Scroll Area

import { DestroyRef, ElementRef, HostAttributeToken, Injector, PLATFORM_ID, effect, inject, runInInjectionContext } from '@angular/core';
import { clsx, type ClassValue } from 'clsx';
import { isPlatformBrowser } from '@angular/common';
import { twMerge } from 'tailwind-merge';

export function hlm(...inputs: ClassValue[]) {
	return twMerge(clsx(inputs));
}

// Global map to track class managers per element
const elementClassManagers = new WeakMap<HTMLElement, ElementClassManager>();
// Global mutation observer for all elements
let globalObserver: MutationObserver | null = null;
const observedElements = new Set<HTMLElement>();

interface ElementClassManager {
	element: HTMLElement;
	sources: Map<number, { classes: Set<string>; order: number }>;
	baseClasses: Set<string>;
	isUpdating: boolean;
	nextOrder: number;
	hasInitialized: boolean;
	restoreRafId: number | null;
	/** Transitions are suppressed until the first effect writes correct classes */
	transitionsSuppressed: boolean;
	/** Original inline transition value to restore after suppression (empty string = none was set) */
	previousTransition: string;
	/** Original inline transition priority to preserve !important when restoring */
	previousTransitionPriority: string;
}

let sourceCounter = 0;

/**
 * This function dynamically adds and removes classes for a given element without requiring
 * the a class binding (e.g. `[class]="..."`) which may interfere with other class bindings.
 *
 * 1. This will merge the existing classes on the element with the new classes.
 * 2. It will also remove any classes that were previously added by this function but are no longer present in the new classes.
 * 3. Multiple calls to this function on the same element will be merged efficiently.
 */
export function classes(computed: () => ClassValue[] | string, options: ClassesOptions = {}) {
	runInInjectionContext(options.injector ?? inject(Injector), () => {
		const elementRef = options.elementRef ?? inject(ElementRef);
		const platformId = inject(PLATFORM_ID);
		const destroyRef = inject(DestroyRef);
		const baseClasses = inject(new HostAttributeToken('class'), { optional: true });

		const element = elementRef.nativeElement;

		// Create unique identifier for this source
		const sourceId = sourceCounter++;

		// Get or create the class manager for this element
		let manager = elementClassManagers.get(element);

		if (!manager) {
			// Initialize base classes from variation (host attribute 'class')
			const initialBaseClasses = new Set<string>();

			if (baseClasses) {
				toClassList(baseClasses).forEach((cls) => initialBaseClasses.add(cls));
			}

			manager = {
				element,
				sources: new Map(),
				baseClasses: initialBaseClasses,
				isUpdating: false,
				nextOrder: 0,
				hasInitialized: false,
				restoreRafId: null,
				transitionsSuppressed: false,
				previousTransition: '',
				previousTransitionPriority: '',
			};
			elementClassManagers.set(element, manager);

			// Setup global observer if needed and register this element
			setupGlobalObserver(platformId);
			observedElements.add(element);

			// Suppress transitions until the first effect writes correct classes and
			// the browser has painted them. This prevents CSS transition animations
			// during hydration when classes change from SSR state to client state.
			if (isPlatformBrowser(platformId)) {
				manager.previousTransition = element.style.getPropertyValue('transition');
				manager.previousTransitionPriority = element.style.getPropertyPriority('transition');
				element.style.setProperty('transition', 'none', 'important');
				manager.transitionsSuppressed = true;
			}
		}

		// Assign order once at registration time
		const sourceOrder = manager.nextOrder++;

		function updateClasses(): void {
			// Get the new classes from the computed function
			const newClasses = toClassList(computed());

			// Update this source's classes, keeping the original order
			manager!.sources.set(sourceId, {
				classes: new Set(newClasses),
				order: sourceOrder,
			});

			// Update the element
			updateElement(manager!);

			// Re-enable transitions after the first effect writes correct classes.
			// Deferred to next animation frame so the browser paints the class change
			// with transitions disabled first, then re-enables them.
			if (manager!.transitionsSuppressed) {
				manager!.transitionsSuppressed = false;
				manager!.restoreRafId = requestAnimationFrame(() => {
					manager!.restoreRafId = null;
					restoreTransitionSuppression(manager!);
				});
			}
		}

		// Register cleanup with DestroyRef
		destroyRef.onDestroy(() => {
			if (manager!.restoreRafId !== null) {
				cancelAnimationFrame(manager!.restoreRafId);
				manager!.restoreRafId = null;
			}

			if (manager!.transitionsSuppressed) {
				manager!.transitionsSuppressed = false;
				restoreTransitionSuppression(manager!);
			}

			// Remove this source from the manager
			manager!.sources.delete(sourceId);

