North Italic - Teiwa ?

I was looking at the script on the Negua helmet and the
inscription "harigastiteiwa..."
This is generally taken to say "Harigasti Teiwa"

I have read others say that Teiwa is in dative case, as in "to Teiwa".
How does one know it is dative? What dictates such a conclusion?

Additionally I understand hari = war and gasti = guest.... thus
Harigasti = 'Guest of the Army'
The possible interpretations I have seen are:

"[dedicated] to the army's friend/guest, Teiwa"
Or
"Harigasti (personal name dedicates this to Teiwa"

Any insight would be appreciated as always
Aydan