package notify

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"io"
	"net"
	"strings"
	"sync"
	"testing"
	"time"

	itransfer "b612.me/notify/internal/transfer"
)

type transferBytesSource struct {
	data         []byte
	failAtOffset int64
	failErr      error
}

type transferBlockingSource struct {
	data      []byte
	releaseCh chan struct{}
	mu        sync.Mutex
	started   int
	active    int
	maxActive int
	startedCh chan struct{}
}

type transferDiscardStream struct{}

func (transferDiscardStream) Read([]byte) (int, error)      { return 0, io.EOF }
func (transferDiscardStream) Write(p []byte) (int, error)   { return len(p), nil }
func (transferDiscardStream) Close() error                  { return nil }
func (transferDiscardStream) ID() string                    { return "discard" }
func (transferDiscardStream) Channel() StreamChannel        { return StreamDataChannel }
func (transferDiscardStream) Metadata() StreamMetadata      { return nil }
func (transferDiscardStream) Context() context.Context      { return context.Background() }
func (transferDiscardStream) LogicalConn() *LogicalConn     { return nil }
func (transferDiscardStream) TransportConn() *TransportConn { return nil }
func (transferDiscardStream) TransportGeneration() uint64   { return 0 }
func (transferDiscardStream) LocalAddr() net.Addr           { return nil }
func (transferDiscardStream) RemoteAddr() net.Addr          { return nil }
func (transferDiscardStream) CloseWrite() error             { return nil }
func (transferDiscardStream) Reset(error) error             { return nil }
func (transferDiscardStream) SetDeadline(time.Time) error   { return nil }
func (transferDiscardStream) SetReadDeadline(time.Time) error {
	return nil
}
func (transferDiscardStream) SetWriteDeadline(time.Time) error {
	return nil
}

type transferWriteCountStream struct {
	buf    bytes.Buffer
	writes int
}

func (s *transferWriteCountStream) Read(p []byte) (int, error)    { return s.buf.Read(p) }
func (s *transferWriteCountStream) Write(p []byte) (int, error)   { s.writes++; return s.buf.Write(p) }
func (s *transferWriteCountStream) Close() error                  { return nil }
func (s *transferWriteCountStream) ID() string                    { return "write-count" }
func (s *transferWriteCountStream) Channel() StreamChannel        { return StreamDataChannel }
func (s *transferWriteCountStream) Metadata() StreamMetadata      { return nil }
func (s *transferWriteCountStream) Context() context.Context      { return context.Background() }
func (s *transferWriteCountStream) LogicalConn() *LogicalConn     { return nil }
func (s *transferWriteCountStream) TransportConn() *TransportConn { return nil }
func (s *transferWriteCountStream) TransportGeneration() uint64   { return 0 }
func (s *transferWriteCountStream) LocalAddr() net.Addr           { return nil }
func (s *transferWriteCountStream) RemoteAddr() net.Addr          { return nil }
func (s *transferWriteCountStream) CloseWrite() error             { return nil }
func (s *transferWriteCountStream) Reset(error) error             { return nil }
func (s *transferWriteCountStream) SetDeadline(time.Time) error   { return nil }
func (s *transferWriteCountStream) SetReadDeadline(time.Time) error {
	return nil
}
func (s *transferWriteCountStream) SetWriteDeadline(time.Time) error {
	return nil
}
func (s *transferWriteCountStream) WriteCount() int { return s.writes }
func (s *transferWriteCountStream) Bytes() []byte   { return append([]byte(nil), s.buf.Bytes()...) }

func newTransferBytesSource(data []byte) *transferBytesSource {
	return &transferBytesSource{
		data:         append([]byte(nil), data...),
		failAtOffset: -1,
	}
}

func newTransferBlockingSource(data []byte) *transferBlockingSource {
	return &transferBlockingSource{
		data:      append([]byte(nil), data...),
		releaseCh: make(chan struct{}, len(data)+1),
		startedCh: make(chan struct{}, len(data)+1),
	}
}

