import type {
  LabelView,
  PageListItemView,
  PondView,
  SidebarSortMode,
  SidebarViewMode,
  TreeNode,
} from '@dorfteich/shared';
import { buildTree, collectSubtreeIds, labelDepth } from '@dorfteich/shared';
import { useQuery, useQueryClient } from '@tanstack/react-query';
import {
  ChevronRight,
  FilePlus,
  FileText,
  Folder,
  FolderOpen,
  Star,
  Trash2,
  Waypoints,
} from 'lucide-react';
import { useMemo, useState } from 'react';
import { useTranslation } from 'react-i18next';
import { Link } from 'react-router-dom';

import { useAuth } from '../auth/auth-context';
import { FormError } from '../components/forms';
import { usePageFavorites } from '../favorites/use-favorites';
import { ImportControl } from '../import/ImportControl';
import { LabelChips } from '../labels/LabelChips';
import { usePondLabels } from '../labels/use-pond-labels';
import { apiGet, apiPatch } from '../lib/api';
import { usePersistentState } from '../lib/use-persistent-state';
import { NewPageForm } from './NewPageForm';
import { dropIndex, neighborsForMove } from './reorder';
import { useCurrentPondRoute } from './use-pond-route';

interface SidebarProps {
  collapsed: boolean;
  /** The resize handle, rendered inside the nav landmark (#166). */
  resizer?: React.ReactNode;
}

const SORT_MODES: SidebarSortMode[] = ['alpha', 'created', 'manual'];
const VIEW_MODES: SidebarViewMode[] = ['folders', 'labels'];

/**
 * Left sidebar: the current pond's page list, sort mode, active-page
 * highlight, "new page" flow (issue #26), and label chips + a
 * descendant-inclusive label filter (issue #44). Since issue #108 pages
 * render as a collapsible tree ("folders") or grouped under the label tree
 * ("labels") — the pond default (`settings.sidebarView`) is owner-set and
 * every user can override it locally. Collapse behavior and the layout
 * contract (`nav.sidebar`, `aria-hidden`) are unchanged from #4/#25.
 */
export function Sidebar({ collapsed, resizer }: SidebarProps): React.JSX.Element {
  const { t } = useTranslation();
  const { pondSlug } = useCurrentPondRoute();

  const pond = useQuery({
    queryKey: ['pond', pondSlug],
    queryFn: () => apiGet<PondView>(`/ponds/${pondSlug}`),
    enabled: pondSlug !== null,
  });

  return (
    <nav
      className={collapsed ? 'sidebar sidebar--collapsed' : 'sidebar'}
      aria-hidden={collapsed}
      inert={collapsed}
      aria-label={t('layout.sidebar.label')}
    >
      {resizer}
      {!pond.data ? (
        <p className="sidebar__hint">{t('layout.sidebar.placeholder')}</p>
      ) : (
        // Keyed by pond so the per-pond persistent hooks (view override,
        // collapsed nodes) mount with the right localStorage key.
        <SidebarContent key={pond.data.id} pond={pond.data} pondSlug={pondSlug!} />
      )}
    </nav>
  );
}

function SidebarContent({
  pond,
  pondSlug,
}: {
  pond: PondView;
  pondSlug: string;
}): React.JSX.Element {
  const { t } = useTranslation();
  const { t: tLabels } = useTranslation('labels');
  const { user } = useAuth();
  const { pageSlug } = useCurrentPondRoute();
  const queryClient = useQueryClient();
  const [creating, setCreating] = useState(false);
  const [filterIds, setFilterIds] = useState<Set<string>>(new Set());
  // The favorites filter (issue #132) — a latching push button, combinable
  // with the label filter; both narrow the same list.
  const [favoritesOnly, setFavoritesOnly] = useState(false);
  const [draggedId, setDraggedId] = useState<string | null>(null);
  const [dropIntoId, setDropIntoId] = useState<string | null>(null);
  const [moveError, setMoveError] = useState<unknown>(null);
  const [announcement, setAnnouncement] = useState('');

