package bus

import (
	"context"
	"errors"
	"sync"
	"testing"
	"time"
)

// recvWithTimeout blocks until a value is delivered or the deadline passes,
// failing the test on timeout. It makes delivery assertions deterministic
// instead of relying on a bare sleep.
func recvWithTimeout[T any](t *testing.T, ch <-chan T, timeout time.Duration) T {
	t.Helper()
	select {
	case v := <-ch:
		return v
	case <-time.After(timeout):
		t.Fatalf("timed out waiting for a delivery after %v", timeout)
		var zero T
		return zero
	}
}

// assertNoRecv fails if a value arrives on ch within d. It is used for the
// negative cases where the registration is already gone, so nothing is ever
// enqueued and the channel stays empty.
func assertNoRecv[T any](t *testing.T, ch <-chan T, d time.Duration) {
	t.Helper()
	select {
	case v := <-ch:
		t.Fatalf("unexpected delivery: %v", v)
	case <-time.After(d):
	}
}

// waitSubs polls the registry until it holds exactly want subscriptions, with a
// deadline, so context-cancellation behavior can be asserted deterministically.
func waitSubs(t *testing.T, b *busImpl, want int) {
	t.Helper()
	deadline := time.Now().Add(2 * time.Second)
	for {
		b.mu.RLock()
		got := len(b.subs)
		b.mu.RUnlock()
		if got == want {
			return
		}
		if time.Now().After(deadline) {
			t.Fatalf("subscriber count = %d, want %d", got, want)
		}
		time.Sleep(time.Millisecond)
	}
}

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

	tests := []struct {
		name    string
		pattern string
		subject string
		want    bool
	}{
		{name: "exact match", pattern: "runtime.loop.start", subject: "runtime.loop.start", want: true},
		{name: "exact mismatch", pattern: "runtime.loop.start", subject: "runtime.loop.stop", want: false},
		{name: "exact subject has more tokens", pattern: "runtime.loop", subject: "runtime.loop.start", want: false},
		{name: "exact subject has fewer tokens", pattern: "runtime.loop.start", subject: "runtime", want: false},
		{name: "gt matches nested", pattern: "runtime.>", subject: "runtime.loop.start", want: true},
		{name: "gt matches one child", pattern: "runtime.>", subject: "runtime.loop", want: true},
		{name: "gt does not match parent", pattern: "runtime.>", subject: "runtime", want: false},
		{name: "gt alone matches nested", pattern: ">", subject: "runtime.loop.start", want: true},
		{name: "gt alone matches single", pattern: ">", subject: "runtime", want: true},
		{name: "star matches one token", pattern: "runtime.*.start", subject: "runtime.loop.start", want: true},
		{name: "star rejects extra token", pattern: "runtime.*.start", subject: "runtime.loop.x.start", want: false},
		{name: "star rejects value mismatch", pattern: "runtime.*.start", subject: "runtime.loop.stop", want: false},
		{name: "star alone matches single", pattern: "*", subject: "runtime", want: true},
	}
	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()
			if got := match(tt.pattern, tt.subject); got != tt.want {
				t.Errorf("match(%q, %q) = %v, want %v", tt.pattern, tt.subject, got, tt.want)
			}
		})
	}
}

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

	b := New()
	defer b.Close()
	got := make(chan any, 4)

	if _, err := b.Subscribe(context.Background(), "runtime.loop.start", func(ctx context.Context, e Event) error {
		got <- e.Payload
		return nil
	}); err != nil {
		t.Fatalf("Subscribe: %v", err)
	}

	if err := b.Publish(context.Background(), "runtime.loop.start", "hit"); err != nil {
		t.Fatalf("Publish: %v", err)
	}
	if p := recvWithTimeout(t, got, 2*time.Second); p != "hit" {
		t.Fatalf("payload = %v, want hit", p)
	}

	if err := b.Publish(context.Background(), "runtime.loop.stop", "miss"); err != nil {
		t.Fatalf("Publish: %v", err)
	}
	assertNoRecv(t, got, 100*time.Millisecond)
}

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

	b := New()
	defer b.Close()
	got := make(chan any, 4)

	if _, err := b.Subscribe(context.Background(), "runtime.>", func(ctx context.Context, e Event) error {
		got <- e.Payload
		return nil
	}); err != nil {
		t.Fatalf("Subscribe: %v", err)
	}

	for _, subject := range []string{"runtime.loop.start", "runtime.loop", "runtime.loop.a.b"} {
		if err := b.Publish(context.Background(), subject, subject); err != nil {
			t.Fatalf("Publish(%q): %v", subject, err)
		}
		if p := recvWithTimeout(t, got, 2*time.Second); p != subject {
			t.Fatalf("payload = %v, want %q", p, subject)
		}
	}

