module ActiveRecord
  module ShardFor
    class ShardRepogitory
      attr_reader :base_class

      # @param [ClusterConfig] cluster_config
      # @param [Class] base_class A AR Model
      def initialize(cluster_config, base_class)
        @base_class = base_class

        shards = cluster_config.connection_registry.map do |key, connection_name|
          [connection_name, generate_model_for_shard(connection_name, key)]
        end

        @shards = Hash[shards]
      end

      # @param [Symbol] connection_name
      # @return [Class] A model class for this shard
      def fetch(connection_name)
        @shards.fetch(connection_name)
      end

      # @param [Object] key sharding key object for connection
      # @return [Class, nil] A AR model class.
      def fetch_by_key(key)
        @shards.find { |_, model| model.assigned_key == key }[1]
      end

      # @return [Array<Class>]
      def all
        @shards.values
      end

      private

      # @param [Symbol] connection_name
      # @param [Range] slot_range
      # @return [Class] A sub class of given AR model.
      #   A sub class has connection setting for specific shard.
      def generate_model_for_shard(connection_name, key)
        class_name = generate_class_name(connection_name)

        model = Class.new(base_class) do
          self.table_name = base_class.table_name
          class << self
            attr_reader :assigned_key
          end
          @assigned_key = key

          module_eval <<-RUBY, __FILE__, __LINE__ + 1
            def self.name
              "#{base_class.name}::#{class_name}"
            end
          RUBY
        end

        model.class_eval { establish_connection(connection_name) }
        model
      end

      # @param [Symbol] connection_name
      # @return [String]
      def generate_class_name(connection_name)
        "ShardFor#{connection_name.to_s.tr('-', '_').classify}"
      end
    end
  end
end