package embeddednats_test

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"math/big"
	"net"
	"os"
	"path/filepath"
	"testing"
	"time"

	"github.com/enmanuel/unibus/pkg/busauth"
	"github.com/enmanuel/unibus/pkg/embeddednats"
	"github.com/nats-io/nats.go"
	server "github.com/nats-io/nats-server/v2/server"
)

// freePort returns an OS-assigned free TCP port on loopback.
func freePort(t *testing.T) int {
	t.Helper()
	l, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("free port: %v", err)
	}
	defer l.Close()
	return l.Addr().(*net.TCPAddr).Port
}

// startNode boots a clustered embedded NATS node. peerRoutePorts are the route
// ports of the OTHER nodes; user/pass gate the route layer (empty disables it);
// routeTLS, when non-nil, secures the routes with mutual TLS.
func startNode(t *testing.T, name string, clientPort, routePort int, peerRoutePorts []int, user, pass string, routeTLS *clusterTLS) *server.Server {
	t.Helper()
	routes := make([]string, 0, len(peerRoutePorts))
	for _, p := range peerRoutePorts {
		// Carry the cluster credentials in the route URL so this node
		// authenticates outbound to its peers' route listeners.
		if user != "" {
			routes = append(routes, fmt.Sprintf("nats://%s:%s@127.0.0.1:%d", user, pass, p))
		} else {
			routes = append(routes, fmt.Sprintf("nats://127.0.0.1:%d", p))
		}
	}
	cc := &embeddednats.ClusterConfig{
		Name:     "unibus-test",
		Host:     "127.0.0.1",
		Port:     routePort,
		Routes:   routes,
		Username: user,
		Password: pass,
	}
	if routeTLS != nil {
		cfg, err := busauth.RouteTLSConfig(routeTLS.cert, routeTLS.key, routeTLS.ca)
		if err != nil {
			t.Fatalf("route TLS for %s: %v", name, err)
		}
		cc.TLS = cfg
	}
	ns, err := embeddednats.StartServer(embeddednats.ServerConfig{
		StoreDir:   t.TempDir(),
		Host:       "127.0.0.1",
		Port:       clientPort,
		ServerName: name,
		Cluster:    cc,
	})
	if err != nil {
		t.Fatalf("start node %s: %v", name, err)
	}
	t.Cleanup(func() { ns.Shutdown(); ns.WaitForShutdown() })
	return ns
}

// waitRoutes waits until ns has at least want established routes, or fails.
func waitRoutes(t *testing.T, ns *server.Server, want int) {
	t.Helper()
	deadline := time.Now().Add(8 * time.Second)
	for time.Now().Before(deadline) {
		if ns.NumRoutes() >= want {
			return
		}
		time.Sleep(50 * time.Millisecond)
	}
	t.Fatalf("node %q never reached %d routes (have %d)", ns.Name(), want, ns.NumRoutes())
}

// stableRouteCount waits for ns's route count to stop changing (the NATS route
// pool opens several connections per peer asynchronously) and returns it, so a
// test can use it as a baseline that an impostor must not increase.
func stableRouteCount(t *testing.T, ns *server.Server) int {
	t.Helper()
	prev := -1
	stableSince := time.Now()
	deadline := time.Now().Add(5 * time.Second)
	for time.Now().Before(deadline) {
		n := ns.NumRoutes()
		if n != prev {
			prev = n
			stableSince = time.Now()
		} else if time.Since(stableSince) >= 750*time.Millisecond {
			return n
		}
		time.Sleep(50 * time.Millisecond)
	}
	return prev
}

// pubSubAcrossNodes connects a subscriber to subURL and a publisher to pubURL,
// publishes one message on subject, and reports whether it arrived within 3s.
// This proves the cluster forwards client subjects between nodes.
func pubSubAcrossNodes(t *testing.T, subURL, pubURL, subject, payload string) bool {
	t.Helper()
	subConn, err := nats.Connect(subURL)
	if err != nil {
		t.Fatalf("subscriber connect %s: %v", subURL, err)
	}
	defer subConn.Close()
	got := make(chan string, 1)
	if _, err := subConn.Subscribe(subject, func(m *nats.Msg) {
		select {
		case got <- string(m.Data):
		default:
		}
	}); err != nil {
		t.Fatalf("subscribe: %v", err)
	}
	if err := subConn.Flush(); err != nil {
		t.Fatalf("flush sub: %v", err)
	}

	pubConn, err := nats.Connect(pubURL)
	if err != nil {
		t.Fatalf("publisher connect %s: %v", pubURL, err)
	}
	defer pubConn.Close()
	// Retry the publish for a moment: route interest propagation across the
	// cluster is asynchronous, so the very first publish can race the gossip.
	deadline := time.Now().Add(3 * time.Second)
	for time.Now().Before(deadline) {
		if err := pubConn.Publish(subject, []byte(payload)); err != nil {
			t.Fatalf("publish: %v", err)
		}
		_ = pubConn.Flush()
		select {
		case v := <-got:
			return v == payload
		case <-time.After(100 * time.Millisecond):
		}
	}
	return false
}

