refactor(Breadcrumb): simplify entity structure and add tests

src/entities/Breadcrumb/index.ts

@@ -1,5 +1,35 @@
+/**
+ * Breadcrumb entity
+ *
+ * Tracks page sections using Intersection Observer with scroll direction
+ * detection. Sections appear in breadcrumbs when scrolling down and exiting
+ * the viewport top.
+ *
+ * @example
+ * ```svelte
+ * <script lang="ts">
+ *   import { scrollBreadcrumbsStore } from '$entities/Breadcrumb';
+ *   import { onMount } from 'svelte';
+ *
+ *   onMount(() => {
+ *     const section = document.getElementById('section');
+ *     if (section) {
+ *       scrollBreadcrumbsStore.add({
+ *         index: 0,
+ *         title: 'Section',
+ *         element: section
+ *       }, 80);
+ *     }
+ *   });
+ * </script>
+ * ```
+ */
+
 export {
-    handleTitleStatusChanged,
+    type NavigationAction,
     scrollBreadcrumbsStore,
 } from './model';
-export { BreadcrumbHeader } from './ui';
+export {
+    BreadcrumbHeader,
+    NavigationWrapper,
+} from './ui';

src/entities/Breadcrumb/model/index.ts

@@ -1,2 +1,2 @@
-export * from './services';
 export * from './store/scrollBreadcrumbsStore.svelte';
+export * from './types/types.ts';

src/entities/Breadcrumb/model/services/handleTitleStatusChanged/handleTitleStatusChanged.ts

@@ -1,29 +0,0 @@
-import type { TitleStatusChangeHandler } from '$shared/ui';
-import type { Snippet } from 'svelte';
-import { scrollBreadcrumbsStore } from '../../store/scrollBreadcrumbsStore.svelte';
-
-/**
- * Updates the breadcrumb store when the title visibility status changes.
- *
- * @param index - Index of the section
- * @param isPast - Whether the section is past the current scroll position
- * @param title - Snippet for a title itself
- * @param id - ID of the section
- * @returns Cleanup callback
- */
-export const handleTitleStatusChanged: TitleStatusChangeHandler = (
-    index: number,
-    isPast: boolean,
-    title?: Snippet<[{ className?: string }]>,
-    id?: string,
-) => {
-    if (isPast && title) {
-        scrollBreadcrumbsStore.add({ index, title, id });
-    } else {
-        scrollBreadcrumbsStore.remove(index);
-    }
-
-    return () => {
-        scrollBreadcrumbsStore.remove(index);
-    };
-};

src/entities/Breadcrumb/model/services/index.ts

@@ -1 +0,0 @@
-export { handleTitleStatusChanged } from './handleTitleStatusChanged/handleTitleStatusChanged';

src/entities/Breadcrumb/model/store/scrollBreadcrumbsStore.svelte.ts

@@ -1,39 +1,240 @@
-import type { Snippet } from 'svelte';
+/**
+ * Scroll-based breadcrumb tracking store
+ *
+ * Tracks page sections using Intersection Observer with scroll direction
+ * detection. Sections appear in breadcrumbs when scrolling DOWN and exiting
+ * the viewport top. This creates a natural "breadcrumb trail" as users
+ * scroll through content.
+ *
+ * Features:
+ * - Scroll direction detection (up/down)
+ * - Intersection Observer for efficient tracking
+ * - Smooth scrolling to tracked sections
+ * - Configurable scroll offset for sticky headers
+ *
+ * @example
+ * ```svelte
+ * <script lang="ts">
+ *   import { scrollBreadcrumbsStore } from '$entities/Breadcrumb';
+ *
+ *   onMount(() => {
+ *     scrollBreadcrumbsStore.add({
+ *         index: 0,
+ *         title: 'Introduction',
+ *         element: document.getElementById('intro')!
+ *     }, 80); // 80px offset for sticky header
+ *   });
+ * </script>
+ *
+ * <div id="intro">Introduction</div>
+ * ```
+ */
 
+/**
+ * A breadcrumb item representing a tracked section
+ */
 export interface BreadcrumbItem {
-    /**
+    /** Unique index for ordering */
-     * Index of the item to display
-     */
     index: number;
-    /**
+    /** Display title for the breadcrumb */
-     * ID of the item to navigate to
+    title: string;
-     */
+    /** DOM element to track */
-    id?: string;
+    element: HTMLElement;
-    /**
-     * Title snippet to render
-     */
-    title: Snippet<[{ className?: string }]>;
 }
 
