package main

import "testing"

func newWindow() *lossWindow {
	w := newLossWindows(1)
	return &w[0]
}

func TestLossWindowContiguousLosesNothing(t *testing.T) {
	w := newWindow()
	for seq := uint64(0); seq < lossSlots+1000; seq++ {
		w.observe(seq)
	}
	if got := w.lost.Load(); got != 0 {
		t.Errorf("lost = %d, want 0", got)
	}
	if got := w.late.Load(); got != 0 {
		t.Errorf("late = %d, want 0", got)
	}
}

func TestLossWindowCountsGapOnceEvicted(t *testing.T) {
	w := newWindow()
	for seq := uint64(0); seq < lossSlots+1000; seq++ {
		if seq == 100 {
			continue
		}
		w.observe(seq)
	}
	if got := w.lost.Load(); got != 1 {
		t.Errorf("lost = %d, want 1", got)
	}
}

// Arriving out of order inside the window is not loss: a sequence is only
// judged once it falls out the far end.
func TestLossWindowOutOfOrderIsNotLoss(t *testing.T) {
	w := newWindow()
	for seq := uint64(99); ; seq-- {
		w.observe(seq)
		if seq == 0 {
			break
		}
	}
	for seq := uint64(100); seq < lossSlots+1000; seq++ {
		w.observe(seq)
	}
	if got := w.lost.Load(); got != 0 {
		t.Errorf("lost = %d, want 0", got)
	}
}

// The other branch of evict: a jump past a whole window writes off everything
// the window held plus the sequences that never landed in it at all.
func TestLossWindowJumpBeyondWindow(t *testing.T) {
	w := newWindow()
	w.observe(0)
	w.observe(200000)

	// Everything below the new base except the one sequence that was seen.
	want := uint64(200000 - lossSlots + 1 - 1)
	if got := w.lost.Load(); got != want {
		t.Errorf("lost = %d, want %d", got, want)
	}
	if got := w.late.Load(); got != 0 {
		t.Errorf("late = %d, want 0", got)
	}
}

func TestLossWindowBelowBaseIsLate(t *testing.T) {
	w := newWindow()
	w.observe(100000)
	w.observe(1000)
	if got := w.late.Load(); got != 1 {
		t.Errorf("late = %d, want 1", got)
	}
	if got := w.lost.Load(); got != 0 {
		t.Errorf("lost = %d, want 0", got)
	}
}

// The first sequence seen starts the window half a span below it, so frames
// another worker is still holding land inside rather than arriving late.
func TestLossWindowStartsHalfAWindowBack(t *testing.T) {
	w := newWindow()
	w.observe(100000)
	if w.base != 100000-lossSlots/2 {
		t.Errorf("base = %d, want %d", w.base, 100000-lossSlots/2)
	}
}