//go:generate goderive .
//
//
// Copyright (c) 2017 anygone contributors (see AUTHORS file)
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//   list of conditions and the following disclaimer.
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//

package satp

import (
	"fmt"
	"net"
	"sync"
	"sync/atomic"
	"unsafe"
)

func EndpointsEqual(this, that *net.UDPAddr) bool {
	return deriveEqual(this, that)
}

type SecurityAssociation struct {
	kd                  KeyDerivation
	endpoints           []*net.UDPAddr
	nextSeqNr           uint32
	initialSeqNrInbound uint32
	seqWindowSize       uint
	seqWindows          *sync.Map
}

func (sa *SecurityAssociation) KeyGenerate(dir Direction, usage KeyUsage, sequenceNumber uint32, out []byte) error {
	return sa.kd.Generate(dir, usage, sequenceNumber, out)
}

func (sa *SecurityAssociation) EndpointUpdate(idx uint, ep *net.UDPAddr) {
	if idx >= uint(len(sa.endpoints)) {
		return // panic???
	}
	atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&(sa.endpoints[idx]))), unsafe.Pointer(ep))
}

func (sa *SecurityAssociation) EndpointCompareAndUpdate(idx uint, ep *net.UDPAddr) bool {
	if idx >= uint(len(sa.endpoints)) {
		return false // panic???
	}
	old := (*net.UDPAddr)(atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&(sa.endpoints[idx])))))
	if !EndpointsEqual(old, ep) {
		atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&(sa.endpoints[idx]))), unsafe.Pointer(ep))
		return true
	}
	return false
}

func (sa *SecurityAssociation) GetEndpointsAndNextSequenceNumber(epsIn []*net.UDPAddr) (seqNum uint32, eps []*net.UDPAddr) {
	seqNum = atomic.AddUint32(&sa.nextSeqNr, 1) - 1
	eps = epsIn
	if eps == nil {
		eps = make([]*net.UDPAddr, len(sa.endpoints))
	}
	for i := range sa.endpoints {
		eps[i] = (*net.UDPAddr)(atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&(sa.endpoints[i])))))
	}
	return
}

func (sa *SecurityAssociation) getSequenceWindow(senderID uint16) *SequenceWindow {
	win, present := sa.seqWindows.Load(senderID)
	if !present {
		var err error
		if win, err = NewSequenceWindow(int(sa.seqWindowSize), sa.initialSeqNrInbound); err != nil {
			panic(fmt.Sprint("unable to create new sequence window:", err)) // return an error instead???
		}
		sa.seqWindows.Store(senderID, win)
	}
	return win.(*SequenceWindow)
}

func (sa *SecurityAssociation) SequenceNumberCheck(senderID uint16, sequenceNumber uint32) bool {
	return sa.getSequenceWindow(senderID).Check(sequenceNumber)
}

func (sa *SecurityAssociation) SequenceNumberCheckAndSet(senderID uint16, sequenceNumber uint32) bool {
	return sa.getSequenceWindow(senderID).CheckAndSet(sequenceNumber)
}

func NewSecurityAssociation(kd KeyDerivation, numEndpoints uint, initialSeqNrOutbound, initialSeqNrInbound uint32, seqWindowSize uint) (sa *SecurityAssociation) {
	sa = &SecurityAssociation{kd: kd}
	// panic if numEndpoints == 0?
	sa.endpoints = make([]*net.UDPAddr, numEndpoints)
	sa.nextSeqNr = initialSeqNrOutbound
	sa.initialSeqNrInbound = initialSeqNrInbound
	sa.seqWindowSize = seqWindowSize
	sa.seqWindows = &sync.Map{}
	return
}