package notify

import (
	"bytes"
	"context"
	"io"
	"os"
	"strconv"
	"sync"
	"testing"
	"time"

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

type memoryTransferResumeStore struct {
	mu        sync.Mutex
	snapshots map[string]TransferSnapshot
}

func newMemoryTransferResumeStore() *memoryTransferResumeStore {
	return &memoryTransferResumeStore{
		snapshots: make(map[string]TransferSnapshot),
	}
}

func (s *memoryTransferResumeStore) SaveTransferSnapshot(_ context.Context, snapshot TransferSnapshot) error {
	s.mu.Lock()
	s.snapshots[memoryTransferResumeStoreKey(snapshot)] = snapshot
	s.mu.Unlock()
	return nil
}

func (s *memoryTransferResumeStore) DeleteTransferSnapshot(_ context.Context, snapshot TransferSnapshot) error {
	s.mu.Lock()
	delete(s.snapshots, memoryTransferResumeStoreKey(snapshot))
	s.mu.Unlock()
	return nil
}

func (s *memoryTransferResumeStore) LoadTransferSnapshots(_ context.Context) ([]TransferSnapshot, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	out := make([]TransferSnapshot, 0, len(s.snapshots))
	for _, snapshot := range s.snapshots {
		out = append(out, snapshot)
	}
	return out, nil
}

func memoryTransferResumeStoreKey(snapshot TransferSnapshot) string {
	return string(rune(snapshot.Direction)) + "|" + snapshot.RuntimeScope + "|" + snapshot.ID
}

type transferOffsetSink struct {
	nextOffset int64
}

func (s *transferOffsetSink) WriteAt(p []byte, off int64) (int, error) {
	if off < 0 {
		return 0, io.ErrShortWrite
	}
	return len(p), nil
}

func (s *transferOffsetSink) NextOffset() int64 {
	if s == nil {
		return 0
	}
	return s.nextOffset
}

func TestTransferResumeStorePersistsAndRecoversSnapshots(t *testing.T) {
	store := newMemoryTransferResumeStore()

	client := NewClient().(*ClientCommon)
	client.SetTransferResumeStore(store)

	runtime := client.getTransferRuntime()
	runtime.ensureTransferDescriptor(fileTransferDirectionSend, clientFileScope(), clientFileScope(), 0, itransfer.Descriptor{
		ID:      "persist-send",
		Channel: itransfer.DataChannel,
		Size:    12,
	})
	runtime.recordSendOptions(fileTransferDirectionSend, clientFileScope(), "persist-send", 4096, 3, 12288)
	runtime.recordSend(fileTransferDirectionSend, clientFileScope(), "persist-send", 5)

	snapshots, err := store.LoadTransferSnapshots(context.Background())
	if err != nil {
		t.Fatalf("LoadTransferSnapshots failed: %v", err)
	}
	if len(snapshots) != 1 {
		t.Fatalf("store snapshot len = %d, want 1", len(snapshots))
	}
	if got, want := snapshots[0].SentBytes, int64(5); got != want {
		t.Fatalf("stored sent bytes = %d, want %d", got, want)
	}
	if got, want := snapshots[0].ChunkSize, 4096; got != want {
		t.Fatalf("stored chunk size = %d, want %d", got, want)
	}
	if got, want := snapshots[0].Parallelism, 3; got != want {
		t.Fatalf("stored parallelism = %d, want %d", got, want)
	}
	if got, want := snapshots[0].MaxInflightBytes, int64(12288); got != want {
		t.Fatalf("stored max inflight bytes = %d, want %d", got, want)
	}

