package mesh

import (
	"context"
	"crypto/tls"
	"encoding/json"
	"sync"
	"testing"
	"time"

	"github.com/example/remote-access-platform/agents/rap-node-agent/internal/fabricproto"
)

func TestQUICSyntheticTransportReroutesOnConnectFailure(t *testing.T) {
	transport := newFakeSyntheticFabricTransport()
	transport.failConnect["quic://dead.example.test:19443"] = true
	transport.responses["quic://fast.example.test:19443"] = testSyntheticAckEnvelope("route-1", 1)
	forward := NewQUICSyntheticTransportFromRouteSets(map[string]FabricRouteSet{
		"node-b": FabricRouteSetForTransportTargets("cluster-a", "node-a", "node-b", []FabricTransportTarget{
			{EndpointID: "dead", PeerID: "node-b", Endpoint: "quic://dead.example.test:19443", Transport: "quic"},
			{EndpointID: "fast", PeerID: "node-b", Endpoint: "quic://fast.example.test:19443", Transport: "quic"},
		}),
	}, transport)
	forward.Timeout = time.Second

	ack, err := forward.SendSynthetic(context.Background(), "node-b", testSyntheticEnvelope("route-1", 1))
	if err != nil {
		t.Fatalf("send synthetic: %v", err)
	}
	if ack.RouteID != "route-1" || ack.MessageType != SyntheticMessageRouteHealthAck {
		t.Fatalf("ack = %+v", ack)
	}
	if got := transport.connectCount("quic://dead.example.test:19443"); got != 1 {
		t.Fatalf("dead connect count = %d, want 1", got)
	}
	if got := transport.connectCount("quic://fast.example.test:19443"); got != 1 {
		t.Fatalf("fast connect count = %d, want 1", got)
	}
}

func TestQUICFabricServerHandlesSyntheticFrames(t *testing.T) {
	server, err := StartQUICFabricServer(context.Background(), QUICFabricServerConfig{
		ListenAddr: "127.0.0.1:0",
		TLSConfig:  testQUICTLSConfig(t),
		SyntheticForwardHandler: func(_ context.Context, envelope SyntheticEnvelope) (SyntheticEnvelope, error) {
			return testSyntheticAckEnvelope(envelope.RouteID, envelope.Sequence), nil
		},
	})
	if err != nil {
		t.Fatalf("start quic fabric server: %v", err)
	}
	defer server.Close()

	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()
	session, err := NewQUICFabricTransport(nil).Connect(ctx, FabricTransportTarget{
		Endpoint: server.Addr().String(),
		TLSConfig: &tls.Config{
			InsecureSkipVerify: true,
			NextProtos:         []string{fabricQUICNextProto},
		},
		Timeout:       time.Second,
		InboundBuffer: 4,
		ErrorBuffer:   4,
	})
	if err != nil {
		t.Fatalf("connect: %v", err)
	}
	defer session.Close()

	payload, err := json.Marshal(testSyntheticEnvelope("route-1", 7))
	if err != nil {
		t.Fatalf("marshal envelope: %v", err)
	}
	if err := session.Send(ctx, fabricproto.Frame{
		Type:         fabricproto.FrameData,
		TrafficClass: fabricproto.TrafficClassReliable,
		StreamID:     SyntheticForwardQUICStreamID,
		Sequence:     42,
		Payload:      payload,
	}); err != nil {
		t.Fatalf("send synthetic frame: %v", err)
	}
	select {
	case frame := <-session.Frames():
		if frame.StreamID != SyntheticForwardQUICStreamID || frame.Sequence != 42 {
			t.Fatalf("frame = %+v", frame)
		}
		ack, err := decodeQUICSyntheticForwardResponse(frame.Payload)
		if err != nil {
			t.Fatalf("decode response: %v", err)
		}
		if ack.RouteID != "route-1" || ack.MessageType != SyntheticMessageRouteHealthAck || ack.Sequence != 7 {
			t.Fatalf("ack = %+v", ack)
		}
	case err := <-session.Errors():
		t.Fatalf("session error: %v", err)
	case <-ctx.Done():
		t.Fatal(ctx.Err())
	}
}

