Adds journal creation to migration.

db/migrate/20130823113842_migrate_legacy_journals.rb

@@ -1,8 +1,101 @@
 class MigrateLegacyJournals < ActiveRecord::Migration
 
+  class AmbiguousJournalsError < ::StandardError
+  end
+
   class IncompleteJournalsError < ::StandardError
   end
 
+  def up
+    check_assumptions
+
+    fetch_legacy_journals.each do |journal|
+
+      # turn id fields into integers.
+      ["id", "journaled_id", "user_id", "version"].each do |f|
+        journal[f] = journal[f].to_i
+      end
+
+      journal["changed_data"] = YAML.load(journal["changed_data"])
+
+      get_journal journal["journaled_id"],
+                  journal["type"],
+                  journal["version"]
+    end
+
+    binding.pry
+
+  end
+
+  def down
+  end
+
+  private
+
+  # gets a journal, and makes sure it has a valid id in the database.
+  def get_journal(id, type, version)
+    journal = fetch_journal(id, type, version)
+
+    if journal.size > 1
+
+      raise AmbiguousJournalsError, <<-MESSAGE.split("\n").map(&:strip!).join(" ") + "\n"
+        It appears there are ambiguous journals. Please make sure
+        journals are consistent and that the unique constraing on id,
+        type and version is met.
+      MESSAGE
+
+    elsif journal.size == 0
+
+      execute <<-SQL
+        INSERT INTO journals(journable_id, journable_type, version, created_at)
+        VALUES (
+          #{quote_value(id)},
+          #{quote_value(type)},
+          #{quote_value(version)},
+          #{quote_value(Time.now)}
+        )
+      SQL
+    end
+
+    journal || fetch_journal(id, type, version)
+  end
+
+  # fetches legacy journals. might me empty.
+  def fetch_legacy_journals
+    ActiveRecord::Base.connection.select_all <<-SQL
+      SELECT *
+      FROM #{quoted_legacy_journals_table_name} AS j
+      ORDER BY j.journaled_id, j.activity_type, j.version
+    SQL
+  end
+
+  # fetches specific journal. might be empty.
+  def fetch_journal(id, type, version)
+    ActiveRecord::Base.connection.select_all <<-SQL
+      SELECT *
+      FROM #{quoted_journals_table_name} AS j
+      WHERE j.journable_id = #{quote_value(id)}
+        AND j.journable_type = #{quote_value(type)}
+        AND j.version = #{quote_value(version)}
+    SQL
+  end
+
+  def quote_value name
+    ActiveRecord::Base.connection.quote name
+  end
+
+  def quoted_table_name name
+    ActiveRecord::Base.connection.quote_table_name name
+  end
+
+  def quoted_legacy_journals_table_name
+    @@quoted_legacy_journals_table_name ||= quote_table_name 'legacy_journals'
+  end
+
+  def quoted_journals_table_name
+    @@quoted_journals_table_name ||= quote_table_name 'journals'
+  end
+
   def check_assumptions
 
     invalid_journals = ActiveRecord::Base.connection.select_values <<-SQL
@@ -36,16 +129,4 @@ class MigrateLegacyJournals < ActiveRecord::Migration
     end
   end
 
-  def up
-    check_assumptions
-    binding.pry
-  end
-
-  def down
-  end
-
-  def quoted_legacy_journals_table_name
-    ActiveRecord::Base.connection.quote_table_name('legacy_journals')
-  end
-
 end