moraine 0.6.0

//! The object store data files live in, named once for the caches.

use std::sync::Arc;

use object_store::ObjectStore;
use serde::{Deserialize, Serialize};

use crate::store::cache;

/// An object store holding data files, named once for the caches that key
/// on it. Build one per store and clone it: a durable store is named by
/// its location, an in-memory one at random, so two `new` calls on one
/// in-memory store name it twice.
#[derive(Clone)]
pub struct DataStore {
    store: Arc<dyn ObjectStore>,
    pub(super) identity: StoreIdentity,
}

impl DataStore {
    /// Names `store` for the caches.
    #[must_use]
    pub fn new(store: Arc<dyn ObjectStore>) -> Self {
        let identity = StoreIdentity::of(&store);
        Self { store, identity }
    }

    /// The store itself.
    #[must_use]
    pub fn object_store(&self) -> &Arc<dyn ObjectStore> {
        &self.store
    }
}

impl std::fmt::Debug for DataStore {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "DataStore({})", self.store)
    }
}

/// Which store a cached file belongs to. A durable store is named by its
/// location, so its entries outlive the process; an in-memory store holds
/// different contents in every instance, so it is named at random and
/// nothing recovered can match it.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub(super) enum StoreIdentity {
    Durable(u128),
    Ephemeral(u128),
}

/// How an in-memory object store names itself, alone or inside a wrapper.
const IN_MEMORY: &str = "InMemory";

impl StoreIdentity {
    pub(super) fn of(store: &Arc<dyn ObjectStore>) -> Self {
        let name = store.to_string();
        if name.contains(IN_MEMORY) {
            Self::Ephemeral(uuid::Uuid::new_v4().as_u128())
        } else {
            Self::Durable(cache::stable_name(&name).as_u128())
        }
    }
}