Can you write a one liner to give me the timestamp for start or end of current week, or month? How about a text representation of a difference between two dates

Can you write a one liner to give me the timestamp for start or end of current week, or month? How about a text representation of a difference between two dates? Relative date string (eg. “2 weeks ago”)? Date comparison between two dates that are in different time zones? Does your date calculations take leap hours and leap seconds into account? Date libraries make all these and many more operations a breeze, while rolling these on your own can be tricky, error prone and you’ll be just wasting your time.