module ChronoModel
  class Adapter < ActiveRecord::ConnectionAdapters::PostgreSQLAdapter

    module Upgrade
      private
        def chrono_upgrade!
          chrono_ensure_schemas

          chrono_upgrade_structure!
        end

        # Locate tables needing a structure upgrade
        #
        def chrono_tables_needing_upgrade
          tables = { }

          on_temporal_schema { self.tables }.each do |table_name|
            next unless is_chrono?(table_name)
            metadata = chrono_metadata_for(table_name)
            version = metadata['chronomodel']

            if version.blank?
              tables[table_name] = { version: nil, priority: 'CRITICAL' }
            elsif version != VERSION
              tables[table_name] = { version: version, priority: 'LOW' }
            end
          end

          return tables
        end

        # Emit a warning about tables needing an upgrade
        #
        def chrono_upgrade_warning
          upgrade = chrono_tables_needing_upgrade.map do |table, desc|
            "#{table} - priority: #{desc[:priority]}"
          end.join('; ')

          return if upgrade.empty?

          logger.warn "ChronoModel: There are tables needing a structure upgrade, and ChronoModel structures need to be recreated."
          logger.warn "ChronoModel: Please run ChronoModel.upgrade! to attempt the upgrade. If you have dependant database objects"
          logger.warn "ChronoModel: the upgrade will fail and you have to drop the dependent objects, run .upgrade! and create them"
          logger.warn "ChronoModel: again. Sorry. Some features or the whole library may not work correctly until upgrade is complete."
          logger.warn "ChronoModel: Tables pending upgrade: #{upgrade}"
        end

        # Upgrades existing structure for each table, if required.
        #
        def chrono_upgrade_structure!
          transaction do

            chrono_tables_needing_upgrade.each do |table_name, desc|

              if desc[:version].blank?
                logger.info "ChronoModel: Upgrading legacy PG 9.0 table #{table_name} to #{VERSION}"
                chrono_upgrade_from_postgres_9_0(table_name)
                logger.info "ChronoModel: legacy #{table_name} upgrade complete"
              else
                logger.info "ChronoModel: upgrading #{table_name} from #{desc[:version]} to #{VERSION}"
                chrono_create_view_for(table_name)
                logger.info "ChronoModel: #{table_name} upgrade complete"
              end

            end
          end
        rescue => e
          message = "ChronoModel structure upgrade failed: #{e.message}. Please drop dependent objects first and then run ChronoModel.upgrade! again."

          # Quite important, output it also to stderr.
          #
          logger.error message
          $stderr.puts message
        end

        def chrono_upgrade_from_postgres_9_0(table_name)
          # roses are red
          # violets are blue
          # and this is the most boring piece of code ever
          history_table = "#{HISTORY_SCHEMA}.#{table_name}"
          p_pkey = primary_key(table_name)

          execute "ALTER TABLE #{history_table} ADD COLUMN validity tsrange;"
          execute """
              UPDATE #{history_table} SET validity = tsrange(valid_from,
                CASE WHEN extract(year from valid_to) = 9999 THEN NULL
                     ELSE valid_to
                END
              );
          """

          execute "DROP INDEX #{history_table}_temporal_on_valid_from;"
          execute "DROP INDEX #{history_table}_temporal_on_valid_from_and_valid_to;"
          execute "DROP INDEX #{history_table}_temporal_on_valid_to;"
          execute "DROP INDEX #{history_table}_inherit_pkey"
          execute "DROP INDEX #{history_table}_recorded_at"
          execute "DROP INDEX #{history_table}_instance_history"
          execute "ALTER TABLE #{history_table} DROP CONSTRAINT #{table_name}_valid_from_before_valid_to;"
          execute "ALTER TABLE #{history_table} DROP CONSTRAINT #{table_name}_timeline_consistency;"
          execute "DROP RULE #{table_name}_upd_first ON #{table_name};"
          execute "DROP RULE #{table_name}_upd_next ON #{table_name};"
          execute "DROP RULE #{table_name}_del ON #{table_name};"
          execute "DROP RULE #{table_name}_ins ON #{table_name};"
          execute "DROP TRIGGER history_ins ON #{TEMPORAL_SCHEMA}.#{table_name};"
          execute "DROP FUNCTION #{TEMPORAL_SCHEMA}.#{table_name}_ins();"
          execute "ALTER TABLE #{history_table} DROP COLUMN valid_from;"
          execute "ALTER TABLE #{history_table} DROP COLUMN valid_to;"

          execute "CREATE EXTENSION IF NOT EXISTS btree_gist;"

          chrono_create_view_for(table_name)
          on_history_schema { add_history_validity_constraint(table_name, p_pkey) }
          on_history_schema { chrono_create_history_indexes_for(table_name, p_pkey) }
        end
      # private
    end

  end

end