package fusenrender

import "bytes"

// An Slice is something we manage in a priority queue.
type Slice[T any] struct {
	Key   []byte // 键
	Value T      // 值
	// 索引是在容器中的位置
	index int
}

// A PriorityQueue implements heap.Interface and holds Items.
type PriorityQueue[T any] []*Slice[T]

func (pq PriorityQueue[T]) Len() int { return len(pq) }

func (pq PriorityQueue[T]) Less(i, j int) bool {
	// 使用字节数组键比较
	return bytes.Compare(pq[i].Key, pq[j].Key) < 0
}

func (pq PriorityQueue[T]) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
	pq[i].index = i
	pq[j].index = j
}

func (pq *PriorityQueue[T]) Push(x any) {
	n := len(*pq)
	item := x.(*Slice[T])
	item.index = n
	*pq = append(*pq, item)
}

func (pq *PriorityQueue[T]) Pop() any {
	old := *pq
	n := len(old)
	item := old[n-1]
	old[n-1] = nil
	item.index = -1
	*pq = old[0 : n-1]
	return item.Value
}

// 这样就可以支持基于[]byte键的优先队列操作了