package main

import (
	"container/list"

	"github.com/filecoin-project/lotus/chain/store"
)

type headBuffer struct {
	buffer *list.List
	size   int
}

func NewHeadBuffer(size int) *headBuffer {
	buffer := list.New()
	buffer.Init()

	return &headBuffer{
		buffer: buffer,
		size:   size,
	}
}

func (h *headBuffer) Push(hc *store.HeadChange) (rethc *store.HeadChange) {
	if h.buffer.Len() == h.size {
		var ok bool

		el := h.buffer.Front()
		rethc, ok = el.Value.(*store.HeadChange)
		if !ok {
			panic("Value from list is not the correct type")
		}

		h.buffer.Remove(el)
	}

	h.buffer.PushBack(hc)

	return
}

func (h *headBuffer) Pop() {
	el := h.buffer.Back()
	if el != nil {
		h.buffer.Remove(el)
	}
}