Exercise Solution: Time Counter

export default function(state, action) {
  switch (action.type) {
    case "SET_ACTIVE_SESSION":
      return {
        ...state,
        activeSession: action.payload
      };
    case "INCREASE_COUNTER":
      //retrieve the activeSession from the action payload
      //however this comes in all caps so convert to lower Case
      const activeSession = action.payload.toLowerCase();
      return {
        ...state,
        [activeSession]: state[activeSession] + 1
      };
    case "DECREASE_COUNTER":
      //retrieve the activeSession (called session here) from the action payload
      const session = action.payload.toLowerCase();
      return {
        ...state,
        [session]: Math.max(0, state[session] - 1)
      };
    default:
      return state;
  }
}