[FAB-7435] Graph struct for service discovery

This change set adds a generic graph that is going to be used
for associating principals with peer identities that satisfy principals.

Change-Id: I2043a332b92683d8f6ae7298e1a4b6a8158c9d0f
Signed-off-by: yacovm <yacovm@il.ibm.com>

Author: yacovm

common/graph/graph.go

@@ -0,0 +1,45 @@
+/*
+Copyright IBM Corp. All Rights Reserved.
+
+SPDX-License-Identifier: Apache-2.0
+*/
+
+package graph
+
+// Vertex defines a vertex of a graph
+type Vertex struct {
+	Id        string
+	Data      interface{}
+	neighbors map[string]*Vertex
+}
+
+// NewVertex creates a new vertex with given id and data
+func NewVertex(id string, data interface{}) *Vertex {
+	return &Vertex{
+		Id:        id,
+		Data:      data,
+		neighbors: make(map[string]*Vertex),
+	}
+}
+
+// NeighborById returns a neighbor vertex with the given id,
+// or nil if no vertex with such an id is a neighbor
+func (v *Vertex) NeighborById(id string) *Vertex {
+	return v.neighbors[id]
+}
+
+// Neighbors returns the neighbors of the vertex
+func (v *Vertex) Neighbors() []*Vertex {
+	var res []*Vertex
+	for _, u := range v.neighbors {
+		res = append(res, u)
+	}
+	return res
+}
+
+// AddNeighbor adds the given vertex as a neighbor
+// of the vertex
+func (v *Vertex) AddNeighbor(u *Vertex) {
+	v.neighbors[u.Id] = u
+	u.neighbors[v.Id] = v
+}

common/graph/graph_test.go

@@ -0,0 +1,25 @@
+/*
+Copyright IBM Corp. All Rights Reserved.
+
+SPDX-License-Identifier: Apache-2.0
+*/
+
+package graph
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestVertex(t *testing.T) {
+	v := NewVertex("1", "1")
+	assert.Equal(t, "1", v.Data)
+	assert.Equal(t, "1", v.Id)
+	u := NewVertex("2", "2")
+	v.AddNeighbor(u)
+	assert.Contains(t, u.Neighbors(), v)
+	assert.Contains(t, v.Neighbors(), u)
+	assert.Equal(t, u, v.NeighborById("2"))
+	assert.Nil(t, v.NeighborById("3"))
+}