package kvmemcache

import (
	"time"
)

func (c *Cache) getItem(key string) *lruItem {
	c.lock.Lock()
	defer c.lock.Unlock()

	elem, ok := c.cache[key]
	if !ok {
		c.stats.Misses++
		return nil
	}

	item := elem.Value.(*lruItem)
	if c.ttl != 0 && time.Since(item.createdAt) > c.ttl {
		c.stats.Expired++
		c.evictKey(key)
		return nil
	}

	c.stats.Hits++
	c.ll.MoveToFront(elem)
	return item
}

func (c *Cache) loadItemFromSource(key string) *lruItem {
	c.updateLock.Lock(key)
	defer c.updateLock.Unlock(key)

	// May have lost update race.
	if item := c.getItem(key); item != nil {
		return item
	}

	val, err := c.src(key)
	item := &lruItem{
		key:   key,
		value: val,
		err:   err,
	}

	if c.ttl != 0 {
		item.createdAt = time.Now()
	}

	c.putItem(key, item)
	return item
}

func (c *Cache) putItem(key string, item *lruItem) {
	c.lock.Lock()
	defer c.lock.Unlock()

	c.cache[key] = c.ll.PushFront(item)

	if c.maxSize > 0 && len(c.cache) > c.maxSize {
		elem := c.ll.Back()
		c.ll.Remove(elem)
		delete(c.cache, elem.Value.(*lruItem).key)
	}
}

func (c *Cache) evictKey(key string) {
	elem, ok := c.cache[key]
	if !ok {
		return
	}
	delete(c.cache, key)
	c.ll.Remove(elem)
}