runtime_config.rs

use serde::Deserialize;

use crate::Factor;

pub trait RuntimeConfigSource<T: Factor> {
    fn get_runtime_config(&mut self) -> anyhow::Result<Option<T::RuntimeConfig>>;
}

pub trait RuntimeConfigFinalizer {
    fn finalize(&mut self) -> anyhow::Result<()>;
}

trait NoRuntimeConfig {}

impl NoRuntimeConfig for () {}

impl<T: Factor> RuntimeConfigSource<T> for T
where
    T::RuntimeConfig: NoRuntimeConfig,
{
    fn get_runtime_config(&mut self) -> anyhow::Result<Option<()>> {
        Ok(None)
    }
}

// All "standard" Spin factors would implement this
pub trait DeserializeRuntimeConfig<'de>: Deserialize<'de> {
    const KEY: &'static str;
}

#[cfg(test)]
mod example {
    use std::collections::HashMap;

    use anyhow::{bail, Context};

    use super::*;

    struct TomlRuntimeConfig {
        table: toml::Table,
        keys_factors: HashMap<&'static str, Vec<&'static str>>,
    }

    impl<'de, T: Factor> RuntimeConfigSource<T> for TomlRuntimeConfig
    where
        T::RuntimeConfig: DeserializeRuntimeConfig<'de>,
    {
        fn get_runtime_config(&mut self) -> anyhow::Result<Option<T>> {
            let key = T::RuntimeConfig::KEY;
            let factor_name = std::any::type_name::<T>();
            self.keys_factors.entry(key).or_default().push(factor_name);
            let Some(value) = self.table.get(key) else {
                return Ok(None);
            };
            Ok(Some(value.clone().try_into().with_context(|| {
                format!("failed to deserialize runtime config for {factor_name}")
            })?))
        }
    }

    impl RuntimeConfigFinalizer for TomlRuntimeConfig {
        fn finalize(&mut self) -> anyhow::Result<()> {
            for key in self.table.keys() {
                match self.keys_factors.get(key) {
                    Some(factors) if factors.len() == 1 => {}
                    Some(factors) => bail!(
                        "multiple factors requested runtime config key {key:?}: {}",
                        factors.join(", ")
                    ),
                    None => bail!("unused runtime config with key {key:?}"),
                }
            }
            Ok(())
        }
    }
}