package link

import (
	"context"
	"encoding/json"
	"errors"
	"io"
	"log"
	"os"
	"sync"
	"testing"
	"time"

	"github.com/nats-io/nats.go"

	"github.com/novox/mesh-controller/internal/broker"
)

// The consume side against a real server, because what is being checked is what the server does.
//
// Reasoning cannot answer any of these: whether a nak-with-delay really comes back, whether the
// delay is honoured, whether terminating a delivery really stops it, or whether an answer published
// to an address carried in the payload reaches a caller waiting on its own inbox. Each is a claim
// about a server, so each is asked of one:
//
//	docker run -d --rm --name t -p 14222:4222 nats:2.10-alpine -js
//	MESH_TEST_NATS=nats://127.0.0.1:14222 go test ./internal/link/ -run TestNats

func aBus(t *testing.T) *broker.JetStream {
	t.Helper()
	url := os.Getenv("MESH_TEST_NATS")
	if url == "" {
		t.Skip("MESH_TEST_NATS unset")
	}
	js, err := broker.Dial(url)
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(js.Close)

	// **Streams purged, consumers removed.** Both halves, and each was learned by getting it wrong.
	//
	// The streams are emptied rather than deleted and recreated, because delete-then-add is not a
	// reset: the server's teardown races the creation, and a test then inherits the previous one's
	// messages — which reads as a redelivery bug in the code under test.
	//
	// The consumers are removed, because deleting a stream used to take them with it and purging
	// does not. A durable *push* consumer that survives between tests keeps pushing to a delivery
	// subject the previous test's subscription has gone from: the messages count as delivered, go
	// nowhere, and the next test waits out its timeout for an announcement the server believes it
	// already sent. The controller recreates what it needs on start, so leaving none is correct.
	if err := broker.AssertMeshStreams(js); err != nil {
		t.Fatal(err)
	}
	clean := func() {
		for _, c := range broker.MeshConsumers() {
			_ = js.Context().DeleteConsumer(c.Stream, c.Name)
		}
		for _, s := range broker.MeshStreams() {
			_ = js.Context().PurgeStream(s.Name)
		}
	}
	clean()
	t.Cleanup(clean)
	return js
}

// serving1 is a controller reading from a real bus, and a way to stop it.
func servingOn(t *testing.T, js *broker.JetStream, l Listener) (*Server, func()) {
	t.Helper()
	s := &Server{inbound: Nats(js), bus: OverNATS{Conn: js.Conn(), JS: js.Context()},
		listener: l, log: quiet()}
	ctx, stop := context.WithCancel(context.Background())
	done := make(chan struct{})
	go func() { defer close(done); _ = s.Serve(ctx) }()
	return s, func() {
		stop()
		<-done
	}
}

// counted records reports and can be told to refuse them, from another goroutine.
type counted struct {
	mu    sync.Mutex
	err   error
	heard []Report
}

func (c *counted) Heard(_ context.Context, r Report) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.err != nil {
		return c.err
	}
	c.heard = append(c.heard, r)
	return nil
}

func (c *counted) refusing(err error) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.err = err
}

func (c *counted) count() int {
	c.mu.Lock()
	defer c.mu.Unlock()
	return len(c.heard)
}

func eventually(t *testing.T, what string, is func() bool) {
	t.Helper()
	deadline := time.Now().Add(8 * time.Second)
	for time.Now().Before(deadline) {
		if is() {
			return
		}
		time.Sleep(20 * time.Millisecond)
	}
	t.Fatalf("%s did not happen within the wait", what)
}

// A report published by a node reaches the controller, is recorded, and is acknowledged — so the
// stream does not hold it. A work queue is the check: what is acknowledged leaves it.
func quiet() *log.Logger { return log.New(io.Discard, "", 0) }

func TestNatsAReportIsHeardAndLeavesTheStream(t *testing.T) {
	js := aBus(t)
	store := &counted{}
	_, stop := servingOn(t, js, store)
	defer stop()

	body, _ := json.Marshal(Report{Node: "anchor", Declared: "d1", Applied: []string{"store"}})
	if _, err := js.Context().Publish(ReportSubject("anchor"), body); err != nil {
		t.Fatal(err)
	}
	eventually(t, "a report being recorded", func() bool { return store.count() == 1 })
	eventually(t, "the report leaving the work queue", func() bool {
		info, err := js.Context().StreamInfo("CONTROL")
		return err == nil && info.State.Msgs == 0
	})
}

// **The store window, in the server.** A report the store cannot take is naked with a delay and
// comes back; once the store is there it is recorded and leaves the stream. The controller holds
// nothing in the meantime — which is what the sequence check below is for: the message is still on
// the server while it waits.
func TestNatsAReportTheStoreCannotTakeIsHeldByTheServerAndComesBack(t *testing.T) {
	js := aBus(t)
	store := &counted{}
	store.refusing(errors.Join(ErrTryAgain, errors.New("the database system is starting up")))
	_, stop := servingOn(t, js, store)
	defer stop()

	body, _ := json.Marshal(Report{Node: "anchor", Declared: "d1", Applied: []string{"store"}})
	if _, err := js.Context().Publish(ReportSubject("anchor"), body); err != nil {
		t.Fatal(err)
	}

