diff --git a/vendor/github.com/gyuho/goraph/graph.go b/vendor/github.com/gyuho/goraph/graph.go
new file mode 100644
index 0000000..87f87c5
--- /dev/null
+++ b/vendor/github.com/gyuho/goraph/graph.go
@@ -0,0 +1,503 @@
+package goraph
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"sync"
+)
+
+// ID is unique identifier.
+type ID interface {
+	// String returns the string ID.
+	String() string
+}
+
+type StringID string
+
+func (s StringID) String() string {
+	return string(s)
+}
+
+// Node is vertex. The ID must be unique within the graph.
+type Node interface {
+	// ID returns the ID.
+	ID() ID
+	String() string
+}
+
+type node struct {
+	id string
+}
+
+var nodeCnt uint64
+
+func NewNode(id string) Node {
+	return &node{
+		id: id,
+	}
+}
+
+func (n *node) ID() ID {
+	return StringID(n.id)
+}
+
+func (n *node) String() string {
+	return n.id
+}
+
+// Edge connects between two Nodes.
+type Edge interface {
+	Source() Node
+	Target() Node
+	Weight() float64
+	String() string
+}
+
+// edge is an Edge from Source to Target.
+type edge struct {
+	src Node
+	tgt Node
+	wgt float64
+}
+
+func NewEdge(src, tgt Node, wgt float64) Edge {
+	return &edge{
+		src: src,
+		tgt: tgt,
+		wgt: wgt,
+	}
+}
+
+func (e *edge) Source() Node {
+	return e.src
+}
+
+func (e *edge) Target() Node {
+	return e.tgt
+}
+
+func (e *edge) Weight() float64 {
+	return e.wgt
+}
+
+func (e *edge) String() string {
+	return fmt.Sprintf("%s -- %.3f -→ %s\n", e.src, e.wgt, e.tgt)
+}
+
+type EdgeSlice []Edge
+
+func (e EdgeSlice) Len() int           { return len(e) }
+func (e EdgeSlice) Less(i, j int) bool { return e[i].Weight() < e[j].Weight() }
+func (e EdgeSlice) Swap(i, j int)      { e[i], e[j] = e[j], e[i] }
+
+// Graph describes the methods of graph operations.
+// It assumes that the identifier of a Node is unique.
+// And weight values is float64.
+type Graph interface {
+	// Init initializes a Graph.
+	Init()
+
+	// GetNodeCount returns the total number of nodes.
+	GetNodeCount() int
+
+	// GetNode finds the Node. It returns nil if the Node
+	// does not exist in the graph.
+	GetNode(id ID) Node
+
+	// GetNodes returns a map from node ID to
+	// empty struct value. Graph does not allow duplicate
+	// node ID or name.
+	GetNodes() map[ID]Node
+
+	// AddNode adds a node to a graph, and returns false
+	// if the node already existed in the graph.
+	AddNode(nd Node) bool
+
+	// DeleteNode deletes a node from a graph.
+	// It returns true if it got deleted.
+	// And false if it didn't get deleted.
+	DeleteNode(id ID) bool
+
+	// AddEdge adds an edge from nd1 to nd2 with the weight.
+	// It returns error if a node does not exist.
+	AddEdge(id1, id2 ID, weight float64) error
+
+	// ReplaceEdge replaces an edge from id1 to id2 with the weight.
+	ReplaceEdge(id1, id2 ID, weight float64) error
+
+	// DeleteEdge deletes an edge from id1 to id2.
+	DeleteEdge(id1, id2 ID) error
+
+	// GetWeight returns the weight from id1 to id2.
+	GetWeight(id1, id2 ID) (float64, error)
+
+	// GetSources returns the map of parent Nodes.
+	// (Nodes that come towards the argument vertex.)
+	GetSources(id ID) (map[ID]Node, error)
+
+	// GetTargets returns the map of child Nodes.
+	// (Nodes that go out of the argument vertex.)
+	GetTargets(id ID) (map[ID]Node, error)
+
+	// String describes the Graph.
+	String() string
+}
+
+// graph is an internal default graph type that
+// implements all methods in Graph interface.
+type graph struct {
+	mu sync.RWMutex // guards the following
+
+	// idToNodes stores all nodes.
+	idToNodes map[ID]Node
+
+	// nodeToSources maps a Node identifer to sources(parents) with edge weights.
+	nodeToSources map[ID]map[ID]float64
+
+	// nodeToTargets maps a Node identifer to targets(children) with edge weights.
+	nodeToTargets map[ID]map[ID]float64
+}
+
+// newGraph returns a new graph.
