module ActiveRecord
  class Migration
    # <tt>ActiveRecord::Migration::CommandRecorder</tt> records commands done during
    # a migration and knows how to reverse those commands. The CommandRecorder
    # knows how to invert the following commands:
    #
    # * add_column
    # * add_index
    # * add_timestamps
    # * create_table
    # * create_join_table
    # * remove_timestamps
    # * rename_column
    # * rename_index
    # * rename_table
    class CommandRecorder
      ReversibleAndIrreversibleMethods = [:create_table, :create_join_table, :rename_table, :add_column, :remove_column,
        :rename_index, :rename_column, :add_index, :remove_index, :add_timestamps, :remove_timestamps,
        :change_column_default, :add_reference, :remove_reference, :transaction,
        :drop_join_table, :drop_table, :execute_block, :enable_extension,
        :change_column, :execute, :remove_columns, :change_column_null,
        :add_foreign_key, :remove_foreign_key
      ]
      include JoinTable

      attr_accessor :commands, :delegate, :reverting

      def initialize(delegate = nil)
        @commands = []
        @delegate = delegate
        @reverting = false
      end

      # While executing the given block, the recorded will be in reverting mode.
      # All commands recorded will end up being recorded reverted
      # and in reverse order.
      # For example:
      #
      #   recorder.revert{ recorder.record(:rename_table, [:old, :new]) }
      #   # same effect as recorder.record(:rename_table, [:new, :old])
      def revert
        @reverting = !@reverting
        previous = @commands
        @commands = []
        yield
      ensure
        @commands = previous.concat(@commands.reverse)
        @reverting = !@reverting
      end

      # record +command+. +command+ should be a method name and arguments.
      # For example:
      #
      #   recorder.record(:method_name, [:arg1, :arg2])
      def record(*command, &block)
        if @reverting
          @commands << inverse_of(*command, &block)
        else
          @commands << (command << block)
        end
      end

      # Returns the inverse of the given command. For example:
      #
      #   recorder.inverse_of(:rename_table, [:old, :new])
      #   # => [:rename_table, [:new, :old]]
      #
      # This method will raise an +IrreversibleMigration+ exception if it cannot
      # invert the +command+.
      def inverse_of(command, args, &block)
        method = :"invert_#{command}"
        raise IrreversibleMigration, <<-MSG.strip_heredoc unless respond_to?(method, true)
          This migration uses #{command} that is not automatically reversible.
          There are two ways to mitigate this problem.
          1. Define up and down methods instead of change method
          2. Use reversible method in change method
        MSG
        send(method, args, &block)
      end

      def respond_to?(*args) # :nodoc:
        super || delegate.respond_to?(*args)
      end

      ReversibleAndIrreversibleMethods.each do |method|
        class_eval <<-EOV, __FILE__, __LINE__ + 1
          def #{method}(*args, &block)          # def create_table(*args, &block)
            record(:"#{method}", args, &block)  #   record(:create_table, args, &block)
          end                                   # end
        EOV
      end
      alias :add_belongs_to :add_reference
      alias :remove_belongs_to :remove_reference

      def change_table(table_name, options = {}) # :nodoc:
        yield delegate.update_table_definition(table_name, self)
      end

      private

      module StraightReversions
        private
        { transaction:       :transaction,
          execute_block:     :execute_block,
          create_table:      :drop_table,
          create_join_table: :drop_join_table,
          add_column:        :remove_column,
          add_timestamps:    :remove_timestamps,
          add_reference:     :remove_reference,
          enable_extension:  :disable_extension
        }.each do |cmd, inv|
          [[inv, cmd], [cmd, inv]].uniq.each do |method, inverse|
            class_eval <<-EOV, __FILE__, __LINE__ + 1
              def invert_#{method}(args, &block)    # def invert_create_table(args, &block)
                [:#{inverse}, args, block]          #   [:drop_table, args, block]
              end                                   # end
            EOV
          end
        end
      end

      include StraightReversions

      def invert_drop_table(args, &block)
        if args.size == 1 && block == nil
          raise ActiveRecord::IrreversibleMigration, "To avoid mistakes, drop_table is only reversible if given options or a block (can be empty)."
        end
        super
      end

      def invert_rename_table(args)
        [:rename_table, args.reverse]
      end

      def invert_remove_column(args)
        raise ActiveRecord::IrreversibleMigration, "remove_column is only reversible if given a type." if args.size <= 2
        super
      end

      def invert_rename_index(args)
        [:rename_index, [args.first] + args.last(2).reverse]
      end

      def invert_rename_column(args)
        [:rename_column, [args.first] + args.last(2).reverse]
      end

      def invert_add_index(args)
        table, columns, options = *args
        options ||= {}

        index_name = options[:name]
        options_hash = index_name ? { name: index_name } : { column: columns }

        [:remove_index, [table, options_hash]]
      end

      def invert_remove_index(args)
        table, options_or_column = *args
        if (options = options_or_column).is_a?(Hash)
          unless options[:column]
            raise ActiveRecord::IrreversibleMigration, "remove_index is only reversible if given a :column option."
          end
          options = options.dup
          [:add_index, [table, options.delete(:column), options]]
        elsif (column = options_or_column).present?
          [:add_index, [table, column]]
        end
      end

      alias :invert_add_belongs_to :invert_add_reference
      alias :invert_remove_belongs_to :invert_remove_reference

      def invert_change_column_default(args)
        table, column, options = *args

        unless options && options.is_a?(Hash) && options.has_key?(:from) && options.has_key?(:to)
          raise ActiveRecord::IrreversibleMigration, "change_column_default is only reversible if given a :from and :to option."
        end

        [:change_column_default, [table, column, from: options[:to], to: options[:from]]]
      end

      def invert_change_column_null(args)
        args[2] = !args[2]
        [:change_column_null, args]
      end

      def invert_add_foreign_key(args)
        from_table, to_table, add_options = args
        add_options ||= {}

        if add_options[:name]
          options = { name: add_options[:name] }
        elsif add_options[:column]
          options = { column: add_options[:column] }
        else
          options = to_table
        end

        [:remove_foreign_key, [from_table, options]]
      end

      def invert_remove_foreign_key(args)
        from_table, to_table, remove_options = args
        raise ActiveRecord::IrreversibleMigration, "remove_foreign_key is only reversible if given a second table" if to_table.nil? || to_table.is_a?(Hash)

        reversed_args = [from_table, to_table]
        reversed_args << remove_options if remove_options

        [:add_foreign_key, reversed_args]
      end

      # Forwards any missing method call to the \target.
      def method_missing(method, *args, &block)
        if @delegate.respond_to?(method)
          @delegate.send(method, *args, &block)
        else
          super
        end
      end
    end
  end
end