package l7

import (
	"context"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"io"
	"log/slog"
	"math/big"
	"net"
	"net/http"
	"net/netip"
	"os"
	"path/filepath"
	"testing"
	"time"

	"golang.org/x/net/http2"
	"golang.org/x/net/http2/h2c"
)

// testCert generates a self-signed TLS certificate for the given hostname
// and writes the cert/key to temporary files, returning their paths.
func testCert(t *testing.T, hostname string) (certPath, keyPath string) {
	t.Helper()

	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatalf("generating key: %v", err)
	}

	tmpl := &x509.Certificate{
		SerialNumber: big.NewInt(1),
		Subject:      pkix.Name{CommonName: hostname},
		DNSNames:     []string{hostname},
		NotBefore:    time.Now().Add(-time.Hour),
		NotAfter:     time.Now().Add(time.Hour),
		KeyUsage:     x509.KeyUsageDigitalSignature,
		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
	}

	certDER, err := x509.CreateCertificate(rand.Reader, tmpl, tmpl, &key.PublicKey, key)
	if err != nil {
		t.Fatalf("creating certificate: %v", err)
	}

	dir := t.TempDir()
	certPath = filepath.Join(dir, "cert.pem")
	keyPath = filepath.Join(dir, "key.pem")

	certFile, err := os.Create(certPath)
	if err != nil {
		t.Fatalf("creating cert file: %v", err)
	}
	pem.Encode(certFile, &pem.Block{Type: "CERTIFICATE", Bytes: certDER})
	certFile.Close()

	keyDER, err := x509.MarshalECPrivateKey(key)
	if err != nil {
		t.Fatalf("marshaling key: %v", err)
	}
	keyFile, err := os.Create(keyPath)
	if err != nil {
		t.Fatalf("creating key file: %v", err)
	}
	pem.Encode(keyFile, &pem.Block{Type: "EC PRIVATE KEY", Bytes: keyDER})
	keyFile.Close()

	return certPath, keyPath
}

// startH2CBackend starts an h2c (HTTP/2 cleartext) backend server that
// responds with the given status and body. Returns the listener address.
func startH2CBackend(t *testing.T, handler http.Handler) string {
	t.Helper()

	h2s := &http2.Server{}
	srv := &http.Server{
		Handler:           h2c.NewHandler(handler, h2s),
		ReadHeaderTimeout: 5 * time.Second,
	}

	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("listen: %v", err)
	}
	t.Cleanup(func() {
		srv.Close()
		ln.Close()
	})

	go srv.Serve(ln)
	return ln.Addr().String()
}

// dialTLSToProxy dials a TCP connection to the proxy, does a TLS handshake
// with the given serverName (skipping cert verification for self-signed),
// and returns an *http.Client configured to use that connection for HTTP/2.
func dialTLSToProxy(t *testing.T, proxyAddr, serverName string) *http.Client {
	t.Helper()

	tlsConf := &tls.Config{
		ServerName:         serverName,
		InsecureSkipVerify: true,
		NextProtos:         []string{"h2"},
	}

	conn, err := tls.DialWithDialer(
		&net.Dialer{Timeout: 5 * time.Second},
		"tcp", proxyAddr, tlsConf,
	)
	if err != nil {
		t.Fatalf("TLS dial: %v", err)
	}
	t.Cleanup(func() { conn.Close() })

	// Create an HTTP/2 client transport over this single connection.
	tr := &http2.Transport{}
	h2conn, err := tr.NewClientConn(conn)
	if err != nil {
		t.Fatalf("creating h2 client conn: %v", err)
	}

	return &http.Client{
		Transport: &singleConnRoundTripper{cc: h2conn},
	}
}

// singleConnRoundTripper is an http.RoundTripper that uses a single HTTP/2
// client connection.
type singleConnRoundTripper struct {
	cc *http2.ClientConn
}

func (s *singleConnRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
	return s.cc.RoundTrip(req)
}

// serveL7Route starts l7.Serve in a goroutine for a single connection.
// Returns when the goroutine completes.
func serveL7Route(t *testing.T, conn net.Conn, peeked []byte, route RouteConfig) {
	t.Helper()
	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
	clientAddr := netip.MustParseAddrPort("203.0.113.50:12345")
	ctx := context.Background()

	go func() {
		l7Err := Serve(ctx, conn, peeked, route, clientAddr, logger)
		if l7Err != nil {
			t.Logf("l7.Serve: %v", l7Err)
		}
	}()
}

func TestL7H2CBackend(t *testing.T) {
	certPath, keyPath := testCert(t, "l7.test")

	// Start an h2c backend.
	backendAddr := startH2CBackend(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("X-Backend", "ok")
		fmt.Fprintf(w, "hello from backend, path=%s", r.URL.Path)
	}))

	// Start a TCP listener for the L7 proxy.
	proxyLn, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("proxy listen: %v", err)
	}
	defer proxyLn.Close()

	route := RouteConfig{
		Backend:        backendAddr,
		TLSCert:        certPath,
		TLSKey:         keyPath,
		ConnectTimeout: 5 * time.Second,
	}