+func newGraph() *graph {
+	return &graph{
+		idToNodes:     make(map[ID]Node),
+		nodeToSources: make(map[ID]map[ID]float64),
+		nodeToTargets: make(map[ID]map[ID]float64),
+		//
+		// without this
+		// panic: assignment to entry in nil map
+	}
+}
+
+// NewGraph returns a new graph.
+func NewGraph() Graph {
+	return newGraph()
+}
+
+func (g *graph) Init() {
+	// (X) g = newGraph()
+	// this only updates the pointer
+	//
+	//
+	// (X) *g = *newGraph()
+	// assignment copies lock value
+
+	g.idToNodes = make(map[ID]Node)
+	g.nodeToSources = make(map[ID]map[ID]float64)
+	g.nodeToTargets = make(map[ID]map[ID]float64)
+}
+
+func (g *graph) GetNodeCount() int {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	return len(g.idToNodes)
+}
+
+func (g *graph) GetNode(id ID) Node {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	return g.idToNodes[id]
+}
+
+func (g *graph) GetNodes() map[ID]Node {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	return g.idToNodes
+}
+
+func (g *graph) unsafeExistID(id ID) bool {
+	_, ok := g.idToNodes[id]
+	return ok
+}
+
+func (g *graph) AddNode(nd Node) bool {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
+	if g.unsafeExistID(nd.ID()) {
+		return false
+	}
+
+	id := nd.ID()
+	g.idToNodes[id] = nd
+	return true
+}
+
+func (g *graph) DeleteNode(id ID) bool {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
+	if !g.unsafeExistID(id) {
+		return false
+	}
+
+	delete(g.idToNodes, id)
+
+	delete(g.nodeToTargets, id)
+	for _, smap := range g.nodeToTargets {
+		delete(smap, id)
+	}
+
+	delete(g.nodeToSources, id)
+	for _, smap := range g.nodeToSources {
+		delete(smap, id)
+	}
+
+	return true
+}
+
+func (g *graph) AddEdge(id1, id2 ID, weight float64) error {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
+	if !g.unsafeExistID(id1) {
+		return fmt.Errorf("%s does not exist in the graph.", id1)
+	}
+	if !g.unsafeExistID(id2) {
+		return fmt.Errorf("%s does not exist in the graph.", id2)
+	}
+
+	if _, ok := g.nodeToTargets[id1]; ok {
+		if v, ok2 := g.nodeToTargets[id1][id2]; ok2 {
+			g.nodeToTargets[id1][id2] = v + weight
+		} else {
+			g.nodeToTargets[id1][id2] = weight
+		}
+	} else {
+		tmap := make(map[ID]float64)
+		tmap[id2] = weight
+		g.nodeToTargets[id1] = tmap
+	}
+	if _, ok := g.nodeToSources[id2]; ok {
+		if v, ok2 := g.nodeToSources[id2][id1]; ok2 {
+			g.nodeToSources[id2][id1] = v + weight
+		} else {
+			g.nodeToSources[id2][id1] = weight
+		}
+	} else {
+		tmap := make(map[ID]float64)
+		tmap[id1] = weight
+		g.nodeToSources[id2] = tmap
+	}
+
+	return nil
+}
+
+func (g *graph) ReplaceEdge(id1, id2 ID, weight float64) error {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
+	if !g.unsafeExistID(id1) {
+		return fmt.Errorf("%s does not exist in the graph.", id1)
+	}
+	if !g.unsafeExistID(id2) {
+		return fmt.Errorf("%s does not exist in the graph.", id2)
+	}
+
+	if _, ok := g.nodeToTargets[id1]; ok {
+		g.nodeToTargets[id1][id2] = weight
+	} else {
+		tmap := make(map[ID]float64)
+		tmap[id2] = weight
+		g.nodeToTargets[id1] = tmap
+	}
+	if _, ok := g.nodeToSources[id2]; ok {
+		g.nodeToSources[id2][id1] = weight
+	} else {
+		tmap := make(map[ID]float64)
+		tmap[id1] = weight
+		g.nodeToSources[id2] = tmap
+	}
+	return nil
+}
+
+func (g *graph) DeleteEdge(id1, id2 ID) error {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+
+	if !g.unsafeExistID(id1) {
+		return fmt.Errorf("%s does not exist in the graph.", id1)
+	}
+	if !g.unsafeExistID(id2) {
+		return fmt.Errorf("%s does not exist in the graph.", id2)
+	}
+
+	if _, ok := g.nodeToTargets[id1]; ok {
+		if _, ok := g.nodeToTargets[id1][id2]; ok {
+			delete(g.nodeToTargets[id1], id2)
+		}
+	}
+	if _, ok := g.nodeToSources[id2]; ok {
