graph/encoding: provide attribute handling out of the box

graph/encoding/dot/decode_test.go

@@ -532,7 +532,13 @@ type dotDirectedGraph struct {
 // newDotDirectedGraph returns a new directed capable of creating user-defined
 // nodes and edges.
 func newDotDirectedGraph() *dotDirectedGraph {
-	return &dotDirectedGraph{DirectedGraph: simple.NewDirectedGraph()}
+	return &dotDirectedGraph{
+		DirectedGraph: simple.NewDirectedGraph(),
+
+		graph: &encoding.Attributes{},
+		node:  &encoding.Attributes{},
+		edge:  &encoding.Attributes{},
+	}
 }
 
 // NewNode returns a new node with a unique node ID for the graph.
@@ -552,7 +558,7 @@ func (g *dotDirectedGraph) DOTAttributers() (graph, node, edge encoding.Attribut
 
 // DOTAttributeSetters implements the dot.AttributeSetters interface.
 func (g *dotDirectedGraph) DOTAttributeSetters() (graph, node, edge encoding.AttributeSetter) {
-	return &g.graph, &g.node, &g.edge
+	return g.graph, g.node, g.edge
 }
 
 // SetDOTID sets the DOT ID of the graph.
@@ -579,7 +585,13 @@ type dotUndirectedGraph struct {
 // newDotUndirectedGraph returns a new undirected capable of creating user-
 // defined nodes and edges.
 func newDotUndirectedGraph() *dotUndirectedGraph {
-	return &dotUndirectedGraph{UndirectedGraph: simple.NewUndirectedGraph()}
+	return &dotUndirectedGraph{
+		UndirectedGraph: simple.NewUndirectedGraph(),
+
+		graph: &encoding.Attributes{},
+		node:  &encoding.Attributes{},
+		edge:  &encoding.Attributes{},
+	}
 }
 
 // NewNode adds a new node with a unique node ID to the graph.
@@ -599,7 +611,7 @@ func (g *dotUndirectedGraph) DOTAttributers() (graph, node, edge encoding.Attrib
 
 // DOTUnmarshalerAttrs implements the dot.UnmarshalerAttrs interface.
 func (g *dotUndirectedGraph) DOTAttributeSetters() (graph, node, edge encoding.AttributeSetter) {
-	return &g.graph, &g.node, &g.edge
+	return g.graph, g.node, g.edge
 }
 
 // SetDOTID sets the DOT ID of the graph.
@@ -705,15 +717,9 @@ func (e *dotEdge) ToPort() (port, compass string) {
 	return e.ToPortLabels.Port, e.ToPortLabels.Compass
 }
 
-// attributes is a helper for global attributes.
-type attributes []encoding.Attribute
-
-func (a attributes) Attributes() []encoding.Attribute {
-	return []encoding.Attribute(a)
-}
-func (a *attributes) SetAttribute(attr encoding.Attribute) error {
-	*a = append(*a, attr)
-	return nil
+type attributes interface {
+	encoding.Attributer
+	encoding.AttributeSetter
 }
 
 const undirectedSelfLoopGraph = `graph {

graph/encoding/dot/encode_test.go

@@ -321,10 +321,6 @@ type graphAttributer struct {
 	edge  encoding.Attributer
 }
 
-type attributer []encoding.Attribute
-
-func (a attributer) Attributes() []encoding.Attribute { return a }
-
 func (g graphAttributer) DOTAttributers() (graph, node, edge encoding.Attributer) {
 	return g.graph, g.node, g.edge
 }
@@ -1192,8 +1188,8 @@ var encodeTests = []struct {
 				{from: 2, to: 4}: {},
 				{from: 3, to: 4}: {{Key: "color", Value: "red"}},
 			}),
-			graph: attributer{{Key: "rankdir", Value: `"LR"`}},
-			node:  attributer{{Key: "fontsize", Value: "16"}, {Key: "shape", Value: "ellipse"}},
+			graph: &encoding.Attributes{{Key: "rankdir", Value: `"LR"`}},
+			node:  &encoding.Attributes{{Key: "fontsize", Value: "16"}, {Key: "shape", Value: "ellipse"}},
 			edge:  nil,
 		},
 

