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* Accessibility utility functions for WCAG 2.1 Level AA compliance
* Provides keyboard navigation, focus management, color contrast checking,
* and screen reader support utilities
*
* @module utils/accessibility
* @category Accessibility
* @korean 접근성 유틸리티
*/
import React from 'react';
import {
KeyboardActions,
FocusIndicatorStyle,
ScreenReaderAnnouncement,
ColorContrastConfig,
WCAGComplianceResult,
WCAGLevel,
AriaAttributes,
createBilingualLabel,
} from '../types/AccessibilityTypes';
import { KOREAN_COLORS } from '../types/constants';
/**
* Handle keyboard navigation events with WCAG compliance
* Supports Tab, Enter, Space, Escape, Arrow keys, Home, End
*
* @param event - Keyboard event
* @param actions - Actions to perform for different keys
*
* @example
* ```tsx
* <div onKeyDown={(e) => handleKeyboardNav(e, {
* onActivate: () => handleClick(),
* onCancel: () => handleClose(),
* onNavigate: (dir) => handleMove(dir),
* })}>
* ```
*/
export function handleKeyboardNav(
event: KeyboardEvent,
actions: KeyboardActions
): void {
const { key, shiftKey } = event;
switch (key) {
case 'Enter':
case ' ':
// Activate element (button, link, etc.)
event.preventDefault();
actions.onActivate?.();
break;
case 'Escape':
// Cancel or close action
event.preventDefault();
actions.onCancel?.();
break;
case 'Tab':
// Tab navigation (forward or backward with Shift)
actions.onTab?.(shiftKey);
break;
case 'ArrowUp':
// Navigate up
event.preventDefault();
actions.onNavigate?.('up');
break;
case 'ArrowDown':
// Navigate down
event.preventDefault();
actions.onNavigate?.('down');
break;
case 'ArrowLeft':
// Navigate left
event.preventDefault();
actions.onNavigate?.('left');
break;
case 'ArrowRight':
// Navigate right
event.preventDefault();
actions.onNavigate?.('right');
break;
case 'Home':
// Jump to start
event.preventDefault();
actions.onJump?.('start');
break;
case 'End':
// Jump to end
event.preventDefault();
actions.onJump?.('end');
break;
}
}
/**
* Get default focus indicator style (WCAG 2.1 Level AA compliant)
* Uses 2px solid outline with high contrast cyan color
* Computed lazily to avoid initialization order dependencies
*/
function getDefaultFocusStyle(): FocusIndicatorStyle {
const rgb = hexToRgb(KOREAN_COLORS.PRIMARY_CYAN);
return {
outlineWidth: 2,
outlineColor: KOREAN_COLORS.PRIMARY_CYAN,
outlineOffset: 2,
outlineStyle: 'solid',
boxShadow: `0 0 0 2px rgba(${rgb.r}, ${rgb.g}, ${rgb.b}, 0.5)`,
transitionDuration: 0.2,
};
}
/**
* Default focus indicator style (WCAG 2.1 Level AA compliant)
* @deprecated Use getDefaultFocusStyle() instead for lazy computation
*/
export const DEFAULT_FOCUS_STYLE: FocusIndicatorStyle = getDefaultFocusStyle();
/**
* Get focus indicator CSS style object
*
* @param isFocused - Whether element is currently focused
* @param customStyle - Optional custom focus style overrides
* @returns CSS style object for focus indicator
*
* @example
* ```tsx
* const [isFocused, setIsFocused] = useState(false);
* <button
* style={getFocusStyle(isFocused)}
* onFocus={() => setIsFocused(true)}
* onBlur={() => setIsFocused(false)}
* >
* ```
*/
export function getFocusStyle(
isFocused: boolean,
customStyle?: Partial<FocusIndicatorStyle>
): React.CSSProperties {
const defaultStyle = getDefaultFocusStyle();