	// "runtime.>" must not match the exact "runtime", and a different root
	// must not match at all.
	if err := b.Publish(context.Background(), "runtime", "miss-root"); err != nil {
		t.Fatalf("Publish: %v", err)
	}
	if err := b.Publish(context.Background(), "other.x", "miss-other"); err != nil {
		t.Fatalf("Publish: %v", err)
	}
	assertNoRecv(t, got, 100*time.Millisecond)
}

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

	b := New()
	defer b.Close()
	got := make(chan any, 4)

	if _, err := b.Subscribe(context.Background(), "runtime.*.start", func(ctx context.Context, e Event) error {
		got <- e.Payload
		return nil
	}); err != nil {
		t.Fatalf("Subscribe: %v", err)
	}

	if err := b.Publish(context.Background(), "runtime.loop.start", "hit"); err != nil {
		t.Fatalf("Publish: %v", err)
	}
	if p := recvWithTimeout(t, got, 2*time.Second); p != "hit" {
		t.Fatalf("payload = %v, want hit", p)
	}

	for _, subject := range []string{"runtime.loop.x.start", "runtime.loop.stop", "runtime.loop"} {
		if err := b.Publish(context.Background(), subject, "miss"); err != nil {
			t.Fatalf("Publish(%q): %v", subject, err)
		}
	}
	assertNoRecv(t, got, 100*time.Millisecond)
}

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

	b := New()
	defer b.Close()
	got := make(chan any, 2)

	unsub, err := b.Subscribe(context.Background(), "a.b", func(ctx context.Context, e Event) error {
		got <- e.Payload
		return nil
	})
	if err != nil {
		t.Fatalf("Subscribe: %v", err)
	}

	if err := b.Publish(context.Background(), "a.b", "first"); err != nil {
		t.Fatalf("Publish: %v", err)
	}
	if p := recvWithTimeout(t, got, 2*time.Second); p != "first" {
		t.Fatalf("payload = %v, want first", p)
	}

	unsub()
	if err := b.Publish(context.Background(), "a.b", "second"); err != nil {
		t.Fatalf("Publish: %v", err)
	}
	assertNoRecv(t, got, 100*time.Millisecond)
}

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

	b := New()
	defer b.Close()

	started := make(chan struct{})
	release := make(chan struct{})
	var once sync.Once
	handler := func(ctx context.Context, e Event) error {
		once.Do(func() { close(started) })
		<-release
		return nil
	}
	if _, err := b.Subscribe(context.Background(), "slow", handler); err != nil {
		t.Fatalf("Subscribe: %v", err)
	}

	if err := b.Publish(context.Background(), "slow", "payload"); err != nil {
		t.Fatalf("Publish: %v", err)
	}

	// The handler started and is still blocked on release. Because Publish has
	// already returned, it did not wait for the handler to finish.
	select {
	case <-started:
	case <-time.After(2 * time.Second):
		t.Fatal("handler did not start")
	}
	select {
	case <-release:
		t.Fatal("handler finished before release was closed")
	case <-time.After(50 * time.Millisecond):
	}
	close(release)
}

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

	b := New()
	defer b.Close()
	got := make(chan any, 1)

	if _, err := b.Subscribe(context.Background(), "a.b", func(ctx context.Context, e Event) error {
		got <- e.Payload
		return nil
	}); err != nil {
		t.Fatalf("Subscribe: %v", err)
	}

	if err := b.Publish(context.Background(), "a.b", "before-close"); err != nil {
		t.Fatalf("Publish: %v", err)
	}
	if p := recvWithTimeout(t, got, 2*time.Second); p != "before-close" {
		t.Fatalf("payload = %v, want before-close", p)
	}

	if err := b.Close(); err != nil {
		t.Fatalf("Close: %v", err)
	}
	if err := b.Publish(context.Background(), "a.b", "after-close"); !errors.Is(err, ErrClosed) {
		t.Fatalf("Publish after Close error = %v, want ErrClosed", err)
	}
	assertNoRecv(t, got, 100*time.Millisecond)
}

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

	b := New()
	defer b.Close()

	for _, subject := range []string{"", ".a", "a.", "a..b"} {
		err := b.Publish(context.Background(), subject, "x")
		if !errors.Is(err, ErrInvalidArgument) {
			t.Errorf("Publish(%q) error = %v, want ErrInvalidArgument", subject, err)
		}
	}
}

