Add graphviz generation and visualization

This requires graphviz to be installed on your machine. If you run the
command with sudo, it will create the files with the original user
ownership to make it easier to remove them without root.

pgraph.go

@@ -19,10 +19,15 @@
 package main
 
 import (
-	//"container/list" // doubly linked list
+	"errors"
 	"fmt"
+	"io/ioutil"
 	"log"
+	"os"
+	"os/exec"
+	"strconv"
 	"sync"
+	"syscall"
 )
 
 //go:generate stringer -type=graphState -output=graphstate_stringer.go
@@ -81,6 +86,11 @@ func NewEdge(name string) *Edge {
 	}
 }
 
+// returns the name of the graph
+func (g *Graph) GetName() string {
+	return g.Name
+}
+
 // set name of the graph
 func (g *Graph) SetName(name string) {
 	g.Name = name
@@ -208,6 +218,88 @@ func (g *Graph) String() string {
 	return fmt.Sprintf("Vertices(%d), Edges(%d)", g.NumVertices(), g.NumEdges())
 }
 
+// output the graph in graphviz format
+// https://en.wikipedia.org/wiki/DOT_%28graph_description_language%29
+func (g *Graph) Graphviz() (out string) {
+	//digraph g {
+	//	label="hello world";
+	//	node [shape=box];
+	//	A [label="A"];
+	//	B [label="B"];
+	//	C [label="C"];
+	//	D [label="D"];
+	//	E [label="E"];
+	//	A -> B [label=f];
+	//	B -> C [label=g];
+	//	D -> E [label=h];
+	//}
+	out += fmt.Sprintf("digraph %v {\n", g.GetName())
+	out += fmt.Sprintf("\tlabel=\"%v\";\n", g.GetName())
+	//out += "\tnode [shape=box];\n"
+	str := ""
+	for i, _ := range g.Adjacency { // reverse paths
+		out += fmt.Sprintf("\t%v [label=\"%v[%v]\"];\n", i.GetName(), i.GetType(), i.GetName())
+		for j, _ := range g.Adjacency[i] {
+			k := g.Adjacency[i][j]
+			// use str for clearer output ordering
+			str += fmt.Sprintf("\t%v -> %v [label=%v];\n", i.GetName(), j.GetName(), k.Name)
+		}
+	}
+	out += str
+	out += "}\n"
+	return
+}
+
+// write out the graphviz data and run the correct graphviz filter command
+func (g *Graph) ExecGraphviz(program, filename string) error {
+
+	switch program {
+	case "dot", "neato", "twopi", "circo", "fdp":
+	default:
+		return errors.New("Invalid graphviz program selected!")
+	}
+
+	if filename == "" {
+		return errors.New("No filename given!")
+	}
+
+	// run as a normal user if possible when run with sudo
+	uid, err1 := strconv.Atoi(os.Getenv("SUDO_UID"))
+	gid, err2 := strconv.Atoi(os.Getenv("SUDO_GID"))
+
+	err := ioutil.WriteFile(filename, []byte(g.Graphviz()), 0644)
+	if err != nil {
+		return errors.New("Error writing to filename!")
+	}
+
+	if err1 == nil && err2 == nil {
+		if err := os.Chown(filename, uid, gid); err != nil {
+			return errors.New("Error changing file owner!")
+		}
+	}
+
+	path, err := exec.LookPath(program)
+	if err != nil {
+		return errors.New("Graphviz is missing!")
+	}
+
+	out := fmt.Sprintf("%v.png", filename)
+	cmd := exec.Command(path, "-Tpng", fmt.Sprintf("-o%v", out), filename)
+
+	if err1 == nil && err2 == nil {
+		cmd.SysProcAttr = &syscall.SysProcAttr{}
+		cmd.SysProcAttr.Credential = &syscall.Credential{
+			Uid: uint32(uid),
+			Gid: uint32(gid),
+		}
+	}
+	_, err = cmd.Output()
+	if err != nil {
+		return errors.New("Error writing to image!")
+	}
+	return nil
+}
+
 // google/golang hackers apparently do not think contains should be a built-in!
 func Contains(s []*Vertex, element *Vertex) bool {
 	for _, v := range s {