	// Accept one connection and run L7 serve.
	go func() {
		conn, err := proxyLn.Accept()
		if err != nil {
			return
		}
		logger := slog.New(slog.NewTextHandler(io.Discard, nil))
		clientAddr := netip.MustParseAddrPort("203.0.113.50:12345")
		// No peeked bytes — the client is connecting directly with TLS.
		Serve(context.Background(), conn, nil, route, clientAddr, logger)
	}()

	// Connect as an HTTP/2 TLS client.
	client := dialTLSToProxy(t, proxyLn.Addr().String(), "l7.test")

	resp, err := client.Get(fmt.Sprintf("https://l7.test/foo"))
	if err != nil {
		t.Fatalf("GET: %v", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != 200 {
		t.Fatalf("status = %d, want 200", resp.StatusCode)
	}

	body, _ := io.ReadAll(resp.Body)
	if got := string(body); got != "hello from backend, path=/foo" {
		t.Fatalf("body = %q, want %q", got, "hello from backend, path=/foo")
	}

	if resp.Header.Get("X-Backend") != "ok" {
		t.Fatalf("X-Backend header missing or wrong")
	}
}

func TestL7ForwardingHeaders(t *testing.T) {
	certPath, keyPath := testCert(t, "headers.test")

	// Backend that echoes the forwarding headers.
	backendAddr := startH2CBackend(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintf(w, "xff=%s xfp=%s xri=%s",
			r.Header.Get("X-Forwarded-For"),
			r.Header.Get("X-Forwarded-Proto"),
			r.Header.Get("X-Real-IP"),
		)
	}))

	proxyLn, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("proxy listen: %v", err)
	}
	defer proxyLn.Close()

	route := RouteConfig{
		Backend:        backendAddr,
		TLSCert:        certPath,
		TLSKey:         keyPath,
		ConnectTimeout: 5 * time.Second,
	}

	go func() {
		conn, err := proxyLn.Accept()
		if err != nil {
			return
		}
		logger := slog.New(slog.NewTextHandler(io.Discard, nil))
		clientAddr := netip.MustParseAddrPort("203.0.113.50:12345")
		Serve(context.Background(), conn, nil, route, clientAddr, logger)
	}()

	client := dialTLSToProxy(t, proxyLn.Addr().String(), "headers.test")
	resp, err := client.Get("https://headers.test/")
	if err != nil {
		t.Fatalf("GET: %v", err)
	}
	defer resp.Body.Close()

	body, _ := io.ReadAll(resp.Body)
	want := "xff=203.0.113.50 xfp=https xri=203.0.113.50"
	if string(body) != want {
		t.Fatalf("body = %q, want %q", body, want)
	}
}

func TestL7BackendUnreachable(t *testing.T) {
	certPath, keyPath := testCert(t, "unreachable.test")

	// Find a port that nothing is listening on.
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("listen: %v", err)
	}
	deadAddr := ln.Addr().String()
	ln.Close()

	proxyLn, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("proxy listen: %v", err)
	}
	defer proxyLn.Close()

	route := RouteConfig{
		Backend:        deadAddr,
		TLSCert:        certPath,
		TLSKey:         keyPath,
		ConnectTimeout: 1 * time.Second,
	}

	go func() {
		conn, err := proxyLn.Accept()
		if err != nil {
			return
		}
		logger := slog.New(slog.NewTextHandler(io.Discard, nil))
		clientAddr := netip.MustParseAddrPort("203.0.113.50:12345")
		Serve(context.Background(), conn, nil, route, clientAddr, logger)
	}()

	client := dialTLSToProxy(t, proxyLn.Addr().String(), "unreachable.test")
	resp, err := client.Get("https://unreachable.test/")
	if err != nil {
		t.Fatalf("GET: %v", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusBadGateway {
		t.Fatalf("status = %d, want 502", resp.StatusCode)
	}
}

func TestL7MultipleRequests(t *testing.T) {
	certPath, keyPath := testCert(t, "multi.test")

	var reqCount int
	backendAddr := startH2CBackend(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		reqCount++
		fmt.Fprintf(w, "req=%d path=%s", reqCount, r.URL.Path)
	}))

	proxyLn, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("proxy listen: %v", err)
	}
	defer proxyLn.Close()

	route := RouteConfig{
		Backend:        backendAddr,
		TLSCert:        certPath,
		TLSKey:         keyPath,
		ConnectTimeout: 5 * time.Second,
	}

	go func() {
		conn, err := proxyLn.Accept()
		if err != nil {
			return
		}
		logger := slog.New(slog.NewTextHandler(io.Discard, nil))
		clientAddr := netip.MustParseAddrPort("203.0.113.50:12345")
		Serve(context.Background(), conn, nil, route, clientAddr, logger)
	}()

	client := dialTLSToProxy(t, proxyLn.Addr().String(), "multi.test")

	// Send multiple requests over the same HTTP/2 connection.
	for i := range 3 {
		path := fmt.Sprintf("/req%d", i)
		resp, err := client.Get(fmt.Sprintf("https://multi.test%s", path))
		if err != nil {
			t.Fatalf("GET %s: %v", path, err)
		}
		body, _ := io.ReadAll(resp.Body)
		resp.Body.Close()

		want := fmt.Sprintf("req=%d path=%s", i+1, path)
		if string(body) != want {
			t.Fatalf("request %d: body = %q, want %q", i, body, want)
		}
	}
}