qgis - How to compute the share of a line that is inside a polygon programatically?

I have two layers, one contains polygon while another consist of line. something like below figure:

Now I want to update line attribute column value through polygon attribute column only when, line is inside or contains or overlap 90% in the polygon. Like above picture it is depicted that polygon contains line almost 60%. How can I check that?

I only know that there are two function intersect and contains both cannot do this job. I tried it with contains but it didn't work as polygon provide area while line provide length so I can't compare both.