package metrics

import (
	"testing"
	"time"
)

// A read that comes back late carries the last readings meanwhile and is used when it lands;
// only one out past gpuStallAfter marks the card stalled, and its return clears that.
func TestGPUReadLateThenStalledThenBack(t *testing.T) {
	defer func(w, s time.Duration) { gpuReadWithin, gpuStallAfter = w, s }(gpuReadWithin, gpuStallAfter)
	gpuReadWithin, gpuStallAfter = 20*time.Millisecond, 10*time.Second
	release := make(chan struct{})
	n := 0.0 // only the read goroutine writes it, one read at a time
	d := &gpuDev{name: "test", card: "card0"}
	d.readFn = func(x *GPU, _ time.Time) {
		n++
		if n == 2 {
			<-release
		}
		x.Usage = n * 10
	}
	t0 := time.Now()
	sample := func(at time.Duration) GPU {
		x := GPU{Name: "test"}
		d.readWithin(&x, t0.Add(at))
		return x
	}
	if x := sample(0); x.Usage != 10 || x.Stalled {
		t.Fatalf("first: %+v", x)
	}
	if x := sample(time.Second); x.Usage != 10 || x.Stalled { // late: the last readings
		t.Fatalf("late: %+v", x)
	}
	if x := sample(5 * time.Second); x.Usage != 10 || x.Stalled {
		t.Fatalf("still late: %+v", x)
	}
	if x := sample(12 * time.Second); !x.Stalled {
		t.Fatalf("out past gpuStallAfter, not stalled: %+v", x)
	}
	if x := sample(12*time.Second + 1); !x.Stalled {
		t.Fatal("stall did not hold")
	}
	close(release)
	time.Sleep(10 * time.Millisecond)
	if x := sample(13 * time.Second); x.Usage != 20 || x.Stalled {
		t.Fatalf("back: %+v", x)
	}
	if x := sample(14 * time.Second); x.Usage != 30 || x.Stalled { // 30: no extra read ran while one was out
		t.Fatalf("next: %+v", x)
	}
}