Refactor Users#upload_avatar method

Moved avatar file upload to ```AvatarUploadService``` class and
```AvatarUploadPolicy```

Address review comments + require missing file in spec

spec/components/avatar_upload_service_spec.rb

@@ -0,0 +1,66 @@
+require "spec_helper"
+require "avatar_upload_service"
+
+describe AvatarUploadService do
+  let(:file) do
+    ActionDispatch::Http::UploadedFile.new({
+      filename: 'logo.png',
+      tempfile: File.new("#{Rails.root}/spec/fixtures/images/logo.png")
+    })
+  end
+
+  let(:url) { "http://cdn.discourse.org/assets/logo.png" }
+
+  describe "#construct" do
+    context "when avatar is in the form of a file upload" do
+      let(:avatar_file) { AvatarUploadService.new(file, :image) }
+
+      it "should have a filesize" do
+        expect(avatar_file.filesize).to eq(2290)
+      end
+
+      it "should have a source as 'image'" do
+        expect(avatar_file.source).to eq(:image)
+      end
+
+      it "is an instance of File class" do
+        file = avatar_file.file
+        expect(file.tempfile).to be_instance_of File
+      end
+
+      it "returns the file object built from File" do
+        file = avatar_file.file
+        file.should be_instance_of(ActionDispatch::Http::UploadedFile)
+        file.original_filename.should == "logo.png"
+      end
+    end
+
+    context "when file is in the form of a URL" do
+      let(:avatar_file) { AvatarUploadService.new(url, :url) }
+
+      before :each do
+        UriAdapter.any_instance.stubs(:open).returns StringIO.new(fixture_file("images/logo.png"))
+      end
+
+      it "should have a filesize" do
+        expect(avatar_file.filesize).to eq(2290)
+      end
+
+      it "should have a source as 'url'" do
+        expect(avatar_file.source).to eq(:url)
+      end
+
+      it "is an instance of Tempfile class" do
+        file = avatar_file.file
+        expect(file.tempfile).to be_instance_of Tempfile
+      end
+
+      it "returns the file object built from URL" do
+        file = avatar_file.file
+        file.should be_instance_of(ActionDispatch::Http::UploadedFile)
+        file.original_filename.should == "logo.png"
+      end
+    end
+  end
+
+end