Add Paperclip::InterpolatedString to store the interpolated string which has an escape flag

lib/paperclip/interpolated_string.rb

+require 'uri'
+
+module Paperclip
+  class InterpolatedString < String
+    def escaped?
+      !!@escaped
+    end
+
+    def escape
+      if !escaped?
+        escaped_string = self.class.new(URI.escape(self))
+        escaped_string.instance_variable_set(:@escaped, true)
+        escaped_string
+      else
+        self
+      end
+    end
+
+    def unescape
+      if escaped?
+        escaped_string = self.class.new(URI.unescape(self))
+        escaped_string.instance_variable_set(:@escaped, false)
+        escaped_string
+      else
+        self
+      end
+    end
+
+    def force_escape
+      @escaped = true
+    end
+  end
+end

test/interpolated_string_test.rb

+require './test/helper'
+
+class InterpolatedStringTest < Test::Unit::TestCase
+  context "inheritance" do
+    should "inherited from String" do
+      assert Paperclip::InterpolatedString.new("paperclip").is_a? String
+    end
+  end
+
+  context "#escape" do
+    subject { Paperclip::InterpolatedString.new("paperclip foo").escape }
+
+    should "returns an InterpolatedString object" do
+      assert subject.is_a? Paperclip::InterpolatedString
+    end
+
+    should "escape the output string" do
+      assert_equal "paperclip%20foo", subject
+    end
+
+    should "not double escape output string" do
+      assert_equal "paperclip%20foo", subject.escape
+    end
+  end
+
+  context "#unescape" do
+    subject { Paperclip::InterpolatedString.new("paperclip%20foo").escape.unescape }
+
+    should "returns an InterpolatedString object" do
+      assert subject.is_a? Paperclip::InterpolatedString
+    end
+
+    should "unescape the output string" do
+      assert_equal "paperclip%20foo", subject
+    end
+
+    should "not double unescape output string" do
+      assert_equal "paperclip%20foo", subject.unescape
+    end
+  end
+
+  context "#escaped?" do
+    subject { Paperclip::InterpolatedString.new("paperclip") }
+
+    should "returns true if string was escaped" do
+      assert subject.escape.escaped?
+    end
+
+    should "returns false if string wasn't escaped" do
+      assert !subject.escaped?
+    end
+  end
+
+  context "#force_escape" do
+    subject { Paperclip::InterpolatedString.new("paperclip") }
+    setup { subject.force_escape }
+
+    should "sets escaped flag to true" do
+      assert subject.escaped?
+    end
+  end
+end