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

/** Relies on `Unstable_TriggerCategory` never carrying a `type` field. */
function isTriggerItem(
  x: Unstable_TriggerItem | Unstable_TriggerCategory,
): x is Unstable_TriggerItem {
  return "type" in x;
}

/** Key event shape accepted by the keyboard handler. */
export type TriggerPopoverKeyEvent = {
  readonly key: string;
  readonly shiftKey: boolean;
  preventDefault(): void;
};

export type TriggerKeyboardResourceOutput = {
  /** Index of the currently highlighted entry within the navigable list. */
  readonly highlightedIndex: number;
  /** ID of the currently highlighted item (for `aria-activedescendant`). */
  readonly highlightedItemId: string | undefined;
  /** Move the highlight to an entry index (e.g. from pointer hover). Out-of-range values are ignored. */
  highlightIndex(index: number): void;
  /** Handle a key event; returns `true` if it was consumed. */
  handleKeyDown(e: TriggerPopoverKeyEvent): boolean;
};

/**
 * Owns keyboard-driven highlight state for the popover. Delegates selection,
 * category drill-in, back, and close to the callbacks supplied by the parent.
 */
const useTriggerKeyboardResource = ({
  navigableList,
  isSearchMode,
  activeCategoryId,
  query,
  popoverId,
  open,
  selectItem,
  selectCategory,
  goBack,
  close,
}: {
  navigableList: readonly (Unstable_TriggerCategory | Unstable_TriggerItem)[];
  isSearchMode: boolean;
  activeCategoryId: string | null;
  query: string;
  popoverId: string;
  open: boolean;
  selectItem: (item: Unstable_TriggerItem) => void;
  selectCategory: (categoryId: string) => void;
  goBack: () => void;
  close: () => void;
}): TriggerKeyboardResourceOutput => {
  const [highlightedIndex, setHighlightedIndex] = useState(0);
  const [highlightScope, setHighlightScope] = useState({
    navigableList,
    isSearchMode,
    activeCategoryId,
  });

  if (
    highlightScope.navigableList !== navigableList ||
    highlightScope.isSearchMode !== isSearchMode ||
    highlightScope.activeCategoryId !== activeCategoryId
  ) {
    setHighlightScope({ navigableList, isSearchMode, activeCategoryId });
    setHighlightedIndex(0);
  }

  const highlightIndex = useEffectEvent((index: number) => {
    if (index < 0 || index >= navigableList.length) return;
    if (index === highlightedIndex) return;
    setHighlightedIndex(index);
  });

  const handleKeyDown = useEffectEvent((e: TriggerPopoverKeyEvent): boolean => {
    if (!open) return false;

    switch (e.key) {
      case "ArrowDown": {
        e.preventDefault();
        setHighlightedIndex((prev) => {
          const len = navigableList.length;
          if (len === 0) return 0;
          return prev < len - 1 ? prev + 1 : 0;
        });
        return true;
      }
      case "ArrowUp": {
        e.preventDefault();
        setHighlightedIndex((prev) => {
          const len = navigableList.length;
          if (len === 0) return 0;
          return prev > 0 ? prev - 1 : len - 1;
        });
        return true;
      }
      case "Enter":
      case "Tab": {
        if (e.shiftKey) return false;
        e.preventDefault();
        const item = navigableList[highlightedIndex];
        if (!item) return true;

        if (isTriggerItem(item)) {
          selectItem(item);
        } else {
          selectCategory(item.id);
        }
        return true;
      }
      case "Escape": {
        e.preventDefault();
        close();
        return true;
      }
      case "Backspace": {
        if (activeCategoryId && query === "") {
          e.preventDefault();
          goBack();
          return true;
        }
        return false;
      }
      default:
        return false;
    }
  });

  const highlightedEntry = navigableList[highlightedIndex];
  const highlightedItemId =
    open && highlightedEntry
      ? `${popoverId}-option-${highlightedEntry.id}`
      : undefined;

  return {
    highlightedIndex,
    highlightedItemId,
    highlightIndex,
    handleKeyDown,
  };
};

export const TriggerKeyboardResource = resource(useTriggerKeyboardResource);