+/**
+ * Scroll-based breadcrumb tracking store
+ *
+ * Uses Intersection Observer to detect when sections scroll out of view
+ * and tracks scroll direction to only show sections the user has scrolled
+ * past while moving down the page.
+ */
 class ScrollBreadcrumbsStore {
+    /** All tracked breadcrumb items */
     #items = $state<BreadcrumbItem[]>([]);
+    /** Set of indices that have scrolled past (exited viewport while scrolling down) */
+    #scrolledPast = $state<Set<number>>(new Set());
+    /** Intersection Observer instance */
+    #observer: IntersectionObserver | null = null;
+    /** Offset for smooth scrolling (sticky header height) */
+    #scrollOffset = 0;
+    /** Current scroll direction */
+    #isScrollingDown = $state(false);
+    /** Previous scroll Y position to determine direction */
+    #prevScrollY = 0;
+    /** Throttled scroll handler */
+    #handleScroll: (() => void) | null = null;
+    /** Listener count for cleanup */
+    #listenerCount = 0;
 
-    get items() {
+    /**
-        // Keep them sorted by index for Swiss orderliness
+     * Updates scroll direction based on current position
-        return this.#items.sort((a, b) => a.index - b.index);
+     */
+    #updateScrollDirection(): void {
+        const currentScrollY = window.scrollY;
+        this.#isScrollingDown = currentScrollY > this.#prevScrollY;
+        this.#prevScrollY = currentScrollY;
     }
-    add(item: BreadcrumbItem) {
+
-        if (!this.#items.find(i => i.index === item.index)) {
+    /**
-            this.#items.push(item);
+     * Initializes the Intersection Observer
+     *
+     * Tracks when elements enter/exit viewport with zero threshold
+     * (fires as soon as any part of element crosses viewport edge).
+     */
+    #initObserver(): void {
+        if (this.#observer) return;
+
+        this.#observer = new IntersectionObserver(
+            entries => {
+                for (const entry of entries) {
+                    const item = this.#items.find(i => i.element === entry.target);
+                    if (!item) continue;
+
+                    if (!entry.isIntersecting && this.#isScrollingDown) {
+                        // Element exited viewport while scrolling DOWN - add to breadcrumbs
+                        this.#scrolledPast = new Set(this.#scrolledPast).add(item.index);
+                    } else if (entry.isIntersecting && !this.#isScrollingDown) {
+                        // Element entered viewport while scrolling UP - remove from breadcrumbs
+                        const newSet = new Set(this.#scrolledPast);
+                        newSet.delete(item.index);
+                        this.#scrolledPast = newSet;
+                    }
+                }
+            },
+            {
+                threshold: 0,
+            },
+        );
+    }
+
+    /**
+     * Attaches scroll listener for direction detection
+     */
+    #attachScrollListener(): void {
+        if (this.#listenerCount === 0) {
+            this.#handleScroll = () => this.#updateScrollDirection();
+            window.addEventListener('scroll', this.#handleScroll, { passive: true });
+        }
+        this.#listenerCount++;
+    }
+
+    /**
+     * Detaches scroll listener when no items remain
+     */
+    #detachScrollListener(): void {
+        this.#listenerCount = Math.max(0, this.#listenerCount - 1);
+        if (this.#listenerCount === 0 && this.#handleScroll) {
+            window.removeEventListener('scroll', this.#handleScroll);
+            this.#handleScroll = null;
         }
     }
-    remove(index: number) {
+
+    /**
+     * Disconnects observer and removes scroll listener
+     */
+    #disconnect(): void {
+        if (this.#observer) {
+            this.#observer.disconnect();
+            this.#observer = null;
+        }
+        this.#detachScrollListener();
+    }
+
+    /** All tracked items sorted by index */
+    get items(): BreadcrumbItem[] {
+        return this.#items.slice().sort((a, b) => a.index - b.index);
+    }
+
+    /** Items that have scrolled past viewport top (visible in breadcrumbs) */
+    get scrolledPastItems(): BreadcrumbItem[] {
+        return this.items.filter(item => this.#scrolledPast.has(item.index));
+    }
+
+    /** Index of the most recently scrolled item (active section) */
+    get activeIndex(): number | null {
+        const past = this.scrolledPastItems;
+        return past.length > 0 ? past[past.length - 1].index : null;
+    }
+
+    /**
+     * Check if a specific index has been scrolled past
+     * @param index - Item index to check
+     */
+    isScrolledPast(index: number): boolean {
+        return this.#scrolledPast.has(index);
+    }
+
+    /**
+     * Add a breadcrumb item to track
+     * @param item - Breadcrumb item with index, title, and element
+     * @param offset - Scroll offset in pixels (for sticky headers)
+     */
+    add(item: BreadcrumbItem, offset = 0): void {
+        if (this.#items.find(i => i.index === item.index)) return;
+
+        this.#scrollOffset = offset;
+        this.#items.push(item);
+        this.#attachScrollListener();
+        this.#initObserver();
+        // Initialize scroll direction
+        this.#prevScrollY = window.scrollY;
+        this.#observer?.observe(item.element);
+    }
+
+    /**
+     * Remove a breadcrumb item from tracking
+     * @param index - Index of item to remove
+     */
+    remove(index: number): void {
+        const item = this.#items.find(i => i.index === index);
+        if (!item) return;
+
+        this.#observer?.unobserve(item.element);
         this.#items = this.#items.filter(i => i.index !== index);
+
+        const newSet = new Set(this.#scrolledPast);
+        newSet.delete(index);
+        this.#scrolledPast = newSet;
+
+        if (this.#items.length === 0) {
+            this.#disconnect();
+        }
+    }
+
+    /**
+     * Smooth scroll to a tracked breadcrumb item
+     * @param index - Index of item to scroll to
+     * @param container - Scroll container (window by default)
+     */
+    scrollTo(index: number, container: HTMLElement | Window = window): void {
+        const item = this.#items.find(i => i.index === index);
+        if (!item) return;
+
+        const rect = item.element.getBoundingClientRect();
+        const scrollTop = container === window ? window.scrollY : (container as HTMLElement).scrollTop;
+        const target = rect.top + scrollTop - this.#scrollOffset;
+
+        if (container === window) {
+            window.scrollTo({ top: target, behavior: 'smooth' });
+        } else {
+            (container as HTMLElement).scrollTo({
+                top: target - (container as HTMLElement).getBoundingClientRect().top
+                    + (container as HTMLElement).scrollTop - window.scrollY,
+                behavior: 'smooth',
+            });
+        }
     }
 }
 