  // Per-user view override (issue #108); `null` follows the pond default.
  const [viewOverride, setViewOverride] = usePersistentState<SidebarViewMode | null>(
    `ui.sidebar.view.${pond.id}`,
    null,
  );
  const view: SidebarViewMode = viewOverride ?? pond.settings.sidebarView;
  const [collapsedIds, setCollapsedIds] = usePersistentState<string[]>(
    `ui.sidebar.collapsedPages.${pond.id}`,
    [],
  );

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

  const { flat, byId } = usePondLabels(pond.id);
  const { ids: favoriteIds } = usePageFavorites(pond.id);

  const isOwner = Boolean(user && user.id === pond.ownerId);

  // A filter on a label matches pages tagged with that label or any of its
  // descendants (permissions/vision: sub-labels belong to their parent).
  const expandedFilter = useMemo(() => {
    const acc = new Set<string>();
    for (const id of filterIds) for (const d of collectSubtreeIds(flat, id)) acc.add(d);
    return acc;
  }, [filterIds, flat]);

  const labelFiltered =
    filterIds.size === 0
      ? pages.data
      : pages.data?.filter((p) => p.labelIds.some((id) => expandedFilter.has(id)));
  const visiblePages = favoritesOnly
    ? labelFiltered?.filter((p) => favoriteIds.has(p.id))
    : labelFiltered;

  // The page tree, built from the list's global sort order (issue #108); a
  // filtered list falls back to the flat rendering, so no filter here.
  const tree = useMemo(() => buildTree(pages.data ?? []), [pages.data]);

  const currentPage = pageSlug ? pages.data?.find((p) => p.slug === pageSlug) : undefined;

  function toggleFilter(id: string, on: boolean): void {
    setFilterIds((prev) => {
      const next = new Set(prev);
      if (on) next.add(id);
      else next.delete(id);
      return next;
    });
  }

  function toggleCollapsed(id: string): void {
    setCollapsedIds(
      collapsedIds.includes(id) ? collapsedIds.filter((c) => c !== id) : [...collapsedIds, id],
    );
  }

  async function setSortMode(mode: SidebarSortMode): Promise<void> {
    await apiPatch(`/ponds/${pond.id}`, { sidebarSort: mode });
    await queryClient.invalidateQueries({ queryKey: ['pond', pondSlug] });
  }

  // Reordering is offered only in manual mode, to the owner, while no label
  // filter narrows the list, and in folder view (label view is read-only).
  const canReorder =
    isOwner && pond.settings.sidebarSort === 'manual' && filterIds.size === 0 && view === 'folders';

  /** Move `movedId` to `newIndex` within its sibling group and persist it.
   * Fractional keys between two siblings keep the group order intact under
   * the pond-wide sequence (issue #106), so no other page is touched. */
  async function moveWithinSiblings(
    movedId: string,
    siblingIds: string[],
    newIndex: number,
    title: string,
  ): Promise<void> {
    setMoveError(null);
    const { afterId, beforeId } = neighborsForMove(siblingIds, movedId, newIndex);
    await apiPatch(`/pages/${movedId}/position`, { afterId, beforeId });
    await queryClient.invalidateQueries({ queryKey: ['pages', pond.id] });
    const position = Math.max(0, Math.min(newIndex, siblingIds.length - 1)) + 1;
    setAnnouncement(
      t('layout.sidebar.reorder.moved', { title, position, count: siblingIds.length }),
    );
  }

