package smtp2shoutrrr

import (
	"context"
	"net"
	"testing"
	"time"

	"github.com/stretchr/testify/require"
)

// loopbackAddr rewrites the bound address to a dialable loopback address.
// The host stays "localhost" because smtp.PlainAuth refuses to authenticate
// when the dialed host differs from the one it was constructed with. It
// reports "" rather than failing the test, because it runs inside
// require.Eventually conditions, which execute on their own goroutine where
// t.FailNow would deadlock instead of reporting.
func loopbackAddr(s *Server) string {
	_, port, err := net.SplitHostPort(s.Addr())
	if err != nil {
		return ""
	}
	return net.JoinHostPort("localhost", port)
}

func canDial(addr string) bool {
	if addr == "" {
		return false
	}
	conn, err := net.DialTimeout("tcp", addr, 200*time.Millisecond)
	if err != nil {
		return false
	}
	return conn.Close() == nil
}

// startServer starts srv on an ephemeral port and blocks until it is bound,
// returning the dial address and the channel Start returns on. Readiness is
// the bind rather than a probe connection: the address is set before Serve
// runs, connections queue in the backlog either way, and a probe that opens
// and drops a connection only adds accept churn and server-side log noise.
func startServer(t *testing.T, srv *Server) (string, context.CancelFunc, <-chan error) {
	t.Helper()

	ctx, cancel := context.WithCancel(context.Background())
	t.Cleanup(cancel)

	stopped := make(chan error, 1)
	go func() {
		stopped <- srv.Start(ctx)
	}()

	require.Eventually(t, func() bool {
		return srv.Addr() != "" || len(stopped) > 0
	}, 5*time.Second, 10*time.Millisecond, "server never started listening")

	// Report why Start gave up rather than letting it look like a slow bind.
	select {
	case err := <-stopped:
		require.NoError(t, err, "server failed to start")
		t.Fatal("server stopped before it began serving")
	default:
	}

	return loopbackAddr(srv), cancel, stopped
}

func testConfig() *Config {
	return &Config{Port: 0, Username: "testuser", Password: "testpass"}
}

func TestServerShutsDownOnContextCancel(t *testing.T) {
	srv := NewSMTPServer(testConfig())
	addr, cancel, stopped := startServer(t, srv)

	cancel()

	select {
	case err := <-stopped:
		require.NoError(t, err)
	case <-time.After(defaultShutdownTimeout + time.Second):
		t.Fatal("server did not shut down after context cancellation")
	}

	require.False(t, canDial(addr), "listener should be released once Start returns")
}

func TestServerStartReturnsListenError(t *testing.T) {
	blocker, err := net.Listen("tcp", "127.0.0.1:0")
	require.NoError(t, err)
	t.Cleanup(func() { _ = blocker.Close() })

	_, port, err := net.SplitHostPort(blocker.Addr().String())
	require.NoError(t, err)

	config := testConfig()
	config.Port = mustAtoi(t, port)

	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	t.Cleanup(cancel)

	require.Error(t, NewSMTPServer(config).Start(ctx))
}

// Regression: go-smtp's Shutdown only closes listeners Serve has registered.
// When the stop won that race, Accept kept running and Start never returned —
// a SIGTERM during startup left a process that only SIGKILL could clear.
func TestServerStartReturnsWhenCancelledBeforeListening(t *testing.T) {
	srv := NewSMTPServer(testConfig())

	ctx, cancel := context.WithCancel(context.Background())
	cancel()

	stopped := make(chan error, 1)
	go func() {
		stopped <- srv.Start(ctx)
	}()

	select {
	case err := <-stopped:
		require.NoError(t, err)
	case <-time.After(10 * time.Second):
		t.Fatal("Start did not return when its context was cancelled before the listener registered")
	}

	require.False(t, canDial(loopbackAddr(srv)), "listener should not be left accepting connections")
}

// Regression: an idle client is only dropped once its read deadline expires,
// so the drain lasts about ReadTimeout. With the shutdown budget set to the
// same value, an ordinary stop surfaced as "context deadline exceeded" and the
// command turned that into a non-zero exit.
func TestServerDrainsIdleConnectionWithoutError(t *testing.T) {
	srv := NewSMTPServer(testConfig())
	srv.backend.ReadTimeout = 300 * time.Millisecond

	addr, cancel, stopped := startServer(t, srv)

	conn, err := net.DialTimeout("tcp", addr, time.Second)
	require.NoError(t, err)
	t.Cleanup(func() { _ = conn.Close() })

	cancel()

	select {
	case err := <-stopped:
		require.NoError(t, err, "an intentional shutdown must not report an error")
	case <-time.After(defaultShutdownTimeout + time.Second):
		t.Fatal("server did not drain the idle connection")
	}
}

// The drain waits out a client's read deadline, so the budget needs real room
// above it. A strict inequality is not enough: a budget one millisecond over
// readTimeout is the same coin flip as one equal to it.
func TestShutdownBudgetLeavesMarginOverReadTimeout(t *testing.T) {
	require.GreaterOrEqual(t, defaultShutdownTimeout, readTimeout+10*time.Second)
}

// Regression: overrunning the drain budget is still an intentional stop.
// Returning that deadline as an error made the command exit non-zero on a
// routine SIGTERM. Driven with a real overrun — a client that stays connected
// past a deliberately short budget — rather than asserted on the constant.
func TestServerReportsNoErrorWhenDrainOverrunsBudget(t *testing.T) {
	srv := NewSMTPServer(testConfig())
	// Long enough that the session outlives the budget, short enough that it
	// does not outlive the test binary.
	srv.backend.ReadTimeout = 3 * time.Second
	srv.shutdownTimeout = 300 * time.Millisecond

	addr, cancel, stopped := startServer(t, srv)

	conn, err := net.DialTimeout("tcp", addr, time.Second)
	require.NoError(t, err)
	t.Cleanup(func() { _ = conn.Close() })

	// Wait for the greeting so the session is registered and genuinely in
	// flight when the drain starts.
	_ = conn.SetReadDeadline(time.Now().Add(2 * time.Second))
	buf := make([]byte, 64)
	_, err = conn.Read(buf)
	require.NoError(t, err)

	start := time.Now()
	cancel()

	select {
	case err := <-stopped:
		require.NoError(t, err, "a drain that outruns its budget is still an intentional stop")
	case <-time.After(srv.backend.ReadTimeout + 5*time.Second):
		t.Fatal("Start did not return after the drain budget expired")
	}

	require.Less(t, time.Since(start), srv.backend.ReadTimeout,
		"Start should return on the budget, not wait out the read deadline")
}

func mustAtoi(t *testing.T, s string) int {
	t.Helper()

	n, err := net.LookupPort("tcp", s)
	require.NoError(t, err)

	return n
}