func (s *transferBytesSource) Size() int64 {
	if s == nil {
		return 0
	}
	return int64(len(s.data))
}

func (s *transferBytesSource) ReadAt(p []byte, off int64) (int, error) {
	if s == nil {
		return 0, io.EOF
	}
	if s.failAtOffset >= 0 && off >= s.failAtOffset {
		if s.failErr != nil {
			return 0, s.failErr
		}
		return 0, errors.New("injected transfer source failure")
	}
	if off >= int64(len(s.data)) {
		return 0, io.EOF
	}
	n := copy(p, s.data[off:])
	if int(off)+n >= len(s.data) {
		return n, io.EOF
	}
	return n, nil
}

func (s *transferBlockingSource) Size() int64 {
	if s == nil {
		return 0
	}
	return int64(len(s.data))
}

func (s *transferBlockingSource) ReadAt(p []byte, off int64) (int, error) {
	if s == nil {
		return 0, io.EOF
	}
	s.mu.Lock()
	s.started++
	s.active++
	if s.active > s.maxActive {
		s.maxActive = s.active
	}
	s.mu.Unlock()
	s.startedCh <- struct{}{}
	<-s.releaseCh
	s.mu.Lock()
	s.active--
	s.mu.Unlock()
	if off >= int64(len(s.data)) {
		return 0, io.EOF
	}
	n := copy(p, s.data[off:])
	if int(off)+n >= len(s.data) {
		return n, io.EOF
	}
	return n, nil
}

func (s *transferBlockingSource) release(n int) {
	if s == nil {
		return
	}
	for i := 0; i < n; i++ {
		s.releaseCh <- struct{}{}
	}
}

func (s *transferBlockingSource) waitStarted(t *testing.T, want int, timeout time.Duration) {
	t.Helper()

	deadline := time.After(timeout)
	for {
		s.mu.Lock()
		started := s.started
		s.mu.Unlock()
		if started >= want {
			return
		}
		select {
		case <-s.startedCh:
		case <-deadline:
			t.Fatalf("timed out waiting for %d blocking reads, got %d", want, started)
		}
	}
}

func (s *transferBlockingSource) startedCount() int {
	if s == nil {
		return 0
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.started
}

func (s *transferBlockingSource) maxActiveCount() int {
	if s == nil {
		return 0
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.maxActive
}

type transferMemorySink struct {
	mu     sync.Mutex
	data   []byte
	closed bool
}

func (s *transferMemorySink) WriteAt(p []byte, off int64) (int, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.closed {
		return 0, io.ErrClosedPipe
	}
	if off < 0 {
		return 0, errTransferSegmentOffset
	}
	end := int(off) + len(p)
	if end > len(s.data) {
		grown := make([]byte, end)
		copy(grown, s.data)
		s.data = grown
	}
	copy(s.data[off:], p)
	return len(p), nil
}

func (s *transferMemorySink) ReadAt(p []byte, off int64) (int, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if off >= int64(len(s.data)) {
		return 0, io.EOF
	}
	n := copy(p, s.data[off:])
	if int(off)+n >= len(s.data) {
		return n, io.EOF
	}
	return n, nil
}

func (s *transferMemorySink) Close() error {
	s.mu.Lock()
	s.closed = true
	s.mu.Unlock()
	return nil
}

func (s *transferMemorySink) Bytes() []byte {
	s.mu.Lock()
	defer s.mu.Unlock()
	return append([]byte(nil), s.data...)
}

func TestTransferClientToServerRoundTripTCP(t *testing.T) {
	server := NewServer().(*ServerCommon)
	if err := UseModernPSKServer(server, integrationSharedSecret, integrationModernPSKOptions()); err != nil {
		t.Fatalf("UseModernPSKServer failed: %v", err)
	}

	sink := &transferMemorySink{}
	acceptCh := make(chan TransferAcceptInfo, 1)
	server.SetTransferHandler(func(info TransferAcceptInfo) (TransferReceiveOptions, error) {
		acceptCh <- info
		return TransferReceiveOptions{
			Sink:           sink,
			VerifyChecksum: true,
		}, nil
	})

