reakit/src/Rover/RoverState.ts

// Credits: https://github.com/stevejay/react-roving-tabindex
import * as React from "react";
import {
  SealedInitialState,
  useSealedState,
} from "reakit-utils/useSealedState";
import {
  unstable_IdState,
  unstable_IdActions,
  unstable_IdInitialState,
  unstable_useIdState,
} from "../Id/IdState";

type Stop = {
  id: string;
  ref: React.RefObject<HTMLElement>;
};

export type RoverState = unstable_IdState & {
  /**
   * Defines the orientation of the rover list.
   */
  orientation?: "horizontal" | "vertical";
  /**
   * A list of element refs and IDs of the roving items.
   */
  stops: Stop[];
  /**
   * The current focused element ID.
   */
  currentId: Stop["id"] | null;
  /**
   * The last focused element ID.
   * @private
   */
  unstable_pastId: Stop["id"] | null;
  /**
   * Stores the number of moves that have been made by calling `move`, `next`,
   * `previous`, `first` or `last`.
   */
  unstable_moves: number;
  /**
   * If enabled:
   *   - Jumps to the first item when moving next from the last item.
   *   - Jumps to the last item when moving previous from the first item.
   */
  loop: boolean;
};

export type RoverActions = unstable_IdActions & {
  /**
   * Registers the element ID and ref in the roving tab index list.
   */
  register: (id: Stop["id"], ref: Stop["ref"]) => void;
  /**
   * Unregisters the roving item.
   */
  unregister: (id: Stop["id"]) => void;
  /**
   * Moves focus to a given element ID.
   */
  move: (id: Stop["id"] | null, unstable_silent?: boolean) => void;
  /**
   * Moves focus to the next element.
   */
  next: () => void;
  /**
   * Moves focus to the previous element.
   */
  previous: () => void;
  /**
   * Moves focus to the first element.
   */
  first: () => void;
  /**
   * Moves focus to the last element.
   */
  last: () => void;
  /**
   * Resets `currentId` and `pastId` states.
   * @private
   */
  unstable_reset: () => void;
  /**
   * Changes the `orientation` state of the roving tab index list.
   * @private
   */
  unstable_orientate: (orientation: RoverState["orientation"]) => void;
};

export type RoverInitialState = unstable_IdInitialState &
  Partial<Pick<RoverState, "orientation" | "currentId" | "loop">>;

export type RoverStateReturn = RoverState & RoverActions;

type RoverAction =
  | { type: "register"; id: Stop["id"]; ref: Stop["ref"] }
  | { type: "unregister"; id: Stop["id"] }
  | { type: "move"; id: Stop["id"] | null; silent?: boolean }
  | { type: "next" }
  | { type: "previous" }
  | { type: "first" }
  | { type: "last" }
  | { type: "reset" }
  | {
      type: "orientate";
      orientation?: RoverState["orientation"];
    };

type RoverReducerState = Omit<RoverState, keyof unstable_IdState>;

function reducer(
  state: RoverReducerState,
  action: RoverAction
): RoverReducerState {
  const {
    stops,
    currentId,
    unstable_pastId: pastId,
    unstable_moves: moves,
    loop,
  } = state;

  switch (action.type) {
    case "register": {
      const { id, ref } = action;
      if (stops.length === 0) {
        return {
          ...state,
          stops: [{ id, ref }],
        };
      }

      const index = stops.findIndex((stop) => stop.id === id);

      if (index >= 0) {
        return state;
      }

      const indexToInsertAt = stops.findIndex((stop) => {
        if (!stop.ref.current || !ref.current) return false;
        // Return true if the new rover element is located earlier in the DOM
        // than stop's element, else false:
        return Boolean(
          stop.ref.current.compareDocumentPosition(ref.current) &
            Node.DOCUMENT_POSITION_PRECEDING
        );
      });