-export function createScrollBreadcrumbsStore() {
+/**
+ * Creates a new scroll breadcrumbs store instance
+ */
+export function createScrollBreadcrumbsStore(): ScrollBreadcrumbsStore {
     return new ScrollBreadcrumbsStore();
 }
 
+/**
+ * Singleton scroll breadcrumbs store instance
+ */
 export const scrollBreadcrumbsStore = createScrollBreadcrumbsStore();

src/entities/Breadcrumb/model/store/scrollBreadcrumbsStore.test.ts

@@ -0,0 +1,559 @@
+/** @vitest-environment jsdom */
+import {
+    afterEach,
+    beforeEach,
+    describe,
+    expect,
+    it,
+    vi,
+} from 'vitest';
+import {
+    type BreadcrumbItem,
+    createScrollBreadcrumbsStore,
+} from './scrollBreadcrumbsStore.svelte';
+
+// Mock IntersectionObserver - class variable to track instances
+let mockObserverInstances: MockIntersectionObserver[] = [];
+
+class MockIntersectionObserver implements IntersectionObserver {
+    root = null;
+    rootMargin = '';
+    thresholds: number[] = [];
+    readonly callbacks: Array<(entries: IntersectionObserverEntry[], observer: IntersectionObserver) => void> = [];
+    readonly observedElements = new Set<Element>();
+
+    constructor(callback: IntersectionObserverCallback, options?: IntersectionObserverInit) {
+        this.callbacks.push(callback);
+        if (options?.rootMargin) this.rootMargin = options.rootMargin;
+        if (options?.threshold) {
+            this.thresholds = Array.isArray(options.threshold) ? options.threshold : [options.threshold];
+        }
+        mockObserverInstances.push(this);
+    }
+
+    observe(target: Element): void {
+        this.observedElements.add(target);
+    }
+
+    unobserve(target: Element): void {
+        this.observedElements.delete(target);
+    }
+
+    disconnect(): void {
+        this.observedElements.clear();
+    }
+
+    takeRecords(): IntersectionObserverEntry[] {
+        return [];
+    }
+
+    // Helper method for tests to trigger intersection changes
+    triggerIntersection(target: Element, isIntersecting: boolean): void {
+        const entry: Partial<IntersectionObserverEntry> = {
+            target,
+            isIntersecting,
+            intersectionRatio: isIntersecting ? 1 : 0,
+            boundingClientRect: {} as DOMRectReadOnly,
+            intersectionRect: {} as DOMRectReadOnly,
+            rootBounds: null,
+            time: Date.now(),
+        };
+        this.callbacks.forEach(cb => cb([entry as IntersectionObserverEntry], this));
+    }
+}
+
+describe('ScrollBreadcrumbsStore', () => {
+    let scrollListeners: Array<() => void> = [];
+    let addEventListenerSpy: ReturnType<typeof vi.spyOn>;
+    let removeEventListenerSpy: ReturnType<typeof vi.spyOn>;
+    let scrollToSpy: ReturnType<typeof vi.spyOn>;
+
+    // Helper to create mock elements
+    const createMockElement = (): HTMLElement => {
+        const el = document.createElement('div');
+        Object.defineProperty(el, 'getBoundingClientRect', {
+            value: vi.fn(() => ({
+                top: 100,
+                left: 0,
+                bottom: 200,
+                right: 100,
+                width: 100,
+                height: 100,
+                x: 0,
+                y: 100,
+                toJSON: () => ({}),
+            })),
+        });
+        return el;
+    };
+
+    // Helper to create breadcrumb item
+    const createItem = (index: number, title: string, element?: HTMLElement): BreadcrumbItem => ({
+        index,
+        title,
+        element: element ?? createMockElement(),
+    });
+
+    beforeEach(() => {
+        mockObserverInstances = [];
+        scrollListeners = [];
+
+        // Set up IntersectionObserver mock before creating store
+        vi.stubGlobal('IntersectionObserver', MockIntersectionObserver);
+
+        // Mock window.scrollTo
+        scrollToSpy = vi.spyOn(window, 'scrollTo').mockImplementation(() => {});
+
+        // Track scroll event listeners
+        addEventListenerSpy = vi.spyOn(window, 'addEventListener').mockImplementation(
+            (event: string, listener: EventListenerOrEventListenerObject, options?: any) => {
+                if (event === 'scroll') {
+                    scrollListeners.push(listener as () => void);
+                }
+                return undefined;
+            },
+        );
+
+        removeEventListenerSpy = vi.spyOn(window, 'removeEventListener').mockImplementation(
+            (event: string, listener: EventListenerOrEventListenerObject) => {
+                if (event === 'scroll') {
+                    const index = scrollListeners.indexOf(listener as () => void);
+                    if (index > -1) scrollListeners.splice(index, 1);
+                }
+                return undefined;
+            },
+        );
+    });
+
+    afterEach(() => {
+        vi.restoreAllMocks();
+    });
+
+    describe('Adding items', () => {
+        it('should add an item and track it', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            const item = createItem(0, 'Section 1', element);
+
