package link

import (
	"context"
	"crypto/ed25519"
	"encoding/json"
	"fmt"
	"os"
	"testing"
	"time"

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

// The host's link against a real server, because every claim here is about one.
//
// Whether binding to a consumer the host did not create works, whether a declaration on the node's
// own subject arrives, whether acknowledging it removes it from the consumer's pending — none of
// that can be reasoned out, and the first two are the ones that would leave a node silently hearing
// nothing:
//
//	docker run -d --rm --name t -p 14223:4222 nats:2.10-alpine -js
//	MESH_TEST_NATS=nats://127.0.0.1:14223 go test ./internal/link/ -run TestNats

func aBus(t *testing.T) (*nats.Conn, nats.JetStreamContext) {
	t.Helper()
	url := os.Getenv("MESH_TEST_NATS")
	if url == "" {
		t.Skip("MESH_TEST_NATS unset")
	}
	conn, err := nats.Connect(url)
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(conn.Close)
	js, err := conn.JetStream()
	if err != nil {
		t.Fatal(err)
	}
	// **Ensured and purged, not deleted and recreated.** Delete-then-add looked like a reset and is
	// not one: a test that did that inherited the previous test's messages, and the symptom was a
	// declaration counted as delivered twice — which reads as a redelivery bug in the code under
	// test rather than as a dirty stream. Purge is defined to empty a stream; recreating one is a
	// race with the server's own teardown.
	for _, want := range []*nats.StreamConfig{
		{Name: "NODES", Subjects: []string{"mesh.node.*.declare"}, MaxMsgsPerSubject: 1},
		{Name: "CONTROL", Subjects: []string{"mesh.control.*.report", "mesh.control.enrol"},
			Retention: nats.WorkQueuePolicy},
	} {
		if _, err := js.StreamInfo(want.Name); err != nil {
			if _, err := js.AddStream(want); err != nil {
				t.Fatal(err)
			}
		}
		if err := js.PurgeStream(want.Name); err != nil {
			t.Fatal(err)
		}
	}
	return conn, js
}

// theMeshMakes is the consumer the controller creates when a node enrols. Made here by the test
// because the host may not: its account reaches no part of the JetStream API, which is the whole
// reason this binds rather than subscribes.
//
// Removed afterwards, and each test names its own node: two tests sharing a consumer name share its
// delivery count and its pending list, and the first thing that goes wrong reads as a fault in the
// host rather than in the test beside it.
func theMeshMakes(t *testing.T, js nats.JetStreamContext, node string) {
	t.Helper()
	t.Cleanup(func() { _ = js.DeleteConsumer("NODES", node) })
	if _, err := js.AddConsumer("NODES", &nats.ConsumerConfig{
		Durable:        node,
		FilterSubject:  DeclareSubject(node),
		AckPolicy:      nats.AckExplicitPolicy,
		AckWait:        300 * time.Second,
		DeliverSubject: "_DELIVER." + node,
	}); err != nil {
		t.Fatal(err)
	}
}

func signedBy(t *testing.T, key ed25519.PrivateKey, declaration []byte) []byte {
	t.Helper()
	body, err := json.Marshal(Signed{
		Declaration: declaration, Signature: ed25519.Sign(key, declaration),
	})
	if err != nil {
		t.Fatal(err)
	}
	return body
}

// A declaration on this node's own subject reaches the host, is applied, and acknowledging it
// empties the consumer — which is what tells the mesh the node has it.
func TestNatsADeclarationReachesTheHostAndIsSettled(t *testing.T) {
	conn, js := aBus(t)
	const node = "settling"
	theMeshMakes(t, js, node)

	public, private, _ := ed25519.GenerateKey(nil)
	m := Membership{Node: node, Signer: public}