	recovered := NewClient().(*ClientCommon)
	recovered.SetTransferResumeStore(store)
	if err := recovered.RecoverTransferSnapshots(context.Background()); err != nil {
		t.Fatalf("RecoverTransferSnapshots failed: %v", err)
	}
	snapshot, ok, err := GetClientTransferSnapshotByIDScope(recovered, "persist-send", clientFileScope())
	if err != nil {
		t.Fatalf("GetClientTransferSnapshotByIDScope failed: %v", err)
	}
	if !ok {
		t.Fatal("recovered snapshot missing")
	}
	if got, want := snapshot.SentBytes, int64(5); got != want {
		t.Fatalf("recovered sent bytes = %d, want %d", got, want)
	}
	if got, want := snapshot.ChunkSize, 4096; got != want {
		t.Fatalf("recovered chunk size = %d, want %d", got, want)
	}
	if got, want := snapshot.Parallelism, 3; got != want {
		t.Fatalf("recovered parallelism = %d, want %d", got, want)
	}
	if got, want := snapshot.MaxInflightBytes, int64(12288); got != want {
		t.Fatalf("recovered max inflight bytes = %d, want %d", got, want)
	}
}

func TestTransferStateRestoreReceiveSessionFromRuntimeSnapshot(t *testing.T) {
	state := newTransferState()
	state.setHandler(func(info TransferAcceptInfo) (TransferReceiveOptions, error) {
		return TransferReceiveOptions{
			Sink: &transferMemorySink{},
		}, nil
	})

	runtime := newTransferRuntime()
	runtime.ensureTransferDescriptor(fileTransferDirectionReceive, "runtime-scope", "public-scope", 0, itransfer.Descriptor{
		ID:      "restore-rx",
		Channel: itransfer.DataChannel,
		Size:    10,
	})
	runtime.recordReceive(fileTransferDirectionReceive, "runtime-scope", "restore-rx", 4)

	session, restored, err := state.restoreReceiveSession(runtime, "public-scope", "runtime-scope", nil, nil, 0, TransferDescriptor{
		ID:      "restore-rx",
		Channel: TransferChannelData,
		Size:    10,
	})
	if err != nil {
		t.Fatalf("restoreReceiveSession failed: %v", err)
	}
	if !restored {
		t.Fatal("restoreReceiveSession should restore session")
	}
	if got, want := session.nextOffsetSnapshot(), int64(4); got != want {
		t.Fatalf("restored next offset = %d, want %d", got, want)
	}
}

func TestTransferAcceptBeginUsesSinkInitialOffset(t *testing.T) {
	state := newTransferState()
	state.setHandler(func(info TransferAcceptInfo) (TransferReceiveOptions, error) {
		return TransferReceiveOptions{
			Sink: &transferOffsetSink{nextOffset: 12},
		}, nil
	})

	resp, err := state.acceptBegin(nil, TransferBeginRequest{
		TransferID: "offset-begin",
		Channel:    TransferChannelData,
		Size:       32,
	}, clientFileScope(), clientFileScope(), 0, nil, nil)
	if err != nil {
		t.Fatalf("acceptBegin failed: %v", err)
	}
	if got, want := resp.NextOffset, int64(12); got != want {
		t.Fatalf("acceptBegin next offset = %d, want %d", got, want)
	}
}

func TestTransferStateRestoreFileReceiveSessionUsesCheckpointOffset(t *testing.T) {
	receiveDir := t.TempDir()
	data := bytes.Repeat([]byte("restore-file-transfer-"), 2048)
	checksum := transferTestChecksum(data)
	packet := FilePacket{
		FileID:   "restore-file",
		Name:     "payload.bin",
		Size:     int64(len(data)),
		Mode:     0o600,
		ModTime:  time.Now().UnixNano(),
		Checksum: checksum,
	}

	originalPool := newFileReceivePool()
	if err := originalPool.setDir(receiveDir); err != nil {
		t.Fatalf("setDir failed: %v", err)
	}
	now := time.Now()
	if _, err := originalPool.onMeta(clientFileScope(), packet, now); err != nil {
		t.Fatalf("onMeta failed: %v", err)
	}
	partial := len(data) / 3
	if _, err := originalPool.onChunk(clientFileScope(), FilePacket{
		FileID: packet.FileID,
		Offset: 0,
		Chunk:  append([]byte(nil), data[:partial]...),
	}, now.Add(10*time.Millisecond)); err != nil {
		t.Fatalf("onChunk failed: %v", err)
	}

