post replacements: record upload source/filename in replacement_url.

* Record "file://#{filename}" as the replacement url when the
  replacement comes from an uploaded file.

* Record the actual url downloaded by the upload process otherwise. This
  may be different from the url given by the user, since the upload
  process may rewrite the url.

app/models/post_replacement.rb

@@ -27,6 +27,12 @@ class PostReplacement < ApplicationRecord
       upload.process_upload
       upload.update(status: "completed", post_id: post.id)
 
+      if replacement_file.present?
+        update(replacement_url: "file://#{replacement_file.original_filename}")
+      else
+        update(replacement_url: upload.source)
+      end
+
       # queue the deletion *before* updating the post so that we use the old
       # md5/file_ext to delete the old files. if saving the post fails,
       # this is rolled back so the job won't run.
@@ -112,7 +118,7 @@ class PostReplacement < ApplicationRecord
     end
 
     def replacement_message
-      linked_source = linked_source(post.source)
+      linked_source = linked_source(replacement_url)
       linked_source_was = linked_source(post.source_was)
 
       <<-EOS.strip_heredoc

test/unit/post_replacement_test.rb

@@ -134,6 +134,7 @@ class PostReplacementTest < ActiveSupport::TestCase
         assert_equal("4ceadc314938bc27f3574053a3e1459a", @post.md5)
         assert_equal("4ceadc314938bc27f3574053a3e1459a", Digest::MD5.file(@post.file_path).hexdigest)
         assert_equal("https://i.pximg.net/img-original/img/2017/04/04/08/54/15/62247350_p0.png", @post.source)
+        assert_equal("https://i.pximg.net/img-original/img/2017/04/04/08/54/15/62247350_p0.png", @post.replacements.last.replacement_url)
       end
 
       should "delete the old files after three days" do
@@ -196,9 +197,11 @@ class PostReplacementTest < ActiveSupport::TestCase
         Tempfile.open do |file|
           file.write(File.read("#{Rails.root}/test/files/test.png"))
           file.seek(0)
+          uploaded_file = ActionDispatch::Http::UploadedFile.new(tempfile: file, filename: "test.png")
 
-          @post.replace!(replacement_file: file, replacement_url: "")
+          @post.replace!(replacement_file: uploaded_file, replacement_url: "")
           assert_equal(@post.md5, Digest::MD5.file(file).hexdigest)
+          assert_equal("file://test.png", @post.replacements.last.replacement_url)
         end
       end
     end