	// Dialled directly rather than through Open: the test server has no TLS, and what is being
	// checked is the subscription and the settling, not the pin — which PinnedConfig owns and its
	// own tests cover.
	l := &natsLink{conn: conn, js: js, node: node,
		arrived: make(chan Declaration, drainDepth), lost: make(chan error, 1)}
	feed := make(chan *nats.Msg, drainDepth)
	sub, err := js.ChanSubscribe(DeclareSubject(node), feed, nats.Bind("NODES", node))
	if err != nil {
		t.Fatalf("the host could not bind to the consumer the mesh made for it: %v", err)
	}
	defer func() { _ = sub.Unsubscribe() }()
	go func() {
		for msg := range feed {
			l.arrived <- natsDeclaration{msg}
		}
	}()

	if _, err := js.Publish(DeclareSubject(node),
		signedBy(t, private, []byte(`{"declared":"d1"}`))); err != nil {
		t.Fatal(err)
	}

	select {
	case d := <-l.Declarations():
		report := handleBody(context.Background(), m, d.Body(),
			func(context.Context, []byte, []byte) Report {
				return Report{Applied: []string{"store"}}
			})
		if report.Refused != "" {
			t.Fatalf("a declaration the mesh signed was refused: %s", report.Refused)
		}
		if err := d.Handled(); err != nil {
			t.Fatalf("the node could not acknowledge its own declaration: %v", err)
		}
	case <-time.After(8 * time.Second):
		t.Fatal("no declaration reached the host")
	}

	// **Nothing pending is the property**; a delivery count is not. Delivery is at-least-once by
	// design, so pinning "delivered exactly once" would be asserting something the mesh does not
	// rely on. What matters is that the acknowledgement landed, so the mesh can tell the node has
	// it — and that no redelivery was needed to get there, which is what would say the node was
	// too slow to answer for its own ack wait.
	deadline := time.Now().Add(5 * time.Second)
	var last string
	for time.Now().Before(deadline) {
		info, err := js.ConsumerInfo("NODES", node)
		switch {
		case err != nil:
			last = err.Error()
		case info.NumAckPending == 0 && info.NumRedelivered == 0:
			return
		default:
			last = fmt.Sprintf("pending %d, redelivered %d", info.NumAckPending, info.NumRedelivered)
		}
		time.Sleep(20 * time.Millisecond)
	}
	t.Fatalf("the declaration was not settled, so the mesh cannot tell the node has it: %s", last)
}

// **A node that was away gets exactly the current declaration and nothing older.** Three pushed
// while nothing is listening leave one on the stream, and it is the newest — the wire-level answer
// to novox/hq issue 107, and the half of the drain that stops being the host's problem.
func TestNatsANodeThatWasAwayGetsOnlyTheNewest(t *testing.T) {
	_, js := aBus(t)
	const node = "returning"
	_, private, _ := ed25519.GenerateKey(nil)

	for _, id := range []string{"d1", "d2", "d3"} {
		if _, err := js.Publish(DeclareSubject(node),
			signedBy(t, private, []byte(`{"declared":"`+id+`"}`))); err != nil {
			t.Fatal(err)
		}
	}
	info, err := js.StreamInfo("NODES")
	if err != nil {
		t.Fatal(err)
	}
	if info.State.Msgs != 1 {
		t.Fatalf("%d declarations survived for one node; a node that was away would apply a backlog "+
			"of things nobody wants any more", info.State.Msgs)
	}

	theMeshMakes(t, js, node)
	feed := make(chan *nats.Msg, drainDepth)
	sub, err := js.ChanSubscribe(DeclareSubject(node), feed, nats.Bind("NODES", node))
	if err != nil {
		t.Fatal(err)
	}
	defer func() { _ = sub.Unsubscribe() }()

	select {
	case msg := <-feed:
		if declaredIn(msg.Data) != "d3" {
			t.Fatalf("the node was given %q rather than the newest", declaredIn(msg.Data))
		}
	case <-time.After(8 * time.Second):
		t.Fatal("the node that was away was given nothing")
	}
}

// A report goes through the stream and a heartbeat does not: the one that must survive the
// controller's store restarting is kept, and the one that must not is not.
func TestNatsAReportIsKeptAndAHeartbeatIsNot(t *testing.T) {
	conn, js := aBus(t)
	bus := OverNATS{Conn: conn, JS: js}
	ctx := context.Background()

	body, _ := json.Marshal(Report{Node: "anchor", Declared: "d1"})
	if err := bus.Report(ctx, "anchor", body); err != nil {
		t.Fatal(err)
	}
	beat, _ := json.Marshal(Alive{Node: "anchor"})
	if err := bus.Alive(ctx, "anchor", beat); err != nil {
		t.Fatal(err)
	}

	info, err := js.StreamInfo("CONTROL")
	if err != nil {
		t.Fatal(err)
	}
	if info.State.Msgs != 1 {
		t.Fatalf("%d messages were kept; a report must be and a heartbeat must not", info.State.Msgs)
	}
}