# frozen_string_literal: true

module Gitlab
  module Database
    module Partitioning
      class PartitionManager
        UnsafeToDetachPartitionError = Class.new(StandardError)

        LEASE_TIMEOUT = 1.minute
        MANAGEMENT_LEASE_KEY = 'database_partition_management_%s'
        RETAIN_DETACHED_PARTITIONS_FOR = 1.week

        def initialize(model, connection: nil)
          @model = model
          @connection = connection || model.connection
          @connection_name = @connection.pool.db_config.name
        end

        def sync_partitions
          return skip_synching_partitions unless table_partitioned?

          Gitlab::AppLogger.info(
            message: "Checking state of dynamic postgres partitions",
            table_name: model.table_name,
            connection_name: @connection_name
          )

          only_with_exclusive_lease(model, lease_key: MANAGEMENT_LEASE_KEY) do
            model.partitioning_strategy.validate_and_fix

            partitions_to_create = missing_partitions
            partitions_to_detach = extra_partitions

            create(partitions_to_create) unless partitions_to_create.empty?
            detach(partitions_to_detach) unless partitions_to_detach.empty?
          end
        rescue StandardError => e
          Gitlab::AppLogger.error(
            message: "Failed to create / detach partition(s)",
            table_name: model.table_name,
            exception_class: e.class,
            exception_message: e.message,
            connection_name: @connection_name
          )
        end

        private

        attr_reader :model, :connection

        def missing_partitions
          return [] unless connection.table_exists?(model.table_name)

          model.partitioning_strategy.missing_partitions
        end

        def extra_partitions
          return [] unless connection.table_exists?(model.table_name)

          model.partitioning_strategy.extra_partitions
        end

        def only_with_exclusive_lease(model, lease_key:)
          lease = Gitlab::ExclusiveLease.new(lease_key % model.table_name, timeout: LEASE_TIMEOUT)

          yield if lease.try_obtain
        ensure
          lease&.cancel
        end

        def create(partitions)
          # with_lock_retries starts a requires_new transaction most of the time, but not on the last iteration
          with_lock_retries do
            connection.transaction(requires_new: false) do # so we open a transaction here if not already in progress
              # Partitions might not get created (IF NOT EXISTS) so explicit locking will not happen.
              # This LOCK TABLE ensures to have exclusive lock as the first step.
              connection.execute "LOCK TABLE #{connection.quote_table_name(model.table_name)} IN ACCESS EXCLUSIVE MODE"

              partitions.each do |partition|
                connection.execute partition.to_sql

                Gitlab::AppLogger.info(message: "Created partition",
                                       partition_name: partition.partition_name,
                                       table_name: partition.table)
              end

              model.partitioning_strategy.after_adding_partitions
            end
          end
        end

        def detach(partitions)
          # with_lock_retries starts a requires_new transaction most of the time, but not on the last iteration
          with_lock_retries do
            connection.transaction(requires_new: false) do # so we open a transaction here if not already in progress
              partitions.each { |p| detach_one_partition(p) }
            end
          end
        end

        def detach_one_partition(partition)
          assert_partition_detachable!(partition)

          connection.execute partition.to_detach_sql

          Postgresql::DetachedPartition.create!(table_name: partition.partition_name,
                                                drop_after: RETAIN_DETACHED_PARTITIONS_FOR.from_now)

          Gitlab::AppLogger.info(
            message: "Detached Partition",
            partition_name: partition.partition_name,
            table_name: partition.table,
            connection_name: @connection_name
          )
        end

        def assert_partition_detachable!(partition)
          parent_table_identifier = "#{connection.current_schema}.#{partition.table}"

          if (example_fk = PostgresForeignKey.by_referenced_table_identifier(parent_table_identifier).first)
            raise UnsafeToDetachPartitionError, "Cannot detach #{partition.partition_name}, it would block while " \
              "checking foreign key #{example_fk.name} on #{example_fk.constrained_table_identifier}"
          end
        end

        def with_lock_retries(&block)
          Gitlab::Database::WithLockRetries.new(
            klass: self.class,
            logger: Gitlab::AppLogger,
            connection: connection
          ).run(&block)
        end

        def table_partitioned?
          Gitlab::Database::SharedModel.using_connection(connection) do
            Gitlab::Database::PostgresPartitionedTable.find_by_name_in_current_schema(model.table_name).present?
          end
        end

        def skip_synching_partitions
          Gitlab::AppLogger.warn(
            message: "Skipping synching partitions",
            table_name: model.table_name,
            connection_name: @connection_name
          )
        end
      end
    end
  end
end