package metrics

import (
	"sync"
	"testing"
	"time"
)

// TestChurnPerMinuteCountsLastFullMinute announces and withdraws prefixes on
// an injected clock and expects each minute's whole count once that minute
// has ended, and 0 for a minute with none.
func TestChurnPerMinuteCountsLastFullMinute(t *testing.T) {
	t.Parallel()

	now := time.Date(2026, 10, 26, 12, 0, 30, 0, time.UTC)
	tracker := New()
	tracker.churnPerMinute.now = func() time.Time { return now }

	expectChurn := func(want int, why string) {
		t.Helper()

		got := tracker.GetChurnPerMinute()
		if got != want {
			t.Fatalf("at %s churn = %d, want %d: %s",
				now.Format(time.TimeOnly), got, want, why)
		}
	}

	const firstMinuteChurn = 2

	tracker.RecordAnnouncement()
	tracker.RecordWithdrawal()
	expectChurn(0, "12:00 has not ended")

	now = time.Date(2026, 10, 26, 12, 1, 59, 0, time.UTC)

	tracker.RecordAnnouncement()
	expectChurn(firstMinuteChurn, "12:00 had one announcement and one withdrawal")

	now = time.Date(2026, 10, 26, 12, 2, 0, 0, time.UTC)

	expectChurn(1, "12:01 had one announcement")

	now = time.Date(2026, 10, 26, 12, 4, 0, 0, time.UTC)

	expectChurn(0, "12:03 had none")

	tracker.RecordWithdrawal()

	now = time.Date(2026, 10, 26, 12, 6, 0, 0, time.UTC)

	expectChurn(0, "12:05 had none, though 12:04 had one withdrawal")
}

// TestChurnPerMinuteCountsConcurrentRecords announces prefixes from several
// goroutines at once and expects every one counted.
func TestChurnPerMinuteCountsConcurrentRecords(t *testing.T) {
	t.Parallel()

	const (
		goroutines          = 8
		recordsPerGoroutine = 1000
	)

	now := time.Date(2026, 10, 26, 12, 0, 0, 0, time.UTC)
	tracker := New()
	tracker.churnPerMinute.now = func() time.Time { return now }

	var wg sync.WaitGroup
	for range goroutines {
		wg.Go(func() {
			for range recordsPerGoroutine {
				tracker.RecordAnnouncement()
			}
		})
	}

	wg.Wait()

	now = now.Add(time.Minute)

	want := goroutines * recordsPerGoroutine
	if got := tracker.GetChurnPerMinute(); got != want {
		t.Fatalf("churn = %d, want %d", got, want)
	}
}