import { useEffectEvent, useMemo, useState } from "react";
import { resource } from "@assistant-ui/tap";
import type {
  Unstable_TriggerAdapter,
  Unstable_TriggerCategory,
  Unstable_TriggerItem,
} from "@assistant-ui/core";
import { matchesTriggerItemQuery } from "./matchesTriggerItemQuery";

export type TriggerNavigationResourceOutput = {
  /** Filtered categories visible in the list (empty in search mode). */
  readonly categories: readonly Unstable_TriggerCategory[];
  /** Filtered items visible in the list. */
  readonly items: readonly Unstable_TriggerItem[];
  /** `true` when the current list is search results rather than categories. */
  readonly isSearchMode: boolean;
  /** Currently drilled-into category id (or `null` for the top level). */
  readonly activeCategoryId: string | null;
  /** Flat list used for keyboard navigation (categories or items). */
  readonly navigableList: readonly (
    | Unstable_TriggerCategory
    | Unstable_TriggerItem
  )[];
  /** Drill into a category. */
  selectCategory(categoryId: string): void;
  /** Return to the top-level category list. */
  goBack(): void;
};

/**
 * Computes categories, items, search results, and navigation state from the
 * adapter + current query. Pure derivation — no side effects on the composer.
 */
const useTriggerNavigationResource = ({
  adapter,
  query,
  open,
}: {
  adapter: Unstable_TriggerAdapter | undefined;
  query: string;
  open: boolean;
}): TriggerNavigationResourceOutput => {
  const [activeCategoryId, setActiveCategoryId] = useState<string | null>(null);
  const [wasOpen, setWasOpen] = useState(open);

  if (wasOpen !== open) {
    setWasOpen(open);
    if (!open) setActiveCategoryId(null);
  }

  const categories = useMemo<readonly Unstable_TriggerCategory[]>(() => {
    if (!open || !adapter) return [];
    return adapter.categories();
  }, [open, adapter]);

  const effectiveActiveCategoryId = open ? activeCategoryId : null;

  const allItems = useMemo<readonly Unstable_TriggerItem[]>(() => {
    if (!effectiveActiveCategoryId || !adapter) return [];
    return adapter.categoryItems(effectiveActiveCategoryId);
  }, [effectiveActiveCategoryId, adapter]);

  const searchResults = useMemo<readonly Unstable_TriggerItem[] | null>(() => {
    if (!open || !adapter || effectiveActiveCategoryId) return null;
    // If categories exist and query is empty, show categories first (not search)
    if (!query && categories.length > 0) return null;
    if (adapter.search) return adapter.search(query);

    // fallback: no adapter.search
    const all: Unstable_TriggerItem[] = [];
    const lower = query.toLowerCase();
    for (const cat of categories) {
      for (const item of adapter.categoryItems(cat.id)) {
        if (matchesTriggerItemQuery(item, lower)) {
          all.push(item);
        }
      }
    }
    return all;
  }, [open, adapter, query, effectiveActiveCategoryId, categories]);

  const isSearchMode = searchResults !== null;

  const filteredCategories = useMemo(() => {
    if (isSearchMode) return [];
    if (!query) return categories;
    const lower = query.toLowerCase();
    return categories.filter((cat) => cat.label.toLowerCase().includes(lower));
  }, [categories, query, isSearchMode]);

  const filteredItems = useMemo(() => {
    if (isSearchMode) return searchResults ?? [];
    if (!query) return allItems;
    const lower = query.toLowerCase();
    return allItems.filter((item) => matchesTriggerItemQuery(item, lower));
  }, [allItems, query, isSearchMode, searchResults]);

  const navigableList = useMemo(() => {
    if (isSearchMode) return searchResults ?? [];
    if (effectiveActiveCategoryId) return filteredItems;
    return filteredCategories;
  }, [
    isSearchMode,
    searchResults,
    effectiveActiveCategoryId,
    filteredItems,
    filteredCategories,
  ]);

  const selectCategory = useEffectEvent((categoryId: string) => {
    setActiveCategoryId(categoryId);
  });

  const goBack = useEffectEvent(() => {
    setActiveCategoryId(null);
  });

  return {
    categories: filteredCategories,
    items: filteredItems,
    isSearchMode,
    activeCategoryId: effectiveActiveCategoryId,
    navigableList,
    selectCategory,
    goBack,
  };
};

export const TriggerNavigationResource = resource(useTriggerNavigationResource);