// --- golden: two-node cluster forwards client subjects across nodes ----------

func TestClusterForwardsAcrossNodes(t *testing.T) {
	rp0, rp1 := freePort(t), freePort(t)
	n0 := startNode(t, "n0", freePort(t), rp0, []int{rp1}, "clusteruser", "clusterpass", nil)
	n1 := startNode(t, "n1", freePort(t), rp1, []int{rp0}, "clusteruser", "clusterpass", nil)

	waitRoutes(t, n0, 1)
	waitRoutes(t, n1, 1)

	if !pubSubAcrossNodes(t, n0.ClientURL(), n1.ClientURL(), "test.cross", "hello-cluster") {
		t.Fatalf("subject published on n1 did not reach subscriber on n0")
	}
}

// --- edge: three-node cluster (HA shape) forwards between non-adjacent nodes --

func TestClusterThreeNodesForward(t *testing.T) {
	rp0, rp1, rp2 := freePort(t), freePort(t), freePort(t)
	n0 := startNode(t, "n0", freePort(t), rp0, []int{rp1, rp2}, "u", "p", nil)
	n1 := startNode(t, "n1", freePort(t), rp1, []int{rp0, rp2}, "u", "p", nil)
	n2 := startNode(t, "n2", freePort(t), rp2, []int{rp0, rp1}, "u", "p", nil)

	waitRoutes(t, n0, 2)
	waitRoutes(t, n1, 2)
	waitRoutes(t, n2, 2)

	// Publish on n2, subscribe on n0: a message must traverse the cluster.
	if !pubSubAcrossNodes(t, n0.ClientURL(), n2.ClientURL(), "test.ha", "three-node") {
		t.Fatalf("subject published on n2 did not reach subscriber on n0")
	}
}

// --- error: a node with the wrong cluster password is rejected as a route -----

func TestClusterRejectsBadRouteAuth(t *testing.T) {
	rp0, rp1 := freePort(t), freePort(t)
	good := startNode(t, "good", freePort(t), rp0, []int{rp1}, "secret", "right", nil)
	_ = startNode(t, "peer", freePort(t), rp1, []int{rp0}, "secret", "right", nil)
	waitRoutes(t, good, 1)
	// Let the route pool settle so the baseline count is stable (NATS opens a
	// pool of route connections per peer, so NumRoutes counts connections, not
	// distinct peers).
	base := stableRouteCount(t, good)

	// Impostor knows the addresses but not the cluster password. It tries to
	// route to `good`; the route handshake must be rejected, so the impostor
	// never establishes a route.
	impostor := startNode(t, "impostor", freePort(t), freePort(t), []int{rp0}, "secret", "WRONG", nil)

	// Give the route layer ample time to (fail to) connect, then assert it never
	// formed: the impostor has zero routes, and `good`'s route count is unchanged
	// (it did not accept a route from the impostor).
	time.Sleep(2 * time.Second)
	if n := impostor.NumRoutes(); n != 0 {
		t.Fatalf("impostor with wrong cluster password formed %d routes, want 0", n)
	}
	if n := good.NumRoutes(); n != base {
		t.Fatalf("legit node route count changed from %d to %d after impostor attempt (it accepted the impostor)", base, n)
	}
}

// --- golden (TLS): mutual-TLS routes forward across nodes ---------------------

func TestClusterMutualTLSForwards(t *testing.T) {
	ca, caKey := genCA(t)
	dir := t.TempDir()
	tlsA := writeNodeCert(t, dir, "a", ca, caKey)
	tlsB := writeNodeCert(t, dir, "b", ca, caKey)

	rp0, rp1 := freePort(t), freePort(t)
	n0 := startNode(t, "n0", freePort(t), rp0, []int{rp1}, "u", "p", tlsA)
	n1 := startNode(t, "n1", freePort(t), rp1, []int{rp0}, "u", "p", tlsB)

	waitRoutes(t, n0, 1)
	waitRoutes(t, n1, 1)

	if !pubSubAcrossNodes(t, n0.ClientURL(), n1.ClientURL(), "test.tls", "mtls-ok") {
		t.Fatalf("subject did not cross the mutual-TLS cluster")
	}
}