	if err := server.Listen("tcp", "127.0.0.1:0"); err != nil {
		t.Fatalf("server Listen failed: %v", err)
	}
	defer func() { _ = server.Stop() }()

	client := NewClient().(*ClientCommon)
	if err := UseModernPSKClient(client, integrationSharedSecret, integrationModernPSKOptions()); err != nil {
		t.Fatalf("UseModernPSKClient failed: %v", err)
	}
	if err := client.Connect("tcp", server.listener.Addr().String()); err != nil {
		t.Fatalf("client Connect failed: %v", err)
	}
	defer func() { _ = client.Stop() }()

	data := bytes.Repeat([]byte("client-transfer-roundtrip-"), 4096)
	checksum := transferTestChecksum(data)
	handle, err := client.SendTransfer(context.Background(), TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:       "tx-client-server",
			Channel:  TransferChannelData,
			Size:     int64(len(data)),
			Checksum: checksum,
			Metadata: map[string]string{"name": "client.bin"},
		},
		Source:           newTransferBytesSource(data),
		ChunkSize:        16 * 1024,
		Parallelism:      2,
		MaxInflightBytes: 64 * 1024,
	})
	if err != nil {
		t.Fatalf("SendTransfer failed: %v", err)
	}
	if err := handle.Wait(context.Background()); err != nil {
		t.Fatalf("transfer wait failed: %v", err)
	}

	select {
	case info := <-acceptCh:
		if info.Descriptor.ID != "tx-client-server" {
			t.Fatalf("accept descriptor id = %q, want %q", info.Descriptor.ID, "tx-client-server")
		}
		if info.Descriptor.Metadata["name"] != "client.bin" {
			t.Fatalf("accept metadata mismatch: %+v", info.Descriptor.Metadata)
		}
	case <-time.After(2 * time.Second):
		t.Fatal("timed out waiting for transfer accept info")
	}

	if got := sink.Bytes(); !bytes.Equal(got, data) {
		t.Fatalf("received data mismatch: got %d bytes, want %d", len(got), len(data))
	}

	clientSnapshot, ok, err := GetClientTransferSnapshotByID(client, "tx-client-server")
	if err != nil {
		t.Fatalf("GetClientTransferSnapshotByID failed: %v", err)
	}
	if !ok {
		t.Fatal("client transfer snapshot missing")
	}
	if clientSnapshot.State != TransferStateDone || clientSnapshot.AckedBytes != int64(len(data)) {
		t.Fatalf("client snapshot mismatch: %+v", clientSnapshot)
	}
	if got, want := clientSnapshot.ChunkSize, 16*1024; got != want {
		t.Fatalf("client snapshot chunk size = %d, want %d", got, want)
	}
	if got, want := clientSnapshot.Parallelism, 2; got != want {
		t.Fatalf("client snapshot parallelism = %d, want %d", got, want)
	}
	if got, want := clientSnapshot.MaxInflightBytes, int64(64*1024); got != want {
		t.Fatalf("client snapshot max inflight bytes = %d, want %d", got, want)
	}

	serverSnapshot, ok, err := GetServerTransferSnapshotByID(server, "tx-client-server")
	if err != nil {
		t.Fatalf("GetServerTransferSnapshotByID failed: %v", err)
	}
	if !ok {
		t.Fatal("server transfer snapshot missing")
	}
	if serverSnapshot.State != TransferStateDone || serverSnapshot.ReceivedBytes != int64(len(data)) {
		t.Fatalf("server snapshot mismatch: %+v", serverSnapshot)
	}
}

func TestTransferServerToClientRoundTripTCP(t *testing.T) {
	server := NewServer().(*ServerCommon)
	if err := UseModernPSKServer(server, integrationSharedSecret, integrationModernPSKOptions()); err != nil {
		t.Fatalf("UseModernPSKServer failed: %v", err)
	}
	if err := server.Listen("tcp", "127.0.0.1:0"); err != nil {
		t.Fatalf("server Listen failed: %v", err)
	}
	defer func() { _ = server.Stop() }()

