From c1bdb46623e3f613d52076dbc6a13461749b11fe Mon Sep 17 00:00:00 2001
From: Brian Picciano <mediocregopher@gmail.com>
Date: Sat, 18 Aug 2018 13:51:38 -0400
Subject: [PATCH] graph: implement SubGraph and Equal

---
 graph/graph.go      | 29 +++++++++++++++++
 graph/graph_test.go | 77 +++++++++++++++++++++++++++++++++++++--------
 2 files changed, 93 insertions(+), 13 deletions(-)

diff --git a/graph/graph.go b/graph/graph.go
index 7f04060..ec1ae4c 100644
--- a/graph/graph.go
+++ b/graph/graph.go
@@ -204,3 +204,32 @@ func (g Graph) Traverse(start Value, next func(v Value, in, out []Edge) (Value,
 		}
 	}
 }
+
+func (g Graph) edgesShared(g2 Graph) bool {
+	for id := range g2.m {
+		if _, ok := g.m[id]; !ok {
+			return false
+		}
+	}
+	return true
+}
+
+// SubGraph returns true if the given Graph shares all of its Edges with this
+// Graph.
+func (g Graph) SubGraph(g2 Graph) bool {
+	// as a quick check before iterating through the edges, if g has fewer edges
+	// than g2 then g2 can't possibly be a sub-graph of it
+	if len(g.m) < len(g2.m) {
+		return false
+	}
+	return g.edgesShared(g2)
+}
+
+// Equal returns true if the given Graph and this Graph have exactly the same
+// Edges.
+func (g Graph) Equal(g2 Graph) bool {
+	if len(g.m) != len(g2.m) {
+		return false
+	}
+	return g.edgesShared(g2)
+}
diff --git a/graph/graph_test.go b/graph/graph_test.go
index 111c871..a9b0e0b 100644
--- a/graph/graph_test.go
+++ b/graph/graph_test.go
@@ -1,6 +1,7 @@
 package graph
 
 import (
+	"fmt"
 	. "testing"
 	"time"
 
@@ -9,7 +10,12 @@ import (
 	"github.com/mediocregopher/mediocre-go-lib/mtest/mchk"
 )
 
+func strV(s string) Value {
+	return Value{ID: s, V: s}
+}
+
 func TestGraph(t *T) {
+	t.Parallel()
 	type state struct {
 		Graph
 
@@ -21,10 +27,6 @@ func TestGraph(t *T) {
 		del Edge
 	}
 
-	strV := func(s string) Value {
-		return Value{ID: s, V: s}
-	}
-
 	chk := mchk.Checker{
 		Init: func() mchk.State {
 			return state{
@@ -118,15 +120,64 @@ func TestGraph(t *T) {
 
 			return s, nil
 		},
-		MaxLength: 10,
-	}
-
-	err := chk.RunCase(
-		params{add: Edge{Tail: strV("4"), Val: strV("d"), Head: strV("4")}},
-		params{del: Edge{Tail: strV("4"), Val: strV("d"), Head: strV("4")}},
-	)
-	if err != nil {
-		t.Fatal(err)
+	}
+
+	if err := chk.RunFor(5 * time.Second); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestSubGraphAndEqual(t *T) {
+	t.Parallel()
+	type state struct {
+		g1, g2                Graph
+		expEqual, expSubGraph bool
+	}
+
+	type params struct {
+		e          Edge
+		add1, add2 bool
+	}
+
+	chk := mchk.Checker{
+		Init: func() mchk.State {
+			return state{expEqual: true, expSubGraph: true}
+		},
+		Next: func(ss mchk.State) mchk.Action {
+			i := mrand.Intn(10)
+			p := params{
+				e: Edge{
+					Tail: strV(mrand.Hex(1)),
+					Val:  strV(mrand.Hex(8)),
+					Head: strV(mrand.Hex(1)),
+				},
+				add1: i != 0,
+				add2: i != 1,
+			}
+			return mchk.Action{Params: p}
+		},
+		Apply: func(ss mchk.State, a mchk.Action) (mchk.State, error) {
+			s, p := ss.(state), a.Params.(params)
+			if p.add1 {
+				s.g1 = s.g1.AddEdge(p.e)
+			}
+			if p.add2 {
+				s.g2 = s.g2.AddEdge(p.e)
+			}
+			s.expSubGraph = s.expSubGraph && p.add1
+			s.expEqual = s.expEqual && p.add1 && p.add2
+
+			if s.g1.SubGraph(s.g2) != s.expSubGraph {
+				return nil, fmt.Errorf("SubGraph expected to return %v", s.expSubGraph)
+			}
+
+			if s.g1.Equal(s.g2) != s.expEqual {
+				return nil, fmt.Errorf("Equal expected to return %v", s.expEqual)
+			}
+
+			return s, nil
+		},
+		MaxLength: 100,
 	}
 
 	if err := chk.RunFor(5 * time.Second); err != nil {