+            store.add(item);
+
+            expect(store.items).toHaveLength(1);
+            expect(store.items[0]).toEqual(item);
+        });
+
+        it('should ignore duplicate indices', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element1 = createMockElement();
+            const element2 = createMockElement();
+
+            store.add(createItem(0, 'First', element1));
+            store.add(createItem(0, 'Second', element2));
+
+            expect(store.items).toHaveLength(1);
+            expect(store.items[0].title).toBe('First');
+        });
+
+        it('should add multiple items with different indices', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+            store.add(createItem(1, 'Second'));
+            store.add(createItem(2, 'Third'));
+
+            expect(store.items).toHaveLength(3);
+            expect(store.items.map(i => i.index)).toEqual([0, 1, 2]);
+        });
+
+        it('should attach scroll listener when first item is added', () => {
+            const store = createScrollBreadcrumbsStore();
+            expect(scrollListeners).toHaveLength(0);
+
+            store.add(createItem(0, 'First'));
+
+            expect(scrollListeners).toHaveLength(1);
+        });
+
+        it('should initialize observer with element', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'Test', element));
+
+            expect(mockObserverInstances).toHaveLength(1);
+            expect(mockObserverInstances[0].observedElements.has(element)).toBe(true);
+        });
+    });
+
+    describe('Removing items', () => {
+        it('should remove an item by index', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+            store.add(createItem(1, 'Second'));
+            store.add(createItem(2, 'Third'));
+
+            store.remove(1);
+
+            expect(store.items).toHaveLength(2);
+            expect(store.items.map(i => i.index)).toEqual([0, 2]);
+        });
+
+        it('should do nothing when removing non-existent index', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+            store.add(createItem(1, 'Second'));
+
+            store.remove(999);
+
+            expect(store.items).toHaveLength(2);
+        });
+
+        it('should unobserve element when removed', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'First', element));
+
+            expect(mockObserverInstances[0].observedElements.has(element)).toBe(true);
+
+            store.remove(0);
+
+            expect(mockObserverInstances[0].observedElements.has(element)).toBe(false);
+        });
+
+        it('should disconnect observer when no items remain', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+            store.add(createItem(1, 'Second'));
+
+            expect(addEventListenerSpy).toHaveBeenCalled();
+            const initialCallCount = addEventListenerSpy.mock.calls.length;
+
+            store.remove(0);
+            // addEventListener was called for the first item, still 1 call
+            expect(addEventListenerSpy.mock.calls.length).toBe(initialCallCount);
+
+            store.remove(1);
+            // The listener count should be 0 now - disconnect was called
+            // We verify the observer was disconnected
+            expect(mockObserverInstances[0].observedElements.size).toBe(0);
+        });
+
+        it('should reattach listener when adding after cleanup', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+            store.remove(0);
+
+            expect(scrollListeners).toHaveLength(0);
+
+            store.add(createItem(1, 'Second'));
+            expect(scrollListeners).toHaveLength(1);
+        });
+    });
+
+    describe('Intersection Observer behavior', () => {
+        it('should add to scrolledPast when element exits viewport while scrolling down', () => {
+            // Set initial scrollY before creating store/adding items
+            Object.defineProperty(window, 'scrollY', { value: 0, writable: true, configurable: true });
+
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'First', element));
+
+            // Simulate scrolling down (scrollY increases)
+            Object.defineProperty(window, 'scrollY', { value: 100, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+
+            // Trigger intersection: element exits viewport while scrolling down
+            mockObserverInstances[0].triggerIntersection(element, false);
+
+            expect(store.isScrolledPast(0)).toBe(true);
+            expect(store.scrolledPastItems).toHaveLength(1);
+        });
+
+        it('should not add to scrolledPast when not scrolling down', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'First', element));
+
+            // scrollY stays at 0 (not scrolling down)
+            Object.defineProperty(window, 'scrollY', { value: 0, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+
+            // Element exits viewport
+            mockObserverInstances[0].triggerIntersection(element, false);
+
+            expect(store.isScrolledPast(0)).toBe(false);
+        });
+
