initial code (#6)

* initial code commit

cmd/nabarr/update.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"github.com/alecthomas/kong"
+	"github.com/blang/semver"
+	"github.com/rhysd/go-github-selfupdate/selfupdate"
+	"os"
+)
+
+type updateFlag string
+
+func (u updateFlag) Decode(ctx *kong.DecodeContext) error { return nil }
+func (u updateFlag) IsBool() bool                         { return true }
+func (u updateFlag) BeforeApply(app *kong.Kong, vars kong.Vars) error {
+	// parse current version
+	v, err := semver.Parse(Version)
+	if err != nil {
+		fmt.Printf("Failed parsing current build version: %v\n", err)
+		app.Exit(1)
+		return nil
+	}
+
+	// detect latest version
+	fmt.Println("Checking for the latest version...")
+	latest, found, err := selfupdate.DetectLatest("l3uddz/nabarr")
+	if err != nil {
+		fmt.Printf("Failed determining latest available version: %v\n", err)
+		app.Exit(1)
+		return nil
+	}
+
+	// check version
+	if !found || latest.Version.LTE(v) {
+		fmt.Printf("Already using the latest version: %v\n", Version)
+		app.Exit(0)
+		return nil
+	}
+
+	// ask update
+	fmt.Printf("Do you want to update to the latest version: %v? (y/n): ", latest.Version)
+	input, err := bufio.NewReader(os.Stdin).ReadString('\n')
+	if err != nil || (input != "y\n" && input != "n\n") {
+		fmt.Println("Failed validating input...")
+		app.Exit(1)
+		return nil
+	} else if input == "n\n" {
+		app.Exit(0)
+		return nil
+	}
+
+	// get existing executable path
+	exe, err := os.Executable()
+	if err != nil {
+		fmt.Printf("Failed locating current executable path: %v\n", err)
+		app.Exit(1)
+		return nil
+	}
+
+	if err := selfupdate.UpdateTo(latest.AssetURL, exe); err != nil {
+		fmt.Printf("Failed updating existing binary to latest release: %v\n", err)
+		app.Exit(1)
+		return nil
+	}
+
+	fmt.Printf("Successfully updated to the latest version: %v\n", latest.Version)
+
+	app.Exit(0)
+	return nil
+}