package notify

import (
	"context"
	"encoding/binary"
	"errors"
	"io"
	"net"
	"sync"
	"sync/atomic"
	"time"
)

const (
	bulkDedicatedBatchMagic         = "NBD2"
	bulkDedicatedBatchVersion       = 1
	bulkDedicatedBatchHeaderLen     = 20
	bulkDedicatedBatchItemHeaderLen = 16
	bulkDedicatedBatchMaxItems      = 32
	bulkDedicatedBatchMaxPlainBytes = 8 * 1024 * 1024
	bulkDedicatedSendQueueSize      = bulkDedicatedBatchMaxItems
	bulkDedicatedReleasePayloadLen  = 12
)

const (
	bulkDedicatedRequestQueued int32 = iota
	bulkDedicatedRequestStarted
	bulkDedicatedRequestCanceled
)

type bulkDedicatedRequestState struct {
	value atomic.Int32
}

type bulkDedicatedBatchItem struct {
	Type    uint8
	Flags   uint8
	Seq     uint64
	Payload []byte
}

type bulkDedicatedSendRequest struct {
	Type    uint8
	Flags   uint8
	Seq     uint64
	Payload []byte
}

type bulkDedicatedBatchRequest struct {
	Ctx      context.Context
	Items    []bulkDedicatedSendRequest
	Deadline time.Time
	Ack      chan error
	State    *bulkDedicatedRequestState
}

type bulkDedicatedSender struct {
	conn        net.Conn
	dataID      uint64
	encrypt     func([]byte) ([]byte, error)
	encodeBatch func([]bulkDedicatedSendRequest) ([]byte, error)
	fail        func(error)

	reqCh    chan bulkDedicatedBatchRequest
	stopCh   chan struct{}
	doneCh   chan struct{}
	stopOnce sync.Once
	flushMu  sync.Mutex
	queued   atomic.Int64

	errMu sync.Mutex
	err   error
}

func newBulkDedicatedSender(conn net.Conn, dataID uint64, encrypt func([]byte) ([]byte, error), encodeBatch func([]bulkDedicatedSendRequest) ([]byte, error), fail func(error)) *bulkDedicatedSender {
	sender := &bulkDedicatedSender{
		conn:        conn,
		dataID:      dataID,
		encrypt:     encrypt,
		encodeBatch: encodeBatch,
		fail:        fail,
		reqCh:       make(chan bulkDedicatedBatchRequest, bulkDedicatedSendQueueSize),
		stopCh:      make(chan struct{}),
		doneCh:      make(chan struct{}),
	}
	go sender.run()
	return sender
}

func (s *bulkDedicatedSender) submitData(ctx context.Context, seq uint64, payload []byte) error {
	if s == nil {
		return errTransportDetached
	}
	items := []bulkDedicatedSendRequest{{
		Type:    bulkFastPayloadTypeData,
		Seq:     seq,
		Payload: append([]byte(nil), payload...),
	}}
	return s.submitBatch(ctx, items, false)
}

func (s *bulkDedicatedSender) submitWrite(ctx context.Context, startSeq uint64, payload []byte, chunkSize int) (int, error) {
	if s == nil {
		return 0, errTransportDetached
	}
	if len(payload) == 0 {
		return 0, nil
	}
	if chunkSize <= 0 {
		chunkSize = defaultBulkChunkSize
	}
	written := 0
	seq := startSeq
	for written < len(payload) {
		var itemBuf [bulkDedicatedBatchMaxItems]bulkDedicatedSendRequest
		items := itemBuf[:0]
		batchBytes := bulkDedicatedBatchHeaderLen
		start := written
		for written < len(payload) && len(items) < bulkDedicatedBatchMaxItems {
			end := written + chunkSize
			if end > len(payload) {
				end = len(payload)
			}
			itemLen := bulkDedicatedSendRequestLenFromPayloadLen(end - written)
			if len(items) > 0 && batchBytes+itemLen > bulkDedicatedBatchMaxPlainBytes {
				break
			}
			items = append(items, bulkDedicatedSendRequest{
				Type:    bulkFastPayloadTypeData,
				Seq:     seq,
				Payload: payload[written:end],
			})
			batchBytes += itemLen
			seq++
			written = end
		}
		if len(items) == 0 {
			end := written + chunkSize
			if end > len(payload) {
				end = len(payload)
			}
			items = append(items, bulkDedicatedSendRequest{
				Type:    bulkFastPayloadTypeData,
				Seq:     seq,
				Payload: payload[written:end],
			})
			seq++
			written = end
		}
		if err := s.submitWriteBatch(ctx, items); err != nil {
			return start, err
		}
		start = written
	}
	return written, nil
}

