Drupal 7 - time and date field to integer and a view summary

1) I need code in PHP for drupal computed field ([login to view URL]) that would calculate difference in days between two dates e.g. : date 1: 1st may 2019 date 2: 20 July 2020 date 2 - date 1 = circa 365 + 80 days = 445 days and provide it as an integer value as a number of years, that I could further use for extra calculations. 445 days (calculated difference) / 365 (average year) = 1.219 that number (difference in days as a number of years) should be the output of the code. 2) some values would be provided as char or string. The code should account for it. A draft version of the code: $value1_energy1 = field_get_items($entity_type, $entity, 'field_energy1'); $value2_energy2 = field_get_items($entity_type, $entity, 'field_energy2'); if ($value2_energy2[0]['value'] > '0') { $entity_field[0]['value'] = $value2_energy2[0]['value']*0.000351 + $value1_energy1 [0]['value']*0.000812; }else{ $entity_field[0]['value'] = $value1_energy1[0]['value']*0.000812; } This is just a basic calculation and: a) there is no date field included b) valued1 and value2 could be provided as a string (and have a space or a comma instead of a dot). 3) those calculated values shoud be summed up in a view There is a view with a list of nodes, and at the bottom of the view we need to provide a sum of those calculated values example of the view with fomulas: [login to view URL]