if (!isFocused) {
return {
// Preserve browser default focus indicator instead of 'none'
transition: `all ${defaultStyle.transitionDuration}s ease`,
};
}
const style = { ...defaultStyle, ...customStyle };
const rgb = hexToRgb(style.outlineColor ?? KOREAN_COLORS.PRIMARY_CYAN);
return {
outline: `${style.outlineWidth}px ${style.outlineStyle} rgb(${rgb.r}, ${rgb.g}, ${rgb.b})`,
outlineOffset: `${style.outlineOffset}px`,
boxShadow: style.boxShadow ?? `0 0 0 2px rgba(${rgb.r}, ${rgb.g}, ${rgb.b}, 0.5)`,
transition: `all ${style.transitionDuration}s ease`,
};
}
/**
* Convert hex color to RGB components
*
* @param hex - Hex color code (0xRRGGBB)
* @returns RGB components
*/
export function hexToRgb(hex: number): { r: number; g: number; b: number } {
return {
r: (hex >> 16) & 255,
g: (hex >> 8) & 255,
b: hex & 255,
};
}
/**
* Calculate contrast ratio between two colors (WCAG 2.1)
*
* @param foreground - Foreground color (hex)
* @param background - Background color (hex)
* @returns Contrast ratio (1-21)
*
* @example
* ```typescript
* const ratio = getContrastRatio(KOREAN_COLORS.TEXT_PRIMARY, KOREAN_COLORS.UI_BACKGROUND_DARK);
* console.log(`Contrast ratio: ${ratio.toFixed(2)}:1`); // Should be >= 4.5:1 for WCAG AA
* ```
*/
export function getContrastRatio(foreground: number, background: number): number {
const fg = hexToRgb(foreground);
const bg = hexToRgb(background);
// Calculate relative luminance (WCAG formula)
const getLuminance = (r: number, g: number, b: number): number => {
const [rs, gs, bs] = [r, g, b].map((c) => {
const sRGB = c / 255;
return sRGB <= 0.03928
? sRGB / 12.92
: Math.pow((sRGB + 0.055) / 1.055, 2.4);
});
return 0.2126 * rs + 0.7152 * gs + 0.0722 * bs;
};
const l1 = getLuminance(fg.r, fg.g, fg.b);
const l2 = getLuminance(bg.r, bg.g, bg.b);
// Contrast ratio formula
const lighter = Math.max(l1, l2);
const darker = Math.min(l1, l2);
return (lighter + 0.05) / (darker + 0.05);
}
/**
* Check if color combination meets WCAG contrast requirements
*
* @param config - Color contrast configuration
* @returns Whether contrast meets WCAG requirements
*
* @example
* ```typescript
* const meetsWCAG = meetsContrastRequirement({
* foreground: KOREAN_COLORS.TEXT_PRIMARY,
* background: KOREAN_COLORS.UI_BACKGROUND_DARK,
* targetRatio: 4.5,
* });
* ```
*/
export function meetsContrastRequirement(config: ColorContrastConfig): boolean {
const ratio = getContrastRatio(config.foreground, config.background);
return ratio >= config.targetRatio;
}
/**
* Get WCAG-compliant foreground color for given background
* Returns white or black depending on which provides better contrast
*
* @param background - Background color (hex)
* @returns Foreground color (hex) that meets WCAG AA
*/
export function getAccessibleForeground(background: number): number {
const whiteRatio = getContrastRatio(KOREAN_COLORS.TEXT_PRIMARY, background);
const blackRatio = getContrastRatio(KOREAN_COLORS.BLACK_SOLID, background);
// Return color with better contrast
return whiteRatio >= blackRatio
? KOREAN_COLORS.TEXT_PRIMARY
: KOREAN_COLORS.BLACK_SOLID;
}
/**
* Announce message to screen readers
* Creates a live region announcement with configurable politeness
*
* @param announcement - Screen reader announcement configuration
*
* @example
* ```typescript
* announceToScreenReader({
