[#473] Implement EigenTrust calculations

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/reputation/eigentrust/calculator/calculator.go

@@ -0,0 +1,91 @@
+package eigentrustcalc
+
+import (
+	"fmt"
+
+	"github.com/nspcc-dev/neofs-node/pkg/services/reputation"
+	"github.com/nspcc-dev/neofs-node/pkg/util"
+)
+
+// Prm groups the required parameters of the Calculator's constructor.
+//
+// All values must comply with the requirements imposed on them.
+// Passing incorrect parameter values will result in constructor
+// failure (error or panic depending on the implementation).
+type Prm struct {
+	// Alpha parameter from origin EigenTrust algortihm
+	// http://ilpubs.stanford.edu:8090/562/1/2002-56.pdf Ch.5.1.
+	//
+	// Must be in range (0, 1).
+	Alpha float64
+
+	// Source of initial node trust values
+	//
+	// Must not be nil.
+	InitialTrustSource InitialTrustSource
+
+	DaughterTrustSource DaughterTrustIteratorProvider
+
+	IntermediateValueTarget IntermediateWriterProvider
+
+	FinalResultTarget IntermediateWriterProvider
+
+	WorkerPool util.WorkerPool
+}
+
+// Calculator is a processor of a single iteration of EigenTrust algorithm.
+//
+// For correct operation, the Calculator must be created
+// using the constructor (New) based on the required parameters
+// and optional components. After successful creation,
+// the Calculator is immediately ready to work through
+// API of external control of calculations and data transfer.
+type Calculator struct {
+	alpha, beta reputation.TrustValue // beta = 1 - alpha
+
+	prm Prm
+
+	opts *options
+}
+
+const invalidPrmValFmt = "invalid parameter %s (%T):%v"
+
+func panicOnPrmValue(n string, v interface{}) {
+	panic(fmt.Sprintf(invalidPrmValFmt, n, v, v))
+}
+
+// New creates a new instance of the Calculator.
+//
+// Panics if at least one value of the parameters is invalid.
+//
+// The created Calculator does not require additional
+// initialization and is completely ready for work.
+func New(prm Prm, opts ...Option) *Calculator {
+	switch {
+	case prm.Alpha <= 0 || prm.Alpha >= 1:
+		panicOnPrmValue("Alpha", prm.Alpha)
+	case prm.InitialTrustSource == nil:
+		panicOnPrmValue("InitialTrustSource", prm.InitialTrustSource)
+	case prm.DaughterTrustSource == nil:
+		panicOnPrmValue("DaughterTrustSource", prm.DaughterTrustSource)
+	case prm.IntermediateValueTarget == nil:
+		panicOnPrmValue("IntermediateValueTarget", prm.IntermediateValueTarget)
+	case prm.FinalResultTarget == nil:
+		panicOnPrmValue("FinalResultTarget", prm.FinalResultTarget)
+	case prm.WorkerPool == nil:
+		panicOnPrmValue("WorkerPool", prm.WorkerPool)
+	}
+
+	o := defaultOpts()
+
+	for _, opt := range opts {
+		opt(o)
+	}
+
+	return &Calculator{
+		alpha: reputation.TrustValueFromFloat64(prm.Alpha),
+		beta:  reputation.TrustValueFromFloat64(1 - prm.Alpha),
+		prm:   prm,
+		opts:  o,
+	}
+}