feat: enhance CssClassBuilder with improved selected classes display and preview functionality

frontends/nextjs/src/components/CssClassBuilder.tsx

@@ -159,9 +159,17 @@ export function CssClassBuilder({ open, onClose, initialValue = '', onSave }: Cs
             )}
           </div>
 
-          {selectedClasses.length > 0 && (
-            <div className="p-4 border rounded-lg bg-muted/50">
-              <Label className="text-xs uppercase tracking-wider mb-2 block">Selected Classes</Label>
+          {selectedClasses.length > 0 ? (
+            <div className="p-4 border rounded-lg bg-muted/50 space-y-3">
+              <div className="flex items-center justify-between">
+                <Label className="text-xs uppercase tracking-wider">Selected Classes</Label>
+                <div className="flex items-center gap-2">
+                  <span className="text-xs text-muted-foreground">{selectedClasses.length} selected</span>
+                  <Button size="sm" variant="ghost" onClick={clearSelectedClasses}>
+                    Clear
+                  </Button>
+                </div>
+              </div>
               <div className="flex flex-wrap gap-2">
                 {selectedClasses.map(cls => (
                   <Badge key={cls} variant="secondary" className="gap-2">
@@ -175,15 +183,46 @@ export function CssClassBuilder({ open, onClose, initialValue = '', onSave }: Cs
                   </Badge>
                 ))}
               </div>
-              <div className="mt-3 p-2 bg-background rounded border font-mono text-sm">
+              <div className="rounded border bg-background p-2 font-mono text-sm">
                 {selectedClasses.join(' ')}
               </div>
             </div>
+          ) : (
+            <div className="p-4 border rounded-lg bg-muted/30 text-sm text-muted-foreground">
+              No classes selected yet. Choose classes to preview and apply.
+            </div>
           )}
 
-          <Tabs defaultValue={filteredCategories[0]?.name || 'custom'} className="flex-1">
-            <ScrollArea className="max-h-[50px]">
-              <TabsList className="w-full">
+          <div className="p-4 border rounded-lg bg-muted/30 space-y-2">
+            <Label className="text-xs uppercase tracking-wider">Preview</Label>
+            <div className="rounded-md border border-dashed bg-background p-3">
+              <div className={`rounded-md p-4 transition-all ${selectedClasses.join(' ')}`}>
+                <div className="text-sm font-semibold">Preview element</div>
+                <div className="text-xs text-muted-foreground">
+                  This sample updates as you add or remove classes.
+                </div>
+                <div className="mt-3 inline-flex items-center rounded-md border px-3 py-1 text-xs">
+                  Sample button
+                </div>
+              </div>
+            </div>
+          </div>
+
+          {filteredCategories.length === 0 && categories.length === 0 && (
+            <div className="rounded-lg border bg-muted/30 p-4 text-sm text-muted-foreground">
+              No CSS categories available yet. Add some in the CSS Classes tab.
+            </div>
+          )}
+
+          {filteredCategories.length === 0 && categories.length > 0 && normalizedSearch && (
+            <div className="rounded-lg border bg-muted/30 p-4 text-sm text-muted-foreground">
+              No classes match &quot;{searchQuery}&quot;.
+            </div>
+          )}
+
+          <Tabs value={activeTab} onValueChange={setActiveTab} className="flex-1">
+            <div className="overflow-x-auto">
+              <TabsList className="w-max">
                 {filteredCategories.map(category => (
                   <TabsTrigger key={category.name} value={category.name}>
                     {category.name}
@@ -191,7 +230,7 @@ export function CssClassBuilder({ open, onClose, initialValue = '', onSave }: Cs
                 ))}
                 <TabsTrigger value="custom">Custom</TabsTrigger>
               </TabsList>
-            </ScrollArea>
+            </div>
 
             {filteredCategories.map(category => (
               <TabsContent key={category.name} value={category.name}>

frontends/nextjs/src/lib/components/component-registry.ts

@@ -1,63 +1,5 @@
-import { componentCatalog } from './component-catalog'
-import type { ComponentDefinition } from './builder-types'
+export type { ComponentTypeDefinition } from './component-registry/types'
 
-export interface ComponentTypeDefinition extends ComponentDefinition {
-  renderingLogic?: {
-    type: 'shadcn' | 'declarative' | 'custom'
-    componentName?: string
-    customRenderer?: string
-  }
-}
-
-export class ComponentRegistry {
-  private components: Map<string, ComponentTypeDefinition> = new Map()
-
-  constructor() {
-    this.loadFromCatalog()
-  }
-
-  private loadFromCatalog(): void {
-    componentCatalog.forEach(comp => {
-      this.registerComponent(comp as ComponentTypeDefinition)
-    })
-  }
-
-  registerComponent(component: ComponentTypeDefinition): void {
-    this.components.set(component.type, component)
-  }
-
-  registerComponents(components: ComponentTypeDefinition[]): void {
-    components.forEach(comp => this.registerComponent(comp))
-  }
-
-  getComponent(type: string): ComponentTypeDefinition | undefined {
-    return this.components.get(type)
-  }
-
-  getAllComponents(): ComponentTypeDefinition[] {
-    return Array.from(this.components.values())
-  }
-
-  getComponentsByCategory(category: string): ComponentTypeDefinition[] {
-    return Array.from(this.components.values()).filter(
-      comp => comp.category === category
-    )
-  }
-
-  hasComponent(type: string): boolean {
-    return this.components.has(type)
-  }
-}
-
-let registryInstance: ComponentRegistry | null = null
-
-export function getComponentRegistry(): ComponentRegistry {
-  if (!registryInstance) {
-    registryInstance = new ComponentRegistry()
-  }
-  return registryInstance
-}
-
-export async function initializeComponentRegistry(): Promise<void> {
-  getComponentRegistry()
-}
+export { ComponentRegistry } from './component-registry/registry-class'
+export { getComponentRegistry } from './component-registry/get-component-registry'
+export { initializeComponentRegistry } from './component-registry/initialize-component-registry'

frontends/nextjs/src/lib/components/component-registry/get-component-registry.ts

@@ -0,0 +1,9 @@
+import { ComponentRegistry } from './registry-class'
+import { componentRegistryState } from './registry-singleton'
+
+export function getComponentRegistry(): ComponentRegistry {
+  if (!componentRegistryState.instance) {
+    componentRegistryState.instance = new ComponentRegistry()
+  }
+  return componentRegistryState.instance
+}

frontends/nextjs/src/lib/components/component-registry/initialize-component-registry.ts

@@ -0,0 +1,5 @@
+import { getComponentRegistry } from './get-component-registry'
+
+export async function initializeComponentRegistry(): Promise<void> {
+  getComponentRegistry()
+}