module MixedGauge
  # Offers database related Rake tasks
  module DatabaseTasks
    class << self
      # @return [Boolean]
      def ar5?
        ActiveRecord::VERSION::MAJOR == 5
      end

      # @return [Boolean]
      def ar4?
        ActiveRecord::VERSION::MAJOR == 4
      end

      # @return [Boolean]
      def ar42?
        ar4? && ActiveRecord::VERSION::MINOR == 2
      end

      # @return [Boolean]
      def ar41?
        ar4? && ActiveRecord::VERSION::MINOR == 1
      end

      # @return [Boolean]
      def ar417_above?
        ar41? && ActiveRecord::VERSION::TINY > 7
      end

      # Show information of database sharding config.
      def info
        puts 'All clusters registered to mixed_gauge'
        puts
        clusters.each do |cluster|
          puts "= Cluster: #{cluster.name} ="
          cluster.connections.each do |name|
            puts "- #{name}"
          end
          puts
        end
      end

      # @private
      # @param [String] task_name
      # @return [Rake::Task]
      def to_rake_task(task_name)
        Rake::Task[task_name]
      end

      # @private
      # @return [Array<Symbol>]
      def cluster_names
        MixedGauge.config.cluster_configs.keys
      end

      # @private
      # @return [Array<MixedGauge::ClusterConfig>]
      def clusters
        MixedGauge.config.cluster_configs.values
      end

      # @private
      # @return [MixedGauge::ClusterConfig]
      # @raise [KeyError]
      def fetch_cluster_config(cluster_name)
        MixedGauge.config.fetch_cluster_config(cluster_name)
      end

      # For mock-ablity
      # @private
      def exit_with_error
        exit 1
      end
    end

    # TasksForMultipleClusters
    module TasksForMultipleClusters
      # @param [String] task_name
      def invoke_task_for_all_clusters(task_name)
        cluster_names.each do |cluster_name|
          invoke_task(task_name, cluster_name)
        end
      end

      # @private
      # @param [String] name
      # @param [Symbol] cluster_name
      def invoke_task(name, cluster_name)
        task_name = "mixed_gauge:#{name}"
        to_rake_task(task_name).invoke(cluster_name.to_s)
        to_rake_task(task_name).reenable
      end
    end
    extend TasksForMultipleClusters

    # Organize cluster config and handle error for invalid args, call single
    # cluster task with each single connection config.
    module TaskOrganizerForSingleClusterTask
      # @param [Hash{Symbol => String}] args
      def create_all_databases(args)
        exec_task_for_all_databases('create', args)
      end

      # @param [Hash{Symbol => String}] args
      def drop_all_databases(args)
        exec_task_for_all_databases('drop', args)
      end

      # @param [Hash{Symbol => String}] args
      def load_schema_all_databases(args)
        exec_task_for_all_databases('load_schema', args)
      end

      private

      # @param [String] task_name
      # @param [Hash{Symbol => String}] args
      def exec_task_for_all_databases(task_name, args)
        cluster_name = cluster_name_or_error(task_name, args)
        cluster = cluster_or_error(cluster_name)
        cluster.connections.each do |connection_name|
          __send__(task_name, connection_name.to_s)
        end
      end

      # @param [String] name A task name
      # @param [Hash{Symbol => String}] args
      # @return [String]
      def cluster_name_or_error(name, args)
        unless (cluster_name = args[:cluster_name])
          $stderr.puts <<-MSG
Missing cluster_name. Find cluster_name via `rake mixed_gauge:info` then call `rake "mixed_gauge:#{name}[$cluster_name]"`.
          MSG
          exit_with_error
        end
        cluster_name
      end

      # @param [String] cluster_name
      # @return [MixedGauge::ClusterConfig]
      def cluster_or_error(cluster_name)
        fetch_cluster_config(cluster_name.to_sym)
      rescue KeyError
        $stderr.puts %(cluster name "#{cluster_name}" not found.)
        exit_with_error
      end
    end
    extend TaskOrganizerForSingleClusterTask

    # Create, drop, load_schema for single connection config.
    module TasksForSingleConnection
      # @param [String] connection_name
      def create(connection_name)
        configuration = ActiveRecord::Base.configurations[connection_name]
        ActiveRecord::Tasks::DatabaseTasks.create(configuration)
        # Re-configure using configuration with database
        ActiveRecord::Base.establish_connection(configuration)
      end

      # @param [String] connection_name
      def drop(connection_name)
        configuration = ActiveRecord::Base.configurations[connection_name]
        ActiveRecord::Tasks::DatabaseTasks.drop(configuration)
      end

      # @param [String] connection_name
      def load_schema(connection_name)
        configuration = ActiveRecord::Base.configurations[connection_name]

        if ar5?
          ActiveRecord::Tasks::DatabaseTasks.load_schema(configuration, :ruby)
        elsif ar42? || ar417_above?
          ActiveRecord::Tasks::DatabaseTasks.load_schema_for(configuration, :ruby)
        elsif ar41?
          ActiveRecord::Base.establish_connection(configuration)
          ActiveRecord::Tasks::DatabaseTasks.load_schema(:ruby)
        else
          raise "This version of ActiveRecord is not supported: v#{ActiveRecord::VERSION::STRING}"
        end
      end
    end
    extend TasksForSingleConnection
  end
end