import type { PageListItemView, PondView, TreeNode } from '@dorfteich/shared';
import { buildTree, collectSubtreeIds } from '@dorfteich/shared';
import { useQuery, useQueryClient } from '@tanstack/react-query';
import { useId, useRef, useState } from 'react';
import { useTranslation } from 'react-i18next';

import { FormError } from '../components/forms';
import { apiGet, apiPatch } from '../lib/api';
import { useDismissable } from '../lib/use-dismissable';
import { useModalFocus } from '../lib/use-modal-focus';

/**
 * "Move to…" dialog (issue #109): an indented parent picker over the page
 * tree. The page's own subtree is disabled (a cycle), the top level is the
 * first option. Works in any sort mode — the accessible counterpart to the
 * sidebar's drag-onto-a-page reparenting. Depth/cycle refusals from the
 * server surface as a translated error inside the dialog.
 */
export function MovePageDialog({
  pageId,
  pondSlug,
  onClose,
  returnFocusRef,
}: {
  pageId: string;
  pondSlug: string;
  onClose: () => void;
  /** Where focus goes after closing when the opening control unmounted. */
  returnFocusRef?: React.RefObject<HTMLElement | null>;
}): React.JSX.Element {
  const { t } = useTranslation('editor');
  const queryClient = useQueryClient();
  const [error, setError] = useState<unknown>(null);
  const [busy, setBusy] = useState(false);
  const dialogRef = useRef<HTMLDivElement>(null);
  const titleId = useId();
  useDismissable(dialogRef, true, onClose);
  useModalFocus(dialogRef, returnFocusRef);

  const pond = useQuery({
    queryKey: ['pond', pondSlug],
    queryFn: () => apiGet<PondView>(`/ponds/${pondSlug}`),
  });
  const pages = useQuery({
    queryKey: ['pages', pond.data?.id, pond.data?.settings.sidebarSort],
    queryFn: () => apiGet<PageListItemView[]>(`/ponds/${pond.data!.id}/pages`),
    enabled: Boolean(pond.data),
  });

  const list = pages.data ?? [];
  const page = list.find((p) => p.id === pageId);
  const [target, setTarget] = useState<string | null | undefined>(undefined);
  const selected = target === undefined ? (page?.parentId ?? null) : target;
  const blocked = collectSubtreeIds(list, pageId);

  /** Depth-first options with their level, for the indented picker. */
  const options: { page: PageListItemView; depth: number }[] = [];
  const walk = (nodes: TreeNode<PageListItemView>[], depth: number): void => {
    for (const node of nodes) {
      options.push({ page: node, depth });
      walk(node.children, depth + 1);
    }
  };
  walk(buildTree(list), 0);

  async function move(): Promise<void> {
    if (!page || selected === page.parentId) {
      onClose();
      return;
    }
    setError(null);
    setBusy(true);
    try {
      // Append at the end of the new sibling group; with no sibling to key
      // after, fall back to the pond's last page so the fresh key is unique.
      const siblings = list.filter((p) => p.parentId === selected && p.id !== pageId);
      const fallback = [...list].reverse().find((p) => p.id !== pageId);
      const afterId = siblings.at(-1)?.id ?? fallback?.id ?? null;
      await apiPatch(`/pages/${pageId}/position`, { afterId, beforeId: null, parentId: selected });
      await queryClient.invalidateQueries({ queryKey: ['pages', pond.data!.id] });
      onClose();
    } catch (err) {
      setError(err);
      setBusy(false);
    }
  }

  return (
    <div className="modal-overlay">
      <div
        className="modal move-dialog"
        role="dialog"
        aria-modal="true"
        aria-labelledby={titleId}
        tabIndex={-1}
        ref={dialogRef}
      >
        <h2 className="modal__title" id={titleId}>
          {t('page.moveTitle')}
        </h2>
        <FormError error={error} />
        <ul className="move-dialog__options">
          <li>
            <label className="move-dialog__option">
              <input
                type="radio"
                name="move-target"
                checked={selected === null}
                onChange={() => setTarget(null)}
              />
              <span>{t('page.moveRoot')}</span>
            </label>
          </li>
          {options.map(({ page: option, depth }) => (
            <li key={option.id} style={{ paddingInlineStart: `${depth * 1}rem` }}>
              <label className="move-dialog__option">
                <input
                  type="radio"
                  name="move-target"
                  disabled={blocked.has(option.id)}
                  checked={selected === option.id}
                  onChange={() => setTarget(option.id)}
                />
                <span>{option.title}</span>
              </label>
            </li>
          ))}
        </ul>
        <div className="modal__actions">
          <button type="button" className="button" disabled={busy} onClick={() => void move()}>
            {t('page.moveAction')}
          </button>
          <button type="button" className="linklike" onClick={onClose}>
            {t('page.moveCancel')}
          </button>
        </div>
      </div>
    </div>
  );
}