	originalPool.mu.Lock()
	checkpointPath := originalPool.checkpointPathLocked(clientFileScope(), packet.FileID)
	originalPool.mu.Unlock()
	if _, err := os.Stat(checkpointPath); err != nil {
		t.Fatalf("checkpoint missing before restore: %v", err)
	}

	runtime := newTransferRuntime()
	runtime.ensureTransferDescriptor(fileTransferDirectionReceive, clientFileScope(), clientFileScope(), 0, itransfer.Descriptor{
		ID:       packet.FileID,
		Channel:  itransfer.DataChannel,
		Size:     int64(len(data)),
		Checksum: checksum,
		Metadata: itransfer.Metadata{
			fileTransferMetadataKindKey:    fileTransferMetadataKindValue,
			fileTransferMetadataNameKey:    packet.Name,
			fileTransferMetadataModeKey:    strconv.FormatUint(uint64(packet.Mode), 10),
			fileTransferMetadataModTimeKey: strconv.FormatInt(packet.ModTime, 10),
		},
	})
	runtime.recordReceive(fileTransferDirectionReceive, clientFileScope(), packet.FileID, int64(partial/2))

	restoredPool := newFileReceivePool()
	if err := restoredPool.setDir(receiveDir); err != nil {
		t.Fatalf("restored setDir failed: %v", err)
	}
	state := newTransferState()
	state.setBuiltinHandler(func(info TransferAcceptInfo) (TransferReceiveOptions, bool, error) {
		sink, err := newFileTransferReceiveSink(restoredPool, clientFileScope(), packet, nil)
		if err != nil {
			return TransferReceiveOptions{}, true, err
		}
		return TransferReceiveOptions{
			Descriptor: cloneTransferDescriptor(info.Descriptor),
			Sink:       sink,
		}, true, nil
	})

	desc := TransferDescriptor{
		ID:       packet.FileID,
		Channel:  TransferChannelData,
		Size:     int64(len(data)),
		Checksum: checksum,
		Metadata: map[string]string{
			fileTransferMetadataKindKey:    fileTransferMetadataKindValue,
			fileTransferMetadataNameKey:    packet.Name,
			fileTransferMetadataModeKey:    strconv.FormatUint(uint64(packet.Mode), 10),
			fileTransferMetadataModTimeKey: strconv.FormatInt(packet.ModTime, 10),
		},
	}
	session, restored, err := state.restoreReceiveSession(runtime, clientFileScope(), clientFileScope(), nil, nil, 0, desc)
	if err != nil {
		t.Fatalf("restoreReceiveSession failed: %v", err)
	}
	if !restored {
		t.Fatal("restoreReceiveSession should restore file session")
	}
	if got, want := session.nextOffsetSnapshot(), int64(partial); got != want {
		t.Fatalf("restored file next offset = %d, want %d", got, want)
	}

	if err := session.writeSegment(runtime, packet.FileID, int64(partial), data[partial:]); err != nil {
		t.Fatalf("writeSegment failed: %v", err)
	}
	if err := session.commit(context.Background(), runtime, packet.FileID); err != nil {
		t.Fatalf("commit failed: %v", err)
	}

	restoredPool.mu.Lock()
	completed := restoredPool.completed[fileReceiveKey(clientFileScope(), packet.FileID)]
	restoredPool.mu.Unlock()
	if completed == nil {
		t.Fatal("completed file session missing after commit")
	}
	received, err := os.ReadFile(completed.finalPath)
	if err != nil {
		t.Fatalf("ReadFile failed: %v", err)
	}
	if !bytes.Equal(received, data) {
		t.Fatalf("restored file content mismatch: got %d want %d", len(received), len(data))
	}
	if _, err := os.Stat(checkpointPath); !os.IsNotExist(err) {
		t.Fatalf("checkpoint should be removed after commit, stat err = %v", err)
	}
}