[1036] Improve case studies search filtering with dynamic facet counts and empty-state UX (#268)

## Summary
- Update case studies filter counts to recalculate from the current
result set (active search + active filters), instead of using
static/global counts.
- Keep existing result filtering behavior unchanged; only count
calculation logic is synchronized with what the user currently sees.

Author: IhorMasechko

website/modules/case-studies-page/index.js

@@ -67,6 +67,26 @@ const buildIndexQuery = function (self, req) {
   return query;
 };
 
+const buildTagCountQuery = function (self, req) {
+  const queryParams = { ...req.query };
+  const searchTerm = SearchService.getSearchTerm(queryParams);
+  delete queryParams.search;
+  delete queryParams.page;
+
+  const query = self.pieces.find(req, {}).applyBuildersSafely(queryParams);
+  self.filterByIndexPage(query, req.data.page);
+
+  const resolved = req.data.searchRelationships || {};
+  const searchCondition = SearchService.buildSearchCondition(
+    searchTerm,
+    resolved,
+  );
+  if (searchCondition) {
+    query.and(searchCondition);
+  }
+  return query;
+};
+
 const runResolveSearchRelationships = async function (self, req) {
   req.data ||= {};
   const reqData = req.data;
@@ -125,10 +145,13 @@ const runApplyEnhancedSearchResults = async function (self, req) {
 
 const runSetupIndexData = async function (self, req) {
   try {
+    const countQuery = buildTagCountQuery(self, req);
+    const caseStudiesForCounts = await countQuery.toArray();
     const tagCounts = await TagCountService.calculateTagCounts(
       req,
       self.apos.modules,
       self.options,
+      caseStudiesForCounts,
     );
     UrlService.attachIndexData(req, tagCounts);
   } catch (error) {

website/modules/case-studies-page/services/TagCountService.js

@@ -49,13 +49,16 @@ class TagCountService {
    * @param {Object} options - Module options
    * @returns {Promise<Array>} Promise resolving to [caseStudies, casesTags, businessPartners] arrays
    */
-  static async fetchCaseStudiesAndTags(req, aposModules, options) {
-    const [caseStudies, casesTags, businessPartners] = await Promise.all([
-      aposModules[options.pieces].find(req).toArray(),
+  static async fetchCaseStudiesAndTags(req, aposModules, options, caseStudies) {
+    const [casesTags, businessPartners] = await Promise.all([
       aposModules['cases-tags'].find(req).toArray(),
       aposModules['business-partner'].find(req).toArray(),
     ]);
-    return [caseStudies, casesTags, businessPartners];
+    let pieces = caseStudies;
+    if (!pieces) {
+      pieces = await aposModules[options.pieces].find(req).toArray();
+    }
+    return [pieces, casesTags, businessPartners];
   }
 
   /**
@@ -96,7 +99,7 @@ class TagCountService {
    * @param {Object} options - Module options
    * @returns {Promise<Object>} Tag counts by type
    */
-  static async calculateTagCounts(req, aposModules, options) {
+  static async calculateTagCounts(req, aposModules, options, caseStudiesInput) {
     const tagCounts = {
       industry: {},
       stack: {},
@@ -105,7 +108,12 @@ class TagCountService {
     };
 
     const [caseStudies, casesTags, businessPartners] =
-      await TagCountService.fetchCaseStudiesAndTags(req, aposModules, options);
+      await TagCountService.fetchCaseStudiesAndTags(
+        req,
+        aposModules,
+        options,
+        caseStudiesInput,
+      );
 
     const tagMap = TagCountService.createIdToSlugMap(casesTags);
     const partnerMap = TagCountService.createIdToSlugMap(businessPartners);