fix importing csv with BOM

lib/active_admin_import/model.rb

@@ -1,12 +1,15 @@
+# encoding: utf-8
+
 module ActiveAdminImport
   class Model
 
     include ActiveModel::Model
     include ActiveModel::Validations
     include ActiveModel::Validations::Callbacks
 
-    validates :file, presence: {message: Proc.new { I18n.t('active_admin_import.no_file_error') }},
-              unless: proc { |me| me.new_record? }
+    validates :file, presence: {
+      message: proc { I18n.t("active_admin_import.no_file_error") }
+    }, unless: proc { |me| me.new_record? }
 
     validate :correct_content_type, if: proc { |me| me.file.present? }
     validate :file_contents_present, if: proc { |me| me.file.present? }
@@ -23,7 +26,6 @@ def initialize(args={})
       assign_attributes(default_attributes.merge(args), true)
     end
 
-
     def assign_attributes(args = {}, new_record = false)
       @attributes.merge!(args)
       @new_record = new_record
@@ -75,23 +77,21 @@ def file_path
     end
 
     def encode_file
-      data = File.read(file_path).encode(force_encoding, invalid: :replace, undef: :replace)
+      data = File.read(file_path)
       File.open(file_path, 'w') do |f|
-        f.write(data)
+        f.write(encode(data))
       end
     end
 
     def uncompress_file
       Zip::File.open(file_path) do |zip_file|
         self.file = Tempfile.new("active-admin-import-unzipped")
         data = zip_file.entries.select { |f| f.file? }.first.get_input_stream.read
-        data = data.encode(force_encoding, invalid: :replace, undef: :replace) if self.force_encoding?
         self.file << data
         self.file.close
       end
     end
 
-
     def csv_allowed_types
       [
           'text/csv',
@@ -103,7 +103,6 @@ def csv_allowed_types
       ]
     end
 
-
     def correct_content_type
       unless file.blank? || file.is_a?(Tempfile)
         errors.add(:file, I18n.t('active_admin_import.file_format_error')) unless csv_allowed_types.include? file_type
@@ -132,6 +131,11 @@ def define_methods_for(attr_name)
       end
     end
 
+    def encode(data)
+      data.encode(force_encoding, "binary",
+                  invalid: :replace, undef: :replace,  replace: "").
+          sub("\xEF\xBB\xBF", "")
+    end
 
     class <<self
       def define_set_method(attr_name)

spec/fixtures/files/authors_bom.csv

@@ -0,0 +1,3 @@
+Name,Last name,Birthday
+John,Doe,1986-05-01
+Jane,Roe,1988-11-16

spec/import_spec.rb

@@ -112,6 +112,16 @@ def upload_file!(name, ext='csv')
         end
       end
 
+      context "BOM" do
+
+        it "should import file with many records" do
+          upload_file!(:authors_bom)
+          expect(page).to have_content "Successfully imported 2 authors"
+          expect(Author.count).to eq(2)
+        end
+
+      end
+
       context "with headers" do
 
         it "should import file with many records" do