  /** Nest `movedId` under `newParentId` (drop onto a row, issue #109),
   * appended at the end of the new sibling group. Cycle/depth refusals from
   * the server show as a translated banner under the tree. */
  async function reparentTo(movedId: string, newParentId: string): Promise<void> {
    setMoveError(null);
    const list = pages.data ?? [];
    const moved = list.find((p) => p.id === movedId);
    const parent = list.find((p) => p.id === newParentId);
    if (!moved || moved.parentId === newParentId) return;
    try {
      // Key after the last sibling of the new group; an empty group falls
      // back to the pond's last page so the fresh key is unique.
      const siblings = list.filter((p) => p.parentId === newParentId && p.id !== movedId);
      const fallback = [...list].reverse().find((p) => p.id !== movedId);
      const afterId = siblings.at(-1)?.id ?? fallback?.id ?? null;
      await apiPatch(`/pages/${movedId}/position`, {
        afterId,
        beforeId: null,
        parentId: newParentId,
      });
      await queryClient.invalidateQueries({ queryKey: ['pages', pond.id] });
      setAnnouncement(
        t('layout.sidebar.reorder.reparented', {
          title: moved.title,
          parent: parent?.title ?? '',
        }),
      );
    } catch (err) {
      setMoveError(err);
    }
  }

  const showFlatFallback = view === 'folders' && (filterIds.size > 0 || favoritesOnly);
  // The label view groups the (possibly favorites-narrowed) list; the label
  // filter stays a folder-view affordance as before (#108).
  const labelViewPages = favoritesOnly
    ? pages.data?.filter((p) => favoriteIds.has(p.id))
    : pages.data;

  return (
    <>
      <div className="sidebar__header">
        <h2 className="sidebar__pond-name">{pond.name}</h2>
        {isOwner && (
          <select
            className="sidebar__sort"
            aria-label={t('layout.sidebar.sortLabel')}
            value={pond.settings.sidebarSort}
            onChange={(event) => void setSortMode(event.target.value as SidebarSortMode)}
          >
            {SORT_MODES.map((mode) => (
              <option key={mode} value={mode}>
                {t(`layout.sidebar.sortMode.${mode}`)}
              </option>
            ))}
          </select>
        )}
      </div>

      <div
        className="sidebar__view-toggle"
        role="group"
        aria-label={t('layout.sidebar.view.toggleLabel')}
      >
        {VIEW_MODES.map((mode) => (
          <button
            key={mode}
            type="button"
            className={`sidebar__view-btn${view === mode ? ' sidebar__view-btn--active' : ''}`}
            aria-pressed={view === mode}
            onClick={() => setViewOverride(mode)}
          >
            {t(`layout.sidebar.view.${mode}`)}
          </button>
        ))}
        {/* Latching favorites filter (issue #132) — narrows either view. */}
        <button
          type="button"
          className={`sidebar__view-btn sidebar__view-btn--favorites${
            favoritesOnly ? ' sidebar__view-btn--active' : ''
          }`}
          aria-pressed={favoritesOnly}
          onClick={() => setFavoritesOnly(!favoritesOnly)}
        >
          <Star aria-hidden fill={favoritesOnly ? 'currentColor' : 'none'} />
          {t('layout.sidebar.favorites.filter')}
        </button>
      </div>

      {view === 'folders' && flat.length > 0 && (
        <details className="sidebar__filter">
          <summary>
            {tLabels('filter.toggle')}
            {filterIds.size > 0 && ` (${filterIds.size})`}
          </summary>
          <ul className="sidebar__filter-list">
            {flat.map((label) => (
              <li
                key={label.id}
                style={{ paddingInlineStart: `${(labelDepth(flat, label.id) - 1) * 1}rem` }}
              >
                <label className="sidebar__filter-option">
                  <input
                    type="checkbox"
                    checked={filterIds.has(label.id)}
                    onChange={(event) => toggleFilter(label.id, event.target.checked)}
                  />
                  <span
                    className="label-chip__swatch"
                    style={{ backgroundColor: label.color }}
                    aria-hidden
                  />
                  <span>{label.name}</span>
                </label>
              </li>
            ))}
          </ul>
          {filterIds.size > 0 && (
            <button
              type="button"
              className="linklike sidebar__filter-clear"
              onClick={() => setFilterIds(new Set())}
            >
              {tLabels('filter.clear')}
            </button>
          )}
        </details>
      )}

