package broker_test

import (
	"testing"
	"time"

	"github.com/uopi/uopi/internal/broker"
)

// BenchmarkFanOut measures the end-to-end latency and throughput of the broker
// fan-out with varying numbers of downstream clients.

func BenchmarkFanOut1Client(b *testing.B)    { benchFanOut(b, 1) }
func BenchmarkFanOut10Clients(b *testing.B)  { benchFanOut(b, 10) }
func BenchmarkFanOut20Clients(b *testing.B)  { benchFanOut(b, 20) }
func BenchmarkFanOut100Clients(b *testing.B) { benchFanOut(b, 100) }

func benchFanOut(b *testing.B, nClients int) {
	b.Helper()

	brk, cancel := newBroker(b)
	defer cancel()

	ref := broker.SignalRef{DS: "stub", Name: "counter_fast"}

	// Subscribe N downstream clients.
	type sub struct {
		ch     chan broker.Update
		cancel func()
	}
	subs := make([]sub, nClients)
	for i := range subs {
		ch := make(chan broker.Update, 512)
		cancelFn, err := brk.Subscribe(ref, ch)
		if err != nil {
			b.Skip("signal not available:", err)
		}
		subs[i] = sub{ch, cancelFn}
	}
	defer func() {
		for _, s := range subs {
			s.cancel()
		}
	}()

	// Warm-up: wait for the first update to arrive on every client.
	timeout := time.After(3 * time.Second)
	for _, s := range subs {
		select {
		case <-s.ch:
		case <-timeout:
			b.Skip("timed out waiting for first update — signal may not exist in stub")
		}
	}

	b.ResetTimer()
	b.ReportAllocs()

	for range b.N {
		// Drain one update from every client channel.
		for _, s := range subs {
			select {
			case <-s.ch:
			case <-time.After(2 * time.Second):
				b.Fatal("timed out waiting for update")
			}
		}
	}
}

// newBroker is defined in broker_test.go (same package broker_test) and shared
// across test files.  It returns a broker pre-populated with the stub DS.

// BenchmarkSubscribeUnsubscribe measures the overhead of adding and removing
// a subscription (the fast path — signal is already active).
func BenchmarkSubscribeUnsubscribe(b *testing.B) {
	brk, cancel := newBroker(b)
	defer cancel()

	ref := broker.SignalRef{DS: "stub", Name: "sine_1hz"}

	// Prime the signal so the fanOut goroutine exists.
	ch0 := make(chan broker.Update, 256)
	unsub0, err := brk.Subscribe(ref, ch0)
	if err != nil {
		b.Fatal(err)
	}
	defer unsub0()

	b.ResetTimer()
	b.ReportAllocs()

	for range b.N {
		ch := make(chan broker.Update, 16)
		unsub, err := brk.Subscribe(ref, ch)
		if err != nil {
			b.Fatal(err)
		}
		unsub()
	}
}