package link

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"errors"
	"math/big"
	"net"
	"strings"
	"testing"
	"time"
)

// A real TLS server with a real self-signed certificate. Not a fake: what is being tested is that
// Go's TLS stack calls this verification before the handshake completes and that a wrong
// certificate is refused there — a fake would assert that the fake refuses it
// (novox/hq ADR 0017).
func server(t *testing.T) (address string, fingerprint string) {
	t.Helper()
	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatal(err)
	}
	template := x509.Certificate{
		SerialNumber: big.NewInt(1),
		Subject:      pkix.Name{CommonName: "mesh-broker"},
		NotBefore:    time.Now().Add(-time.Hour),
		NotAfter:     time.Now().Add(time.Hour),
	}
	der, err := x509.CreateCertificate(rand.Reader, &template, &template, &key.PublicKey, key)
	if err != nil {
		t.Fatal(err)
	}

	listener, err := tls.Listen("tcp", "127.0.0.1:0", &tls.Config{
		Certificates: []tls.Certificate{{Certificate: [][]byte{der}, PrivateKey: key}},
		MinVersion:   tls.VersionTLS12,
	})
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { listener.Close() })

	go func() {
		for {
			conn, err := listener.Accept()
			if err != nil {
				return
			}
			go func() {
				// Complete the handshake, then close. Enough for a client to have checked.
				_ = conn.(*tls.Conn).Handshake()
				conn.Close()
			}()
		}
	}()
	return listener.Addr().String(), Fingerprint(der)
}

func TestTheRightBrokerIsAccepted(t *testing.T) {
	address, pin := server(t)
	conn, err := Dial(address, pin, 5*time.Second)
	if err != nil {
		t.Fatalf("the broker its token describes was refused: %v", err)
	}
	conn.Close()
}

func TestADifferentBrokerIsRefused(t *testing.T) {
	// The case the pin exists for: something else answering at that address. Since the host
	// applies whatever the link delivers, connecting to the wrong mesh is the whole machine.
	address, _ := server(t)
	_, other := server(t)

	_, err := Dial(address, other, 5*time.Second)
	if err == nil {
		t.Fatal("a broker presenting a different certificate was accepted")
	}
	if !errors.Is(err, ErrWrongCertificate) {
		t.Fatalf("refused, but not as a wrong certificate: %v", err)
	}
	if !strings.Contains(err.Error(), "retrying will not help") {
		t.Error("the error reads like a connection problem; this one must not be retried")
	}
}

func TestNothingIsSentToTheWrongBroker(t *testing.T) {
	// ADR 0004 requires the check to happen *before* anything is sent. Asserted by counting what
	// the wrong server received: a handshake, and no application bytes.
	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatal(err)
	}
	template := x509.Certificate{
		SerialNumber: big.NewInt(2),
		Subject:      pkix.Name{CommonName: "impostor"},
		NotBefore:    time.Now().Add(-time.Hour),
		NotAfter:     time.Now().Add(time.Hour),
	}
	der, err := x509.CreateCertificate(rand.Reader, &template, &template, &key.PublicKey, key)
	if err != nil {
		t.Fatal(err)
	}
	listener, err := tls.Listen("tcp", "127.0.0.1:0", &tls.Config{
		Certificates: []tls.Certificate{{Certificate: [][]byte{der}, PrivateKey: key}},
		MinVersion:   tls.VersionTLS12,
	})
	if err != nil {
		t.Fatal(err)
	}
	defer listener.Close()

	received := make(chan int, 1)
	go func() {
		conn, err := listener.Accept()
		if err != nil {
			received <- -1
			return
		}
		defer conn.Close()
		_ = conn.SetReadDeadline(time.Now().Add(2 * time.Second))
		buf := make([]byte, 512)
		n, _ := conn.Read(buf)
		received <- n
	}()

	// A pin for a certificate this server does not have.
	_, elsewhere := server(t)
	if _, err := Dial(listener.Addr().String(), elsewhere, 5*time.Second); err == nil {
		t.Fatal("the impostor was accepted")
	}
	if n := <-received; n > 0 {
		t.Errorf("%d application byte(s) reached a broker that failed the pin", n)
	}
}

func TestAMalformedPinIsRefusedBeforeConnecting(t *testing.T) {
	// Caught here rather than at the handshake, so a mistyped token fails while a person is
	// looking at it.
	for _, bad := range []string{"", "sha256:short", strings.Repeat("a", 64),
		"sha256:" + strings.Repeat("z", 64), "md5:" + strings.Repeat("a", 64)} {
		if _, err := PinnedConfig(bad); err == nil {
			t.Errorf("%q was accepted as a fingerprint", bad)
		}
	}
}

func TestAnUnreachableBrokerIsAnOrdinaryFailure(t *testing.T) {
	// Must not read as a wrong certificate: one is a network problem worth retrying, the other
	// means the mesh was substituted.
	_, pin := server(t)
	listener, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err)
	}
	address := listener.Addr().String()
	listener.Close()

	_, err = Dial(address, pin, 2*time.Second)
	if err == nil {
		t.Fatal("dialling a closed port succeeded")
	}
	if errors.Is(err, ErrWrongCertificate) {
		t.Error("an unreachable broker was reported as presenting the wrong certificate")
	}
}