add basic functionality for calculate days

app.py

@@ -1,15 +1,22 @@
 from PIL import Image
+from datetime import date
 
 
-def calculate_days(*dob) -> int:
+def calculate_days(*dob: int) -> int:
     """ Calculate number of days left to live based on date of birth """
-    return 3
+    average_life_expectancy = 26098         # actually half a day above the average human life expectancy (71.5 yrs)
+    days_lived = abs(date.today() - date(*dob)).days
+    days_left = average_life_expectancy - days_lived
+
+    return days_left
 
 
 def generate_calendar(days: int):
     """ Generate a calendar based on the number of days """
     # TODO: scale square pics based on the number of days
-    with Image.open('square.jpg') as square, Image.open('background.png') as background:
+    square_path = 'img/square.jpg'
+    background_path = 'img/background.png'
+    with Image.open(square_path) as square, Image.open(background_path) as background:
         print(background.format, background.size, background.mode)
 
         for day in range(days):
@@ -20,5 +27,5 @@ def generate_calendar(days: int):
 
 
 if __name__ == '__main__':
-    days = calculate_days(10, 10, 1995)
-    generate_calendar(days)
+    days = calculate_days(1995, 10, 10)
+    # generate_calendar(days)