	client := NewClient().(*ClientCommon)
	if err := UseModernPSKClient(client, integrationSharedSecret, integrationModernPSKOptions()); err != nil {
		t.Fatalf("UseModernPSKClient failed: %v", err)
	}
	sink := &transferMemorySink{}
	client.SetTransferHandler(func(info TransferAcceptInfo) (TransferReceiveOptions, error) {
		return TransferReceiveOptions{
			Sink:           sink,
			VerifyChecksum: true,
		}, nil
	})
	if err := client.Connect("tcp", server.listener.Addr().String()); err != nil {
		t.Fatalf("client Connect failed: %v", err)
	}
	defer func() { _ = client.Stop() }()

	logical := waitForTransferControlLogicalConn(t, server, 2*time.Second)
	data := bytes.Repeat([]byte("server-transfer-roundtrip-"), 3072)
	checksum := transferTestChecksum(data)

	handle, err := server.SendTransferLogical(context.Background(), logical, TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:       "tx-server-client",
			Channel:  TransferChannelControl,
			Size:     int64(len(data)),
			Checksum: checksum,
		},
		Source:    newTransferBytesSource(data),
		ChunkSize: 8 * 1024,
	})
	if err != nil {
		t.Fatalf("SendTransferLogical failed: %v", err)
	}
	if err := handle.Wait(context.Background()); err != nil {
		t.Fatalf("transfer wait failed: %v", err)
	}

	if got := sink.Bytes(); !bytes.Equal(got, data) {
		t.Fatalf("received data mismatch: got %d bytes, want %d", len(got), len(data))
	}

	serverSnapshot, ok, err := GetServerTransferSnapshotByID(server, "tx-server-client")
	if err != nil {
		t.Fatalf("GetServerTransferSnapshotByID failed: %v", err)
	}
	if !ok {
		t.Fatal("server transfer snapshot missing")
	}
	if serverSnapshot.State != TransferStateDone || serverSnapshot.AckedBytes != int64(len(data)) {
		t.Fatalf("server snapshot mismatch: %+v", serverSnapshot)
	}

	clientSnapshot, ok, err := GetClientTransferSnapshotByID(client, "tx-server-client")
	if err != nil {
		t.Fatalf("GetClientTransferSnapshotByID failed: %v", err)
	}
	if !ok {
		t.Fatal("client transfer snapshot missing")
	}
	if clientSnapshot.State != TransferStateDone || clientSnapshot.ReceivedBytes != int64(len(data)) {
		t.Fatalf("client snapshot mismatch: %+v", clientSnapshot)
	}
}

func TestTransferResumeAfterPartialFailureTCP(t *testing.T) {
	server := NewServer().(*ServerCommon)
	if err := UseModernPSKServer(server, integrationSharedSecret, integrationModernPSKOptions()); err != nil {
		t.Fatalf("UseModernPSKServer failed: %v", err)
	}
	sink := &transferMemorySink{}
	server.SetTransferHandler(func(info TransferAcceptInfo) (TransferReceiveOptions, error) {
		return TransferReceiveOptions{
			Sink:           sink,
			VerifyChecksum: true,
		}, nil
	})
	if err := server.Listen("tcp", "127.0.0.1:0"); err != nil {
		t.Fatalf("server Listen failed: %v", err)
	}
	defer func() { _ = server.Stop() }()

	client := NewClient().(*ClientCommon)
	if err := UseModernPSKClient(client, integrationSharedSecret, integrationModernPSKOptions()); err != nil {
		t.Fatalf("UseModernPSKClient failed: %v", err)
	}
	if err := client.Connect("tcp", server.listener.Addr().String()); err != nil {
		t.Fatalf("client Connect failed: %v", err)
	}
	defer func() { _ = client.Stop() }()

	data := bytes.Repeat([]byte("resume-transfer-"), 8192)
	checksum := transferTestChecksum(data)
	firstSourceErr := errors.New("injected transfer source failure")
	firstSource := newTransferBytesSource(data)
	firstSource.failAtOffset = 32 * 1024
	firstSource.failErr = firstSourceErr

