register gala UnitSystem -> galax Unitsystem converter

Signed-off-by: nstarman <nstarman@users.noreply.github.com>

src/galax/potential/_potential/utils.py

@@ -1,6 +1,5 @@
 """galax: Galactic Dynamix in Jax."""
 
-
 from functools import singledispatch
 from typing import Any
 
@@ -41,3 +40,19 @@ def _from_named(value: str, /) -> UnitSystem:
 
     msg = f"cannot convert {value} to a UnitSystem"
     raise NotImplementedError(msg)
+
+
+##############################################################################
+# Gala compatibility
+# TODO: move this to an interoperability module
+
+# isort: split
+from galax.utils._optional_deps import HAS_GALA  # noqa: E402
+
+if HAS_GALA:
+    from gala.units import UnitSystem as GalaUnitSystem
+
+    @converter_to_usys.register
+    def _from_gala(value: GalaUnitSystem, /) -> UnitSystem:
+        # TODO: transfer all informatino, not just core units
+        return UnitSystem(*value._core_units)  # noqa: SLF001

tests/unit/potential/test_utils.py

@@ -12,6 +12,7 @@
     galactic,
     solarsystem,
 )
+from galax.utils._optional_deps import HAS_GALA
 
 
 class TestConverterToUtils:
@@ -45,6 +46,14 @@ def test_from_name(self):
         with pytest.raises(NotImplementedError):
             converter_to_usys("invalid_value")
 
+    @pytest.mark.skipif(not HAS_GALA, reason="requires gala")
+    def test_from_gala(self):
+        """Test conversion from gala."""
+        from gala.units import UnitSystem as GalaUnitSystem
+
+        value = GalaUnitSystem(u.km, u.s, u.Msun, u.radian)
+        assert converter_to_usys(value) == UnitSystem(*value._core_units)
+
 
 # ============================================================================