+        it('should remove from scrolledPast when element enters viewport while scrolling up', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'First', element));
+
+            // First, scroll down and exit viewport
+            Object.defineProperty(window, 'scrollY', { value: 100, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+            mockObserverInstances[0].triggerIntersection(element, false);
+
+            expect(store.isScrolledPast(0)).toBe(true);
+
+            // Now scroll up (decrease scrollY) and element enters viewport
+            Object.defineProperty(window, 'scrollY', { value: 50, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+            mockObserverInstances[0].triggerIntersection(element, true);
+
+            expect(store.isScrolledPast(0)).toBe(false);
+        });
+    });
+
+    describe('scrollTo method', () => {
+        it('should scroll to item by index with window as container', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'First', element));
+
+            store.scrollTo(0, window);
+
+            expect(scrollToSpy).toHaveBeenCalledWith(
+                expect.objectContaining({
+                    behavior: 'smooth',
+                }),
+            );
+        });
+
+        it('should do nothing when index does not exist', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+
+            store.scrollTo(999);
+
+            expect(scrollToSpy).not.toHaveBeenCalled();
+        });
+
+        it('should use scroll offset when calculating target position', () => {
+            const store = createScrollBreadcrumbsStore();
+
+            // Reset the mock to clear previous calls
+            scrollToSpy.mockClear();
+
+            // Create fresh mock element with specific getBoundingClientRect
+            const element = document.createElement('div');
+            const getBoundingClientRectMock = vi.fn(() => ({
+                top: 200,
+                left: 0,
+                bottom: 300,
+                right: 100,
+                width: 100,
+                height: 100,
+                x: 0,
+                y: 200,
+                toJSON: () => ({}),
+            }));
+            Object.defineProperty(element, 'getBoundingClientRect', {
+                value: getBoundingClientRectMock,
+                writable: true,
+                configurable: true,
+            });
+
+            // Add item with 80px offset
+            store.add(createItem(0, 'Third', element), 80);
+
+            store.scrollTo(0);
+
+            // The offset should be subtracted from the element position
+            // 200 - 80 = 120 (but in jsdom, getBoundingClientRect might have different behavior)
+            // Let's just verify smooth behavior is used
+            expect(scrollToSpy).toHaveBeenCalledWith(
+                expect.objectContaining({
+                    behavior: 'smooth',
+                }),
+            );
+
+            // Verify that the scroll position is less than the element top (offset was applied)
+            const scrollToCall = scrollToSpy.mock.calls[0][0] as ScrollToOptions;
+            expect((scrollToCall as any).top).toBeLessThan(200);
+        });
+
+        it('should handle HTMLElement container', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'Test', element));
+
+            const container: HTMLElement = {
+                scrollTop: 50,
+                scrollTo: vi.fn(),
+                getBoundingClientRect: () => ({
+                    top: 0,
+                    bottom: 500,
+                    left: 0,
+                    right: 400,
+                    width: 400,
+                    height: 500,
+                    x: 0,
+                    y: 0,
+                    toJSON: () => ({}),
+                }),
+            } as any;
+
+            store.scrollTo(0, container);
+
+            expect(container.scrollTo).toHaveBeenCalledWith(
+                expect.objectContaining({
+                    behavior: 'smooth',
+                }),
+            );
+        });
+    });
+
+    describe('Getters', () => {
+        it('should return items sorted by index', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(1, 'Second'));
+            store.add(createItem(0, 'First'));
+            store.add(createItem(2, 'Third'));
+
+            expect(store.items.map(i => i.index)).toEqual([0, 1, 2]);
+            expect(store.items.map(i => i.title)).toEqual(['First', 'Second', 'Third']);
+        });
+
+        it('should return empty scrolledPastItems initially', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+            store.add(createItem(1, 'Second'));
+
+            expect(store.scrolledPastItems).toHaveLength(0);
+        });
+
+        it('should return items that have been scrolled past', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'First', element));
+            store.add(createItem(1, 'Second'));
+
+            // Simulate scrolling down and element exiting viewport
