package internal

import (
	"testing"
	"time"

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

func TestInflightOperationMustEndBeforeSwap(t *testing.T) {
	var swapped bool
	ch := make(chan struct{})

	l := StateLocker{}
	op1 := l.Start()

	go func() {
		l.SwapActiveState(func() {})
		swapped = true
		ch <- struct{}{}
	}()

	require.False(t, swapped, "Swap should wait the end of the in-flight operation.")

	l.End(op1)

	select {
	case <-ch:
		require.True(t, swapped, "Swap should've been completed. ")
	case <-time.After(50 * time.Millisecond):
		t.Fatal("Swap was not concluded after 50 milliseconds.")
	}
}

func TestEnsureIndexIsConsistent(t *testing.T) {
	l := StateLocker{}
	op1 := l.Start()
	l.End(op1)

	l.SwapActiveState(func() {})

	op2 := l.Start()
	l.End(op2)

	op3 := l.Start()
	l.End(op3)

	l.SwapActiveState(func() {})

	op4 := l.Start()
	l.End(op4)

	require.Equal(t, op1, op4, "two operations separated by two swaps should have the same index.")
	require.Equal(t, op2, op3, "two operations with no swap in between should have the same index.")

	require.Equal(t, 0, op1, "first index should be 0")
	require.Equal(t, 1, op2, "second index should be 1")
}

func TestTwoSwapsCanHappenWithoutOperationsInBetween(t *testing.T) {
	l := StateLocker{}

	require.Equal(t, 1, l.ColdIdx(), "first cold index should be 1")
	l.SwapActiveState(func() {})
	require.Equal(t, 0, l.ColdIdx(), "second cold index should be 0")
	l.SwapActiveState(func() {})
	require.Equal(t, 1, l.ColdIdx(), "third cold index should be 1")
}

func BenchmarkStateLocker_StartEnd(b *testing.B) {
	l := StateLocker{}

	b.ReportAllocs()

	for i := 0; i < b.N; i++ {
		l.End(l.Start())
	}
}

func BenchmarkStateLocker_SwapActiveState(b *testing.B) {

	b.ReportAllocs()

	for i := 0; i < b.N; i++ {
		l := StateLocker{}
		l.SwapActiveState(func() {})
	}
}