[#137] sdk: Implement netmap filtering and selection

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/netmap/selector.go

@@ -0,0 +1,98 @@
+package netmap
+
+import (
+	"fmt"
+	"sort"
+
+	"github.com/nspcc-dev/hrw"
+	"github.com/nspcc-dev/neofs-api-go/v2/netmap"
+)
+
+// processSelectors processes selectors and returns error is any of them is invalid.
+func (c *Context) processSelectors(p *netmap.PlacementPolicy) error {
+	for _, s := range p.GetSelectors() {
+		if s == nil {
+			return fmt.Errorf("%w: SELECT", ErrMissingField)
+		} else if s.GetFilter() != MainFilterName {
+			_, ok := c.Filters[s.GetFilter()]
+			if !ok {
+				return fmt.Errorf("%w: SELECT FROM '%s'", ErrFilterNotFound, s.GetFilter())
+			}
+		}
+		c.Selectors[s.GetName()] = s
+		result, err := c.getSelection(p, s)
+		if err != nil {
+			return err
+		}
+		c.Selections[s.GetName()] = result
+	}
+	return nil
+}
+
+// GetNodesCount returns amount of buckets and nodes in every bucket
+// for a given placement policy.
+func GetNodesCount(p *netmap.PlacementPolicy, s *netmap.Selector) (int, int) {
+	switch s.GetClause() {
+	case netmap.Same:
+		return 1, int(p.GetContainerBackupFactor() * s.GetCount())
+	default:
+		return int(s.GetCount()), int(p.GetContainerBackupFactor())
+	}
+}
+
+// getSelection returns nodes grouped by s.attribute.
+func (c *Context) getSelection(p *netmap.PlacementPolicy, s *netmap.Selector) ([]Nodes, error) {
+	bucketCount, nodesInBucket := GetNodesCount(p, s)
+	m := c.getSelectionBase(s)
+	if len(m) < bucketCount {
+		return nil, fmt.Errorf("%w: '%s'", ErrNotEnoughNodes, s.GetName())
+	}
+
+	keys := make(sort.StringSlice, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	if len(c.pivot) == 0 {
+		// deterministic order in case of zero seed
+		keys.Sort()
+	}
+
+	nodes := make([]Nodes, 0, len(m))
+	for i := range keys {
+		ns := m[keys[i]]
+		if len(ns) >= nodesInBucket {
+			nodes = append(nodes, ns[:nodesInBucket])
+		}
+	}
+	if len(nodes) < bucketCount {
+		return nil, fmt.Errorf("%w: '%s'", ErrNotEnoughNodes, s.GetName())
+	}
+	if len(c.pivot) != 0 {
+		weights := make([]float64, len(nodes))
+		for i := range nodes {
+			weights[i] = GetBucketWeight(nodes[i], c.aggregator(), c.weightFunc)
+		}
+		hrw.SortSliceByWeightIndex(nodes, weights, c.pivotHash)
+	}
+	return nodes[:bucketCount], nil
+}
+
+// getSelectionBase returns nodes grouped by selector attribute.
+func (c *Context) getSelectionBase(s *netmap.Selector) map[string]Nodes {
+	f := c.Filters[s.GetFilter()]
+	isMain := s.GetFilter() == MainFilterName
+	result := map[string]Nodes{}
+	for i := range c.Netmap.Nodes {
+		if isMain || c.match(f, c.Netmap.Nodes[i]) {
+			v := c.Netmap.Nodes[i].Attribute(s.GetAttribute())
+			result[v] = append(result[v], c.Netmap.Nodes[i])
+		}
+	}
+
+	if len(c.pivot) != 0 {
+		for _, ns := range result {
+			hrw.SortSliceByWeightValue(ns, ns.Weights(c.weightFunc), c.pivotHash)
+		}
+	}
+	return result
+}