Get the second most recent activity

# Table: UserActivity
# 
# +---------------+---------+
# | Column Name   | Type    |
# +---------------+---------+
# | username      | varchar |
# | activity      | varchar |
# | startDate     | Date    |
# | endDate       | Date    |
# +---------------+---------+
# This table may contain duplicates rows.
# This table contains information about the activity performed by each user in a period of time.
# A person with username performed an activity from startDate to endDate.
# 
#  
# 
# Write a solution to show the second most recent activity of each user.
# 
# If the user only has one activity, return that one. A user cannot perform more than one activity at the same time.
# 
# Return the result table in any order.
# 
# The result format is in the following example.
#
# Example 1:
# Input:
# UserActivity table:
# +------------+--------------+-------------+-------------+
# | username   | activity     | startDate   | endDate     |
# +------------+--------------+-------------+-------------+
# | Alice      | Travel       | 2020-02-12  | 2020-02-20  |
# | Alice      | Dancing      | 2020-02-21  | 2020-02-23  |
# | Alice      | Travel       | 2020-02-24  | 2020-02-28  |
# | Bob        | Travel       | 2020-02-11  | 2020-02-18  |
# +------------+--------------+-------------+-------------+
# Output:
# +------------+--------------+-------------+-------------+
# | username   | activity     | startDate   | endDate     |
# +------------+--------------+-------------+-------------+
# | Alice      | Dancing      | 2020-02-21  | 2020-02-23  |
# | Bob        | Travel       | 2020-02-11  | 2020-02-18  |
# +------------+--------------+-------------+-------------+
# Explanation:
# The most recent activity of Alice is Travel from 2020-02-24 to 2020-02-28, before that she was dancing from 2020-02-21 to 2020-02-23.
# Bob only has one record, we just take that one.

import pandas as pd

def second_most_recent(user_activity: pd.DataFrame) -> pd.DataFrame:
  user_activity['rank'] = user_activity.groupby('username')['endDate'].rank(method='first', ascending=False)
  counts = user_activity.groupby('username')['activity'].transform('count')
  result = user_activity[(user_activity['rank'] == 2) | (counts == 1)]
  return result[['username', 'activity', 'startDate', 'endDate']]