feat: implement batch progress reporting

lib/activerecord-import/import.rb

@@ -805,17 +805,29 @@ def import_without_validations_or_callbacks( column_names, array_of_attributes,
       if supports_import?
         # generate the sql
         post_sql_statements = connection.post_sql_statements( quoted_table_name, options )
+        import_size = values_sql.size
+
+        batch_size = options[:batch_size] || import_size
+        run_proc = options[:batch_size].to_i.positive? && options[:batch_progress].respond_to?( :call )
+        progress_proc = options[:batch_progress]
+        current_batch = 0
+        batches = (import_size / batch_size.to_f).ceil
 
-        batch_size = options[:batch_size] || values_sql.size
         values_sql.each_slice(batch_size) do |batch_values|
+          batch_started_at = Time.now.to_i
+
           # perform the inserts
           result = connection.insert_many( [insert_sql, post_sql_statements].flatten,
             batch_values,
             options,
             "#{model_name} Create Many" )
+
           number_inserted += result.num_inserts
           ids += result.ids
           results += result.results
+          current_batch += 1
+
+          progress_proc.call(import_size, batches, current_batch, Time.now.to_i - batch_started_at) if run_proc
         end
       else
         transaction(requires_new: true) do

test/import_test.rb

@@ -405,6 +405,15 @@
         assert_equal 3, result.num_inserts if Topic.supports_import?
       end
     end
+
+    it "should accept and call an optional callable to run after each batch" do
+      lambda_called = 0
+
+      my_proc = ->(_row_count, _batches, _batch, _duration) { lambda_called += 1 }
+      Topic.import Build(10, :topics), batch_size: 4, batch_progress: my_proc
+
+      assert_equal 3, lambda_called
+    end
   end
 
   context "with :synchronize option" do