/**
 * Focus Trap Utility
 * Traps keyboard focus within a specified container for accessibility
 */

const FOCUSABLE_ELEMENTS = [
  'a[href]',
  'button:not([disabled])',
  'textarea:not([disabled])',
  'input:not([disabled])',
  'select:not([disabled])',
  '[tabindex]:not([tabindex="-1"])',
].join(',');

export function getFocusableElements(container: HTMLElement): HTMLElement[] {
  return Array.from(container.querySelectorAll<HTMLElement>(FOCUSABLE_ELEMENTS)).filter(
    (el) => !el.hasAttribute('disabled') && el.offsetParent !== null
  );
}

export function trapFocus(container: HTMLElement): () => void {
  const focusableElements = getFocusableElements(container);
  
  if (focusableElements.length === 0) return () => {};

  const firstElement = focusableElements[0];
  const lastElement = focusableElements[focusableElements.length - 1];

  // Store the element that had focus before the trap
  const previouslyFocusedElement = document.activeElement as HTMLElement;

  // Focus the first element
  firstElement.focus();

  const handleKeyDown = (e: KeyboardEvent) => {
    if (e.key !== 'Tab') return;

    if (e.shiftKey) {
      // Shift + Tab
      if (document.activeElement === firstElement) {
        e.preventDefault();
        lastElement.focus();
      }
    } else {
      // Tab
      if (document.activeElement === lastElement) {
        e.preventDefault();
        firstElement.focus();
      }
    }
  };

  container.addEventListener('keydown', handleKeyDown);

  // Return cleanup function
  return () => {
    container.removeEventListener('keydown', handleKeyDown);
    // Restore focus to the previously focused element
    if (previouslyFocusedElement && typeof previouslyFocusedElement.focus === 'function') {
      previouslyFocusedElement.focus();
    }
  };
}

export function restoreFocus(element: HTMLElement | null) {
  if (element && typeof element.focus === 'function') {
    element.focus();
  }
}