      {view === 'labels' ? (
        labelViewPages && labelViewPages.length > 0 ? (
          <LabelGroupedPages
            pages={labelViewPages}
            labels={flat}
            pondSlug={pondSlug}
            pageSlug={pageSlug}
          />
        ) : (
          <p className="sidebar__hint">
            {favoritesOnly ? t('layout.sidebar.favorites.empty') : t('layout.sidebar.empty')}
          </p>
        )
      ) : showFlatFallback ? (
        visiblePages && visiblePages.length > 0 ? (
          <ul className="sidebar__pages">
            {visiblePages.map((p) => (
              <li key={p.id} className="sidebar__page-item">
                <PageLink page={p} pondSlug={pondSlug} pageSlug={pageSlug} />
                <LabelChips labelIds={p.labelIds} byId={byId} />
              </li>
            ))}
          </ul>
        ) : (
          <p className="sidebar__hint">
            {filterIds.size > 0 ? tLabels('filter.none') : t('layout.sidebar.favorites.empty')}
          </p>
        )
      ) : tree.length > 0 ? (
        <ul className="sidebar__pages sidebar__pages--tree">
          <PageTreeLevel
            nodes={tree}
            pondSlug={pondSlug}
            pageSlug={pageSlug}
            byId={byId}
            favoriteIds={favoriteIds}
            collapsedIds={collapsedIds}
            onToggleCollapsed={toggleCollapsed}
            canReorder={canReorder}
            draggedId={draggedId}
            setDraggedId={setDraggedId}
            dropIntoId={dropIntoId}
            setDropIntoId={setDropIntoId}
            onMove={moveWithinSiblings}
            onReparent={reparentTo}
          />
        </ul>
      ) : (
        <p className="sidebar__hint">{t('layout.sidebar.empty')}</p>
      )}

      {moveError !== null && <FormError error={moveError} />}

      {creating && (
        <NewPageForm
          pondId={pond.id}
          pondSlug={pondSlug}
          parentId={currentPage?.id ?? null}
          parentTitle={currentPage?.title}
          onCreated={() => {
            setCreating(false);
            void queryClient.invalidateQueries({ queryKey: ['pages', pond.id] });
          }}
          onCancel={() => setCreating(false)}
        />
      )}

      {/* Keyboard/drag reordering announcements for screen readers. */}
      <p className="visually-hidden sidebar__announce" role="status" aria-live="polite">
        {announcement}
      </p>

      {/* All four actions live as an icon row pinned to the sidebar's
          bottom (#124): graph, new page, import, trash — hover hints via
          title. The graph is for every member (#112); trash is owner-only. */}
      <div className="sidebar__footer">
        <Link
          to={`/p/${pondSlug}/graph`}
          className="icon-button sidebar__graph-link"
          title={t('graph:link')}
          aria-label={t('graph:link')}
        >
          <Waypoints aria-hidden />
        </Link>
        <button
          type="button"
          className="icon-button sidebar__new-page"
          title={t('layout.sidebar.newPageHint')}
          aria-label={t('layout.sidebar.newPageHint')}
          aria-expanded={creating}
          onClick={() => setCreating(!creating)}
        >
          <FilePlus aria-hidden />
        </button>
        <ImportControl pondId={pond.id} pondSlug={pondSlug} />
        {isOwner && (
          <Link
            to={`/p/${pondSlug}/trash`}
            className="icon-button sidebar__trash-link"
            title={t('editor:trash.showLink')}
            aria-label={t('editor:trash.showLink')}
          >
            <Trash2 aria-hidden />
          </Link>
        )}
      </div>
    </>
  );
}

function PageLink({
  page,
  pondSlug,
  pageSlug,
}: {
  page: PageListItemView;
  pondSlug: string;
  pageSlug: string | null;
}): React.JSX.Element {
  return (
    <Link
      to={`/p/${pondSlug}/${page.slug}`}
      className={page.slug === pageSlug ? 'sidebar__page sidebar__page--active' : 'sidebar__page'}
      aria-current={page.slug === pageSlug ? 'page' : undefined}
      draggable={false}
    >
      {page.title}
    </Link>
  );
}

interface PageTreeLevelProps {
  nodes: TreeNode<PageListItemView>[];
  pondSlug: string;
  pageSlug: string | null;
  byId: Map<string, LabelView>;
  favoriteIds: Set<string>;
  collapsedIds: string[];
  onToggleCollapsed: (id: string) => void;
  canReorder: boolean;
  draggedId: string | null;
  setDraggedId: (id: string | null) => void;
  dropIntoId: string | null;
  setDropIntoId: (id: string | null) => void;
  onMove: (movedId: string, siblingIds: string[], newIndex: number, title: string) => Promise<void>;
  onReparent: (movedId: string, newParentId: string) => Promise<void>;
}