	firstHandle, err := client.SendTransfer(context.Background(), TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:       "tx-resume",
			Channel:  TransferChannelData,
			Size:     int64(len(data)),
			Checksum: checksum,
		},
		Source:    firstSource,
		ChunkSize: 16 * 1024,
	})
	if err != nil {
		t.Fatalf("first SendTransfer failed: %v", err)
	}
	if err := firstHandle.Wait(context.Background()); err == nil || !strings.Contains(err.Error(), firstSourceErr.Error()) {
		t.Fatalf("first transfer wait error = %v, want injected source failure", err)
	}

	partial := waitForTransferSnapshot(t, server, "tx-resume", 3*time.Second)
	if partial.State == TransferStateDone {
		t.Fatalf("partial snapshot unexpectedly done: %+v", partial)
	}

	secondHandle, err := client.SendTransfer(context.Background(), TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:       "tx-resume",
			Channel:  TransferChannelData,
			Size:     int64(len(data)),
			Checksum: checksum,
		},
		Source:    newTransferBytesSource(data),
		ChunkSize: 16 * 1024,
	})
	if err != nil {
		t.Fatalf("second SendTransfer failed: %v", err)
	}
	if err := secondHandle.Wait(context.Background()); err != nil {
		t.Fatalf("second transfer wait failed: %v", err)
	}

	if got := sink.Bytes(); !bytes.Equal(got, data) {
		t.Fatalf("received data mismatch after resume: got %d bytes, want %d", len(got), len(data))
	}

	clientSnapshot, ok := latestClientTransferSnapshotByID(t, client, "tx-resume")
	if !ok {
		t.Fatal("client transfer snapshot missing")
	}
	if clientSnapshot.State != TransferStateDone || clientSnapshot.AckedBytes != int64(len(data)) {
		t.Fatalf("client snapshot mismatch after resume: %+v", clientSnapshot)
	}

	serverSnapshot, ok := latestServerTransferSnapshotByID(t, server, "tx-resume")
	if !ok {
		t.Fatal("server transfer snapshot missing")
	}
	if serverSnapshot.State != TransferStateDone || serverSnapshot.ReceivedBytes != int64(len(data)) {
		t.Fatalf("server snapshot mismatch after resume: %+v", serverSnapshot)
	}
}

func TestSendTransferSegmentsDoesNotCallResumeDuringSteadyState(t *testing.T) {
	data := bytes.Repeat([]byte("steady-state-transfer-"), 4)
	resumeCalls := 0
	target := transferSendTarget{
		sequenceEn: func(value interface{}) ([]byte, error) {
			return []byte("segment"), nil
		},
		sendResume: func(ctx context.Context, req TransferResumeRequest) (TransferResumeResponse, error) {
			resumeCalls++
			return TransferResumeResponse{TransferID: req.TransferID, Accepted: true}, nil
		},
	}
	opt := TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:      "tx-no-steady-resume",
			Channel: TransferChannelData,
			Size:    int64(len(data)),
		},
		Source:           newTransferBytesSource(data),
		ChunkSize:        16,
		MaxInflightBytes: 16,
	}

	if err := sendTransferSegments(context.Background(), transferDiscardStream{}, target, opt, 0, transferSendHooks{}); err != nil {
		t.Fatalf("sendTransferSegments failed: %v", err)
	}
	if resumeCalls != 0 {
		t.Fatalf("sendResume call count = %d, want 0", resumeCalls)
	}
}

func TestSendTransferSegmentsAggregatesSmallFrames(t *testing.T) {
	data := bytes.Repeat([]byte("aggregate-transfer-"), 16)
	chunkSize := 8
	stream := &transferWriteCountStream{}
	target := transferSendTarget{
		sequenceEn: func(value interface{}) ([]byte, error) {
			segment, ok := value.(itransfer.Segment)
			if !ok {
				t.Fatalf("encoded value type = %T, want itransfer.Segment", value)
			}
			return append([]byte(nil), segment.Payload...), nil
		},
	}
	opt := TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:      "tx-aggregate",
			Channel: TransferChannelData,
			Size:    int64(len(data)),
		},
		Source:    newTransferBytesSource(data),
		ChunkSize: chunkSize,
	}

