/**
 * Shared focus trap for modal/drawer surfaces (improvement-plan P2-3.2).
 *
 * Promoted from the proven implementation in components/mcp/modal.tsx:
 * - moves focus inside the container on activate ([data-autofocus] first),
 * - keeps the Tab cycle within the container,
 * - calls onEscape for the Escape key (capture phase),
 * - restores focus to the previously focused element on deactivate.
 */
import { useEffect, useRef } from 'react';
import type { RefObject } from 'react';

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

export interface UseFocusTrapOptions {
  /** Whether the trap is active (modal/drawer open). */
  active: boolean;
  /** Called when Escape is pressed while the trap is active. */
  onEscape?: () => void;
}

export function useFocusTrap<T extends HTMLElement>(
  containerRef: RefObject<T>,
  { active, onEscape }: UseFocusTrapOptions,
): void {
  const previousFocusRef = useRef<HTMLElement | null>(null);
  // Keep the latest callback without re-binding listeners on every render.
  const onEscapeRef = useRef(onEscape);
  onEscapeRef.current = onEscape;

  useEffect(() => {
    if (!active) {
      return;
    }

    previousFocusRef.current = document.activeElement as HTMLElement | null;

    // Move focus to the first focusable element (or the container itself).
    const focusFirst = () => {
      const container = containerRef.current;
      if (!container) {
        return;
      }
      if (container.contains(document.activeElement)) {
        return;
      }
      const target = container.querySelector<HTMLElement>(
        `[data-autofocus], ${FOCUSABLE_SELECTOR}`,
      );
      (target || container).focus();
    };
    const raf = requestAnimationFrame(focusFirst);

    const onKeyDown = (e: KeyboardEvent) => {
      if (e.key === 'Escape') {
        e.stopPropagation();
        onEscapeRef.current?.();
        return;
      }
      if (e.key !== 'Tab') {
        return;
      }
      const container = containerRef.current;
      if (!container) {
        return;
      }
      const focusables = Array.from(
        container.querySelectorAll<HTMLElement>(FOCUSABLE_SELECTOR),
      ).filter((el) => !el.hasAttribute('disabled'));
      if (focusables.length === 0) {
        return;
      }
      const first = focusables[0];
      const last = focusables[focusables.length - 1];
      if (e.shiftKey && document.activeElement === first) {
        e.preventDefault();
        last.focus();
      } else if (!e.shiftKey && document.activeElement === last) {
        e.preventDefault();
        first.focus();
      }
    };

    document.addEventListener('keydown', onKeyDown, true);
    return () => {
      cancelAnimationFrame(raf);
      document.removeEventListener('keydown', onKeyDown, true);
      previousFocusRef.current?.focus?.();
    };
  }, [active, containerRef]);
}