graph/encoding/graphql: add new package for decoding GraphQL output

graph/encoding/graphql/decode.go

@@ -0,0 +1,157 @@
+// Copyright ©2017 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 graphql
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+
+	"gonum.org/v1/gonum/graph"
+	"gonum.org/v1/gonum/graph/encoding"
+)
+
+// Unmarshal parses the the JSON-encoded data and stores the result in dst.
+// Node IDs are obtained from the JSON fields identified by the uid parameter.
+// UIDs obtained from the JSON encoding must map to unique node ID values
+// consistently across the JSON-encoded spanning tree.
+func Unmarshal(data []byte, uid string, dst encoding.Builder) error {
+	if uid == "" {
+		return errors.New("graphql: invalid UID field name")
+	}
+	var src json.RawMessage
+	err := json.Unmarshal(data, &src)
+	if err != nil {
+		return err
+	}
+	gen := generator{dst: dst, uidName: uid, nodes: make(map[string]graph.Node)}
+	return gen.walk(src, nil, "")
+}
+
+// StringIDSetter is a graph node that can set its ID based on the given uid string.
+type StringIDSetter interface {
+	SetIDFromString(uid string) error
+}
+
+// LabelSetter is a graph edge that can set its label.
+type LabelSetter interface {
+	SetLabel(string)
+}
+
+type generator struct {
+	dst encoding.Builder
+
+	// uidName is the name of the UID field in the source JSON.
+	uidName string
+	// nodes maps from GraphQL UID string to graph.Node.
+	nodes map[string]graph.Node
+}
+
+func (g *generator) walk(src json.RawMessage, node graph.Node, attr string) error {
+	switch src[0] {
+	case '{':
+		var val map[string]json.RawMessage
+		err := json.Unmarshal(src, &val)
+		if err != nil {
+			return err
+		}
+		if next, ok := val[g.uidName]; !ok {
+			if node != nil {
+				var buf bytes.Buffer
+				err := json.Compact(&buf, src)
+				if err != nil {
+					panic(err)
+				}
+				return fmt.Errorf("graphql: no UID for node: `%s`", &buf)
+			}
+		} else {
+			var v interface{}
+			err = json.Unmarshal(next, &v)
+			if err != nil {
+				return err
+			}
+			value := fmt.Sprint(v)
+			child, ok := g.nodes[value]
+			if !ok {
+				child = g.dst.NewNode()
+				s, ok := child.(StringIDSetter)
+				if !ok {
+					return errors.New("graphql: cannot set UID")
+				}
+				err = s.SetIDFromString(value)
+				if err != nil {
+					return err
+				}
+				g.nodes[value] = child
+				g.dst.AddNode(child)
+			}
+			if node != nil {
+				e := g.dst.NewEdge(node, child)
+				if s, ok := e.(LabelSetter); ok {
+					s.SetLabel(attr)
+				}
+				g.dst.SetEdge(e)
+			}
+			node = child
+		}
+		for attr, src := range val {
+			if attr == g.uidName {
+				continue
+			}
+			err = g.walk(src, node, attr)
+			if err != nil {
+				return err
+			}
+		}
+
+	case '[':
+		var val []json.RawMessage
+		err := json.Unmarshal(src, &val)
+		if err != nil {
+			return err
+		}
+		for _, src := range val {
+			err = g.walk(src, node, attr)
+			if err != nil {
+				return err
+			}
+		}
+
+	default:
+		var v interface{}
+		err := json.Unmarshal(src, &v)
+		if err != nil {
+			return err
+		}
+		if attr == g.uidName {
+			value := fmt.Sprint(v)
+			if s, ok := node.(StringIDSetter); ok {
+				if _, ok := g.nodes[value]; !ok {
+					err = s.SetIDFromString(value)
+					if err != nil {
+						return err
+					}
+					g.nodes[value] = node
+				}
+			} else {
+				return errors.New("graphql: cannot set ID")
+			}
+		} else if s, ok := node.(encoding.AttributeSetter); ok {
+			var value string
+			if _, ok := v.(float64); ok {
+				value = string(src)
+			} else {
+				value = fmt.Sprint(v)
+			}
+			err = s.SetAttribute(encoding.Attribute{Key: attr, Value: value})
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}