	// Held: the message is the server's, unacknowledged, and still in the stream.
	eventually(t, "the report being redelivered at least once", func() bool {
		info, err := js.Context().ConsumerInfo("CONTROL", broker.ControllerName)
		return err == nil && info.NumRedelivered >= 1
	})
	info, err := js.Context().StreamInfo("CONTROL")
	if err != nil || info.State.Msgs != 1 {
		t.Fatalf("a held report did not stay on the server: %+v, %v", info, err)
	}
	if store.count() != 0 {
		t.Fatalf("a report was recorded by a store that was refusing it")
	}

	store.refusing(nil)
	eventually(t, "the report being recorded once the store was back",
		func() bool { return store.count() == 1 })
	eventually(t, "the recorded report leaving the work queue", func() bool {
		info, err := js.Context().StreamInfo("CONTROL")
		return err == nil && info.State.Msgs == 0
	})
}

// A report about a declaration the mesh has moved past is settled without being acted on, and
// leaves the stream rather than coming back for ever.
func TestNatsASupersededReportIsSettledAndNotActedOn(t *testing.T) {
	js := aBus(t)
	store := &sentAndHeardSafely{sent: "d2"}
	_, stop := servingOn(t, js, store)
	defer stop()

	body, _ := json.Marshal(Report{Node: "anchor", Declared: "d1", Applied: []string{"store"}})
	if _, err := js.Context().Publish(ReportSubject("anchor"), body); err != nil {
		t.Fatal(err)
	}
	eventually(t, "the superseded report leaving the stream", func() bool {
		info, err := js.Context().StreamInfo("CONTROL")
		return err == nil && info.State.Msgs == 0
	})
	if store.count() != 0 {
		t.Fatalf("a report about a superseded declaration was acted on")
	}
}

// sentAndHeardSafely is sentAndHeard, read from two goroutines.
type sentAndHeardSafely struct {
	mu    sync.Mutex
	sent  string
	heard []Report
}

func (s *sentAndHeardSafely) Heard(_ context.Context, r Report) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.heard = append(s.heard, r)
	return nil
}

func (s *sentAndHeardSafely) Outstanding(context.Context, string) (string, error) {
	return s.sent, nil
}

func (s *sentAndHeardSafely) count() int {
	s.mu.Lock()
	defer s.mu.Unlock()
	return len(s.heard)
}

// **An enrolment answered through a reply address the stream would have eaten.**
//
// The caller waits on its own inbox and states that address in the request's payload. The check is
// that the answer arrives there — which is the whole reason the address is a field rather than the
// transport's reply, and this is the test design 25 §2 asks for so the reason cannot quietly become
// folklore.
func TestNatsAnEnrolmentIsAnsweredOnTheAddressInItsPayload(t *testing.T) {
	js := aBus(t)
	s := &Server{inbound: Nats(js), bus: OverNATS{Conn: js.Conn(), JS: js.Context()},
		enroller: enrolsAs{reply: EnrolReply{Accepted: true, Node: "anchor"}}, log: quiet()}
	ctx, stop := context.WithCancel(context.Background())
	defer stop()
	go func() { _ = s.Serve(ctx) }()

	inbox := nats.NewInbox()
	answers, err := js.Conn().SubscribeSync(inbox)
	if err != nil {
		t.Fatal(err)
	}
	body, _ := json.Marshal(EnrolRequest{Node: "anchor", Secret: "t", ReplyTo: inbox})
	if _, err := js.Context().Publish(EnrolSubject, body); err != nil {
		t.Fatal(err)
	}

	msg, err := answers.NextMsg(8 * time.Second)
	if err != nil {
		t.Fatalf("no answer reached the address the request named: %v", err)
	}
	var reply EnrolReply
	if err := json.Unmarshal(msg.Data, &reply); err != nil {
		t.Fatal(err)
	}
	if !reply.Accepted || reply.Node != "anchor" {
		t.Fatalf("the answer was not the mesh's: %+v", reply)
	}
	// And the address really is not the one the transport carried: what the consumer saw was its
	// own ack subject, which is why this had to travel in the payload.
	if msg.Subject != inbox {
		t.Fatalf("the answer arrived on %s, not the address the request named", msg.Subject)
	}
}

// enrolsAs answers every request the same way.
type enrolsAs struct{ reply EnrolReply }

func (e enrolsAs) Enrol(context.Context, EnrolRequest) (EnrolReply, error) { return e.reply, nil }

// A heartbeat is core NATS: it reaches the controller and nothing is persisted, so the stream the
// reports live in stays empty.
func TestNatsAHeartbeatIsHeardAndNothingIsKept(t *testing.T) {
	js := aBus(t)
	store := &counted{}
	_, stop := servingOn(t, js, store)
	defer stop()

