Persist event filter state across reload and navigation

contao/templates/frontend/event_filter.html.twig

@@ -124,6 +124,8 @@
     const orgWidget = orgSelect?.closest('.widget-select');
     const resetButton = filters.querySelector('#eventfilter-reset');
     const status = filters.querySelector('#eventfilter-status');
+    const stateStorageKey = 'event-filter-state';
+    const stateQueryKey = 'event_filter';
 
     const animationMs = 220;
     let hideTimers = new WeakMap();
@@ -182,6 +184,109 @@
     const locationTom = initTomSelect(locationSelect);
     const orgTom = initTomSelect(orgSelect);
 
+    const hasOptionValue = (selectElement, value) => {
+        if (!selectElement) {
+            return false;
+        }
+
+        return Array.from(selectElement.options).some((option) => option.value === value);
+    };
+
+    const rawValueToFilterState = (rawValue) => {
+        const value = (rawValue || '').trim();
+
+        if (!value) {
+            return { type: 'all', value: '' };
+        }
+
+        if (value.startsWith('tag-') && hasOptionValue(tagSelect, value)) {
+            return { type: 'tag', value: value.replace('tag-', '') };
+        }
+
+        if (value.startsWith('location-') && hasOptionValue(locationSelect, value)) {
+            return { type: 'location', value: value.replace('location-', '') };
+        }
+
+        if (value.startsWith('org-') && hasOptionValue(orgSelect, value)) {
+            return { type: 'org', value: value.replace('org-', '') };
+        }
+
+        return { type: 'all', value: '' };
+    };
+
+    const filterStateToRawValue = (filterState) => {
+        if (!filterState.value || filterState.type === 'all') {
+            return '';
+        }
+
+        if (filterState.type === 'tag') {
+            return `tag-${filterState.value}`;
+        }
+
+        if (filterState.type === 'location') {
+            return `location-${filterState.value}`;
+        }
+
+        if (filterState.type === 'org') {
+            return `org-${filterState.value}`;
+        }
+
+        return '';
+    };
+
+    const readUrlState = () => {
+        const url = new URL(window.location.href);
+        return (url.searchParams.get(stateQueryKey) || '').trim();
+    };
+
+    const writeUrlState = (value) => {
+        const url = new URL(window.location.href);
+
+        if (value) {
+            url.searchParams.set(stateQueryKey, value);
+        } else {
+            url.searchParams.delete(stateQueryKey);
+        }
+
+        window.history.replaceState(window.history.state, '', url);
+    };
+
+    const readStoredState = () => {
+        try {
+            return (window.sessionStorage.getItem(stateStorageKey) || '').trim();
+        } catch (error) {
+            return '';
+        }
+    };
+
+    const writeStoredState = (value) => {
+        try {
+            if (value) {
+                window.sessionStorage.setItem(stateStorageKey, value);
+            } else {
+                window.sessionStorage.removeItem(stateStorageKey);
+            }
+        } catch (error) {
+            // noop
+        }
+    };
+
+    const syncState = (filterState) => {
+        const rawValue = filterStateToRawValue(filterState);
+        writeStoredState(rawValue);
+        writeUrlState(rawValue);
+    };
+
+    const applyControlState = (filterState) => {
+        const tagValue = filterState.type === 'tag' ? `tag-${filterState.value}` : '';
+        const locationValue = filterState.type === 'location' ? `location-${filterState.value}` : '';
+        const orgValue = filterState.type === 'org' ? `org-${filterState.value}` : '';
+
+        setSelectValue(tagSelect, tagTom, tagValue);
+        setSelectValue(locationSelect, locationTom, locationValue);
+        setSelectValue(orgSelect, orgTom, orgValue);
+    };
+
     const setSelectValue = (selectElement, tomInstance, value) => {
         if (!selectElement) {
             return;
@@ -314,6 +419,7 @@
         });
 
         updateStatus(filterState);
+        syncState(filterState);
     };
 
     tagSelect?.addEventListener('change', () => {
@@ -375,5 +481,16 @@
         applyFilter({ type: 'all', value: '' });
     });
 
-    applyFilter(currentFilter);
+    const urlState = readUrlState();
+    const storedState = readStoredState();
+    const initialState = rawValueToFilterState(urlState || storedState);
+
+    applyControlState(initialState);
+    applyFilter(initialState);
+
+    window.addEventListener('popstate', () => {
+        const stateFromUrl = rawValueToFilterState(readUrlState());
+        applyControlState(stateFromUrl);
+        applyFilter(stateFromUrl);
+    });
 </script>