commit d2d9b562007fbcad78879e40ef73cfeb6adfdee2
Author: Paul Pound <ppound@upei.ca>
Date:   Thu Aug 27 13:31:54 2026 -0300

    initial commit

diff --git a/README.md b/README.md
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+# Preserve Advanced Search
+
+Keeps the advanced search `a[]` query parameters attached to the facet slider
+URLs that Facets builds server-side, so clicking a slider doesn't drop the
+user's advanced search criteria.
+
+Replaces the equivalent code that previously lived in individual themes
+(`THEME.libraries.yml` + `THEME_preprocess_page()`).
+
+## Install
+
+Copy this directory to `web/modules/custom/preserve_advanced_search` on each
+site, then:
+
+    drush en preserve_advanced_search
+    drush cr
+
+## Scope
+
+`hook_library_info_alter()` appends this module's library to the dependencies of
+`facets_range_nouislider/facets_range_nouislider`. It therefore loads only on
+pages that actually render a noUiSlider facet — not site-wide, and with no route
+list to maintain per site.
+
+Library info is cached, so run `drush cr` after deploying or the alter won't
+take effect.
+
+If a site configures its facets with the **Facets core** slider widget
+(`facets_range_widget`) instead of `facets_range_nouislider`, add that
+extension's library to the alter as well. Both submodules write to
+`drupalSettings.facets.sliders`, so the JavaScript itself needs no change — only
+the attachment point does.
+
+## Notes
+
+- Load order is guaranteed by the dependency: our script is loaded ahead of
+  `slider.js`, so `Drupal.behaviors.preserveAdvancedSearchParams` is registered
+  first and runs first. `facets_range_nouislider`'s `slider.js` is additionally
+  marked `defer: true` while ours is not, and non-deferred scripts always
+  execute before deferred ones — so the ordering holds twice over.
+- `rebuildUrl()` is idempotent (it strips all `a[]` params before re-adding the
+  current ones), so re-running on AJAX rebuilds is safe.
+- The JS handles both `sliderSettings.url` and `sliderSettings.urls`. Range
+  widgets collapse the parent's `urls` map into a single `url`
+  (`RangeNoUiSliderWidget::build()`); single-handle widgets keep `urls`. Both
+  branches are live — don't remove either.
diff --git a/js/preserve-advanced-search.js b/js/preserve-advanced-search.js
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+(function (Drupal, drupalSettings) {
+  'use strict';
+
+  Drupal.behaviors.preserveAdvancedSearchParams = {
+    attach: function (context, settings) {
+
+      // Capture the a[] advanced search params from the current URL
+      const rawSearch = window.location.search;
+      const aParams = rawSearch
+        .substring(1)
+        .split('&')
+        .filter(part => part.startsWith('a%5B') || part.startsWith('a['))
+        .join('&');
+
+      if (!aParams) return;
+
+      const sliders = settings.facets && settings.facets.sliders;
+      if (!sliders) return;
+
+      // Replace any a[] params in a URL with the current page's a[] params.
+      // The current URL is always the source of truth — the server-built
+      // slider URL may contain stale or partial a[] params.
+      function rebuildUrl(url) {
+        if (!url) return url;
+        const parts = url.split('?');
+        const basePath = parts[0];
+        const query = parts[1] || '';
+
+        // Keep everything that is NOT an a[] param (i.e. the f[] facet params)
+        const keptParams = query
+          .split('&')
+          .filter(p => p.length > 0)
+          .filter(p => !p.startsWith('a%5B') && !p.startsWith('a['))
+          .join('&');
+
+        const finalQuery = [keptParams, aParams].filter(Boolean).join('&');
+        return basePath + '?' + finalQuery;
+      }
+
+      // Range sliders expose a single `url`; single-handle sliders expose a
+      // `urls` map keyed by value. Handle both — which one is present depends
+      // on the widget the facet is configured with.
+      Object.keys(sliders).forEach(function (key) {
+        const sliderSettings = sliders[key];
+
+        if (sliderSettings.url) {
+          sliderSettings.url = rebuildUrl(sliderSettings.url);
+        }
+
+        if (sliderSettings.urls) {
+          Object.keys(sliderSettings.urls).forEach(function (urlKey) {
+            sliderSettings.urls[urlKey] = rebuildUrl(sliderSettings.urls[urlKey]);
+          });
+        }
+      });
+    }
+  };
+
+})(Drupal, drupalSettings);
diff --git a/preserve_advanced_search.info.yml b/preserve_advanced_search.info.yml
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+name: 'Preserve Advanced Search'
+type: module
+description: 'Keeps advanced search a[] query parameters attached to facet slider URLs built by the server.'
+package: 'Custom'
+core_version_requirement: ^10 || ^11
diff --git a/preserve_advanced_search.libraries.yml b/preserve_advanced_search.libraries.yml
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+++ b/preserve_advanced_search.libraries.yml
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+preserve-advanced-search:
+  version: VERSION
+  js:
+    js/preserve-advanced-search.js: {}
+  dependencies:
+    - core/drupal
+    - core/drupalSettings
diff --git a/preserve_advanced_search.module b/preserve_advanced_search.module
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+<?php
+
+/**
+ * @file
+ * Preserves advanced search a[] parameters on facet slider URLs.
+ */
+
+/**
+ * Implements hook_library_info_alter().
+ *
+ * Attaches the fix-up library as a dependency of the slider widget library
+ * rather than to every page. This scopes it to the pages that actually render
+ * a slider, and guarantees our script loads first so the behavior is
+ * registered — and therefore runs — before the slider reads
+ * drupalSettings.facets.sliders.
+ */
+function preserve_advanced_search_library_info_alter(array &$libraries, $extension)
+{
+    if ($extension !== 'facets_range_nouislider') {
+        return;
+    }
+
+    if (isset($libraries['facets_range_nouislider'])) {
+        $libraries['facets_range_nouislider']['dependencies'][] = 'preserve_advanced_search/preserve-advanced-search';
+    }
+}