Enable custom 404 pages for enhanced user experience

Site administrators can now select published entries as custom 404 pages,
providing branded error handling that keeps users engaged instead of showing
generic browser errors. This improves site cohesion and reduces bounce rates
when visitors encounter broken links.

REDMINE-21049

Author: tf

admins/pageflow/sites.rb

@@ -30,7 +30,8 @@ module Pageflow
         :copyright_link_label,
         :privacy_link_url,
         :home_url,
-        :cutoff_mode_name
+        :cutoff_mode_name,
+        :custom_404_entry_id
       ] + permitted_admin_form_input_params
     end
 

app/views/admin/sites/_fields.html.erb

@@ -23,6 +23,12 @@
   <%= f.input :sitemap_enabled, hint: t('pageflow.admin.sites.sitemap_hint',
                                         site_host: @site&.persisted? ? @site.host : '<host>') %>
 
+  <%= f.input :custom_404_entry_id,
+              as: :select,
+              collection: @site&.persisted? ? @site.entries.published_without_password_protection.pluck(:title, :id) : [],
+              include_blank: t('pageflow.admin.sites.custom_404_entry.none'),
+              hint: t('pageflow.admin.sites.custom_404_entry.hint') %>
+
   <% account_config.admin_form_inputs.find_all_for(:site).each do |form_input| %>
     <%= form_input.build(f) %>
   <% end %>

config/locales/new/custom_404_entry.de.yml

@@ -0,0 +1,11 @@
+de:
+  pageflow:
+    admin:
+      sites:
+        custom_404_entry:
+          none: "(Standard 404-Seite verwenden)"
+          hint: "Wählen Sie einen Eintrag aus, der als benutzerdefinierte 404-Seite angezeigt werden soll. Nur veröffentlichte Einträge ohne Passwortschutz sind verfügbar."
+  activerecord:
+    attributes:
+      pageflow/site:
+        custom_404_entry_id: "Benutzerdefinierte 404-Seite"

config/locales/new/custom_404_entry.en.yml

@@ -0,0 +1,11 @@
+en:
+  pageflow:
+    admin:
+      sites:
+        custom_404_entry:
+          none: "(Use default 404 page)"
+          hint: "Select an entry to display as the custom 404 page. Only published entries without password protection are available."
+  activerecord:
+    attributes:
+      pageflow/site:
+        custom_404_entry_id: "Custom 404 page"

spec/controllers/admin/sites_controller_spec.rb

@@ -216,6 +216,15 @@ def self.name
 
         expect(response.body).to have_select('Cutoff mode', options: ['(None)', 'Some Cutoff Mode'])
       end
+
+      it 'displays empty custom 404 entry select for new sites' do
+        account = create(:account)
+
+        sign_in(create(:user, :admin), scope: :user)
+        get(:new, params: {account_id: account})
+
+        expect(response.body).to have_select('Custom 404 page', options: ['(Use default 404 page)'])
+      end
     end
 
     describe '#edit' do
@@ -240,6 +249,28 @@ def self.name
 
         expect(response.body).to have_selector('[name="site[custom_field]"]')
       end
+
+      it 'displays custom 404 entry select for existing sites' do
+        site = create(:site)
+        entry = create(:entry, :published, site: site)
+
+        sign_in(create(:user, :admin), scope: :user)
+        get(:edit, params: {account_id: site.account, id: site})
+
+        expect(response.body).to have_select('Custom 404 page')
+      end
+
+      it 'displays only published entries without password protection in custom 404 entry select' do
+        site = create(:site)
+        published_entry = create(:entry, :published, site: site, title: 'Published Entry')
+        unpublished_entry = create(:entry, site: site, title: 'Unpublished Entry')
+        password_protected_entry = create(:entry, :published_with_password, site: site, password: 'secret', title: 'Protected Entry')
+
+        sign_in(create(:user, :admin), scope: :user)
+        get(:edit, params: {account_id: site.account, id: site})
+
+        expect(response.body).to have_select('Custom 404 page', options: ['(Use default 404 page)', 'Published Entry'])
+      end
     end
 
     describe '#create' do
@@ -342,6 +373,40 @@ def self.name
 
         expect(account.sites.last.custom_field).to eq(nil)
       end
+
+      it 'sets custom_404_entry_id when provided' do
+        site = create(:site)
+        entry = create(:entry, :published, site: site)
+
+        sign_in(create(:user, :admin), scope: :user)
+        patch(:update,
+              params: {
+                account_id: site.account,
+                id: site,
+                site: {
+                  custom_404_entry_id: entry.id
+                }
+              })
+
+        expect(site.reload.custom_404_entry_id).to eq(entry.id)
+      end
+
+      it 'allows nil custom_404_entry_id' do
+        account = create(:account)
+
+        sign_in(create(:user, :admin), scope: :user)
+        post(:create,
+             params: {
+               account_id: account,
+               site: {
+                 name: 'test site',
+                 custom_404_entry_id: ''
+               }
+             })
+
+        site = account.sites.last
+        expect(site.custom_404_entry_id).to be_nil
+      end
     end
 
     describe '#update' do
@@ -438,6 +503,41 @@ def self.name
 
         expect(site.reload.custom_field).to eq(nil)
       end
+
+      it 'updates custom_404_entry_id when provided' do
+        site = create(:site)
+        entry = create(:entry, :published, site: site)
+
+        sign_in(create(:user, :admin), scope: :user)
+        patch(:update,
+              params: {
+                account_id: site.account,
+                id: site,
+                site: {
+                  custom_404_entry_id: entry.id
+                }
+              })
+
+        expect(site.reload.custom_404_entry_id).to eq(entry.id)
+      end
+
+      it 'clears custom_404_entry_id when set to blank' do
+        site = create(:site)
+        entry = create(:entry, :published, site: site)
+        site.update!(custom_404_entry: entry)
+
+        sign_in(create(:user, :admin), scope: :user)
+        patch(:update,
+              params: {
+                account_id: site.account,
+                id: site,
+                site: {
+                  custom_404_entry_id: ''
+                }
+              })
+
+        expect(site.reload.custom_404_entry_id).to be_nil
+      end
     end
   end
 end