package streamer

import (
	"context"
	"errors"
	"io"
	"net/http"
	"net/http/httptest"
	"runtime"
	"sync/atomic"
	"testing"
	"time"

	"git.eeqj.de/sneak/routewatch/internal/logger"
	"git.eeqj.de/sneak/routewatch/internal/metrics"
	"git.eeqj.de/sneak/routewatch/internal/ristypes"
)

func TestNewStreamer(t *testing.T) {
	t.Parallel()

	logger := logger.New()
	metricsTracker := metrics.New()
	s := New(logger, metricsTracker)

	if s == nil {
		t.Fatal("New() returned nil")
	}

	if s.logger != logger {
		t.Error("logger not set correctly")
	}

	if s.client == nil {
		t.Error("HTTP client not initialized")
	}

	if s.handlers == nil {
		t.Error("handlers slice not initialized")
	}

	if s.metrics != metricsTracker {
		t.Error("metrics tracker not set correctly")
	}

	if s.idleTimeout != streamIdleTimeout {
		t.Errorf("idleTimeout = %s, want %s", s.idleTimeout, streamIdleTimeout)
	}

	if s.minBackoff != minBackoffDelay {
		t.Errorf("minBackoff = %s, want %s", s.minBackoff, minBackoffDelay)
	}
}

// TestStreamDoesNotLeakTickersAcrossReconnects drives many short-lived
// connections (each stream call is one reconnect cycle) and asserts the
// goroutine count returns to its starting value. Each connection starts two
// ticker goroutines; before the fix they lived until the streamer's lifetime
// context was cancelled, so every reconnect leaked two.
//
//nolint:paralleltest // counts goroutines, so no other test may run alongside
func TestStreamDoesNotLeakTickersAcrossReconnects(t *testing.T) {
	// The handler returns immediately, so the response body is empty and each
	// stream call ends at once, standing in for a dropped connection.
	srv := httptest.NewServer(http.HandlerFunc(
		func(_ http.ResponseWriter, _ *http.Request) {}))
	defer srv.Close()

	s := New(logger.New(), metrics.New())
	s.url = srv.URL

	// One warm-up connection so any persistent HTTP transport goroutine exists
	// before we take the baseline.
	err := s.stream(context.Background())
	if !errors.Is(err, errStreamEnded) {
		t.Fatalf("warm-up stream returned %v, want %v", err, errStreamEnded)
	}

	s.client.CloseIdleConnections()

	baseline := settledGoroutineCount()

	const reconnects = 20
	for range reconnects {
		err := s.stream(context.Background())
		if !errors.Is(err, errStreamEnded) {
			t.Fatalf("stream returned %v, want %v", err, errStreamEnded)
		}
	}

	s.client.CloseIdleConnections()

	if !waitForGoroutines(baseline) {
		t.Fatalf("goroutines did not return to baseline %d after %d reconnects, got %d",
			baseline, reconnects, runtime.NumGoroutine())
	}
}

// updateLine is one UPDATE message as RIS Live sends it.
const updateLine = `{"type":"ris_message","data":{"type":"UPDATE",` +
	`"peer":"192.0.2.1","peer_asn":"64496","timestamp":1700000000}}` + "\n"

// updateHandler wants UPDATE messages. For each one it handles it sends on
// handled if there is room, and otherwise does nothing; a nil handled is
// never sent on.
type updateHandler struct {
	handled chan struct{}
}

func (updateHandler) WantsMessage(messageType string) bool {
	return messageType == "UPDATE"
}

func (updateHandler) QueueCapacity() int { return 10 }

func (h updateHandler) HandleMessage(*ristypes.RISMessage) {
	select {
	case h.handled <- struct{}{}:
	default:
	}
}

// flush sends what w has buffered to the client. The writers httptest servers
// hand to handlers can always do that.
func flush(w http.ResponseWriter) {
	flusher, ok := w.(http.Flusher)
	if ok {
		flusher.Flush()
	}
}

// TestStopBeforeMessageReachesQueues stops the streamer after the read loop
// has checked for cancellation but before it hands the message to the handler
// queues. That is the gap a stop from another goroutine can land in, and it
// used to end in "send on closed channel". The raw handler runs in that gap on
// the read loop itself, so calling Stop from it hits the gap every time.
func TestStopBeforeMessageReachesQueues(t *testing.T) {
	t.Parallel()

	srv := httptest.NewServer(http.HandlerFunc(
		func(w http.ResponseWriter, _ *http.Request) {
			_, _ = io.WriteString(w, updateLine)
		}))
	defer srv.Close()

	s := New(logger.New(), metrics.New())
	s.url = srv.URL
	s.RegisterHandler(updateHandler{})
	s.RegisterRawHandler(func(string) { s.Stop() })

	// Start would run the stream in the background, where the test cannot
	// wait for it. Setting cancel as Start does lets Stop cancel the stream
	// run here instead.
	ctx, cancel := context.WithCancel(context.Background())
	s.cancel = cancel

	err := s.stream(ctx)
	if !errors.Is(err, context.Canceled) {
		t.Fatalf("stream returned %v, want %v", err, context.Canceled)
	}

