Extract cache into own crate

time-cache/.gitignore

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+/target
+**/*.rs.bk
+Cargo.lock

time-cache/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "time-cache"
+version = "0.1.0"
+

time-cache/Cargo.toml

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+[package]
+name = "time-cache"
+version = "0.1.0"
+authors = ["Valentin Brandl <vbrandl@riseup.net>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

time-cache/src/lib.rs

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+use std::{
+    collections::HashMap,
+    hash::Hash,
+    time::{Duration, Instant},
+};
+
+pub struct Cache<K, V> {
+    cache: HashMap<K, CacheEntry<V>>,
+    duration: Duration,
+}
+
+impl<K, V> Cache<K, V>
+where
+    K: Eq + Hash,
+{
+    pub fn new(duration: Duration) -> Self {
+        Self {
+            cache: HashMap::new(),
+            duration,
+        }
+    }
+
+    pub fn get(&self, key: &K) -> CacheResult<&V> {
+        if let Some(entry) = self.cache.get(key) {
+            if Self::is_valid(Instant::now(), entry) {
+                CacheResult::Cached(&entry.1)
+            } else {
+                CacheResult::Invalid
+            }
+        } else {
+            CacheResult::Empty
+        }
+    }
+
+    pub fn invalidate(&mut self, key: &K) -> bool {
+        self.cache.remove(key).is_some()
+    }
+
+    pub fn store(&mut self, key: K, value: V) -> Option<V> {
+        self.cache
+            .insert(key, CacheEntry::new(value, self.duration))
+            .map(|old| old.1)
+    }
+
+    pub fn clear(&mut self) {
+        let now = Instant::now();
+        self.cache.retain(|_, v| !Self::is_valid(now, v));
+    }
+
+    fn is_valid(when: Instant, entry: &CacheEntry<V>) -> bool {
+        entry.0 >= when
+    }
+}
+
+pub enum CacheResult<T> {
+    Cached(T),
+    Invalid,
+    Empty,
+}
+
+struct CacheEntry<T>(Instant, T);
+
+impl<T> CacheEntry<T> {
+    fn new(value: T, duration: Duration) -> Self {
+        CacheEntry(Instant::now() + duration, value)
+    }
+}
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+}