app.py

import streamlit as st
import datetime
from math import ceil

st.write("Find out your 500-day, 1000-day, etc., anniversaries")
date_str=st.text_area("Enter a date (format: yyyy-mm-dd): ")
today = datetime.datetime.now().date() 

# Convert the input string to a datetime object
try:
    date = datetime.datetime.strptime(date_str, "%Y-%m-%d")

# Calculate the dates 500, 1000, 1500, 2000, and 2500 days after the input date
    dates_after = []
    cutoff=(today - date.date()).days+2001
    day_list=list(range(500,2501,500))+list(range(3000,cutoff,1000))
    for days in day_list:
        delta = datetime.timedelta(days=days)
        dates_after.append(date + delta)
    
# Calculate the next multiple of 500 days after the current date
    delta_days = 500*(ceil((today - date.date()).days/500))
    next_multiple = date + datetime.timedelta(days=delta_days)

# Print the results
    st.write("Input date:", date.strftime("%Y-%m-%d"))
    st.write("Next multiple of 500:", str(delta_days), "days on", next_multiple.strftime("%Y-%m-%d"),"\n")
    for i, date_after in enumerate(dates_after):
        st.write(f"{day_list[i]} days after input date:", date_after.strftime("%Y-%m-%d"))

except ValueError:
    st.write("Write date in format yyyy-mm-dd")