import { ScrollSpyState, ScrollSpyAction, ScrollSpyActionType } from "./types";

export const scrollSpyInitialState = {
  index: 0,
  page: 1,
};

export const reducer = (
  state: ScrollSpyState = scrollSpyInitialState,
  action: ScrollSpyAction,
) => {
  switch (action.type) {
    case ScrollSpyActionType.UPDATE:
      return state.index !== action.index
        ? {
            ...state,
            index: action.index,
            page: action.index + 1,
          }
        : state;
    default:
      return state;
  }
};