import pandas as pd
data = {'SKU': ['A', 'A', 'A', 'A',
                'B','B','B','B',
                'C','C','C','C',
                'D', 'D', 'D', 'D',
                'E', 'E', 'E', 'E',
                'F', 'F', 'F', 'F'],
        'Current_Stock': [2,0,0,0, 
                          0,0,-1,-1,
                          2,-1,0,1,
                          2,2,3,1,
                          2,0,0,1,
                          2,-1,1,0],
        'Date_Updated': ['2024/7/26', '2024/7/27','2024/7/28', '2024/7/29'
                         '2024/7/26', '2024/7/27','2024/7/28', '2024/7/29',
                         '2024/7/26', '2024/7/27','2024/7/28', '2024/7/29',
                         '2024/7/26', '2024/7/27','2024/7/28', '2024/7/29',
                         '2024/7/26', '2024/7/27','2024/7/28', '2024/7/29',
                         '2024/7/26', '2024/7/27','2024/7/28', '2024/7/29']}

df = pd.DataFrame(data)


result = pd.DataFrame({'SKU': ['A', 'B', 'C', 'D', 'E', 'F'],
                       'Days_Out_of_Stock': [3,4,0,0,0,1]}) 

My desire is to calculate number days of out of stock, which is

• If all days which current_stock < 1, the number days of out of stock = sum of all days (Eg: sku B)
• If any recent days is restocked, the number days of out of stock will be calculated again from that day (Eg: sku C)
  Thanks for advance