Redmine Computable Custom Field

A mapping should be usable as a rule of assignment. When mapping for example two custom field values then the user should be able to define what the outcome should be when two certain values come together:

mapping(cfs[1], cfs[2])

where cfs[1] is element of {1,2,3} and cfs[2] is element of {1,2,3}

with the rule of assignment cfs[1], cfs[2], result defines as follows

1,1,1
1,2,2
1,3,3
2,1,4
2,2,5
2,3,6
...

To implement this feature an additional field for the rule of assignment is needed. Moreover, the value lookup needs to be implemented.

In order to allow qualitative values it should be usable with key/value custom fields.