package agent

import (
	"context"
	"math/rand"
	"sync/atomic"
	"testing"
	"time"
)

// Pieces fetched side by side are used in their order, never more than
// depth at once in flight.
func TestOrderedKeepsOrder(t *testing.T) {
	var inFlight, most int32
	var got []int
	err := ordered(context.Background(), 20, 3, func(ctx context.Context, i int) ([]byte, error) {
		n := atomic.AddInt32(&inFlight, 1)
		for {
			m := atomic.LoadInt32(&most)
			if n <= m || atomic.CompareAndSwapInt32(&most, m, n) {
				break
			}
		}
		time.Sleep(time.Duration(rand.Intn(5)) * time.Millisecond)
		atomic.AddInt32(&inFlight, -1)
		return []byte{byte(i)}, nil
	}, func(i int, b []byte) error {
		if int(b[0]) != i {
			t.Errorf("piece %d carries %d", i, b[0])
		}
		got = append(got, i)
		return nil
	})
	if err != nil || len(got) != 20 {
		t.Fatalf("got %v, %v", got, err)
	}
	for i, v := range got {
		if v != i {
			t.Fatalf("order: %v", got)
		}
	}
	if most > 3 || most < 2 {
		t.Fatalf("at most %d in flight", most)
	}
}