package transfer

import (
	"context"
	"errors"
	"path/filepath"
	"sync"
	"testing"
	"time"

	"commilitia.net/cdrop/internal/db"
	"commilitia.net/cdrop/internal/hub"
)

// recHub records SendTo calls without spinning up real SSE clients.
// We can't easily mock *hub.Hub directly because it's a concrete type — instead
// we feed it a fake DeviceLister and ignore the broadcast side; the fact that
// SendTo to a non-connected client returns false is acceptable here.
type recordingLister struct {
	mu    sync.Mutex
	calls int
}

func (r *recordingLister) ListDevicesByUser(_ context.Context, _ string) ([]db.Device, error) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.calls++
	return nil, nil
}

func newTestHub() *hub.Hub {
	return hub.New(&recordingLister{})
}

func openTestDB(t *testing.T) *db.Queries {
	t.Helper()
	dbPath := filepath.Join(t.TempDir(), "x.db")
	conn, err := db.Open(dbPath)
	if err != nil {
		t.Fatalf("open: %v", err)
	}
	t.Cleanup(func() { _ = conn.Close() })
	if err := db.Bootstrap(context.Background(), conn); err != nil {
		t.Fatalf("bootstrap: %v", err)
	}
	return db.New(conn)
}

func newTestService(t *testing.T) *Service {
	t.Helper()
	q := openTestDB(t)
	h := newTestHub()
	t.Cleanup(h.Close)
	return NewService(q, h, nil, nil, nil)
}

// fakeRelay records Register/Release calls and can be primed to fail Register,
// standing in for *relay.Manager so the transfer wiring can be exercised without
// importing relay.
type fakeRelay struct {
	registers   [][4]string // {id, userID, sender, receiver}
	releases    []string
	registerErr error
}

func (f *fakeRelay) Register(id, userID, sender, receiver string) error {
	if f.registerErr != nil {
		return f.registerErr
	}
	f.registers = append(f.registers, [4]string{id, userID, sender, receiver})
	return nil
}

func (f *fakeRelay) Release(id string) { f.releases = append(f.releases, id) }

func newTestServiceWithRelay(t *testing.T, r RelayController) *Service {
	t.Helper()
	q := openTestDB(t)
	h := newTestHub()
	t.Cleanup(h.Close)
	return NewService(q, h, r, nil, nil)
}

func TestInit_AllowsZeroByteFile(t *testing.T) {
	svc := newTestService(t)
	if _, err := svc.Init(context.Background(), InitParams{
		UserID: "u", SenderName: "s", ReceiverName: "r",
		FileName: "empty.txt", FileSize: 0,
	}); err != nil {
		t.Errorf("0-byte file must be accepted (brief §2 不限大小); got %v", err)
	}
}

func TestInit_PersistsPending(t *testing.T) {
	svc := newTestService(t)
	id, err := svc.Init(context.Background(), InitParams{
		UserID:       "alice",
		SenderName:   "tab-1",
		ReceiverName: "tab-2",
		FileName:     "doc.pdf",
		FileSize:     1024,
	})
	if err != nil {
		t.Fatalf("init: %v", err)
	}
	if id == "" {
		t.Fatal("expected non-empty id")
	}

	sess, err := svc.queries.GetTransferSession(context.Background(), id)
	if err != nil {
		t.Fatalf("get: %v", err)
	}
	if sess.State != StatePending {
		t.Errorf("state: got %q, want %q", sess.State, StatePending)
	}
	if sess.UserID != "alice" || sess.SenderName != "tab-1" || sess.ReceiverName != "tab-2" {
		t.Errorf("unexpected fields: %+v", sess)
	}
}

func TestInit_RejectsBadInput(t *testing.T) {
	svc := newTestService(t)
	bad := []InitParams{
		{UserID: "u", SenderName: "", ReceiverName: "r", FileName: "f", FileSize: 1},
		{UserID: "u", SenderName: "s", ReceiverName: "", FileName: "f", FileSize: 1},
		{UserID: "u", SenderName: "s", ReceiverName: "s", FileName: "f", FileSize: 1}, // self
		{UserID: "u", SenderName: "s", ReceiverName: "r", FileName: "", FileSize: 1},
		{UserID: "u", SenderName: "s", ReceiverName: "r", FileName: "f", FileSize: -1},
	}
	for i, p := range bad {
		if _, err := svc.Init(context.Background(), p); err == nil {
			t.Errorf("case %d should error: %+v", i, p)
		}
	}
}