	// Given time to subscribe: a core subscription that is not yet up misses what is published,
	// which is the guarantee a heartbeat has and not a fault.
	eventually(t, "the heartbeat subscription coming up", func() bool {
		body, _ := json.Marshal(Alive{Node: "anchor"})
		_ = js.Conn().Publish(AliveSubject("anchor"), body)
		_ = js.Conn().Flush()
		return store.count() >= 1
	})
	info, err := js.Context().StreamInfo("CONTROL")
	if err != nil || info.State.Msgs != 0 {
		t.Fatalf("a heartbeat was persisted, and the mesh's least valuable message now competes "+
			"for retention with its most valuable: %+v, %v", info, err)
	}
}

// The two events the controller follows arrive over one durable consumer with two filters, and it
// can acknowledge them.
//
// **Both halves are the point.** A consumer with several filter subjects is a 2.10 feature and this
// is the first thing in the mesh to use one; and a delivery from the events stream is acknowledged
// on a different ack subject from a delivery from the control stream, which the controller's own
// permission list has to cover or every announcement is redelivered for ever.
func TestNatsTheEventsTheControllerFollowsArriveAndAreAcknowledged(t *testing.T) {
	js := aBus(t)
	told := &toldAbout{}
	s := &Server{inbound: Nats(js), bus: OverNATS{Conn: js.Conn(), JS: js.Context()}, log: quiet()}
	if err := s.Follows(told); err != nil {
		t.Fatal(err)
	}
	if err := s.Answers(replaysWith{}); err != nil {
		t.Fatal(err)
	}
	ctx, stop := context.WithCancel(context.Background())
	defer stop()
	go func() { _ = s.Serve(ctx) }()

	moved, _ := json.Marshal(Upgraded{Module: "gitea", Commit: "abcdef0123"})
	if _, err := js.Context().Publish(broker.ControllerFollows[0], moved); err != nil {
		t.Fatal(err)
	}
	if _, err := js.Context().Publish(broker.ControllerFollows[1], []byte(`{}`)); err != nil {
		t.Fatal(err)
	}

	eventually(t, "the catalogue's upgrade reaching the controller",
		func() bool { return told.count() == 1 })
	eventually(t, "both announcements being acknowledged", func() bool {
		info, err := js.Context().ConsumerInfo("EVENTS", broker.ControllerName)
		return err == nil && info.NumAckPending == 0 && info.Delivered.Consumer == 2
	})
}

type toldAbout struct {
	mu   sync.Mutex
	saw  []Upgraded
	fail error
}

func (u *toldAbout) Upgraded(_ context.Context, m Upgraded) error {
	u.mu.Lock()
	defer u.mu.Unlock()
	if u.fail != nil {
		return u.fail
	}
	u.saw = append(u.saw, m)
	return nil
}

func (u *toldAbout) count() int {
	u.mu.Lock()
	defer u.mu.Unlock()
	return len(u.saw)
}

// A store that never comes back: the report is let go once the bound passes, and it leaves the
// stream rather than being held for ever. The bound is the controller's, not the server's — nothing
// here sets max-deliver, and that is deliberate (streams.go).
func TestNatsAReportIsLetGoOnceTheStoreHasBeenGoneTooLong(t *testing.T) {
	js := aBus(t)
	store := &counted{}
	store.refusing(errors.Join(ErrTryAgain, errors.New("connection refused")))
	s := &Server{inbound: Nats(js), bus: OverNATS{Conn: js.Conn(), JS: js.Context()},
		listener: store, log: quiet(), giveUp: 1500 * time.Millisecond}
	ctx, stop := context.WithCancel(context.Background())
	defer stop()
	go func() { _ = s.Serve(ctx) }()

	body, _ := json.Marshal(Report{Node: "anchor", Declared: "d1", Applied: []string{"store"}})
	if _, err := js.Context().Publish(ReportSubject("anchor"), body); err != nil {
		t.Fatal(err)
	}
	eventually(t, "the report being let go once the bound passed", func() bool {
		info, err := js.Context().StreamInfo("CONTROL")
		return err == nil && info.State.Msgs == 0
	})
	if store.count() != 0 {
		t.Fatalf("a report was recorded by a store that never came back")
	}
}

// A merge announcement is not what these tests are about; taken and forgotten.
func (t *toldAbout) SourceMoved(context.Context, SourceMoved) error { return nil }

// Every subject the controller follows decodes to a kind, and decoding never reaches past the
// list: the day the list was three long and the decoder named a fourth, every message panicked
// the control plane (2026-09-28).
func TestEverySubjectTheControllerFollowsDecodesToAKind(t *testing.T) {
	for _, subject := range broker.ControllerFollows {
		if _, ok := kindOfSubject(subject); !ok {
			t.Errorf("%s is followed and decodes to nothing", subject)
		}
	}
	if _, ok := kindOfSubject("mesh.mod.nobody.event.nothing"); ok {
		t.Error("a subject nobody follows decoded to a kind")
	}
}