func (s *bulkDedicatedSender) submitWriteBatch(ctx context.Context, items []bulkDedicatedSendRequest) error {
	if s == nil {
		return errTransportDetached
	}
	if len(items) == 0 {
		return nil
	}
	if submitted, err := s.tryDirectSubmitBatch(ctx, items); submitted {
		return err
	}
	queuedItems := make([]bulkDedicatedSendRequest, len(items))
	copy(queuedItems, items)
	return s.submitBatch(ctx, queuedItems, true)
}

func (s *bulkDedicatedSender) submitControl(ctx context.Context, frameType uint8, flags uint8, seq uint64, payload []byte) error {
	if s == nil {
		return errTransportDetached
	}
	items := []bulkDedicatedSendRequest{{
		Type:  frameType,
		Flags: flags,
		Seq:   seq,
	}}
	if len(payload) > 0 {
		items[0].Payload = append([]byte(nil), payload...)
	}
	return s.submitBatch(ctx, items, true)
}

func (s *bulkDedicatedSender) submitBatch(ctx context.Context, items []bulkDedicatedSendRequest, wait bool) error {
	if s == nil {
		return errTransportDetached
	}
	if ctx == nil {
		ctx = context.Background()
	}
	if err := s.errSnapshot(); err != nil {
		return err
	}
	req := bulkDedicatedBatchRequest{
		Ctx:   ctx,
		Items: items,
		State: &bulkDedicatedRequestState{},
	}
	if deadline, ok := ctx.Deadline(); ok {
		req.Deadline = deadline
	}
	if wait {
		req.Ack = make(chan error, 1)
	}
	s.queued.Add(1)
	select {
	case <-ctx.Done():
		s.queued.Add(-1)
		return normalizeStreamDeadlineError(ctx.Err())
	case <-s.stopCh:
		s.queued.Add(-1)
		return s.stoppedErr()
	case s.reqCh <- req:
		if !wait {
			return nil
		}
		return s.waitAck(req)
	}
}

func (s *bulkDedicatedSender) tryDirectSubmitBatch(ctx context.Context, items []bulkDedicatedSendRequest) (bool, error) {
	if s == nil {
		return true, errTransportDetached
	}
	if ctx == nil {
		ctx = context.Background()
	}
	if len(items) == 0 {
		return true, nil
	}
	if err := s.errSnapshot(); err != nil {
		return true, err
	}
	select {
	case <-ctx.Done():
		return true, normalizeStreamDeadlineError(ctx.Err())
	case <-s.stopCh:
		return true, s.stoppedErr()
	default:
	}
	if s.queued.Load() != 0 {
		return false, nil
	}
	if !s.flushMu.TryLock() {
		return false, nil
	}
	defer s.flushMu.Unlock()
	if s.queued.Load() != 0 {
		return false, nil
	}
	if err := s.errSnapshot(); err != nil {
		return true, err
	}
	select {
	case <-ctx.Done():
		return true, normalizeStreamDeadlineError(ctx.Err())
	case <-s.stopCh:
		return true, s.stoppedErr()
	default:
	}
	deadline, _ := ctx.Deadline()
	if err := s.flush(items, deadline); err != nil {
		err = normalizeDedicatedBulkSendError(err)
		s.setErr(err)
		s.failPending(err)
		if s.fail != nil {
			go s.fail(err)
		}
		return true, err
	}
	return true, nil
}

func (s *bulkDedicatedSender) waitAck(req bulkDedicatedBatchRequest) error {
	if s == nil {
		return errTransportDetached
	}
	ctx := req.Ctx
	if ctx == nil {
		ctx = context.Background()
	}
	select {
	case err := <-req.Ack:
		return normalizeDedicatedBulkSendError(err)
	case <-ctx.Done():
		if req.tryCancel() {
			return normalizeStreamDeadlineError(ctx.Err())
		}
		return normalizeDedicatedBulkSendError(<-req.Ack)
	}
}