/** Fraction of a row's height (top and bottom) that reads as "drop between";
 * the middle band drops INTO the page (reparent, issue #109). */
const EDGE_ZONE = 0.3;

/** One sibling group of the folder view (issue #108), rendered recursively.
 * Reordering (buttons and drag-between at the row edges) stays within the
 * group; dropping onto a row's middle nests the dragged page under it. */
function PageTreeLevel(props: PageTreeLevelProps): React.JSX.Element {
  const { t } = useTranslation();
  const {
    nodes,
    pondSlug,
    pageSlug,
    byId,
    favoriteIds,
    collapsedIds,
    onToggleCollapsed,
    canReorder,
    draggedId,
    setDraggedId,
    dropIntoId,
    setDropIntoId,
    onMove,
    onReparent,
  } = props;
  const siblingIds = nodes.map((n) => n.id);

  function dropZone(event: React.DragEvent<HTMLLIElement>): 'into' | 'between' {
    const rect = event.currentTarget.getBoundingClientRect();
    const y = event.clientY - rect.top;
    return y > rect.height * EDGE_ZONE && y < rect.height * (1 - EDGE_ZONE) ? 'into' : 'between';
  }

  return (
    <>
      {nodes.map((node, index) => {
        const hasChildren = node.children.length > 0;
        const isCollapsed = collapsedIds.includes(node.id);
        const itemClasses = [
          'sidebar__page-item',
          canReorder ? 'sidebar__page-item--draggable' : '',
          dropIntoId === node.id ? 'sidebar__page-item--drop-into' : '',
        ]
          .filter(Boolean)
          .join(' ');
        return (
          <li
            key={node.id}
            className={itemClasses}
            draggable={canReorder}
            onDragStart={
              canReorder
                ? (event) => {
                    event.stopPropagation();
                    setDraggedId(node.id);
                    event.dataTransfer.effectAllowed = 'move';
                  }
                : undefined
            }
            onDragEnd={
              canReorder
                ? () => {
                    setDraggedId(null);
                    setDropIntoId(null);
                  }
                : undefined
            }
            onDragOver={
              canReorder
                ? (event) => {
                    event.preventDefault();
                    event.stopPropagation();
                    const into = draggedId && draggedId !== node.id && dropZone(event) === 'into';
                    setDropIntoId(into ? node.id : null);
                  }
                : undefined
            }
            onDrop={
              canReorder
                ? (event) => {
                    event.preventDefault();
                    event.stopPropagation();
                    setDropIntoId(null);
                    if (!draggedId || draggedId === node.id) return;
                    if (dropZone(event) === 'into') {
                      // Middle band: nest the dragged page under this one.
                      void onReparent(draggedId, node.id);
                    } else {
                      // Edge bands reorder — inside one sibling group only.
                      if (!siblingIds.includes(draggedId)) return;
                      const rect = event.currentTarget.getBoundingClientRect();
                      const after = event.clientY - rect.top > rect.height / 2;
                      const target = dropIndex(siblingIds, draggedId, node.id, after);
                      const title = nodes.find((n) => n.id === draggedId)?.title ?? '';
                      void onMove(draggedId, siblingIds, target, title);
                    }
                    setDraggedId(null);
                  }
                : undefined
            }
          >
            <span className="sidebar__tree-row">
              {hasChildren ? (
                <button
                  type="button"
                  className={
                    isCollapsed ? 'sidebar__caret sidebar__caret--collapsed' : 'sidebar__caret'
                  }
                  aria-expanded={!isCollapsed}
                  // Deliberately WITHOUT the page title: e2e locators match
                  // accessible names by substring (#101 convention), and a
                  // title like "Editor…" would collide with the mode toggle.
                  aria-label={t(
                    isCollapsed ? 'layout.sidebar.view.expand' : 'layout.sidebar.view.collapseNode',
                  )}
                  onClick={() => onToggleCollapsed(node.id)}
                >
                  <ChevronRight aria-hidden />
                </button>
              ) : (
                <span className="sidebar__caret sidebar__caret--leaf" aria-hidden />
              )}
              {/* Favorites carry a golden icon (issue #132). */}
              <span
                className={
                  favoriteIds.has(node.id)
                    ? 'sidebar__page-icon sidebar__page-icon--favorite'
                    : 'sidebar__page-icon'
                }
                aria-hidden
              >
                {hasChildren ? isCollapsed ? <Folder /> : <FolderOpen /> : <FileText />}
              </span>
              <PageLink page={node} pondSlug={pondSlug} pageSlug={pageSlug} />
              {canReorder && (
                <span className="sidebar__reorder">
                  <button
                    type="button"
                    className="sidebar__reorder-btn"
                    aria-label={t('layout.sidebar.reorder.up')}
                    disabled={index === 0}
                    onClick={() => void onMove(node.id, siblingIds, index - 1, node.title)}
                  >
                    ↑
                  </button>
                  <button
                    type="button"
                    className="sidebar__reorder-btn"
                    aria-label={t('layout.sidebar.reorder.down')}
                    disabled={index === nodes.length - 1}
                    onClick={() => void onMove(node.id, siblingIds, index + 1, node.title)}
                  >
                    ↓
                  </button>
                </span>
              )}
              <LabelChips labelIds={node.labelIds} byId={byId} />
            </span>
            {hasChildren && !isCollapsed && (
              <ul className="sidebar__pages sidebar__tree-children">
                <PageTreeLevel {...props} nodes={node.children} />
              </ul>
            )}
          </li>
        );
      })}
    </>
  );
}