graph/encoding/encoding.go

@@ -34,3 +34,36 @@ type Attributer interface {
 type Attribute struct {
 	Key, Value string
 }
+
+// Attributes is a helper type providing simple attribute handling.
+type Attributes []Attribute
+
+// Attributes returns all of the receiver's attributes.
+func (a *Attributes) Attributes() []Attribute {
+	return *a
+}
+
+// SetAttribute sets attr in the receiver. Calling SetAttribute with an
+// Attribute with a Key that is in the collection replaces the existing
+// value and calling with an empty Value removes the attribute from the
+// collection if it exists. SetAttribute always returns nil.
+func (a *Attributes) SetAttribute(attr Attribute) error {
+	if attr.Key == "" {
+		return nil
+	}
+	for i, v := range *a {
+		if v.Key == attr.Key {
+			if attr.Value == "" {
+				(*a)[i] = (*a)[len(*a)-1]
+				*a = (*a)[:len(*a)-1]
+				return nil
+			}
+			(*a)[i].Value = attr.Value
+			return nil
+		}
+	}
+	if attr.Value != "" {
+		*a = append(*a, attr)
+	}
+	return nil
+}

graph/encoding/encoding_test.go

@@ -0,0 +1,121 @@
+// Copyright ©2021 The Gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package encoding
+
+import (
+	"sort"
+	"testing"
+)
+
+var setAttributesTests = []struct {
+	attr   *Attributes
+	opName string
+	op     func(AttributeSetter) error
+	want   *Attributes
+}{
+	{
+		attr:   &Attributes{},
+		opName: "noop",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "", Value: "bar"})
+		},
+		want: &Attributes{},
+	},
+	{
+		attr:   &Attributes{},
+		opName: "add attr to empty",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: "bar"})
+		},
+		want: &Attributes{{Key: "foo", Value: "bar"}},
+	},
+	{
+		attr:   &Attributes{},
+		opName: "remove attr from empty",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: ""})
+		},
+		want: &Attributes{},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}},
+		opName: "add attr to non-empty",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "bif", Value: "fud"})
+		},
+		want: &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}},
+		opName: "remove attr from singleton",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: ""})
+		},
+		want: &Attributes{},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+		opName: "remove first attr from pair",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: ""})
+		},
+		want: &Attributes{{Key: "bif", Value: "fud"}},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+		opName: "remove second attr from pair",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "bif", Value: ""})
+		},
+		want: &Attributes{{Key: "foo", Value: "bar"}},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+		opName: "replace first attr in pair",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: "not bar"})
+		},
+		want: &Attributes{{Key: "foo", Value: "not bar"}, {Key: "bif", Value: "fud"}},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+		opName: "replace second attr in pair",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "bif", Value: "not fud"})
+		},
+		want: &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "not fud"}},
+	},
+}
+
+func TestSetAttributes(t *testing.T) {
+	for _, test := range setAttributesTests {
+		err := test.op(test.attr)
+		if err != nil {
+			t.Errorf("unexpected error for %q: %v", test.opName, err)
+			continue
+		}
+		if !sameAttributes(test.attr, test.want) {
+			t.Errorf("unexpected result from %q:\ngot: %+v\nwant:%+v", test.opName, test.attr, test.want)
+		}
+	}
+}
+
+func sameAttributes(a, b Attributer) bool {
+	aAttr := a.Attributes()
+	bAttr := b.Attributes()
+	if len(aAttr) != len(bAttr) {
+		return false
+	}
+	aAttr = append(aAttr[:0:0], aAttr...)
+	sort.Slice(aAttr, func(i, j int) bool { return aAttr[i].Key < aAttr[j].Key })
+	bAttr = append(bAttr[:0:0], bAttr...)
+	sort.Slice(bAttr, func(i, j int) bool { return bAttr[i].Key < bAttr[j].Key })
+	for i, a := range aAttr {
+		if bAttr[i] != a {
+			return false
+		}
+	}
+	return true
+}