func (s *bulkDedicatedSender) stop() {
	if s == nil {
		return
	}
	s.stopOnce.Do(func() {
		s.setErr(errTransportDetached)
		close(s.stopCh)
	})
	<-s.doneCh
}

func (s *bulkDedicatedSender) run() {
	defer close(s.doneCh)

	for {
		req, ok := s.nextRequest()
		if !ok {
			return
		}
		if !req.tryStart() {
			s.finishRequest(req, req.canceledErr())
			continue
		}
		if err := req.contextErr(); err != nil {
			s.finishRequest(req, err)
			continue
		}
		s.flushMu.Lock()
		err := s.errSnapshot()
		if err == nil {
			err = s.flush(req.Items, req.Deadline)
		}
		s.flushMu.Unlock()
		if err != nil {
			err = normalizeDedicatedBulkSendError(err)
			s.setErr(err)
			s.finishRequest(req, err)
			s.failPending(err)
			if s.fail != nil {
				go s.fail(err)
			}
			return
		}
		s.finishRequest(req, nil)
	}
}

func (r bulkDedicatedBatchRequest) contextErr() error {
	if r.Ctx == nil {
		return nil
	}
	select {
	case <-r.Ctx.Done():
		return normalizeStreamDeadlineError(r.Ctx.Err())
	default:
		return nil
	}
}

func (r bulkDedicatedBatchRequest) tryStart() bool {
	if r.State == nil {
		return true
	}
	return r.State.value.CompareAndSwap(bulkDedicatedRequestQueued, bulkDedicatedRequestStarted)
}

func (r bulkDedicatedBatchRequest) tryCancel() bool {
	if r.State == nil {
		return false
	}
	return r.State.value.CompareAndSwap(bulkDedicatedRequestQueued, bulkDedicatedRequestCanceled)
}

func (r bulkDedicatedBatchRequest) canceledErr() error {
	if err := r.contextErr(); err != nil {
		return err
	}
	return context.Canceled
}

func (s *bulkDedicatedSender) nextRequest() (bulkDedicatedBatchRequest, bool) {
	select {
	case <-s.stopCh:
		s.failPending(s.stoppedErr())
		return bulkDedicatedBatchRequest{}, false
	case req := <-s.reqCh:
		return req, true
	}
}

func (s *bulkDedicatedSender) flush(batch []bulkDedicatedSendRequest, deadline time.Time) error {
	if s == nil || s.conn == nil {
		return errTransportDetached
	}
	var (
		payload []byte
		err     error
	)
	if s.encodeBatch != nil {
		payload, err = s.encodeBatch(batch)
	} else {
		plain, plainErr := encodeBulkDedicatedBatchPlain(s.dataID, batch)
		if plainErr != nil {
			return plainErr
		}
		payload, err = s.encrypt(plain)
	}
	if err != nil {
		return err
	}
	return writeBulkDedicatedRecordWithDeadline(s.conn, payload, deadline)
}

func (s *bulkDedicatedSender) ack(req bulkDedicatedBatchRequest, err error) {
	if req.Ack != nil {
		req.Ack <- err
	}
}

func (s *bulkDedicatedSender) finishRequest(req bulkDedicatedBatchRequest, err error) {
	if s != nil {
		s.queued.Add(-1)
	}
	s.ack(req, err)
}

func (s *bulkDedicatedSender) failPending(err error) {
	for {
		select {
		case item := <-s.reqCh:
			s.finishRequest(item, err)
		default:
			return
		}
	}
}

func (s *bulkDedicatedSender) setErr(err error) {
	if s == nil || err == nil {
		return
	}
	s.errMu.Lock()
	if s.err == nil {
		s.err = err
	}
	s.errMu.Unlock()
}

func (s *bulkDedicatedSender) errSnapshot() error {
	if s == nil {
		return errTransportDetached
	}
	s.errMu.Lock()
	defer s.errMu.Unlock()
	return s.err
}

