Add difference with model solution

Author: nygrenh

app/controllers/submissions_controller.rb

@@ -7,7 +7,7 @@ class SubmissionsController < ApplicationController
   before_action :get_course_and_exercise
 
   # Manually checked for #show and index
-  skip_authorization_check only: [:show, :index]
+  skip_authorization_check only: [:show, :index, :difference_with_solution]
 
   def index
     respond_to do |format|
@@ -195,6 +195,41 @@ def update_by_exercise
     redirect_to exercise_path(@exercise), notice: 'Reruns scheduled'
   end
 
+  def difference_with_solution
+    respond_access_denied unless current_user.administrator?
+    @course ||= @submission.course
+    @exercise ||= @submission.exercise
+    @organization = @course.organization
+    add_course_breadcrumb
+    add_exercise_breadcrumb
+    add_submission_breadcrumb
+    add_breadcrumb 'Difference with model solution'
+
+    submission_files = SourceFileList.for_submission(@submission)
+    solution_files = SourceFileList.for_solution(@exercise.solution)
+    files_in_list = Set.new
+    @files = []
+    submission_files.each do |file|
+      # TODO: In some exercises files may be named differently. Some kind of
+      # similarity metric would be nice here
+      model = solution_files.find { |solution_file| file.path == solution_file.path}
+      @files << {
+        path: file.path,
+        submission_contents: file.contents,
+        model_contents: (model.nil? ? '' : model.contents)
+      }
+      files_in_list << file.path
+    end
+    solution_files.each do |file|
+      next if files_in_list.include?(file.path)
+      @files << {
+        path: file.path,
+        submission_contents: '',
+        model_contents: model.contents
+      }
+    end
+  end
+
   private
 
   def course_transaction
@@ -205,8 +240,9 @@ def course_transaction
 
   # Ugly manual access control :/
   def get_course_and_exercise
-    if params[:id]
-      @submission = Submission.find(params[:id])
+    submission_id = params[:id] || params[:submission_id]
+    if submission_id
+      @submission = Submission.find(submission_id)
       authorize! :read, @submission
       @course = @submission.course
       @exercise = @submission.exercise

app/views/submissions/_submission_details.html.erb

@@ -65,6 +65,7 @@
 
         <% if current_user.administrator? && @submission.sandbox  %>
           <li>Sandbox used: <%= @submission.sandbox %></li>
+          <li><%= link_to 'Difference with model solution', submission_difference_with_solution_path(@submission) %> (only for admins)</li>
         <% end %>
       </ul>
 

app/views/submissions/difference_with_solution.html.erb

@@ -0,0 +1,43 @@
+<h1>Submission difference</h1>
+
+<div class="alert alert-warning">
+  This is a naive and experimental feature that calculates the
+  difference between this submission and the model solution.
+  This may sometimes be helpful when trying to figure out what's wrong with
+  a submission.
+</div>
+
+<% @files.each do |file| %>
+  <div class="card">
+    <div class="card-body">
+    <h2><%= file[:path] %></h2>
+    <div class="code-pair" data-path="<%= file[:path] %>">
+      <div class="submission-code"><%= file[:submission_contents] %></div>
+      <div class="model-code"><%= file[:model_contents] %></div>
+    </div>
+    </div>
+  </div>
+  <br>
+<% end %>
+
+<script src="https://cdnjs.cloudflare.com/ajax/libs/diff_match_patch/20121119/diff_match_patch.js" integrity="sha256-qsdlWiFdhEjZXZhx6NikCsPZqvONgasszEPBzSZ7j6M=" crossorigin="anonymous"></script>
+
+<script>
+  var dmp = new diff_match_patch();
+  document.querySelectorAll('.code-pair').forEach(function (pairElement) {
+    var path = pairElement.dataset.path;
+    var submissionCode = pairElement.querySelector('.submission-code').innerHTML;
+    var modelCode = pairElement.querySelector('.model-code').innerHTML;
+    var diff = dmp.diff_main(modelCode, submissionCode);
+    var outputHtml = dmp.diff_prettyHtml(diff).replace(/&para;/g, '');
+    pairElement.innerHTML = outputHtml;
+  });
+</script>
+
+<style>
+  ins, .code-pair span {
+    font-family: monospace;
+    white-space: pre;
+    text-decoration: none;
+  }
+</style>

config/routes.rb

@@ -248,6 +248,7 @@
     resources :files, only: [:index]
     resources :reviews, only: [:index, :new, :create]
     resources :full_zip, only: [:index]
+    get 'difference_with_solution', to: 'submissions#difference_with_solution'
   end
 
   get 'paste/:paste_key', to: 'submissions#show', as: 'paste'