	if err := sendTransferSegments(context.Background(), stream, target, opt, 0, transferSendHooks{}); err != nil {
		t.Fatalf("sendTransferSegments failed: %v", err)
	}

	expectedFrames := (len(data) + chunkSize - 1) / chunkSize
	if got := stream.WriteCount(); got >= expectedFrames {
		t.Fatalf("write count = %d, want less than frame count %d", got, expectedFrames)
	}
	if got := countTransferFrames(stream.Bytes()); got != expectedFrames {
		t.Fatalf("frame count = %d, want %d", got, expectedFrames)
	}
}

func TestSendTransferSegmentsUsesParallelReadPrefetch(t *testing.T) {
	data := bytes.Repeat([]byte("p"), 32)
	source := newTransferBlockingSource(data)
	target := transferSendTarget{
		sequenceEn: func(value interface{}) ([]byte, error) {
			segment, ok := value.(itransfer.Segment)
			if !ok {
				t.Fatalf("encoded value type = %T, want itransfer.Segment", value)
			}
			return append([]byte(nil), segment.Payload...), nil
		},
	}
	opt := TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:      "tx-parallel-prefetch",
			Channel: TransferChannelData,
			Size:    int64(len(data)),
		},
		Source:           source,
		ChunkSize:        8,
		Parallelism:      4,
		MaxInflightBytes: 64,
	}

	errCh := make(chan error, 1)
	go func() {
		errCh <- sendTransferSegments(context.Background(), transferDiscardStream{}, target, opt, 0, transferSendHooks{})
	}()

	source.waitStarted(t, 4, time.Second)
	source.release(8)

	select {
	case err := <-errCh:
		if err != nil {
			t.Fatalf("sendTransferSegments failed: %v", err)
		}
	case <-time.After(time.Second):
		t.Fatal("timed out waiting for parallel sendTransferSegments")
	}

	if got := source.maxActiveCount(); got < 2 {
		t.Fatalf("max active reads = %d, want at least 2", got)
	}
}

func TestSendTransferSegmentsMaxInflightBytesCapsParallelReads(t *testing.T) {
	data := bytes.Repeat([]byte("w"), 32)
	source := newTransferBlockingSource(data)
	target := transferSendTarget{
		sequenceEn: func(value interface{}) ([]byte, error) {
			segment, ok := value.(itransfer.Segment)
			if !ok {
				t.Fatalf("encoded value type = %T, want itransfer.Segment", value)
			}
			return append([]byte(nil), segment.Payload...), nil
		},
	}
	opt := TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:      "tx-window-prefetch",
			Channel: TransferChannelData,
			Size:    int64(len(data)),
		},
		Source:           source,
		ChunkSize:        8,
		Parallelism:      4,
		MaxInflightBytes: 16,
	}

	errCh := make(chan error, 1)
	go func() {
		errCh <- sendTransferSegments(context.Background(), transferDiscardStream{}, target, opt, 0, transferSendHooks{})
	}()

	source.waitStarted(t, 2, time.Second)
	time.Sleep(50 * time.Millisecond)
	if got := source.startedCount(); got != 2 {
		t.Fatalf("started reads = %d, want 2 before release", got)
	}

	source.release(8)

	select {
	case err := <-errCh:
		if err != nil {
			t.Fatalf("sendTransferSegments failed: %v", err)
		}
	case <-time.After(time.Second):
		t.Fatal("timed out waiting for window-limited sendTransferSegments")
	}

	if got := source.maxActiveCount(); got > 2 {
		t.Fatalf("max active reads = %d, want at most 2", got)
	}
}