func TestTransition_HappyPath_PendingToDone(t *testing.T) {
	svc := newTestService(t)
	ctx := context.Background()
	id, err := svc.Init(ctx, InitParams{
		UserID: "u", SenderName: "s", ReceiverName: "r",
		FileName: "f", FileSize: 1024,
	})
	if err != nil {
		t.Fatalf("init: %v", err)
	}

	steps := []struct {
		state, mode string
	}{
		{StateAccepted, ""},
		{StateP2PActive, ModeP2P},
		{StateDone, ""},
	}
	for _, step := range steps {
		if err := svc.Transition(ctx, "u", id, step.state, step.mode, "", 1024); err != nil {
			t.Fatalf("transition to %s: %v", step.state, err)
		}
	}
	sess, _ := svc.queries.GetTransferSession(ctx, id)
	if sess.State != StateDone {
		t.Errorf("final state: got %q, want %q", sess.State, StateDone)
	}
	if sess.Mode == nil || *sess.Mode != ModeP2P {
		t.Errorf("mode: got %v, want %q", sess.Mode, ModeP2P)
	}
	if sess.FinishedAt == nil {
		t.Error("FinishedAt should be set on terminal state")
	}
}

func TestTransition_FallbackToRelayThenDone(t *testing.T) {
	svc := newTestService(t)
	ctx := context.Background()
	id, _ := svc.Init(ctx, InitParams{
		UserID: "u", SenderName: "s", ReceiverName: "r",
		FileName: "f", FileSize: 10,
	})
	for _, st := range []string{StateAccepted, StateP2PActive, StateRelayActive, StateDone} {
		mode := ""
		switch st {
		case StateP2PActive:
			mode = ModeP2P
		case StateRelayActive:
			mode = ModeRelay
		}
		if err := svc.Transition(ctx, "u", id, st, mode, "", 0); err != nil {
			t.Fatalf("transition to %s: %v", st, err)
		}
	}
}

// Entering RELAY_ACTIVE must reserve a relay slot, recording the transfer's two
// participants so the relay endpoints can later reject anyone else (R1/G2).
func TestTransition_RegistersRelayOnFallback(t *testing.T) {
	fr := &fakeRelay{}
	svc := newTestServiceWithRelay(t, fr)
	ctx := context.Background()
	id, _ := svc.Init(ctx, InitParams{
		UserID: "u", SenderName: "laptop", ReceiverName: "phone",
		FileName: "f", FileSize: 10,
	})
	if err := svc.Transition(ctx, "u", id, StateAccepted, "", "", 0); err != nil {
		t.Fatalf("accept: %v", err)
	}
	if err := svc.Transition(ctx, "u", id, StateRelayActive, ModeRelay, "", 0); err != nil {
		t.Fatalf("fallback: %v", err)
	}
	if len(fr.registers) != 1 {
		t.Fatalf("expected 1 Register call, got %d", len(fr.registers))
	}
	if got := fr.registers[0]; got != [4]string{id, "u", "laptop", "phone"} {
		t.Errorf("Register args: got %v", got)
	}
}

// When the relay is full, the fallback must NOT advance the transfer into relay
// mode: Transition surfaces ErrRelayUnavailable and the persisted state is
// unchanged so the client can retry.
func TestTransition_RelayFullSurfacesUnavailable(t *testing.T) {
	fr := &fakeRelay{registerErr: errors.New("too many")}
	svc := newTestServiceWithRelay(t, fr)
	ctx := context.Background()
	id, _ := svc.Init(ctx, InitParams{
		UserID: "u", SenderName: "s", ReceiverName: "r",
		FileName: "f", FileSize: 10,
	})
	if err := svc.Transition(ctx, "u", id, StateAccepted, "", "", 0); err != nil {
		t.Fatalf("accept: %v", err)
	}
	err := svc.Transition(ctx, "u", id, StateRelayActive, ModeRelay, "", 0)
	if !errors.Is(err, ErrRelayUnavailable) {
		t.Fatalf("expected ErrRelayUnavailable, got %v", err)
	}
	sess, _ := svc.queries.GetTransferSession(ctx, id)
	if sess.State != StateAccepted {
		t.Errorf("state must be unchanged on relay-full; got %q, want ACCEPTED", sess.State)
	}
}