+		if _, ok := g.nodeToSources[id2][id1]; ok {
+			delete(g.nodeToSources[id2], id1)
+		}
+	}
+	return nil
+}
+
+func (g *graph) GetWeight(id1, id2 ID) (float64, error) {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	if !g.unsafeExistID(id1) {
+		return 0, fmt.Errorf("%s does not exist in the graph.", id1)
+	}
+	if !g.unsafeExistID(id2) {
+		return 0, fmt.Errorf("%s does not exist in the graph.", id2)
+	}
+
+	if _, ok := g.nodeToTargets[id1]; ok {
+		if v, ok := g.nodeToTargets[id1][id2]; ok {
+			return v, nil
+		}
+	}
+	return 0.0, fmt.Errorf("there is no edge from %s to %s", id1, id2)
+}
+
+func (g *graph) GetSources(id ID) (map[ID]Node, error) {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	if !g.unsafeExistID(id) {
+		return nil, fmt.Errorf("%s does not exist in the graph.", id)
+	}
+
+	rs := make(map[ID]Node)
+	if _, ok := g.nodeToSources[id]; ok {
+		for n := range g.nodeToSources[id] {
+			rs[n] = g.idToNodes[n]
+		}
+	}
+	return rs, nil
+}
+
+func (g *graph) GetTargets(id ID) (map[ID]Node, error) {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	if !g.unsafeExistID(id) {
+		return nil, fmt.Errorf("%s does not exist in the graph.", id)
+	}
+
+	rs := make(map[ID]Node)
+	if _, ok := g.nodeToTargets[id]; ok {
+		for n := range g.nodeToTargets[id] {
+			rs[n] = g.idToNodes[n]
+		}
+	}
+	return rs, nil
+}
+
+func (g *graph) String() string {
+	g.mu.RLock()
+	defer g.mu.RUnlock()
+
+	buf := new(bytes.Buffer)
+	for id1, nd1 := range g.idToNodes {
+		nmap, _ := g.GetTargets(id1)
+		for id2, nd2 := range nmap {
+			weight, _ := g.GetWeight(id1, id2)
+			fmt.Fprintf(buf, "%s -- %.3f -→ %s\n", nd1, weight, nd2)
+		}
+	}
+	return buf.String()
+}
+
+// NewGraphFromJSON returns a new Graph from a JSON file.
+// Here's the sample JSON data:
+//
+//	{
+//	    "graph_00": {
+//	        "S": {
+//	            "A": 100,
+//	            "B": 14,
+//	            "C": 200
+//	        },
+//	        "A": {
+//	            "S": 15,
+//	            "B": 5,
+//	            "D": 20,
+//	            "T": 44
+//	        },
+//	        "B": {
+//	            "S": 14,
+//	            "A": 5,
+//	            "D": 30,
+//	            "E": 18
+//	        },
+//	        "C": {
+//	            "S": 9,
+//	            "E": 24
+//	        },
+//	        "D": {
+//	            "A": 20,
+//	            "B": 30,
+//	            "E": 2,
+//	            "F": 11,
+//	            "T": 16
+//	        },
+//	        "E": {
+//	            "B": 18,
+//	            "C": 24,
+//	            "D": 2,
+//	            "F": 6,
+//	            "T": 19
+//	        },
+//	        "F": {
+//	            "D": 11,
+//	            "E": 6,
+//	            "T": 6
+//	        },
+//	        "T": {
+//	            "A": 44,
+//	            "D": 16,
+//	            "F": 6,
+//	            "E": 19
+//	        }
+//	    },
+//	}
+//
+func NewGraphFromJSON(rd io.Reader, graphID string) (Graph, error) {
+	js := make(map[string]map[string]map[string]float64)
+	dec := json.NewDecoder(rd)
+	for {
+		if err := dec.Decode(&js); err == io.EOF {
+			break
+		} else if err != nil {
+			return nil, err
+		}
+	}
+	if _, ok := js[graphID]; !ok {
+		return nil, fmt.Errorf("%s does not exist", graphID)
+	}
+	gmap := js[graphID]
+
+	g := newGraph()
+	for id1, mm := range gmap {
+		nd1 := g.GetNode(StringID(id1))
+		if nd1 == nil {
+			nd1 = NewNode(id1)
+			if ok := g.AddNode(nd1); !ok {
+				return nil, fmt.Errorf("%s already exists", nd1)
+			}
+		}
+		for id2, weight := range mm {
+			nd2 := g.GetNode(StringID(id2))
+			if nd2 == nil {
+				nd2 = NewNode(id2)
+				if ok := g.AddNode(nd2); !ok {
+					return nil, fmt.Errorf("%s already exists", nd2)
+				}
+			}
+			g.ReplaceEdge(nd1.ID(), nd2.ID(), weight)
+		}
+	}
+
+	return g, nil
+}