Restore deleted data journals with a migration

Restoring the predecessor's information, or the work package's
information, depending on where the journal version is at.

app/models/journal.rb

@@ -101,6 +101,14 @@ class Journal < ApplicationRecord
     predecessor
   end
 
+  def successor
+    @successor ||= self.class
+                       .where(journable_type:, journable_id:)
+                       .where("#{self.class.table_name}.version > ?", version)
+                       .order(version: :asc)
+                       .first
+  end
+
   def noop?
     (!notes || notes&.empty?) && get_changes.empty?
   end

db/migrate/20220818074159_fix_deleted_data_journals.rb

@@ -0,0 +1,107 @@
+class FixDeletedDataJournals < ActiveRecord::Migration[7.0]
+  def up
+    get_missing_journals.each do |journable_type, relation|
+      puts "Cleaning up journals on #{journable_type}"
+
+      relation.find_each { |journal| fix_journal_data(journal) }
+
+      count = relation.count
+      raise "There shouldn't be any missing data left for #{journable_type}, but found #{count}" if count > 0
+    end
+  end
+
+  def down
+    # nothing to do
+  end
+
+  def fix_journal_data(journal)
+    # Best case, no successor
+    # restore data from work package itself
+    if journal.successor.nil?
+      raise "Previous also has data nil" if (journal.previous && journal.previous.data.nil?)
+      insert_journal_data(journal, journal.previous, write_message: false)
+    elsif predecessor = journal.previous
+      # Case 2, we do have a predecessor
+      take_over_from_predecessor(journal, predecessor)
+    elsif journal.successor
+      # Case 3, We are the first, but have a successor
+      # Look for data in the successor
+      take_over_from_successor(journal, journal.successor)
+    else
+      raise "This should not happen for #{journal.inspect}"
+    end
+  end
+
+  def insert_journal_data(journal, predecessor, write_message: false)
+    service = Journals::CreateService.new(journal.journable, User.system)
+    insert_sql = service.instance_eval { insert_data_sql('placeholder', predecessor) }
+
+    result = Journal.connection.uncached do
+      ::Journal
+        .connection
+        .select_one(insert_sql)
+
+    end
+
+    raise "ID is missing #{result.inspect}" unless result['id']
+
+    if write_message
+      update_with_new_data!(journal, result['id'])
+    else
+      journal.update_column(:data_id, result['id'])
+    end
+  end
+
+  def get_missing_journals
+    Journal
+      .pluck('DISTINCT(journable_type)')
+      .to_h do |journable_type|
+      journable_type = 'WorkPackage'
+      journal_class = journable_type.constantize.journal_class
+      table_name = journal_class.table_name
+
+      relation = Journal
+        .joins("LEFT OUTER JOIN #{table_name} ON journals.data_type = '#{journal_class.to_s}' AND #{table_name}.id = journals.data_id")
+        .where("#{table_name}.id IS NULL")
+        .where(journable_type: journable_type)
+        .where.not(data_type: nil) # Ignore special tenants with data_type nil errors
+        .order('journals.version ASC')
+        .includes(:journable)
+
+      [journable_type, relation]
+    end
+  end
+
+  def take_over_from_predecessor(journal, predecessor)
+    raise "Related journal does not have data, this shouldn't be!" if predecessor.data.nil?
+    new_data = predecessor.data.dup
+    new_data.save!
+
+    update_with_new_data!(journal, new_data.id)
+  end
+
+  def take_over_from_successor(journal, successor)
+    # The successor itself may also have its data deleted.
+    # in this case, look for the first journal with data, or insert
+    new_data =
+      if successor.data.nil?
+        first_journal_with_data = journal.journable.journals.detect { |j| j.data.present? }
+        return insert_journal_data(journal, journal.previous, write_message: true) if first_journal_with_data.nil?
+
+        first_journal_with_data.data.dup
+      else
+        successor.data.dup
+      end
+
+    new_data.save!
+    update_with_new_data!(journal, new_data.id)
+  end
+
+  def update_with_new_data!(journal, data_id)
+    notes = journal.notes
+    notes << "\n" unless notes.empty?
+    notes << "_(This activity had to be modified by the system and may be missing some changes or contain changes from previous or following activities.)_"
+
+    journal.update_columns(notes:, data_id: data_id)
+  end
+end