* message: '공격 성공 | Attack successful',
* politeness: 'polite',
* delay: 100,
* });
* ```
*/
let liveRegionInstance: HTMLElement | null = null;
export function announceToScreenReader(
announcement: ScreenReaderAnnouncement
): void {
const { message, politeness = 'polite', delay = 0 } = announcement;
setTimeout(() => {
// Create or get existing live region
if (!liveRegionInstance) {
liveRegionInstance = document.createElement('div');
liveRegionInstance.id = 'sr-live-region';
liveRegionInstance.setAttribute('aria-live', politeness);
liveRegionInstance.setAttribute('aria-atomic', 'true');
liveRegionInstance.style.cssText = `
position: absolute;
left: -10000px;
width: 1px;
height: 1px;
overflow: hidden;
`;
document.body.appendChild(liveRegionInstance);
}
// Update politeness level if changed
if (liveRegionInstance.getAttribute('aria-live') !== politeness) {
liveRegionInstance.setAttribute('aria-live', politeness);
}
// Update message
liveRegionInstance.textContent = message;
// Clear message after 3 seconds
setTimeout(() => {
if (liveRegionInstance) {
liveRegionInstance.textContent = '';
}
}, 3000);
}, delay);
}
/**
* Clean up screen reader live region (for testing or app unmount)
*/
export function cleanupScreenReaderRegion(): void {
if (liveRegionInstance && liveRegionInstance.parentNode) {
liveRegionInstance.parentNode.removeChild(liveRegionInstance);
liveRegionInstance = null;
}
}
/**
* Trap focus within a container element
* Prevents focus from leaving the container (e.g., for modals)
*
* @param container - Container element to trap focus within
* @returns Cleanup function to remove focus trap
*
* @example
* ```typescript
* useEffect(() => {
* const cleanup = trapFocus(modalRef.current);
* return cleanup;
* }, []);
* ```
*/
export function trapFocus(container: HTMLElement | null): () => void {
if (!container) return () => {};
const focusableElements = getFocusableElements(container);
const firstElement = focusableElements[0];
const lastElement = focusableElements[focusableElements.length - 1];
const handleKeyDown = (event: KeyboardEvent) => {
if (event.key !== 'Tab') return;
if (event.shiftKey) {
// Shift + Tab: Move focus backward
if (document.activeElement === firstElement) {
event.preventDefault();
lastElement?.focus();
}
} else {
// Tab: Move focus forward
if (document.activeElement === lastElement) {
event.preventDefault();
firstElement?.focus();
}
}
};
container.addEventListener('keydown', handleKeyDown);
// Set initial focus
firstElement?.focus();
// Return cleanup function
return () => {
container.removeEventListener('keydown', handleKeyDown);
};
}
/**
* Get all focusable elements within a container
*
* @param container - Container element
* @returns Array of focusable elements
*/
export function getFocusableElements(
container: HTMLElement
): HTMLElement[] {
const selector = [
'a[href]',
'button:not([disabled])',
'input:not([disabled])',
'select:not([disabled])',
'textarea:not([disabled])',
'[tabindex]:not([tabindex="-1"])',
].join(', ');
return Array.from(container.querySelectorAll<HTMLElement>(selector));
}
/**
* Validate WCAG 2.1 Level AA compliance for a component
*
* Note: Color contrast checking requires access to computed styles,
* which is not available in all testing environments. This validation
* focuses on structural accessibility attributes.
