interface ButtonProps extends React.ButtonHTMLAttributes<HTMLButtonElement> {
  variant?: 'primary' | 'secondary';
  isLoading?: boolean;
}

function AccessibleButton({
  children,
  variant = 'primary',
  isLoading = false,
  disabled,
  ...props
}: ButtonProps) {
  return (
    <button
      // Disable when loading
      disabled={disabled || isLoading}
      // Announce loading state to screen readers
      aria-busy={isLoading}
      // Describe the button's current state
      aria-disabled={disabled || isLoading}
      className={cn(
        // Visible focus ring
        'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-offset-2',
        // Minimum touch target size (44x44px)
        'min-h-[44px] min-w-[44px]',
        variant === 'primary' && 'bg-primary text-primary-foreground',
        (disabled || isLoading) && 'opacity-50 cursor-not-allowed',
      )}
      {...props}
    >
      {isLoading ? (
        <>
          <span className="sr-only">Loading</span>
          <Spinner aria-hidden="true" />
        </>
      ) : (
        children
      )}
    </button>
  );
}

interface DialogProps {
  isOpen: boolean;
  onClose: () => void;
  title: string;
  children: React.ReactNode;
}

function AccessibleDialog({isOpen, onClose, title, children}: DialogProps) {
  const dialogRef = React.useRef<HTMLDialogElement>(null);
  const titleId = React.useId();
  const descriptionId = React.useId();

  React.useEffect(() => {
    const dialog = dialogRef.current;
    if (!dialog) return;

    if (isOpen) {
      dialog.showModal();
    } else {
      dialog.close();
    }
  }, [isOpen]);

  return (
    <dialog
      ref={dialogRef}
      aria-labelledby={titleId}
      aria-describedby={descriptionId}
      onClose={onClose}
      className="backdrop:bg-black/50 bg-background rounded-lg shadow-lg max-w-md w-full p-6"
    >
      <h2 id={titleId} className="text-lg font-semibold">
        {title}
      </h2>
      <div id={descriptionId}>{children}</div>
      <button onClick={onClose} className="absolute top-4 right-4" aria-label="Close dialog">
        <X className="h-4 w-4" />
      </button>
    </dialog>
  );
}

function AccessibleForm() {
  const [errors, setErrors] = React.useState<Record<string, string>>({});

  return (
    <form aria-describedby="form-errors" noValidate>
      {/* Error summary for screen readers */}
      {Object.keys(errors).length > 0 && (
        <div
          id="form-errors"
          role="alert"
          aria-live="assertive"
          className="bg-destructive/10 border border-destructive p-4 rounded-md mb-4"
        >
          <h2 className="font-semibold text-destructive">Please fix the following errors:</h2>
          <ul className="list-disc list-inside mt-2">
            {Object.entries(errors).map(([field, message]) => (
              <li key={field}>
                <a href={`#${field}`} className="underline">
                  {message}
                </a>
              </li>
            ))}
          </ul>
        </div>
      )}

      {/* Required field with error */}
      <div className="space-y-2">
        <label htmlFor="email" className="block font-medium">
          Email address
          <span aria-hidden="true" className="text-destructive ml-1">
            *
          </span>
          <span className="sr-only">(required)</span>
        </label>
        <input
          id="email"
          name="email"
          type="email"
          required
          aria-required="true"
          aria-invalid={!!errors.email}
          aria-describedby={errors.email ? 'email-error' : 'email-hint'}
          className={cn('w-full px-3 py-2 border rounded-md', errors.email && 'border-destructive')}
        />
        {errors.email ? (
          <p id="email-error" className="text-sm text-destructive" role="alert">
            {errors.email}
          </p>
        ) : (
          <p id="email-hint" className="text-sm text-muted-foreground">
            We'll never share your email.
          </p>
        )}
      </div>

      <button type="submit" className="mt-4">
        Submit
      </button>
    </form>
  );
}

function SkipLink() {
  return (
    <a
      href="#main-content"
      className={cn(
        // Hidden by default, visible on focus
        'sr-only focus:not-sr-only',
        'focus:absolute focus:top-4 focus:left-4 focus:z-50',
        'focus:bg-background focus:px-4 focus:py-2 focus:rounded-md',
        'focus:ring-2 focus:ring-primary',
      )}
    >
      Skip to main content
    </a>
  );
}

// In layout
function Layout({children}) {
  return (
    <>
      <SkipLink />
      <header>...</header>
      <nav aria-label="Main navigation">...</nav>
      <main id="main-content" tabIndex={-1}>
        {children}
      </main>
      <footer>...</footer>
    </>
  );
}

function useAnnounce() {
  const [message, setMessage] = React.useState('');
  const [priority, setPriority] = React.useState<'polite' | 'assertive'>('polite');

  const announce = React.useCallback((text: string, level: 'polite' | 'assertive' = 'polite') => {
    setMessage(''); // Clear first to ensure re-announcement
    setPriority(level);
    setTimeout(() => setMessage(text), 100);
  }, []);

  const Announcer = () => (
    <div
      role={priority === 'assertive' ? 'alert' : 'status'}
      aria-live={priority}
      aria-atomic="true"
      className="sr-only"
    >
      {message}
    </div>
  );

  return {announce, Announcer};
}

// Usage
function SearchResults({results, isLoading}) {
  const {announce, Announcer} = useAnnounce();

  React.useEffect(() => {
    if (!isLoading && results) {
      announce(`${results.length} results found`);
    }
  }, [results, isLoading, announce]);

  return (
    <>
      <Announcer />
      <ul>{/* results */}</ul>
    </>
  );
}

// Contrast ratio utilities
function getContrastRatio(foreground: string, background: string): number {
  const fgLuminance = getLuminance(foreground);
  const bgLuminance = getLuminance(background);
  const lighter = Math.max(fgLuminance, bgLuminance);
  const darker = Math.min(fgLuminance, bgLuminance);
  return (lighter + 0.05) / (darker + 0.05);
}

// WCAG requirements
const CONTRAST_REQUIREMENTS = {
  // Normal text (<18pt or <14pt bold)
  normalText: {
    AA: 4.5,
    AAA: 7,
  },
  // Large text (>=18pt or >=14pt bold)
  largeText: {
    AA: 3,
    AAA: 4.5,
  },
  // UI components and graphics
  uiComponents: {
    AA: 3,
  },
};