// --- error (TLS): a node whose cert is not signed by the bus CA cannot join ---

func TestClusterRejectsUnsignedNode(t *testing.T) {
	ca, caKey := genCA(t)
	dir := t.TempDir()
	tlsGood := writeNodeCert(t, dir, "good", ca, caKey)
	tlsPeer := writeNodeCert(t, dir, "peer", ca, caKey)

	// The impostor signs its node cert with a DIFFERENT CA, and pins only that
	// CA. The legit nodes' RequireAndVerifyClientCert against the bus CA rejects
	// it; the impostor likewise rejects the legit node's cert. No route forms.
	otherCA, otherKey := genCA(t)
	tlsImpostor := writeNodeCert(t, dir, "impostor", otherCA, otherKey)

	rp0, rp1 := freePort(t), freePort(t)
	good := startNode(t, "good", freePort(t), rp0, []int{rp1}, "u", "p", tlsGood)
	_ = startNode(t, "peer", freePort(t), rp1, []int{rp0}, "u", "p", tlsPeer)
	waitRoutes(t, good, 1)
	base := stableRouteCount(t, good)

	impostor := startNode(t, "impostor", freePort(t), freePort(t), []int{rp0}, "u", "p", tlsImpostor)
	time.Sleep(2 * time.Second)
	if n := impostor.NumRoutes(); n != 0 {
		t.Fatalf("impostor with unsigned cert formed %d routes, want 0", n)
	}
	if n := good.NumRoutes(); n != base {
		t.Fatalf("legit node route count changed from %d to %d after unsigned impostor attempt (it accepted the impostor)", base, n)
	}
}

// --- cert helpers ------------------------------------------------------------

type clusterTLS struct{ cert, key, ca string } // PEM file paths

// genCA creates a self-signed ECDSA CA certificate and its key.
func genCA(t *testing.T) (*x509.Certificate, *ecdsa.PrivateKey) {
	t.Helper()
	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatalf("gen CA key: %v", err)
	}
	tmpl := &x509.Certificate{
		SerialNumber:          big.NewInt(1),
		Subject:               pkix.Name{CommonName: "unibus-test-CA"},
		NotBefore:             time.Now().Add(-time.Hour),
		NotAfter:              time.Now().Add(24 * time.Hour),
		KeyUsage:              x509.KeyUsageCertSign | x509.KeyUsageDigitalSignature,
		BasicConstraintsValid: true,
		IsCA:                  true,
	}
	der, err := x509.CreateCertificate(rand.Reader, tmpl, tmpl, &key.PublicKey, key)
	if err != nil {
		t.Fatalf("create CA cert: %v", err)
	}
	caCert, err := x509.ParseCertificate(der)
	if err != nil {
		t.Fatalf("parse CA cert: %v", err)
	}
	return caCert, key
}

// writeNodeCert issues a node certificate signed by ca (SAN 127.0.0.1/::1,
// usable as both server and client) and writes cert/key/ca PEM files, returning
// their paths for RouteTLSConfig.
func writeNodeCert(t *testing.T, dir, name string, ca *x509.Certificate, caKey *ecdsa.PrivateKey) *clusterTLS {
	t.Helper()
	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatalf("gen node key: %v", err)
	}
	tmpl := &x509.Certificate{
		SerialNumber: big.NewInt(time.Now().UnixNano()),
		Subject:      pkix.Name{CommonName: name},
		NotBefore:    time.Now().Add(-time.Hour),
		NotAfter:     time.Now().Add(24 * time.Hour),
		KeyUsage:     x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth},
		IPAddresses:  []net.IP{net.ParseIP("127.0.0.1"), net.ParseIP("::1")},
		DNSNames:     []string{"localhost"},
	}
	der, err := x509.CreateCertificate(rand.Reader, tmpl, ca, &key.PublicKey, caKey)
	if err != nil {
		t.Fatalf("create node cert: %v", err)
	}
	certPath := filepath.Join(dir, name+".crt")
	keyPath := filepath.Join(dir, name+".key")
	caPath := filepath.Join(dir, name+"-ca.crt")

	writePEM(t, certPath, "CERTIFICATE", der)
	keyDER, err := x509.MarshalECPrivateKey(key)
	if err != nil {
		t.Fatalf("marshal node key: %v", err)
	}
	writePEM(t, keyPath, "EC PRIVATE KEY", keyDER)
	writePEM(t, caPath, "CERTIFICATE", ca.Raw)
	return &clusterTLS{cert: certPath, key: keyPath, ca: caPath}
}

func writePEM(t *testing.T, path, blockType string, der []byte) {
	t.Helper()
	b := pem.EncodeToMemory(&pem.Block{Type: blockType, Bytes: der})
	if err := os.WriteFile(path, b, 0o600); err != nil {
		t.Fatalf("write %s: %v", path, err)
	}
}