package soko

type stateCost struct {
	state     *State
	cost      int
	distances Ints
}

type stateCostQueue struct {
	first *stateCostQueueItem
}

type stateCostQueueItem struct {
	Value *stateCost
	Next  *stateCostQueueItem
}

func (q *stateCostQueue) Empty() bool {
	return q.first == nil
}

func (q *stateCostQueue) Get() *stateCost {
	if q.Empty() {
		panic("nothing in queue")
	}
	first := q.first
	q.first = first.Next
	return first.Value
}

func (q *stateCostQueue) Put(value *stateCost) {
	priority := value.cost
	item := &stateCostQueueItem{value, nil}
	if q.Empty() {
		q.first = item
		return
	}
	if priority < q.first.Value.cost {
		item.Next = q.first
		q.first = item
		return
	}
	curr := q.first
	for curr.Next != nil {
		if priority < curr.Next.Value.cost {
			item.Next = curr.Next
			curr.Next = item
			return
		}
		curr = curr.Next
	}
	curr.Next = item
}

func (q *stateCostQueue) Update(value *stateCost) {
	var prev *stateCostQueueItem
	curr := q.first
	for curr.Value != value {
		prev = curr
		curr = curr.Next
		if curr == nil {
			panic("not in queue")
		}
	}
	if prev == nil {
		q.first = curr.Next
	} else {
		prev.Next = curr.Next
	}
	q.Put(value)
}