Add Messenger bot capable of verification

The only ability of this current bot is to verify the webhook on the
Facebook developer panel.

cmd/bot/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/paked/configure"
+	"github.com/paked/messenger"
+)
+
+var (
+	conf        = configure.New()
+	verifyToken = conf.String("verify-token", "mad-skrilla", "The token used to verify facebook")
+	verify      = conf.Bool("should-verify", false, "Whether or not the app should verify itself")
+)
+
+func main() {
+	conf.Use(configure.NewFlag())
+	conf.Use(configure.NewEnvironment())
+	conf.Use(configure.NewJSONFromFile("config.json"))
+
+	conf.Parse()
+
+	m := messenger.New(messenger.MessengerOptions{
+		Verify:      *verify,
+		VerifyToken: *verifyToken,
+	})
+
+	fmt.Println("Serving messenger bot on localhost:8080")
+	http.ListenAndServe("localhost:8080", m.Handler())
+}

messenger.go

@@ -0,0 +1,46 @@
+package messenger
+
+import (
+	"fmt"
+	"net/http"
+)
+
+const (
+	WebhookURL = "/webhook"
+)
+
+type MessengerOptions struct {
+	Verify      bool
+	VerifyToken string
+}
+
+type Messenger struct {
+	mux *http.ServeMux
+}
+
+func New(mo MessengerOptions) *Messenger {
+	m := &Messenger{
+		mux: http.NewServeMux(),
+	}
+
+	if mo.Verify {
+		m.mux.HandleFunc(WebhookURL, newVerifyHandler(mo.VerifyToken))
+	}
+
+	return m
+}
+
+func (m *Messenger) Handler() http.Handler {
+	return m.mux
+}
+
+func newVerifyHandler(token string) func(w http.ResponseWriter, r *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if r.FormValue("hub.verify_token") == token {
+			fmt.Fprintln(w, r.FormValue("hub.challenge"))
+			return
+		}
+
+		fmt.Fprintln(w, "Incorrect verify token.")
+	}
+}