implement conversions for units

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ome-metadata"
-version = "0.1.0"
+version = "0.2.0"
 edition = "2024"
 rust-version = "1.85.1"
 authors = ["Wim Pomp <w.pomp@nki.nl>"]
@@ -20,6 +20,7 @@ crate-type = ["cdylib", "rlib"]
 
 [dependencies]
 anyhow = "1.0.98"
+enum-utils = "0.1.2"
 serde = { version = "1.0.219", features = ["derive"] }
 quick-xml = {  version = "0.37.5", features = ["serialize"] }
 

src/py.rs

@@ -1,9 +1,124 @@
+use anyhow::anyhow;
 use crate::Ome;
+use crate::ome::{
+    Convert, UnitsElectricPotential, UnitsFrequency, UnitsLength, UnitsPower,
+    UnitsPressure, UnitsTemperature, UnitsTime,
+};
+use pyo3::exceptions::PyValueError;
 use pyo3::prelude::*;
+use pyo3::IntoPyObjectExt;
+
+/// helper class to be used for unpickling
+#[pyclass(module = "ome_metadata.ome_metadata_rs")]
+struct Constructor;
+
+#[pymethods]
+impl Constructor {
+    #[new]
+    fn new() -> Self {
+        Self
+    }
+
+    fn __getstate__(&self) -> (u8,) {
+        (0,)
+    }
+
+    fn __setstate__(&self, _state: (u8,)) {}
+
+    #[staticmethod]
+    fn __call__(py: Python, class: String, variant: String) -> PyResult<Bound<PyAny>> {
+        match class.as_str() {
+            "ElectricPotential" => ElectricPotential::new(&variant)?.into_bound_py_any(py),
+            "Frequency" => Frequency::new(&variant)?.into_bound_py_any(py),
+            "Length" => Length::new(&variant)?.into_bound_py_any(py),
+            "Power" => Power::new(&variant)?.into_bound_py_any(py),
+            "Pressure" => Pressure::new(&variant)?.into_bound_py_any(py),
+            "Temperature" => Temperature::new(&variant)?.into_bound_py_any(py),
+            "Time" => Time::new(&variant)?.into_bound_py_any(py),
+            _ => Err(anyhow!("cannot parse class {}", class).into())
+        }
+    }
+}
+
+macro_rules! impl_enum_into_py_object {
+    ($($s:ident: $t:ty $(,)?)*) => {
+        $(
+            #[pyclass(module = "ome_metadata.ome_metadata_rs")]
+            pub struct $s {
+                inner: $t,
+            }
+
+            #[pymethods]
+            impl $s {
+                #[new]
+                fn new(unit: &str) -> PyResult<Self> {
+                    match unit.parse() {
+                        Ok(unit) => Ok(Self { inner: unit }),
+                        Err(_) => Err(PyErr::new::<PyValueError, _>(format!("Invalid unit: {}", unit)))
+                    }
+                }
+
+                /// convert a value between units
+                fn convert(&self, unit: &str, value: f64) -> PyResult<f64> {
+                    match unit.parse() {
+                        Ok(unit) => Ok(self.inner.convert(&unit, value)?),
+                        Err(_) => Err(PyErr::new::<PyValueError, _>(format!("Invalid unit: {}", unit)))
+                    }
+                }
+
+                /// all possible variants of this enum that can be constructed or converted into
+                #[staticmethod]
+                fn variants() -> Vec<String> {
+                    <$t>::variants().iter().map(|v| format!("{:?}", v)).collect()
+                }
+
+                fn __repr__(&self) -> String {
+                    format!("{:?}", self.inner)
+                }
+
+                fn __str__(&self) -> String {
+                    format!("{:?}", self.inner)
+                }
+
+                fn __reduce__(&self) -> PyResult<(Constructor, (String, String))> {
+                    Ok((Constructor, (stringify!($s).to_string(), format!("{:?}", self.inner))))
+                }
+            }
+
+            impl<'py> IntoPyObject<'py> for $t {
+                type Target = $s;
+                type Output = Bound<'py, Self::Target>;
+                type Error = PyErr;
+                fn into_pyobject(self, py: Python<'py>) -> PyResult<Self::Output> {
+                    Bound::new(py, $s { inner: self })
+                }
+            }
+        )*
+    };
+}
+
+impl_enum_into_py_object! {
+    ElectricPotential: UnitsElectricPotential
+    Frequency: UnitsFrequency
+    Length: UnitsLength
+    Power: UnitsPower
+    Pressure: UnitsPressure
+    Temperature: UnitsTemperature
+    Time: UnitsTime
+}
 
 #[pymodule]
 #[pyo3(name = "ome_metadata_rs")]
 fn ome_metadata_rs(m: &Bound<'_, PyModule>) -> PyResult<()> {
+    m.add_class::<Constructor>()?;
+    m.add_class::<ElectricPotential>()?;
+    m.add_class::<Frequency>()?;
+    m.add_class::<Length>()?;
+    m.add_class::<Power>()?;
+    m.add_class::<Pressure>()?;
+    m.add_class::<Temperature>()?;
+    m.add_class::<Time>()?;
+
     #[pyfn(m)]
     fn ome(text: &str) -> PyResult<Ome> {
         Ok(text.parse()?)