func (s *bulkDedicatedSender) stoppedErr() error {
	if err := s.errSnapshot(); err != nil {
		return err
	}
	return errTransportDetached
}

func bulkDedicatedSendRequestLen(req bulkDedicatedSendRequest) int {
	return bulkDedicatedSendRequestLenFromPayloadLen(len(req.Payload))
}

func bulkDedicatedSendRequestLenFromPayloadLen(payloadLen int) int {
	return bulkDedicatedBatchItemHeaderLen + payloadLen
}

func encodeBulkDedicatedReleasePayload(bytes int64, chunks int) ([]byte, error) {
	if bytes <= 0 && chunks <= 0 {
		return nil, errBulkFastPayloadInvalid
	}
	if chunks < 0 {
		return nil, errBulkFastPayloadInvalid
	}
	payload := make([]byte, bulkDedicatedReleasePayloadLen)
	binary.BigEndian.PutUint64(payload[:8], uint64(bytes))
	binary.BigEndian.PutUint32(payload[8:12], uint32(chunks))
	return payload, nil
}

func decodeBulkDedicatedReleasePayload(payload []byte) (int64, int, error) {
	if len(payload) != bulkDedicatedReleasePayloadLen {
		return 0, 0, errBulkFastPayloadInvalid
	}
	bytes := int64(binary.BigEndian.Uint64(payload[:8]))
	chunks := int(binary.BigEndian.Uint32(payload[8:12]))
	if bytes <= 0 && chunks <= 0 {
		return 0, 0, errBulkFastPayloadInvalid
	}
	return bytes, chunks, nil
}

func encodeBulkDedicatedBatchPlain(dataID uint64, items []bulkDedicatedSendRequest) ([]byte, error) {
	if dataID == 0 || len(items) == 0 {
		return nil, errBulkFastPayloadInvalid
	}
	total := bulkDedicatedBatchPlainLen(items)
	buf := make([]byte, total)
	if err := writeBulkDedicatedBatchPlain(buf, dataID, items); err != nil {
		return nil, err
	}
	return buf, nil
}

func encodeBulkDedicatedBatchPayloadFast(encode transportFastPlainEncoder, secretKey []byte, dataID uint64, items []bulkDedicatedSendRequest) ([]byte, error) {
	if encode == nil {
		return nil, errTransportPayloadEncryptFailed
	}
	plainLen := bulkDedicatedBatchPlainLen(items)
	return encode(secretKey, plainLen, func(dst []byte) error {
		return writeBulkDedicatedBatchPlain(dst, dataID, items)
	})
}

func bulkDedicatedBatchPlainLen(items []bulkDedicatedSendRequest) int {
	total := bulkDedicatedBatchHeaderLen
	for _, item := range items {
		total += bulkDedicatedSendRequestLen(item)
	}
	return total
}

func writeBulkDedicatedBatchPlain(buf []byte, dataID uint64, items []bulkDedicatedSendRequest) error {
	if dataID == 0 || len(items) == 0 {
		return errBulkFastPayloadInvalid
	}
	if len(buf) != bulkDedicatedBatchPlainLen(items) {
		return errBulkFastPayloadInvalid
	}
	copy(buf[:4], bulkDedicatedBatchMagic)
	buf[4] = bulkDedicatedBatchVersion
	binary.BigEndian.PutUint64(buf[8:16], dataID)
	binary.BigEndian.PutUint32(buf[16:20], uint32(len(items)))
	offset := bulkDedicatedBatchHeaderLen
	for _, item := range items {
		buf[offset] = item.Type
		buf[offset+1] = item.Flags
		binary.BigEndian.PutUint64(buf[offset+4:offset+12], item.Seq)
		binary.BigEndian.PutUint32(buf[offset+12:offset+16], uint32(len(item.Payload)))
		offset += bulkDedicatedBatchItemHeaderLen
		copy(buf[offset:offset+len(item.Payload)], item.Payload)
		offset += len(item.Payload)
	}
	return nil
}