	// A second Stop must not close the queues again.
	s.Stop()
}

// TestReconnectWhenStreamEnds has the server end the first response
// normally, as when RIS Live restarts. The streamer must treat that as a
// disconnect and connect again.
func TestReconnectWhenStreamEnds(t *testing.T) {
	t.Parallel()

	endResponse := func(http.ResponseWriter, *http.Request) {}
	checkReconnect(t, endResponse, streamIdleTimeout)
}

// TestReconnectWhenStreamGoesIdle has the server hold the first response
// open without sending anything. The streamer must drop it once the idle
// timeout passes and connect again.
func TestReconnectWhenStreamGoesIdle(t *testing.T) {
	t.Parallel()

	const idleTimeout = 50 * time.Millisecond

	holdResponse := func(w http.ResponseWriter, r *http.Request) {
		flush(w)
		<-r.Context().Done()
	}
	checkReconnect(t, holdResponse, idleTimeout)
}

// TestReconnectWhenServerNeverAnswers has the server accept the first
// request and never answer it, not even with headers. The streamer must give
// up on it once the idle timeout passes and connect again.
func TestReconnectWhenServerNeverAnswers(t *testing.T) {
	t.Parallel()

	const idleTimeout = 50 * time.Millisecond

	neverAnswer := func(_ http.ResponseWriter, r *http.Request) {
		<-r.Context().Done()
	}
	checkReconnect(t, neverAnswer, idleTimeout)
}

// TestStreamNotDroppedWhileLinesArrive has the server send lines well within
// the idle timeout for several times the timeout, then end the response. Each
// line must start the idle timeout over, so the stream lasts until the server
// ends it instead of being dropped as idle.
func TestStreamNotDroppedWhileLinesArrive(t *testing.T) {
	t.Parallel()

	const (
		idleTimeout  = 100 * time.Millisecond
		lineInterval = idleTimeout / 10
		sendFor      = 5 * idleTimeout
	)

	srv := httptest.NewServer(http.HandlerFunc(
		func(w http.ResponseWriter, _ *http.Request) {
			deadline := time.Now().Add(sendFor)
			for time.Now().Before(deadline) {
				_, _ = io.WriteString(w, updateLine)

				flush(w)
				time.Sleep(lineInterval)
			}
		}))
	defer srv.Close()

	s := New(logger.New(), metrics.New())
	s.url = srv.URL
	s.idleTimeout = idleTimeout

	err := s.stream(context.Background())
	if !errors.Is(err, errStreamEnded) {
		t.Fatalf("stream returned %v, want %v", err, errStreamEnded)
	}
}

// checkReconnect runs a streamer against a fake RIS Live server. The first
// response is served by firstResponse; every later one carries one UPDATE
// line and then stays open. The streamer must come back for a second
// response, must not be marked connected when it does, and must handle the
// UPDATE in it.
func checkReconnect(
	t *testing.T, firstResponse http.HandlerFunc, idleTimeout time.Duration,
) {
	t.Helper()

	const maxWait = 5 * time.Second

	tracker := metrics.New()
	connectedAtReconnect := make(chan bool, 1)

	var requests atomic.Int32

	srv := httptest.NewServer(http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			if requests.Add(1) == 1 {
				firstResponse(w, r)

				return
			}

			select {
			case connectedAtReconnect <- tracker.IsConnected():
			default:
			}

			_, _ = io.WriteString(w, updateLine)

			flush(w)
			<-r.Context().Done()
		}))
	defer srv.Close()

	s := New(logger.New(), tracker)
	s.url = srv.URL
	s.idleTimeout = idleTimeout
	s.minBackoff = time.Millisecond
	handler := updateHandler{handled: make(chan struct{}, 1)}
	s.RegisterHandler(handler)

	err := s.Start(t.Context())
	if err != nil {
		t.Fatalf("Start returned error: %v", err)
	}
	defer s.Stop()

	select {
	case <-handler.handled:
	case <-time.After(maxWait):
		t.Fatalf("no message from a second response handled within %s", maxWait)
	}

	if <-connectedAtReconnect {
		t.Error("streamer was still marked connected when it came back " +
			"for a second response")
	}
}

// settledGoroutineCount lets transient goroutines finish, then reports the
// current count.
func settledGoroutineCount() int {
	prev := runtime.NumGoroutine()

	for range 20 {
		time.Sleep(10 * time.Millisecond)

		cur := runtime.NumGoroutine()
		if cur == prev {
			return cur
		}

		prev = cur
	}

	return prev
}

// waitForGoroutines waits until the goroutine count drops to target or below.
func waitForGoroutines(target int) bool {
	for range 100 {
		if runtime.NumGoroutine() <= target {
			return true
		}

		time.Sleep(10 * time.Millisecond)
	}

	return false
}