FIX: Make site tasks work with duplicated uploads (#13972)

Uploads can be reused between site settings. This change allows the same
upload to be exported only once and then the same file is reused. The
same applies to import.

lib/tasks/site.rake

@@ -8,6 +8,7 @@ class ZippedSiteStructure
 
   def initialize(path, create: false)
     @zip = Zip::File.open(path, create)
+    @uploads = {}
   end
 
   def close
@@ -41,26 +42,53 @@ class ZippedSiteStructure
       return nil
     end
 
+    if @uploads[upload.id].present?
+      puts "  - Already exported upload #{upload_or_id_or_url} to #{@uploads[upload.id][:path]}"
+      return @uploads[upload.id]
+    end
+
     local_path = upload.local? ? Discourse.store.path_for(upload) : Discourse.store.download(upload).path
     zip_path = File.join('uploads', File.basename(local_path))
+    zip_path = get_unique_path(zip_path)
 
     puts "  - Exporting upload #{upload_or_id_or_url} to #{zip_path}"
     @zip.add(zip_path, local_path)
 
-    { filename: upload.original_filename, path: zip_path }
+    @uploads[upload.id] ||= { filename: upload.original_filename, path: zip_path }
   end
 
   def get_upload(upload, opts = {})
     return nil if upload.blank?
 
+    if @uploads[upload['path']].present?
+      puts "  - Already imported upload #{upload['filename']} from #{upload['path']}"
+      return @uploads[upload['path']]
+    end
+
     puts "  - Importing upload #{upload['filename']} from #{upload['path']}"
 
     tempfile = Tempfile.new(upload['filename'], binmode: true)
     tempfile.write(@zip.get_input_stream(upload['path']).read)
     tempfile.rewind
 
-    UploadCreator.new(tempfile, upload['filename'], opts)
+    @uploads[upload['path']] ||= UploadCreator.new(tempfile, upload['filename'], opts).create_for(Discourse::SYSTEM_USER_ID)
-      .create_for(Discourse::SYSTEM_USER_ID)
+  end
+
+  private
+
+  def get_unique_path(path)
+    return path if @zip.find_entry(path).blank?
+
+    extname = File.extname(path)
+    basename = File.basename(path, extname)
+    dirname = File.dirname(path)
+
+    i = 0
+    loop do
+      i += 1
+      path = File.join(dirname, "#{basename}_#{i}#{extname}")
+      return path if @zip.find_entry(path).blank?
+    end
   end
 end