Add Caching (#5)

Add in a simple templated cache used for memoization.  For something
that requires key/value, then use hashicorp/lru.

Author: spjmurray

charts/core/Chart.yaml

@@ -4,7 +4,7 @@ description: A Helm chart for deploying Unikorn Core
 
 type: application
 
-version: v0.1.4
-appVersion: v0.1.4
+version: v0.1.5
+appVersion: v0.1.5
 
 icon: https://assets.unikorn-cloud.org/images/logos/dark-on-light/icon.svg

pkg/util/cache/timeout_cache.go

@@ -0,0 +1,55 @@
+/*
+Copyright 2024 the Unikorn Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cache
+
+import (
+	"time"
+)
+
+// TimeoutCache provides a cache with timeout.
+type TimeoutCache[V any] struct {
+	value   V
+	refresh time.Duration
+	invalid time.Time
+}
+
+// New gets a new cache.
+func New[V any](refresh time.Duration) *TimeoutCache[V] {
+	return &TimeoutCache[V]{
+		refresh: refresh,
+	}
+}
+
+// Get returns the cached value if set and it hasn't timed out
+// and returns true.  If it has timed out, it will return V's
+// zero value and false, and will need to be set again.
+//
+//nolint:nonamedreturns
+func (m *TimeoutCache[V]) Get() (value V, ok bool) {
+	if time.Now().After(m.invalid) {
+		return
+	}
+
+	return m.value, true
+}
+
+// Set remembers the value and resets the invalid time based
+// on when the cache was set.
+func (m *TimeoutCache[V]) Set(value V) {
+	m.invalid = time.Now().Add(m.refresh)
+	m.value = value
+}