Don't lean on filesystem so much

src/filesystem.rs

@@ -1,10 +1,11 @@
 use std::{
-    collections::HashMap,
+    any::Any,
+    collections::{HashMap, hash_map::Entry},
     fs,
     ops::Deref,
     path::PathBuf,
     sync::{
-        Arc, Mutex,
+        Arc, Mutex, RwLock,
         atomic::{AtomicU64, Ordering},
     },
 };
@@ -16,42 +17,56 @@ use serde::{Deserialize, Serialize};
 #[derive(Clone)]
 pub struct Persistence {
     config_dir: Option<PathBuf>,
-    versions: Arc<Mutex<HashMap<String, Arc<AtomicU64>>>>,
+    states: Arc<Mutex<HashMap<String, Arc<dyn Any + Send + Sync>>>>,
 }
 
 impl Persistence {
     pub fn new() -> Self {
         Self {
             config_dir: init_config_dir(),
-            versions: Arc::new(Mutex::new(HashMap::new())),
+            states: Arc::new(Mutex::new(HashMap::new())),
         }
     }
 
     pub fn config<T: ConfigCompatible>(&self, file: &str) -> Config<T> {
-        let latest_version = self
-            .versions
-            .lock()
-            .unwrap()
-            .entry(file.to_string())
-            .or_default()
-            .clone();
-        let path = self
-            .config_dir
-            .as_ref()
-            .map(|p| p.join(file).with_extension("json"));
-        let value = if let Some(p) = path.as_ref()
-            && let Ok(bytes) = fs::read(p)
-            && let Ok(v) = serde_json::from_slice(&bytes)
-        {
-            v
-        } else {
-            T::default()
+        let state = {
+            let mut lock = self.states.lock().unwrap();
+            match lock.entry(file.to_string()) {
+                Entry::Vacant(e) => {
+                    let path = self
+                        .config_dir
+                        .as_ref()
+                        .map(|p| p.join(file).with_extension("json"));
+                    let value = if let Some(p) = path.as_ref()
+                        && let Ok(bytes) = fs::read(p)
+                        && let Ok(v) = serde_json::from_slice(&bytes)
+                    {
+                        v
+                    } else {
+                        T::default()
+                    };
+
+                    let state = Arc::new(ConfigState {
+                        current: RwLock::new(value),
+                        version: AtomicU64::new(0),
+                        path,
+                    });
+                    e.insert(state.clone());
+                    state
+                }
+                Entry::Occupied(e) => e
+                    .get()
+                    .clone()
+                    .downcast()
+                    .expect("same config file accessed with two types"),
+            }
         };
+        let value = state.current.read().unwrap().clone();
+        let version = state.version.load(Ordering::Relaxed);
         Config {
             value,
-            version: latest_version.load(Ordering::Relaxed),
-            latest_version,
-            path,
+            version,
+            state,
         }
     }
 
@@ -90,16 +105,27 @@ fn project_dirs() -> Option<ProjectDirs> {
     ProjectDirs::from("com", "virtual-boy", "Lemur")
 }
 
-pub trait ConfigCompatible: Clone + Default + Eq + Serialize + for<'a> Deserialize<'a> {}
-impl<T: Clone + Default + Eq + Serialize + for<'a> Deserialize<'a>> ConfigCompatible for T {}
+pub trait ConfigCompatible:
+    Send + Sync + 'static + Clone + Default + Eq + Serialize + for<'a> Deserialize<'a>
+{
+}
+impl<T: Send + Sync + 'static + Clone + Default + Eq + Serialize + for<'a> Deserialize<'a>>
+    ConfigCompatible for T
+{
+}
 
-// A wrapper for a T (probably) stored on the filesystem.
-// Cheap to dereference, easy to sync changes to all copies.
+struct ConfigState<T> {
+    current: RwLock<T>,
+    version: AtomicU64,
+    path: Option<PathBuf>,
+}
+
+// A wrapper for a config struct, loaded from disk and referenced across the codebase.
+// Cheap to read, and lets you sync changes to all copies.
 pub struct Config<T> {
     value: T,
     version: u64,
-    latest_version: Arc<AtomicU64>,
-    path: Option<PathBuf>,
+    state: Arc<ConfigState<T>>,
 }
 
 impl<T> Deref for Config<T> {
@@ -112,32 +138,30 @@ impl<T> Deref for Config<T> {
 
 impl<T: ConfigCompatible> Config<T> {
     pub fn refresh(&mut self) {
-        let version = self.latest_version.load(Ordering::Relaxed);
+        let version = self.state.version.load(Ordering::Relaxed);
         if self.version == version {
             return;
         }
-        if let Some(path) = &self.path
-            && let Ok(bytes) = fs::read(path)
-            && let Ok(latest) = serde_json::from_slice(&bytes)
-        {
-            self.value = latest;
-        }
+        self.value = self.state.current.read().unwrap().clone();
         self.version = version;
     }
 
-    pub fn update(&mut self, update: impl FnOnce(&mut T)) {
+    pub fn update(&mut self, mut update: impl FnMut(&mut T)) {
         let mut new_value = self.value.clone();
         update(&mut new_value);
         if self.value == new_value {
             return;
         }
-        if let Some(path) = &self.path
-            && let Ok(bytes) = serde_json::to_vec(&new_value)
+
+        let mut current = self.state.current.write().unwrap();
+        update(&mut current);
+        if let Some(path) = &self.state.path
+            && let Ok(bytes) = serde_json::to_vec(&*current)
         {
             let _ = fs::write(path, bytes);
         }
-        let version = self.latest_version.fetch_add(1, Ordering::Relaxed) + 1;
-        self.value = new_value.clone();
+        let version = self.state.version.fetch_add(1, Ordering::Relaxed) + 1;
+        self.value = current.clone();
         self.version = version;
     }
 }