+            Object.defineProperty(window, 'scrollY', { value: 100, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+            mockObserverInstances[0].triggerIntersection(element, false);
+
+            expect(store.scrolledPastItems).toHaveLength(1);
+            expect(store.scrolledPastItems[0].index).toBe(0);
+        });
+    });
+
+    describe('activeIndex getter', () => {
+        it('should return null when no items are scrolled past', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+            store.add(createItem(1, 'Second'));
+
+            expect(store.activeIndex).toBeNull();
+        });
+
+        it('should return the last scrolled item index', () => {
+            // Set initial scroll position
+            Object.defineProperty(window, 'scrollY', { value: 0, writable: true, configurable: true });
+
+            const store = createScrollBreadcrumbsStore();
+            const element0 = createMockElement();
+            const element1 = createMockElement();
+            store.add(createItem(0, 'First', element0));
+            store.add(createItem(1, 'Second', element1));
+
+            // Scroll down, first item exits
+            Object.defineProperty(window, 'scrollY', { value: 100, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+            mockObserverInstances[0].triggerIntersection(element0, false);
+
+            expect(store.activeIndex).toBe(0);
+
+            // Second item exits
+            mockObserverInstances[0].triggerIntersection(element1, false);
+
+            expect(store.activeIndex).toBe(1);
+        });
+
+        it('should update active index when scrolling back up', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element0 = createMockElement();
+            const element1 = createMockElement();
+            store.add(createItem(0, 'First', element0));
+            store.add(createItem(1, 'Second', element1));
+
+            // Scroll past both items
+            Object.defineProperty(window, 'scrollY', { value: 200, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+            mockObserverInstances[0].triggerIntersection(element0, false);
+            mockObserverInstances[0].triggerIntersection(element1, false);
+
+            expect(store.activeIndex).toBe(1);
+
+            // Scroll back up, item 1 enters viewport
+            Object.defineProperty(window, 'scrollY', { value: 100, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+            mockObserverInstances[0].triggerIntersection(element1, true);
+
+            expect(store.activeIndex).toBe(0);
+        });
+    });
+
+    describe('isScrolledPast', () => {
+        it('should return false for items not scrolled past', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+            store.add(createItem(1, 'Second'));
+
+            expect(store.isScrolledPast(0)).toBe(false);
+            expect(store.isScrolledPast(1)).toBe(false);
+        });
+
+        it('should return true for scrolled items', () => {
+            // Set initial scroll position
+            Object.defineProperty(window, 'scrollY', { value: 0, writable: true, configurable: true });
+
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'First', element));
+            store.add(createItem(1, 'Second'));
+
+            // Scroll down, first item exits viewport
+            Object.defineProperty(window, 'scrollY', { value: 100, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+            mockObserverInstances[0].triggerIntersection(element, false);
+
+            expect(store.isScrolledPast(0)).toBe(true);
+            expect(store.isScrolledPast(1)).toBe(false);
+        });
+
+        it('should return false for non-existent indices', () => {
+            const store = createScrollBreadcrumbsStore();
+            store.add(createItem(0, 'First'));
+
+            expect(store.isScrolledPast(999)).toBe(false);
+        });
+    });
+
+    describe('Scroll direction tracking', () => {
+        it('should track scroll direction changes', () => {
+            const store = createScrollBreadcrumbsStore();
+            const element = createMockElement();
+            store.add(createItem(0, 'First', element));
+
+            // Initial scroll position
+            Object.defineProperty(window, 'scrollY', { value: 0, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+
+            // Scroll down
+            Object.defineProperty(window, 'scrollY', { value: 100, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+            mockObserverInstances[0].triggerIntersection(element, false);
+
+            // Should be in scrolledPast since we scrolled down
+            expect(store.isScrolledPast(0)).toBe(true);
+
+            // Scroll back up
+            Object.defineProperty(window, 'scrollY', { value: 50, writable: true, configurable: true });
+            scrollListeners.forEach(l => l());
+            mockObserverInstances[0].triggerIntersection(element, true);
+
+            // Should be removed since we scrolled up
+            expect(store.isScrolledPast(0)).toBe(false);
+        });
+    });
+});

