Automatic invoice number generation

[BeyerMart]

Currently, the invoices are numbered consecutively, but what happens when we have to add a digit?
Should all other invoice numbers then get leading zeros?
What if someone wants a suffix (or "midfix") instead of a prefix?
Should these cases be considered?

This issue is for general discussion about this feature, if and how we should implement it. @overheadhunter @tobihagemann What are your thoughts about this?

[overheadhunter]

Can't we use

String.format("%s-%03d", invoiceNumberPrefix, sequenceNumber); // results in "example-003"

With the prefix being configurable via the UI?

[BeyerMart]

After a call with @tobihagemann we agreed to drop this feature because every company will have a completely different setup of their invoices numbers. There isn't any kind of specification on how companies need to count them. It is basically a "random" String, which the users should input themself.

[infeo]

On the other hand, from the user view as a "simple developer", i would like to wish a feature to use a simple default invoice scheme which is more than just a single number. It does not have to be configurable, but some good default.