package heap

import (
	"bytes"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/pilorama"
)

type MinPairingHeap struct {
	head *phNode
	size int
}

type phNode struct {
	val     *pilorama.NodeInfo
	key     []byte
	child   *phNode
	sibling *phNode
}

func NewPairing() *MinPairingHeap {
	return &MinPairingHeap{}
}

func (m *MinPairingHeap) Insert(infos ...pilorama.NodeInfo) {
	for i := range infos {
		tmp := &phNode{key: infos[i].Meta.GetAttr(pilorama.AttributeFilename), val: &infos[i]}
		m.head = meld(tmp, m.head)
		m.size++
	}
}

func (m *MinPairingHeap) IsEmpty() bool {
	return m.head == nil
}

func (m *MinPairingHeap) ExtractMin() pilorama.NodeInfo {
	val := m.head.val
	m.head = mergePairs(m.head.child)
	m.size--
	return *val
}

func meld(m1, m2 *phNode) *phNode {
	if m1 == nil {
		return m2
	}
	if m2 == nil {
		return m1
	}
	if bytes.Compare(m1.key, m2.key) == -1 {
		m1.child, m2.sibling = m2, m1.child
		return m1
	}
	m2.child, m1.sibling = m1, m2.child
	return m2
}

func mergePairs(n *phNode) *phNode {
	if n == nil {
		return nil
	}
	if n.sibling == nil {
		return n
	}
	tmp := n.sibling.sibling
	return meld(meld(n, n.sibling), mergePairs(tmp))
}