[#265] innerring: Select containers to audit

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/innerring/processors/audit/scheduler.go

@@ -0,0 +1,60 @@
+package audit
+
+import (
+	"sort"
+	"strings"
+
+	"github.com/nspcc-dev/neofs-api-go/pkg/container"
+	"github.com/nspcc-dev/neofs-node/pkg/innerring/invoke"
+	"github.com/pkg/errors"
+)
+
+var ErrInvalidIRNode = errors.New("node is not in the inner ring list")
+
+func (ap *Processor) selectContainersToAudit(epoch uint64) ([]*container.ID, error) {
+	containers, err := invoke.ListContainers(ap.morphClient, ap.containerContract)
+	if err != nil {
+		return nil, errors.Wrap(err, "can't get list of containers to start audit")
+	}
+
+	// consider getting extra information about container complexity from
+	// audit contract there
+
+	sort.Slice(containers, func(i, j int) bool {
+		return strings.Compare(containers[i].String(), containers[j].String()) < 0
+	})
+
+	ind := ap.irList.Index()
+	irSize := ap.irList.InnerRingSize()
+
+	if ind < 0 || ind >= irSize {
+		return nil, ErrInvalidIRNode
+	}
+
+	return Select(containers, epoch, uint64(ind), uint64(irSize)), nil
+}
+
+func Select(ids []*container.ID, epoch, index, size uint64) []*container.ID {
+	if index >= size {
+		return nil
+	}
+
+	var a, b uint64
+
+	ln := uint64(len(ids))
+	pivot := ln % size
+	delta := ln / size
+
+	index = (index + epoch) % size
+	if index < pivot {
+		a = delta + 1
+	} else {
+		a = delta
+		b = pivot
+	}
+
+	from := a*index + b
+	to := a*(index+1) + b
+
+	return ids[from:to]
+}