func TestSendTransferSegmentsNormalizesDirectOptions(t *testing.T) {
	data := bytes.Repeat([]byte("n"), 32)
	stream := &transferWriteCountStream{}
	target := transferSendTarget{
		sequenceEn: func(value interface{}) ([]byte, error) {
			segment, ok := value.(itransfer.Segment)
			if !ok {
				t.Fatalf("encoded value type = %T, want itransfer.Segment", value)
			}
			return append([]byte(nil), segment.Payload...), nil
		},
	}
	opt := TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:      "tx-direct-normalize",
			Channel: TransferChannelData,
		},
		Source:      newTransferBytesSource(data),
		Parallelism: 4,
	}

	if err := sendTransferSegments(context.Background(), stream, target, opt, 0, transferSendHooks{}); err != nil {
		t.Fatalf("sendTransferSegments failed: %v", err)
	}
	if got := countTransferFrames(stream.Bytes()); got == 0 {
		t.Fatal("frame count = 0, want at least 1")
	}
}

func waitForTransferReceivedBytes(t *testing.T, server *ServerCommon, transferID string, minBytes int64, timeout time.Duration) TransferSnapshot {
	t.Helper()

	deadline := time.Now().Add(timeout)
	for time.Now().Before(deadline) {
		snapshot, ok := latestServerTransferSnapshotByID(t, server, transferID)
		if ok && snapshot.ReceivedBytes >= minBytes {
			return snapshot
		}
		time.Sleep(10 * time.Millisecond)
	}
	t.Fatalf("timed out waiting for server transfer snapshot %q to reach %d bytes", transferID, minBytes)
	return TransferSnapshot{}
}

func waitForTransferSnapshot(t *testing.T, server *ServerCommon, transferID string, timeout time.Duration) TransferSnapshot {
	t.Helper()

	deadline := time.Now().Add(timeout)
	for time.Now().Before(deadline) {
		snapshot, ok := latestServerTransferSnapshotByID(t, server, transferID)
		if ok {
			return snapshot
		}
		time.Sleep(10 * time.Millisecond)
	}
	t.Fatalf("timed out waiting for server transfer snapshot %q to appear", transferID)
	return TransferSnapshot{}
}

func latestClientTransferSnapshotByID(t *testing.T, client *ClientCommon, transferID string) (TransferSnapshot, bool) {
	t.Helper()
	if client == nil || transferID == "" {
		return TransferSnapshot{}, false
	}
	snapshots, err := GetClientTransferSnapshots(client)
	if err != nil {
		t.Fatalf("GetClientTransferSnapshots failed: %v", err)
	}
	return latestTransferSnapshotByID(snapshots, transferID)
}

func latestServerTransferSnapshotByID(t *testing.T, server *ServerCommon, transferID string) (TransferSnapshot, bool) {
	t.Helper()
	if server == nil || transferID == "" {
		return TransferSnapshot{}, false
	}
	snapshots, err := GetServerTransferSnapshots(server)
	if err != nil {
		t.Fatalf("GetServerTransferSnapshots failed: %v", err)
	}
	return latestTransferSnapshotByID(snapshots, transferID)
}

func latestTransferSnapshotByID(snapshots []TransferSnapshot, transferID string) (TransferSnapshot, bool) {
	var matched TransferSnapshot
	found := false
	for _, snapshot := range snapshots {
		if snapshot.ID != transferID {
			continue
		}
		if !found || snapshot.UpdatedAt.After(matched.UpdatedAt) || (snapshot.UpdatedAt.Equal(matched.UpdatedAt) && snapshot.ReceivedBytes > matched.ReceivedBytes) {
			matched = snapshot
			found = true
		}
	}
	return matched, found
}

func transferTestChecksum(data []byte) string {
	sum := sha256.Sum256(data)
	return hex.EncodeToString(sum[:])
}

func countTransferFrames(data []byte) int {
	count := 0
	for len(data) > 0 {
		if len(data) < transferFrameHeaderSize {
			return count
		}
		size := int(binary.BigEndian.Uint32(data[:transferFrameHeaderSize]))
		data = data[transferFrameHeaderSize:]
		if size < 0 || len(data) < size {
			return count
		}
		data = data[size:]
		count++
	}
	return count
}