lru.go

package main

import (
	"container/list"
)

type Lru struct {
	maxsize int
	order   *list.List
	elems   map[string]*list.Element
}

type lruitem struct {
	key   string
	value interface{}
}

func NewLru(size int) *Lru {
	return &Lru{
		maxsize: size,
		order:   list.New(),
		elems:   make(map[string]*list.Element),
	}
}

func (lru *Lru) Add(key string, value interface{}) {
	if elem, ok := lru.elems[key]; ok {
		lru.order.MoveToFront(elem)
		elem.Value = &lruitem{key: key, value: value}
		return
	}

	elem := lru.order.PushFront(&lruitem{key: key, value: value})
	lru.elems[key] = elem

	if len(lru.elems) > lru.maxsize {
		value := lru.order.Remove(lru.order.Back())
		delete(lru.elems, value.(*lruitem).key)
	}
}

func (lru *Lru) Delete(key string) bool {
	elem, ok := lru.elems[key]
	if ok {
		lru.order.Remove(elem)
		delete(lru.elems, key)
	}
	return ok
}

func (lru *Lru) Get(key string) (value interface{}, ok bool) {
	if elem, ok := lru.elems[key]; ok {
		lru.order.MoveToFront(elem)
		value = elem.Value.(*lruitem).value
		return value, true
	}
	return nil, false
}