			// If no more sources, clean up the manager
			if (manager!.sources.size === 0) {
				cleanupManager(element);
			} else {
				// Update element without this source's classes
				updateElement(manager!);
			}
		});

		/**
		 * We need this effect to track changes to the computed classes. Ideally, we would use
		 * afterRenderEffect here, but that doesn't run in SSR contexts, so we use a standard
		 * effect which works in both browser and SSR.
		 */
		effect(updateClasses);
	});
}

function restoreTransitionSuppression(manager: ElementClassManager): void {
	const prev = manager.previousTransition;
	if (prev) {
		manager.element.style.setProperty('transition', prev, manager.previousTransitionPriority || undefined);
	} else {
		manager.element.style.removeProperty('transition');
	}
}

// eslint-disable-next-line @typescript-eslint/no-wrapper-object-types
function setupGlobalObserver(platformId: Object): void {
	if (isPlatformBrowser(platformId) && !globalObserver) {
		// Create single global observer that watches the entire document
		globalObserver = new MutationObserver((mutations) => {
			for (const mutation of mutations) {
				if (mutation.type === 'attributes' && mutation.attributeName === 'class') {
					const element = mutation.target as HTMLElement;
					const manager = elementClassManagers.get(element);

					// Only process elements we're managing
					if (manager && observedElements.has(element)) {
						if (manager.isUpdating) continue; // Ignore changes we're making

						// Update base classes to include any externally added classes
						const currentClasses = toClassList(element.className);
						const allSourceClasses = new Set<string>();

						// Collect all classes from all sources
						for (const source of manager.sources.values()) {
							for (const className of source.classes) {
								allSourceClasses.add(className);
							}
						}

						// Any classes not from sources become new base classes
						manager.baseClasses.clear();

						for (const className of currentClasses) {
							if (!allSourceClasses.has(className)) {
								manager.baseClasses.add(className);
							}
						}

						updateElement(manager);
					}
				}
			}
		});

		// Start observing the entire document for class attribute changes
		globalObserver.observe(document, {
			attributes: true,
			attributeFilter: ['class'],
			subtree: true, // Watch all descendants
		});
	}
}

function updateElement(manager: ElementClassManager): void {
	if (manager.isUpdating) return; // Prevent recursive updates

	manager.isUpdating = true;

	// Handle initialization: capture base classes after first source registration
	if (!manager.hasInitialized && manager.sources.size > 0) {
		// Get current classes on element (may include SSR classes)
		const currentClasses = toClassList(manager.element.className);

		// Get all classes that will be applied by sources
		const allSourceClasses = new Set<string>();
		for (const source of manager.sources.values()) {
			source.classes.forEach((className) => allSourceClasses.add(className));
		}

		// Only consider classes as "base" if they're not produced by any source
		// This prevents SSR-rendered classes from being preserved as base classes
		currentClasses.forEach((className) => {
			if (!allSourceClasses.has(className)) {
				manager.baseClasses.add(className);
			}
		});

		manager.hasInitialized = true;
	}

	// Get classes from all sources, sorted by registration order (later takes precedence)
	const sortedSources = Array.from(manager.sources.entries()).sort(([, a], [, b]) => a.order - b.order);

	const allSourceClasses: string[] = [];
	for (const [, source] of sortedSources) {
		allSourceClasses.push(...source.classes);
	}

	// Combine base classes with all source classes, ensuring base classes take precedence
	const classesToApply =
		allSourceClasses.length > 0 || manager.baseClasses.size > 0
			? hlm([...allSourceClasses, ...manager.baseClasses])
			: '';

	// Apply the classes to the element
	if (manager.element.className !== classesToApply) {
		manager.element.className = classesToApply;
	}

	manager.isUpdating = false;
}

function cleanupManager(element: HTMLElement): void {
	// Remove from global tracking
	observedElements.delete(element);
	elementClassManagers.delete(element);

	// If no more elements being tracked, cleanup global observer
	if (observedElements.size === 0 && globalObserver) {
		globalObserver.disconnect();
		globalObserver = null;
	}
}

interface ClassesOptions {
	elementRef?: ElementRef<HTMLElement>;
	injector?: Injector;
}

// Cache for parsed class lists to avoid repeated string operations
const classListCache = new Map<string, string[]>();

function toClassList(className: string | ClassValue[]): string[] {
	// For simple string inputs, use cache to avoid repeated parsing
	if (typeof className === 'string' && classListCache.has(className)) {
		return classListCache.get(className)!;
	}

	const result = clsx(className)
		.split(' ')
		.filter((c) => c.length > 0);

	// Cache string results, but limit cache size to prevent memory growth
	if (typeof className === 'string' && classListCache.size < 1000) {
		classListCache.set(className, result);
	}

	return result;
}