      // findIndex returns -1 when the new rover should be inserted
      // at the end of stops (the compareDocumentPosition test
      // always returns false in that case).
      if (indexToInsertAt === -1) {
        return {
          ...state,
          stops: [...stops, { id, ref }],
        };
      }
      return {
        ...state,
        stops: [
          ...stops.slice(0, indexToInsertAt),
          { id, ref },
          ...stops.slice(indexToInsertAt),
        ],
      };
    }
    case "unregister": {
      const { id } = action;
      const nextStops = stops.filter((stop) => stop.id !== id);
      if (nextStops.length === stops.length) {
        return state;
      }

      return {
        ...state,
        stops: nextStops,
        unstable_pastId: pastId && pastId === id ? null : pastId,
        currentId: currentId && currentId === id ? null : currentId,
      };
    }
    case "move": {
      const { id, silent } = action;
      const nextMoves = silent ? moves : moves + 1;

      if (id === null) {
        return {
          ...state,
          currentId: null,
          unstable_pastId: currentId,
          unstable_moves: nextMoves,
        };
      }

      const index = stops.findIndex((stop) => stop.id === id);

      // Item doesn't exist, so we don't count a move
      if (index === -1) {
        return state;
      }

      if (stops[index].id === currentId) {
        return { ...state, unstable_moves: nextMoves };
      }

      return {
        ...state,
        currentId: stops[index].id,
        unstable_pastId: currentId,
        unstable_moves: nextMoves,
      };
    }
    case "next": {
      if (currentId == null) {
        return reducer(state, { type: "move", id: stops[0] && stops[0].id });
      }
      const index = stops.findIndex((stop) => stop.id === currentId);

      // If loop is truthy, turns [0, currentId, 2, 3] into [currentId, 2, 3, 0]
      // Otherwise turns into [currentId, 2, 3]
      const reorderedStops = [
        ...stops.slice(index + 1),
        ...(loop ? stops.slice(0, index) : []),
      ];

      const nextIndex =
        reorderedStops.findIndex((stop) => stop.id === currentId) + 1;

      return reducer(state, {
        type: "move",
        id: reorderedStops[nextIndex] && reorderedStops[nextIndex].id,
      });
    }
    case "previous": {
      const { stops: _, ...nextState } = reducer(
        { ...state, stops: stops.slice().reverse() },
        { type: "next" }
      );
      return {
        ...state,
        ...nextState,
      };
    }
    case "first": {
      const stop = stops[0];
      return reducer(state, { type: "move", id: stop && stop.id });
    }
    case "last": {
      const stop = stops[stops.length - 1];
      return reducer(state, { type: "move", id: stop && stop.id });
    }
    case "reset": {
      return {
        ...state,
        currentId: null,
        unstable_pastId: null,
      };
    }
    case "orientate":
      return { ...state, orientation: action.orientation };
    default:
      throw new Error();
  }
}

export function useRoverState(
  initialState: SealedInitialState<RoverInitialState> = {}
): RoverStateReturn {
  const {
    orientation,
    currentId = null,
    loop = false,
    ...sealed
  } = useSealedState(initialState);
  const [state, dispatch] = React.useReducer(reducer, {
    orientation,
    stops: [],
    currentId,
    unstable_pastId: null,
    unstable_moves: 0,
    loop,
  });

  const idState = unstable_useIdState(sealed);

  return {
    ...idState,
    ...state,
    register: useAction((id, ref) => dispatch({ type: "register", id, ref })),
    unregister: useAction((id) => dispatch({ type: "unregister", id })),
    move: useAction((id, silent) => dispatch({ type: "move", id, silent })),
    next: useAction(() => dispatch({ type: "next" })),
    previous: useAction(() => dispatch({ type: "previous" })),
    first: useAction(() => dispatch({ type: "first" })),
    last: useAction(() => dispatch({ type: "last" })),
    unstable_reset: useAction(() => dispatch({ type: "reset" })),
    unstable_orientate: useAction((o) =>
      dispatch({ type: "orientate", orientation: o })
    ),
  };
}

function useAction<T extends (...args: any[]) => any>(fn: T) {
  return React.useCallback(fn, []);
}