func decodeBulkDedicatedBatchPlain(payload []byte) (uint64, []bulkDedicatedBatchItem, bool, error) {
	if len(payload) < 4 || string(payload[:4]) != bulkDedicatedBatchMagic {
		return 0, nil, false, nil
	}
	if len(payload) < bulkDedicatedBatchHeaderLen {
		return 0, nil, true, errBulkFastPayloadInvalid
	}
	if payload[4] != bulkDedicatedBatchVersion {
		return 0, nil, true, errBulkFastPayloadInvalid
	}
	dataID := binary.BigEndian.Uint64(payload[8:16])
	count := int(binary.BigEndian.Uint32(payload[16:20]))
	if dataID == 0 || count <= 0 {
		return 0, nil, true, errBulkFastPayloadInvalid
	}
	items := make([]bulkDedicatedBatchItem, 0, count)
	offset := bulkDedicatedBatchHeaderLen
	for i := 0; i < count; i++ {
		if len(payload)-offset < bulkDedicatedBatchItemHeaderLen {
			return 0, nil, true, errBulkFastPayloadInvalid
		}
		itemType := payload[offset]
		switch itemType {
		case bulkFastPayloadTypeData, bulkFastPayloadTypeClose, bulkFastPayloadTypeReset, bulkFastPayloadTypeRelease:
		default:
			return 0, nil, true, errBulkFastPayloadInvalid
		}
		flags := payload[offset+1]
		seq := binary.BigEndian.Uint64(payload[offset+4 : offset+12])
		dataLen := int(binary.BigEndian.Uint32(payload[offset+12 : offset+16]))
		offset += bulkDedicatedBatchItemHeaderLen
		if dataLen < 0 || len(payload)-offset < dataLen {
			return 0, nil, true, errBulkFastPayloadInvalid
		}
		items = append(items, bulkDedicatedBatchItem{
			Type:    itemType,
			Flags:   flags,
			Seq:     seq,
			Payload: payload[offset : offset+dataLen],
		})
		offset += dataLen
	}
	if offset != len(payload) {
		return 0, nil, true, errBulkFastPayloadInvalid
	}
	return dataID, items, true, nil
}

func decodeDedicatedBulkInboundItems(expectedDataID uint64, plain []byte) ([]bulkDedicatedBatchItem, error) {
	if dataID, items, matched, err := decodeBulkDedicatedBatchPlain(plain); matched {
		if err != nil {
			return nil, err
		}
		if expectedDataID == 0 || dataID != expectedDataID {
			return nil, errBulkFastPayloadInvalid
		}
		return items, nil
	}
	frame, matched, err := decodeBulkFastFrame(plain)
	if err != nil {
		return nil, err
	}
	if !matched || expectedDataID == 0 || frame.DataID != expectedDataID {
		return nil, errBulkFastPayloadInvalid
	}
	return []bulkDedicatedBatchItem{{
		Type:    frame.Type,
		Flags:   frame.Flags,
		Seq:     frame.Seq,
		Payload: frame.Payload,
	}}, nil
}

func normalizeDedicatedBulkSendError(err error) error {
	switch {
	case err == nil:
		return nil
	case errors.Is(err, net.ErrClosed):
		return errTransportDetached
	default:
		return normalizeStreamDeadlineError(err)
	}
}

func dispatchDedicatedBulkInboundItem(bulk *bulkHandle, item bulkDedicatedBatchItem) error {
	if bulk == nil {
		return io.ErrClosedPipe
	}
	switch item.Type {
	case bulkFastPayloadTypeData:
		return bulk.pushOwnedChunkNoReset(item.Payload)
	case bulkFastPayloadTypeClose:
		if item.Flags&bulkFastPayloadFlagFullClose != 0 {
			bulk.markPeerClosed()
			return nil
		}
		bulk.markRemoteClosed()
		return nil
	case bulkFastPayloadTypeReset:
		resetErr := errBulkReset
		if len(item.Payload) > 0 {
			resetErr = bulkRemoteResetError(string(item.Payload))
		}
		bulk.markReset(bulkResetError(resetErr))
		return nil
	case bulkFastPayloadTypeRelease:
		bytes, chunks, err := decodeBulkDedicatedReleasePayload(item.Payload)
		if err != nil {
			return err
		}
		bulk.releaseOutboundWindow(bytes, chunks)
		return nil
	default:
		return errBulkFastPayloadInvalid
	}
}