type fakeSyntheticFabricTransport struct {
	mu          sync.Mutex
	failConnect map[string]bool
	responses   map[string]SyntheticEnvelope
	connects    map[string]int
}

func newFakeSyntheticFabricTransport() *fakeSyntheticFabricTransport {
	return &fakeSyntheticFabricTransport{
		failConnect: map[string]bool{},
		responses:   map[string]SyntheticEnvelope{},
		connects:    map[string]int{},
	}
}

func (t *fakeSyntheticFabricTransport) Connect(_ context.Context, target FabricTransportTarget) (FabricTransportSession, error) {
	endpoint := target.Endpoint
	t.mu.Lock()
	t.connects[endpoint]++
	fail := t.failConnect[endpoint]
	response := t.responses[endpoint]
	t.mu.Unlock()
	if fail {
		return nil, ErrSyntheticPeerUnavailable
	}
	return &fakeSyntheticFabricSession{
		response: response,
		frames:   make(chan fabricproto.Frame, 16),
		errors:   make(chan error, 1),
		done:     make(chan struct{}),
	}, nil
}

func (t *fakeSyntheticFabricTransport) Close() error {
	return nil
}

func (t *fakeSyntheticFabricTransport) connectCount(endpoint string) int {
	t.mu.Lock()
	defer t.mu.Unlock()
	return t.connects[endpoint]
}

type fakeSyntheticFabricSession struct {
	response SyntheticEnvelope
	frames   chan fabricproto.Frame
	errors   chan error
	done     chan struct{}
	once     sync.Once
}

func (s *fakeSyntheticFabricSession) Send(_ context.Context, frame fabricproto.Frame) error {
	if frame.Type != fabricproto.FrameData {
		return nil
	}
	responsePayload, _ := json.Marshal(quicSyntheticForwardResponse{Envelope: s.response})
	go func() {
		select {
		case <-s.done:
		case s.frames <- fabricproto.Frame{
			Type:         fabricproto.FrameData,
			TrafficClass: frame.TrafficClass,
			StreamID:     frame.StreamID,
			Sequence:     frame.Sequence,
			Payload:      responsePayload,
		}:
		}
	}()
	return nil
}

func (s *fakeSyntheticFabricSession) Frames() <-chan fabricproto.Frame {
	return s.frames
}

func (s *fakeSyntheticFabricSession) Errors() <-chan error {
	return s.errors
}

func (s *fakeSyntheticFabricSession) Close() error {
	s.once.Do(func() {
		close(s.done)
	})
	return nil
}

func (s *fakeSyntheticFabricSession) Closed() bool {
	select {
	case <-s.done:
		return true
	default:
		return false
	}
}

func testSyntheticEnvelope(routeID string, sequence uint64) SyntheticEnvelope {
	now := time.Now().UTC()
	return SyntheticEnvelope{
		ProtocolVersion: ProtocolVersion,
		RouteID:         routeID,
		ClusterID:       "cluster-a",
		From:            PeerIdentity{ClusterID: "cluster-a", NodeID: "node-a"},
		To:              PeerIdentity{ClusterID: "cluster-a", NodeID: "node-b"},
		Channel:         SyntheticChannelFabricControl,
		MessageType:     SyntheticMessageRouteHealth,
		TTL:             8,
		HopCount:        1,
		Visited:         []string{"node-a"},
		Sequence:        sequence,
		SentAt:          now,
	}
}

func testSyntheticAckEnvelope(routeID string, sequence uint64) SyntheticEnvelope {
	ack := testSyntheticEnvelope(routeID, sequence)
	ack.From = PeerIdentity{ClusterID: "cluster-a", NodeID: "node-b"}
	ack.To = PeerIdentity{ClusterID: "cluster-a", NodeID: "node-a"}
	ack.MessageType = SyntheticMessageRouteHealthAck
	ack.Visited = []string{"node-a", "node-b"}
	return ack
}