feat: created simple LRU cache

Author: Oudwins

pkg/cache/lru.go

@@ -0,0 +1,89 @@
+package lru
+
+import "sync"
+
+type node struct {
+	key  string
+	val  string
+	prev *node
+	next *node
+}
+
+type Cache interface {
+	Get(string) string
+	Set(string, string)
+}
+
+type LRU struct {
+	maxCapacity int
+	capacity    int
+	cache       map[string]*node
+	head        *node
+	tail        *node
+	mutex       sync.Mutex
+}
+
+func (lru *LRU) Get(key string) string {
+	lru.mutex.Lock()
+	defer lru.mutex.Unlock()
+	n := lru.cache[key]
+	if n == nil {
+		return ""
+	}
+
+	lru.remove(n)
+	lru.insertRight(n)
+
+	return n.val
+}
+
+func (lru *LRU) Set(key, value string) {
+	lru.mutex.Lock()
+	defer lru.mutex.Unlock()
+	if n := lru.cache[key]; n != nil {
+		lru.remove(n)
+	}
+
+	n := &node{key: key, val: value}
+	lru.cache[key] = n
+	lru.insertRight(n)
+
+	// evict
+	if lru.capacity > lru.maxCapacity {
+		delete(lru.cache, lru.tail.next.key)
+		lru.remove(lru.tail.next)
+	}
+
+}
+
+func (lru *LRU) insertRight(n *node) {
+	prev := lru.head.prev
+	prev.next = n
+	n.prev = prev
+	n.next = lru.head
+	lru.head.prev = n
+}
+
+func (lru *LRU) remove(n *node) {
+	prev := n.prev
+	nxt := n.next
+	prev.next = nxt
+	nxt.prev = prev
+	n.prev = nil
+	n.next = nil
+	lru.capacity--
+}
+
+func Make(maxCapacity int) Cache {
+	head := &node{}
+	tail := &node{}
+	tail.next = head
+	head.prev = tail
+	return &LRU{
+		maxCapacity: maxCapacity,
+		capacity:    0,
+		cache:       make(map[string]*node),
+		head:        head,
+		tail:        tail,
+	}
+}