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

	b := New()
	defer b.Close()

	for _, pattern := range []string{"", ".a", "a.", "a..b", "a.>.b"} {
		_, err := b.Subscribe(context.Background(), pattern, func(ctx context.Context, e Event) error { return nil })
		if !errors.Is(err, ErrInvalidArgument) {
			t.Errorf("Subscribe(%q) error = %v, want ErrInvalidArgument", pattern, err)
		}
	}
}

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

	b := New()
	defer b.Close()

	_, err := b.Subscribe(context.Background(), "a.b", nil)
	if !errors.Is(err, ErrInvalidArgument) {
		t.Fatalf("Subscribe(nil) error = %v, want ErrInvalidArgument", err)
	}
}

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

	b := New()
	if err := b.Close(); err != nil {
		t.Fatalf("Close: %v", err)
	}

	if err := b.Publish(context.Background(), "a.b", "x"); !errors.Is(err, ErrClosed) {
		t.Fatalf("Publish after Close error = %v, want ErrClosed", err)
	}
	if _, err := b.Subscribe(context.Background(), "a.b", func(ctx context.Context, e Event) error { return nil }); !errors.Is(err, ErrClosed) {
		t.Fatalf("Subscribe after Close error = %v, want ErrClosed", err)
	}
	if err := b.Close(); err != nil {
		t.Fatalf("second Close error = %v, want nil", err)
	}
}

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

	b := New(WithQueueSize(1))
	defer b.Close()

	started := make(chan struct{})
	release := make(chan struct{})
	var once sync.Once
	if _, err := b.Subscribe(context.Background(), "d", func(ctx context.Context, e Event) error {
		once.Do(func() { close(started) })
		<-release
		return nil
	}); err != nil {
		t.Fatalf("Subscribe: %v", err)
	}

	if err := b.Publish(context.Background(), "d", "first"); err != nil {
		t.Fatalf("Publish first: %v", err)
	}
	select {
	case <-started:
	case <-time.After(2 * time.Second):
		t.Fatal("handler did not start; worker failed to drain")
	}

	// The worker is now blocked in the handler, so it consumed "first" and the
	// single-slot buffer is empty. The next enqueue fills it; the two after
	// that find it full and are dropped.
	for _, payload := range []string{"fill1", "fill2", "fill3"} {
		if err := b.Publish(context.Background(), "d", payload); err != nil {
			t.Fatalf("Publish %s: %v", payload, err)
		}
	}
	if got := b.Dropped(); got != 2 {
		t.Fatalf("Dropped() = %d, want 2", got)
	}
	close(release)
}

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

	b := New()
	defer b.Close()
	got := make(chan any, 1)

	ctx, cancel := context.WithCancel(context.Background())
	if _, err := b.Subscribe(ctx, "a.b", func(ctx context.Context, e Event) error {
		got <- e.Payload
		return nil
	}); err != nil {
		t.Fatalf("Subscribe: %v", err)
	}

	cancel()
	waitSubs(t, b, 0)

	if err := b.Publish(context.Background(), "a.b", "after-cancel"); err != nil {
		t.Fatalf("Publish: %v", err)
	}
	assertNoRecv(t, got, 100*time.Millisecond)
}

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

	b := New(WithQueueSize(8))
	defer b.Close()

	const workers = 8
	const iterations = 200
	var wg sync.WaitGroup
	for w := 0; w < workers; w++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for i := 0; i < iterations; i++ {
				if i%3 == 0 {
					unsub, err := b.Subscribe(context.Background(), "c", func(ctx context.Context, e Event) error {
						return nil
					})
					if err == nil {
						unsub()
					}
					continue
				}
				_ = b.Publish(context.Background(), "c", i)
				_ = b.Publish(context.Background(), "c.x", i)
			}
		}()
	}
	wg.Wait()

	if err := b.Close(); err != nil {
		t.Fatalf("Close: %v", err)
	}
}

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

	b := New()
	var wg sync.WaitGroup
	for i := 0; i < 8; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			_ = b.Publish(context.Background(), "a.b", 1)
			_, _ = b.Subscribe(context.Background(), "a.b", func(ctx context.Context, e Event) error { return nil })
			_ = b.Close()
		}()
	}
	wg.Wait()

	if err := b.Close(); err != nil {
		t.Fatalf("Close: %v", err)
	}
}