/**
 * The label view (issue #108): pages grouped under the hierarchical label
 * tree, read-only. A page tagged with several labels appears under each;
 * untagged pages collect in a trailing "unlabeled" group.
 */
function LabelGroupedPages({
  pages,
  labels,
  pondSlug,
  pageSlug,
}: {
  pages: PageListItemView[];
  labels: LabelView[];
  pondSlug: string;
  pageSlug: string | null;
}): React.JSX.Element {
  const { t } = useTranslation();
  const unlabeled = pages.filter((p) => p.labelIds.length === 0);

  return (
    <div className="sidebar__label-view">
      {labels.map((label) => {
        const tagged = pages.filter((p) => p.labelIds.includes(label.id));
        if (tagged.length === 0) return null;
        return (
          <section
            key={label.id}
            className="sidebar__label-group"
            style={{ paddingInlineStart: `${(labelDepth(labels, label.id) - 1) * 0.75}rem` }}
          >
            <h3 className="sidebar__label-heading">
              <span
                className="label-chip__swatch"
                style={{ backgroundColor: label.color }}
                aria-hidden
              />
              {label.name}
            </h3>
            <ul className="sidebar__pages">
              {tagged.map((p) => (
                <li key={p.id} className="sidebar__page-item">
                  <PageLink page={p} pondSlug={pondSlug} pageSlug={pageSlug} />
                </li>
              ))}
            </ul>
          </section>
        );
      })}
      {unlabeled.length > 0 && (
        <section className="sidebar__label-group sidebar__label-group--unlabeled">
          <h3 className="sidebar__label-heading">{t('layout.sidebar.view.unlabeled')}</h3>
          <ul className="sidebar__pages">
            {unlabeled.map((p) => (
              <li key={p.id} className="sidebar__page-item">
                <PageLink page={p} pondSlug={pondSlug} pageSlug={pageSlug} />
              </li>
            ))}
          </ul>
        </section>
      )}
    </div>
  );
}