Extract csv file handling to CSV::Storage

Adds `CSV::Storage` to perform the reading and writing to csv files. The
new class is used in the `Dataset` and the `Gateway`. The connection is
passed in to the dataset to keep the command functionality working.

lib/rom/csv/dataset.rb

@@ -1,17 +1,24 @@
 require 'rom/memory/dataset'
+require 'rom/csv/storage'
 
 module ROM
   module CSV
+    # Type definition used to constrain the `connection` option
+    StorageType = Types.Definition(Storage).constrained(type: Storage)
+
     # Dataset for CSV
     #
     # @api public
     class Dataset < ROM::Memory::Dataset
-      option :path,
+
+      # Connection to the file
+      #
+      # @return [Storage]
+      #
+      # @api private
+      option :connection,
              optional: true,
-             type: Types::Strict::String
-      option :file_options,
-             default: proc { {} },
-             type: Types::Strict::Hash
+             type: StorageType
 
       # Convert each CSV::Row to a hash
       #
@@ -21,23 +28,11 @@ def self.row_proc
       end
 
       def reload!
-        @data = load_data
+        @data = connection.load
       end
 
       def sync!
-        write_data && reload!
-      end
-
-      def write_data
-        ::CSV.open(path, 'wb', file_options) do |csv|
-          data.to_a.each do |tuple|
-            csv << tuple
-          end
-        end
-      end
-
-      def load_data
-        ::CSV.table(path, file_options).by_row!
+        connection.dump(data) && reload!
       end
 
       def count

lib/rom/csv/gateway.rb

@@ -2,6 +2,7 @@
 require 'rom/initializer'
 require 'rom/csv/dataset'
 require 'rom/csv/commands'
+require 'rom/csv/storage'
 
 # Ruby Object Mapper
 #
@@ -72,7 +73,7 @@ class Gateway < ROM::Gateway
       def initialize(*)
         super
         @datasets = {}
-        @connection = ::CSV.table(path, csv_options).by_row!
+        @connection = Storage.new(path, csv_options)
       end
 
       # Return dataset with the given name
@@ -94,7 +95,7 @@ def [](name)
       #
       # @api public
       def dataset(name)
-        datasets[name] = Dataset.new(connection, dataset_options)
+        datasets[name] = Dataset.new(connection.load, connection: connection)
       end
 
       # Check if dataset exists
@@ -105,12 +106,6 @@ def dataset(name)
       def dataset?(name)
         datasets.key?(name)
       end
-
-      private
-
-      def dataset_options
-        { path: path, file_options: csv_options }
-      end
     end
   end
 end

lib/rom/csv/storage.rb

@@ -0,0 +1,52 @@
+require 'csv'
+require 'rom/initializer'
+
+module ROM
+  module CSV
+    # CSV file storage for datasets
+    #
+    # @api private
+    class Storage
+      extend Initializer
+
+      # Path to the file
+      #
+      # @return [String]
+      #
+      # @api private
+      param :path,
+            type: Types::Strict::String
+
+      # Options for file passed to `CSV`
+      #
+      # @return [Hash]
+      #
+      # @api private
+      param :csv_options,
+            default: proc { {} },
+            type: Types::Strict::Hash
+
+      # Dump the data to the file at `path`
+      #
+      # @return [undefined]
+      #
+      # @api public
+      def dump(data)
+        ::CSV.open(path, 'wb', csv_options) do |csv|
+          data.to_a.each do |tuple|
+            csv << tuple
+          end
+        end
+      end
+
+      # Load the data from the file at `path`
+      #
+      # @return [CSV::Table]
+      #
+      # @api public
+      def load
+        ::CSV.table(path, csv_options).by_row!
+      end
+    end
+  end
+end

lib/rom/csv/types.rb

@@ -4,6 +4,10 @@ module ROM
   module CSV
     module Types
       include ROM::Types
+
+      def self.Definition(primitive)
+        Dry::Types::Definition.new(primitive)
+      end
     end
   end
 end