chore(backend): add cache package

Signed-off-by: detj <[email protected]>

backend/api/cache/lru.go

@@ -0,0 +1,76 @@
+package cache
+
+import (
+	"container/list"
+	"sync"
+)
+
+// LRUCache represents a thread-safe
+// LRU cache.
+type LRUCache struct {
+	cap   int
+	cache map[string]*list.Element
+	list  *list.List
+	mu    sync.Mutex
+}
+
+type entry struct {
+	key   string
+	value any
+}
+
+// New initialized a new LRU cache
+// with given capacity.
+func NewLRUCache(cap int) *LRUCache {
+	return &LRUCache{
+		cap:   cap,
+		cache: make(map[string]*list.Element),
+		list:  list.New(),
+	}
+}
+
+// Get retrieves a value from the cache
+// and marks it as recently used.
+func (c *LRUCache) Get(key string) (any, bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if elem, ok := c.cache[key]; ok {
+		c.list.MoveToFront(elem)
+		return elem.Value.(*entry).value, true
+	}
+
+	return nil, false
+}
+
+// Put inserts a value into the cache, evicting
+// the least recently used item if necessary.
+func (c *LRUCache) Put(key string, value any) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if elem, ok := c.cache[key]; ok {
+		c.list.MoveToFront(elem)
+		elem.Value.(*entry).value = value
+		return
+	}
+
+	if c.list.Len() >= c.cap {
+		c.evict()
+	}
+
+	e := &entry{key, value}
+	elem := c.list.PushFront(e)
+	c.cache[key] = elem
+}
+
+// evict removes the least recently
+// used item from the cache.
+func (c *LRUCache) evict() {
+	elem := c.list.Back()
+	if elem != nil {
+		c.list.Remove(elem)
+		kv := elem.Value.(*entry)
+		delete(c.cache, kv.key)
+	}
+}