale) {
+                                        node&.head&.title || node&.draft&.title
+                                      },
+      }.merge(extra.stringify_keys)
+   )
+  end
+
+  def actor_name
+    metadata["username"] || "unknown"
+  end
+
+  def subject_name
+    metadata["human_readable_node_name"] || node&.unique_name || "deleted node"
+  end
+end