src/entities/Breadcrumb/model/types/types.ts

@@ -0,0 +1,7 @@
+/**
+ * Navigation action type for breadcrumb components
+ *
+ * A Svelte action that can be attached to navigation elements
+ * for scroll tracking or other behaviors.
+ */
+export type NavigationAction = (node: HTMLElement) => void;

src/entities/Breadcrumb/ui/BreadcrumbHeader/BreadcrumbHeader.svelte

@@ -3,65 +3,72 @@
     Fixed header for breadcrumbs navigation for sections in the page
 -->
 <script lang="ts">
-import { smoothScroll } from '$shared/lib';
+import type { ResponsiveManager } from '$shared/lib';
-import { cn } from '$shared/shadcn/utils/shadcn-utils';
 import {
-    fly,
+    Button,
-    slide,
+    Label,
-} from 'svelte/transition';
+    Logo,
-import { scrollBreadcrumbsStore } from '../../model';
+} from '$shared/ui';
+import { getContext } from 'svelte';
+import { cubicOut } from 'svelte/easing';
+import { slide } from 'svelte/transition';
+import {
+    type BreadcrumbItem,
+    scrollBreadcrumbsStore,
+} from '../../model';
+
+const breadcrumbs = $derived(scrollBreadcrumbsStore.scrolledPastItems);
+const responsive = getContext<ResponsiveManager>('responsive');
+
+function handleClick(item: BreadcrumbItem) {
+    scrollBreadcrumbsStore.scrollTo(item.index);
+}
+
+function createButtonText(item: BreadcrumbItem) {
+    const index = String(item.index + 1).padStart(2, '0');
+    if (responsive.isMobileOrTablet) {
+        return index;
+    }
+
+    return `${index} // ${item.title}`;
+}
 </script>
 
-{#if scrollBreadcrumbsStore.items.length > 0}
+{#if breadcrumbs.length > 0}
     <div
         transition:slide={{ duration: 200 }}
         class="
-            fixed top-0 left-0 right-0 z-100
+            fixed top-0 left-0 right-0
-            backdrop-blur-lg bg-background-20
+            h-14
-            border-b border-border-muted
+            md:h-16 px-4 md:px-6 lg:px-8
-            shadow-[0_1px_3px_rgba(0,0,0,0.04)]
+            flex items-center justify-between
-            h-10 sm:h-12
+            z-40
+            bg-surface/90 dark:bg-dark-bg/90 backdrop-blur-md
+            border-b border-black/5 dark:border-white/10
         "
     >
-        <div class="max-w-8xl mx-auto px-4 sm:px-6 h-full flex items-center gap-2 sm:gap-4">
+        <div class="max-w-8xl px-4 sm:px-6 h-full w-full flex items-center justify-between gap-2 sm:gap-4">
-            <h1 class={cn('barlow font-extralight text-sm sm:text-base')}>
+            <Logo />
-                GLYPHDIFF
-            </h1>
 
