lru: init

lru/lru.go

@@ -0,0 +1,106 @@
+package lru
+
+import (
+	"container/list"
+	"time"
+)
+
+type LRU[T any] struct {
+	queue    *list.List
+	items    map[string]*list.Element
+	capacity int
+}
+type item[T any] struct {
+	key   string
+	value *T
+	eol   time.Time
+}
+
+func New[T any](capacity int) *LRU[T] {
+	return &LRU[T]{
+		queue:    list.New(),
+		items:    make(map[string]*list.Element, capacity),
+		capacity: capacity,
+	}
+}
+
+func (lru *LRU[T]) Set(key string, value T, ttl time.Duration) (evicted bool) {
+	eol := time.Now().Add(ttl)
+
+	if element, ok := lru.items[key]; ok {
+		lru.queue.MoveToFront(element)
+		item := element.Value.(*item[T])
+		item.value = &value
+		item.eol = eol
+
+		return
+	}
+
+	if lru.queue.Len() == lru.capacity {
+		lru.evict()
+		evicted = true
+	}
+
+	item := &item[T]{
+		key:   key,
+		value: &value,
+		eol:   eol,
+	}
+
+	element := lru.queue.PushFront(item)
+	lru.items[item.key] = element
+
+	return
+}
+
+func (lru *LRU[T]) Get(name string) (value T, ok bool) {
+	element, ok := lru.items[name]
+	if !ok {
+		return value, false
+	}
+
+	item := element.Value.(*item[T])
+	if item.expired() {
+		lru.delete(element)
+
+		return value, false
+	}
+
+	lru.queue.MoveToFront(element)
+
+	return *item.value, true
+}
+
+func (lru *LRU[T]) evict() {
+	element := lru.queue.Back()
+	if element == nil {
+		return
+	}
+
+	for { // find first expired
+		item := element.Value.(*item[T])
+
+		if item.expired() {
+			lru.delete(element)
+
+			return
+		}
+
+		element = element.Prev()
+
+		if element == nil {
+			break // probably expired not found
+		}
+	}
+
+	lru.delete(lru.queue.Back()) // delete oldest if no one expired
+}
+
+func (lru *LRU[T]) delete(element *list.Element) {
+	lru.queue.Remove(element)
+	delete(lru.items, element.Value.(*item[T]).key)
+}
+
+func (i *item[T]) expired() bool {
+	return time.Now().After(i.eol)
+}