Creating script field with 'worked time' and 'billable time',

[jmarko]

Hi,
is there any chance to get work and billable time from issue and put it to custom field and than work with it. Idea is that in this field we calculate working/billable hours from this issue and all linked issues, so we can automatically see all time spent for one problem. Also show it to customer (if its possible trough portal).
I guess its possible with script-runner but I cannot find code for getting those times from issue. Can anyone show me please? I quite new to script-runner groovy..
Thank you.  

[jmarko]

Anyone please?