*
* @param element - Element to validate
* @param config - Validation configuration
* @returns Compliance validation result
*/
export function validateWCAGCompliance(
element: HTMLElement | null,
config?: {
checkKeyboard?: boolean;
checkFocusVisible?: boolean;
checkAria?: boolean;
}
): WCAGComplianceResult {
const {
checkKeyboard = true,
checkFocusVisible = true,
checkAria = true,
} = config ?? {};
const issues: string[] = [];
let keyboardAccessible = true;
const colorContrast = true; // Note: Requires computed styles - use getContrastRatio() directly for color validation
let focusVisible = true;
let ariaLabels = true;
if (!element) {
issues.push('Element not found');
return {
level: WCAGLevel.A,
compliant: false,
criteria: {
keyboardAccessible: false,
colorContrast: false,
focusVisible: false,
ariaLabels: false,
semanticHTML: false,
errorIdentification: false,
},
issues,
};
}
// Check keyboard accessibility
if (checkKeyboard) {
const isInteractive =
element.tagName === 'BUTTON' ||
element.tagName === 'A' ||
element.tagName === 'INPUT' ||
element.hasAttribute('onclick');
if (isInteractive && element.getAttribute('tabindex') === '-1') {
keyboardAccessible = false;
issues.push('Interactive element not keyboard accessible');
}
}
// Check ARIA labels
if (checkAria) {
const hasAriaLabel =
element.hasAttribute('aria-label') ||
element.hasAttribute('aria-labelledby');
const hasTextContent = element.textContent?.trim();
if (!hasAriaLabel && !hasTextContent) {
ariaLabels = false;
issues.push('Missing ARIA label or text content');
}
}
// Check focus indicator
if (checkFocusVisible) {
const computedStyle = window.getComputedStyle(element);
const outline = computedStyle.outline;
if (outline === 'none' || outline === '') {
focusVisible = false;
issues.push('Missing visible focus indicator');
}
}
const allPass =
keyboardAccessible && colorContrast && focusVisible && ariaLabels;
return {
level: allPass ? WCAGLevel.AA : WCAGLevel.A,
compliant: allPass,
criteria: {
keyboardAccessible,
colorContrast, // Note: Always true - use getContrastRatio() for actual color validation
focusVisible,
ariaLabels,
semanticHTML: true, // Requires manual verification
errorIdentification: true, // Requires manual verification
},
issues,
};
}
/**
* Create comprehensive ARIA attributes for a component
*
* @param label - Bilingual label (Korean | English)
* @param role - ARIA role
* @param additionalAttrs - Additional ARIA attributes
* @returns Complete ARIA attributes object
*
* @example
* ```tsx
* const ariaProps = createAriaAttributes(
* createBilingualLabel('공격', 'Attack'),
* 'button',
* { 'aria-pressed': isPressed }
* );
* <button {...ariaProps}>
* ```
*/
export function createAriaAttributes(
label: string | { korean: string; english: string },
role?: AriaAttributes['role'],
additionalAttrs?: Partial<AriaAttributes>
): AriaAttributes {
const bilingualLabel =
typeof label === 'string'
? label
: createBilingualLabel(label.korean, label.english).label;
return {
role,
'aria-label': bilingualLabel,
...additionalAttrs,
};
}
/**
* Check if element is currently visible
* Useful for skip-to-content and focus management
*
* @param element - Element to check
* @returns Whether element is visible
*/
export function isElementVisible(element: HTMLElement | null): boolean {
if (!element) return false;
const style = window.getComputedStyle(element);
return (
style.display !== 'none' &&
style.visibility !== 'hidden' &&
style.opacity !== '0' &&
element.offsetParent !== null
);
}
/**
* Focus first error element in a form
* Useful for form validation accessibility
*
* @param container - Form container
*/
export function focusFirstError(container: HTMLElement): void {
const errorElements = container.querySelectorAll<HTMLElement>(
'[aria-invalid="true"]'
);
if (errorElements.length > 0) {
errorElements[0].focus();
announceToScreenReader({
message: '오류가 발견되었습니다 | Errors found',
politeness: 'assertive',
});
}
}
/**
* Create skip to content link for keyboard navigation
* Returns a link that allows users to skip to main content
*
* @param targetId - ID of main content element
* @returns Skip link element
*/
export function createSkipLink(targetId: string): HTMLAnchorElement {
const skipLink = document.createElement('a');
skipLink.href = `#${targetId}`;
skipLink.textContent = '본문으로 건너뛰기 | Skip to content';
skipLink.className = 'skip-link';
skipLink.style.cssText = `
position: absolute;
top: -40px;
left: 0;
background: #00e6e6;
color: #000;
padding: 8px;
text-decoration: none;
z-index: 10000;
font-weight: bold;
`;
// Show on focus
skipLink.addEventListener('focus', () => {
skipLink.style.top = '0';
});
// Hide on blur
skipLink.addEventListener('blur', () => {
skipLink.style.top = '-40px';
});
return skipLink;
}
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