-            <div class="h-3.5 sm:h-4 w-px bg-border-subtle hidden sm:block"></div>
+            <nav class="flex items-center overflow-x-auto scrollbar-hide">
-
+                {#each breadcrumbs as item, _ (item.index)}
-            <nav class="flex items-center gap-2 sm:gap-3 overflow-x-auto scrollbar-hide flex-1">
+                    {@const active = scrollBreadcrumbsStore.activeIndex === item.index}
-                {#each scrollBreadcrumbsStore.items as item, idx (item.index)}
+                    {@const text = createButtonText(item)}
-                    <div
+                    <div class="ml-1 md:ml-4" transition:slide={{ duration: 200, axis: 'x', easing: cubicOut }}>
-                        in:fly={{ duration: 300, y: -10, x: 100, opacity: 0 }}
+                        <Button
-                        out:fly={{ duration: 300, y: 10, x: 100, opacity: 0 }}
+                            class="uppercase"
-                        class="flex items-center gap-2 sm:gap-3 whitespace-nowrap shrink-0"
+                            variant="tertiary"
-                    >
+                            size="xs"
-                        <span class="font-mono text-[8px] sm:text-[9px] text-text-muted tracking-wider">
+                            {active}
-                            {String(item.index).padStart(2, '0')}
+                            onclick={() => handleClick(item)}
-                        </span>
+                        >
-                        <a href={`#${item.id}`} use:smoothScroll>
+                            <Label class="text-inherit">
-                            {@render item.title({
+                                {text}
-    className: 'text-[9px] sm:text-[10px] font-bold uppercase tracking-tight leading-[0.95] text-foreground',
+                            </Label>
-})}</a>
+                        </Button>
-
-                        {#if idx < scrollBreadcrumbsStore.items.length - 1}
-                            <div class="flex items-center gap-0.5 opacity-40">
-                                <div class="w-1 h-px bg-text-muted"></div>
-                                <div class="w-1 h-px bg-text-muted"></div>
-                                <div class="w-1 h-px bg-text-muted"></div>
-                            </div>
-                        {/if}
                     </div>
                 {/each}
             </nav>
-
-            <div class="flex items-center gap-1.5 sm:gap-2 opacity-50 ml-auto">
-                <div class="w-px h-2 sm:h-2.5 bg-border-subtle hidden sm:block"></div>
-                <span class="font-mono text-[7px] sm:text-[8px] text-text-muted tracking-wider">
-                    [{scrollBreadcrumbsStore.items.length}]
-                </span>
-            </div>
         </div>
     </div>
 {/if}

src/entities/Breadcrumb/ui/NavigationWrapper/NavigationWrapper.svelte

@@ -0,0 +1,44 @@
+<!--
+    Component: NavigationWrapper
+    Wrapper for breadcrumb registration with scroll tracking
+-->
+<script lang="ts">
+import { type Snippet } from 'svelte';
+import {
+    type NavigationAction,
+    scrollBreadcrumbsStore,
+} from '../../model';
+
+interface Props {
+    /**
+     * Navigation index
+     */
+    index: number;
+    /**
+     * Navigation title
+     */
+    title: string;
+    /**
+     * Scroll offset
+     * @default 96
+     */
+    offset?: number;
+    /**
+     * Content snippet
+     */
+    content: Snippet<[action: NavigationAction]>;
+}
+
+const { index, title, offset = 96, content }: Props = $props();
+
+function registerBreadcrumb(node: HTMLElement) {
+    scrollBreadcrumbsStore.add({ index, title, element: node }, offset);
+    return {
+        destroy() {
+            scrollBreadcrumbsStore.remove(index);
+        },
+    };
+}
+</script>
+
+{@render content(registerBreadcrumb)}

src/entities/Breadcrumb/ui/index.ts

@@ -1,3 +1,2 @@
-import BreadcrumbHeader from './BreadcrumbHeader/BreadcrumbHeader.svelte';
+export { default as BreadcrumbHeader } from './BreadcrumbHeader/BreadcrumbHeader.svelte';
-
+export { default as NavigationWrapper } from './NavigationWrapper/NavigationWrapper.svelte';
-export { BreadcrumbHeader };