[#137] sdk: Implement netmap filtering and selection

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

pkg/netmap/context.go

@@ -0,0 +1,81 @@
+package netmap
+
+import (
+	"errors"
+
+	"github.com/nspcc-dev/hrw"
+	"github.com/nspcc-dev/neofs-api-go/v2/netmap"
+)
+
+// Context contains references to named filters and cached numeric values.
+type Context struct {
+	// Netmap is a netmap structure to operate on.
+	Netmap *Netmap
+	// Filters stores processed filters.
+	Filters map[string]*netmap.Filter
+	// Selectors stores processed selectors.
+	Selectors map[string]*netmap.Selector
+	// Selections stores result of selector processing.
+	Selections map[string][]Nodes
+
+	// numCache stores parsed numeric values.
+	numCache map[*netmap.Filter]uint64
+	// pivot is a seed for HRW.
+	pivot []byte
+	// pivotHash is a saved HRW hash of pivot
+	pivotHash uint64
+	// aggregator is returns aggregator determining bucket weight.
+	// By default it returns mean value from IQR interval.
+	aggregator func() aggregator
+	// weightFunc is a weighting function for determining node priority.
+	// By default in combines favours low price and high capacity.
+	weightFunc weightFunc
+}
+
+// Various validation errors.
+var (
+	ErrMissingField      = errors.New("netmap: nil field")
+	ErrInvalidFilterName = errors.New("netmap: filter name is invalid")
+	ErrInvalidNumber     = errors.New("netmap: number value expected")
+	ErrInvalidFilterOp   = errors.New("netmap: invalid filter operation")
+	ErrFilterNotFound    = errors.New("netmap: filter not found")
+	ErrNonEmptyFilters   = errors.New("netmap: simple filter must no contain sub-filters")
+	ErrNotEnoughNodes    = errors.New("netmap: not enough nodes to SELECT from")
+	ErrSelectorNotFound  = errors.New("netmap: selector not found")
+	ErrUnnamedTopFilter  = errors.New("netmap: all filters on top level must be named")
+)
+
+// NewContext creates new context. It contains various caches.
+// In future it may create hierarchical netmap structure to work with.
+func NewContext(nm *Netmap) *Context {
+	return &Context{
+		Netmap:     nm,
+		Filters:    make(map[string]*netmap.Filter),
+		Selectors:  make(map[string]*netmap.Selector),
+		Selections: make(map[string][]Nodes),
+
+		numCache:   make(map[*netmap.Filter]uint64),
+		aggregator: newMeanIQRAgg,
+		weightFunc: GetDefaultWeightFunc(nm.Nodes),
+	}
+}
+
+func (c *Context) setPivot(pivot []byte) {
+	if len(pivot) != 0 {
+		c.pivot = pivot
+		c.pivotHash = hrw.Hash(pivot)
+	}
+}
+
+// GetDefaultWeightFunc returns default weighting function.
+func GetDefaultWeightFunc(ns Nodes) weightFunc {
+	mean := newMeanAgg()
+	min := newMinAgg()
+	for i := range ns {
+		mean.Add(float64(ns[i].Capacity))
+		min.Add(float64(ns[i].Price))
+	}
+	return newWeightFunc(
+		newSigmoidNorm(mean.Compute()),
+		newReverseMinNorm(min.Compute()))
+}