package lru

import (
	"container/list"
	"s1d3sw1ped/steamcache2/vfs/types"
)

// LRUList represents a least recently used list for cache eviction
type LRUList[T any] struct {
	list *list.List
	elem map[string]*list.Element
}

// NewLRUList creates a new LRU list
func NewLRUList[T any]() *LRUList[T] {
	return &LRUList[T]{
		list: list.New(),
		elem: make(map[string]*list.Element),
	}
}

// Add adds an item to the front of the LRU list
func (l *LRUList[T]) Add(key string, item T) {
	elem := l.list.PushFront(item)
	l.elem[key] = elem
}

// MoveToFront moves an item to the front of the LRU list
func (l *LRUList[T]) MoveToFront(key string, timeUpdater *types.BatchedTimeUpdate) {
	if elem, exists := l.elem[key]; exists {
		l.list.MoveToFront(elem)
		// Update the FileInfo in the element with new access time
		if fi, ok := any(elem.Value).(interface {
			UpdateAccessBatched(*types.BatchedTimeUpdate)
		}); ok {
			fi.UpdateAccessBatched(timeUpdater)
		}
	}
}

// Remove removes an item from the LRU list
func (l *LRUList[T]) Remove(key string) (T, bool) {
	if elem, exists := l.elem[key]; exists {
		delete(l.elem, key)
		if item, ok := l.list.Remove(elem).(T); ok {
			return item, true
		}
	}
	var zero T
	return zero, false
}

// Len returns the number of items in the LRU list
func (l *LRUList[T]) Len() int {
	return l.list.Len()
}

// Back returns the least recently used item (at the back of the list)
func (l *LRUList[T]) Back() *list.Element {
	return l.list.Back()
}

// Front returns the most recently used item (at the front of the list)
func (l *LRUList[T]) Front() *list.Element {
	return l.list.Front()
}