func TestTransition_RejectsInvalidJump(t *testing.T) {
	svc := newTestService(t)
	ctx := context.Background()
	id, _ := svc.Init(ctx, InitParams{
		UserID: "u", SenderName: "s", ReceiverName: "r",
		FileName: "f", FileSize: 10,
	})
	// PENDING → DONE 仍非法（必须先 ACCEPTED 或 P2P_ACTIVE / RELAY_ACTIVE 至少一步）
	if err := svc.Transition(ctx, "u", id, StateDone, "", "", 0); err == nil {
		t.Error("PENDING→DONE should be rejected")
	}
}

func TestTransition_PendingToActiveAllowed(t *testing.T) {
	// Race tolerance: sender may call /p2p before receiver's /accept commits.
	svc := newTestService(t)
	ctx := context.Background()
	id, _ := svc.Init(ctx, InitParams{
		UserID: "u", SenderName: "s", ReceiverName: "r",
		FileName: "f", FileSize: 10,
	})
	if err := svc.Transition(ctx, "u", id, StateP2PActive, ModeP2P, "", 0); err != nil {
		t.Errorf("PENDING→P2P_ACTIVE should be allowed: %v", err)
	}
}

func TestTransition_AcceptedToDoneAllowed(t *testing.T) {
	// Race tolerance: receiver may finish receiving (call /done) before /p2p ever fired.
	svc := newTestService(t)
	ctx := context.Background()
	id, _ := svc.Init(ctx, InitParams{
		UserID: "u", SenderName: "s", ReceiverName: "r",
		FileName: "f", FileSize: 10,
	})
	if err := svc.Transition(ctx, "u", id, StateAccepted, "", "", 0); err != nil {
		t.Fatalf("PENDING→ACCEPTED: %v", err)
	}
	if err := svc.Transition(ctx, "u", id, StateDone, "", "", 10); err != nil {
		t.Errorf("ACCEPTED→DONE should be allowed (race-tolerant): %v", err)
	}
}

func TestTransition_RejectsForeignUser(t *testing.T) {
	svc := newTestService(t)
	ctx := context.Background()
	id, _ := svc.Init(ctx, InitParams{
		UserID: "alice", SenderName: "s", ReceiverName: "r",
		FileName: "f", FileSize: 10,
	})
	if err := svc.Transition(ctx, "mallory", id, StateAccepted, "", "", 0); err == nil {
		t.Error("foreign user must be forbidden")
	}
}

func TestTransition_NotFound(t *testing.T) {
	svc := newTestService(t)
	if err := svc.Transition(context.Background(), "u", "nope", StateAccepted, "", "", 0); err == nil {
		t.Error("unknown id should error")
	}
}

func TestExpirePending_CancelsOldSessions(t *testing.T) {
	svc := newTestService(t)
	ctx := context.Background()

	old := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
	svc.now = func() time.Time { return old }

	id, _ := svc.Init(ctx, InitParams{
		UserID: "u", SenderName: "s", ReceiverName: "r",
		FileName: "f", FileSize: 10,
	})

	// jump 200s into the future; PendingTTL is 120s so this should expire.
	svc.now = func() time.Time { return old.Add(200 * time.Second) }
	n, err := svc.ExpirePending(ctx, PendingTTL)
	if err != nil {
		t.Fatalf("expire: %v", err)
	}
	if n != 1 {
		t.Errorf("expired count: got %d, want 1", n)
	}
	sess, _ := svc.queries.GetTransferSession(ctx, id)
	if sess.State != StateCancelled {
		t.Errorf("state: got %q, want %q", sess.State, StateCancelled)
	}
	if sess.FailReason == nil || *sess.FailReason != "pending_timeout" {
		t.Errorf("fail_reason: got %v, want pending_timeout", sess.FailReason)
	}
}

func TestExpirePending_LeavesFreshAlone(t *testing.T) {
	svc := newTestService(t)
	ctx := context.Background()
	id, _ := svc.Init(ctx, InitParams{
		UserID: "u", SenderName: "s", ReceiverName: "r",
		FileName: "f", FileSize: 10,
	})
	n, err := svc.ExpirePending(ctx, PendingTTL)
	if err != nil {
		t.Fatalf("expire: %v", err)
	}
	if n != 0 {
		t.Errorf("expired count: got %d, want 0", n)
	}
	sess, _ := svc.queries.GetTransferSession(ctx, id)
	if sess.State != StatePending {
		t.Errorf("state: got %q, want PENDING", sess.State)
	}
}