Find media attachments by URL

flag=media_links_use_attachment_id

Test plan
- Test with NQ -> NQ copy to
- Add a media attachment link into a New Quiz
- Use "copy to" to copy the NQ to a new course
- Ensure media_attachment link is updated
  with new file ID

Change-Id: I051f7fb8f93fb79759aacc8576fc5179e0b3e766
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/333489
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Eric Saupe <eric.saupe@instructure.com>
Reviewed-by: Jacob DeWar <jacob.dewar@instructure.com>
QA-Review: Jacob DeWar <jacob.dewar@instructure.com>
Product-Review: Mysti Lilla <mysti@instructure.com>

app/models/context.rb

@@ -253,10 +253,7 @@ module Context
     user = User.find(params[:user_id]) if params[:user_id]
     context = course || group || user
 
-    media_obj = MediaObject.where(media_id: params[:media_object_id]).first if params[:media_object_id]
-    context = media_obj.context if media_obj
-
-    return nil unless context
+    return nil unless context || params[:controller] == "media_objects"
 
     case params[:controller]
     when "files"
@@ -296,7 +293,12 @@ module Context
                  context.context_modules.find_by(id: params[:id])
                end
     when "media_objects"
-      object = media_obj
+      object = if params[:media_object_id]
+                 MediaObject.where(media_id: params[:media_object_id]).first
+               elsif params[:attachment_id]
+                 # get possibly replaced attachment, see app/models/attachment.rb find_attachment_possibly_replaced
+                 Attachment.find_by(id: params[:attachment_id])&.context&.attachments&.find_by(id: params[:attachment_id])
+               end
     when "context"
       object = context.users.find(params[:id]) if params[:action] == "roster_user" && params[:id]
     else

spec/models/context_spec.rb

@@ -127,6 +127,7 @@ describe Context do
       expect(Context.find_asset_by_url("/courses/#{@course.id}/files/#{@attachment.id}/download?wrap=1")).to eq @attachment
       expect(Context.find_asset_by_url("/courses/#{@course.id}/files/#{@attachment.id}/?wrap=1")).to eq @attachment
       expect(Context.find_asset_by_url("/courses/#{@course.id}/file_contents/course%20files//#{@attachment.name}")).to eq @attachment
+      expect(Context.find_asset_by_url("/media_attachments_iframe/#{@attachment.id}?type=video&embedded=true")).to eq @attachment
     end
 
     it "finds folders" do