Warn user when they sign up for a talk in a different language

app/helpers/application_helper.rb

@@ -3,6 +3,7 @@ module ApplicationHelper
     attributes = {}
     attributes[:loggedin_uid] = current_user.id if user_signed_in?
     attributes[:is_shiftcoordinator] = 1 if current_user&.shiftcoordinator?
+    attributes[:languages_from] = current_user.languages_from unless current_user&.languages_from.blank?
     { data: attributes }
   end
 end

app/javascript/controllers/session_controller.js

@@ -33,6 +33,23 @@ export default class extends Controller {
     });
   }
 
+  verifyLanguages(event) {
+    const languagesFrom = document.body.dataset.languagesFrom;
+    const languageSession = this.element.dataset.language;
+    if (!languagesFrom) {
+      return;
+    }
+    if (!languagesFrom.split(',').includes(languageSession)) {
+      const response = confirm("You are signing up for a talk with language " + languageSession + ", which you claim not to understand!");
+      if (response) {
+        return;
+      } else {
+        event.preventDefault();
+        event.stopImmediatePropagation(); // don't continue with further actions on the same element
+      }
+    }
+  }
+
   submitWithPrompt(event) {
     event.preventDefault();
 

app/views/candidates/_user_avatar.html.erb

@@ -14,8 +14,11 @@
 </span>
 <% if !user.languages_from.blank? || !user.languages_to.blank? %>
 <small class="text-2xs uppercase font-light bg-black/10 rounded-sm p-1 ml-1">
+  <% if !user.languages_from.blank? && !user.languages_from.split(',').include?(session.language) %>
+  <span aria-help="User doesn't understand the language of the talk" title="User doesn't understand the language of the talk">⚠️</span>
+  <% end %>
   <%= user.languages_from %>
-    <% if user.languages_from && user.languages_to %>→<% end %>
+  <span aria-label="to">→</span>
   <%= user.languages_to %>
 </small>
 <% end %>

app/views/sessions/_session.html.erb

 <% unassigned_users = User.all - session.assignments.collect(&:user) %>
-<%= turbo_frame_tag dom_id(session), method: "morph", class: "w-full", data: { controller: "session" } do %>
+<%= turbo_frame_tag dom_id(session), method: "morph", class: "w-full", data: { controller: "session", language: session.language } do %>
   <div class="session shadow hover:shadow-lg overflow-scroll text-sm w-full !h-full min-h-full hover:!min-h-max <%= session.translators_needed? ? "translators-needed" : "no-translators-needed" %> <%= session.backup_needed? ? "backup-needed" : "no-backup-needed" %> <%= session.assignees? ? "has-assignees" : "no-assignees" %> <%= (session.ends_at < Time.now ? "past" : "") %>">
     <h4>
       <small class="text-2xs uppercase font-light bg-black/10 rounded-sm p-1 mr-1 lang-<%= session.language %>"><%= session.language %></small>
@@ -24,11 +24,11 @@
         <%= link_to conference_session_candidates_path(session.conference, session), class: "pr-1 only-candidate hidden", title: "Withdraw", aria_label: "Withdraw", data: { turbo_method: :delete, turbo_frame: dom_id(session) }, method: :delete do %>
           🙅
         <% end %>
-        <%= link_to conference_session_candidates_path(session.conference, session), class: "pr-1 only-no-candidate hidden", title: "Volunteer Myself", aria_label: "Volunteer Myself", data: { turbo_method: :post, turbo_frame: dom_id(session) } do %>
+        <%= link_to conference_session_candidates_path(session.conference, session), class: "pr-1 only-no-candidate hidden", title: "Volunteer Myself", aria_label: "Volunteer Myself", data: { action: "session#verifyLanguages", turbo_method: :post, turbo_frame: dom_id(session) } do %>
           🙋
         <% end %>
         <%= form_with url: conference_session_candidates_path(session.conference, session), method: :post, class: "inline", data: { turbo_frame: dom_id(session) } do |form| %>
-          <%= link_to conference_session_candidates_path(session.conference, session), class: "pr-1 only-no-candidate hidden", title: "Volunteer (with special skills)", aria_label: "Volunteer (with special skills)", data: { action: "session#submitWithPrompt", prompt: "Why are you especially qualified? (Please keep it short, thanks)", turbo_prefetch:"false" } do %>
+          <%= link_to conference_session_candidates_path(session.conference, session), class: "pr-1 only-no-candidate hidden", title: "Volunteer (with special skills)", aria_label: "Volunteer (with special skills)", data: { action: "session#verifyLanguages session#submitWithPrompt", prompt: "Why are you especially qualified? (Please keep it short, thanks)", turbo_prefetch:"false" } do %>
               🙌
           <% end %>
         <% end %>