Add support for auto update CLI (#36)

Readme.md

@@ -256,5 +256,11 @@ service.name: <+project.name>
 
 If not all the required flags are provided we will fall back to prompt based technique to capture all the required details.
 
+## To update the CLI
+To update to a new version of the CLI
+```shell
+harness-upgrade update
+```
+
 ## Contact
 If you face any issues please reach out to us or feel free to create a GitHub issue.

main.go

@@ -200,6 +200,14 @@ func main() {
 		EnableBashCompletion: true,
 		Suggest:              true,
 		Commands: []*cli.Command{
+			{
+				Name:    "update",
+				Aliases: []string{"upgrade"},
+				Usage:   "Check for updates and upgrade the CLI",
+				Action: func(context *cli.Context) error {
+					return cliWrapper(Update, context)
+				},
+			},
 			{
 				Name:  "account-summary",
 				Usage: "Get a summary of an account",

release.go

@@ -14,10 +14,7 @@ type GithubRelease struct {
 	TagName    string `json:"tag_name"`
 }
 
-func CheckGithubForReleases() {
-	if Version == "development" {
-		return
-	}
+func GetNewRelease() (newVersion string) {
 	resp, err := http.Get("https://api.github.com/repos/harness/migrator/releases")
 	if err != nil {
 		return
@@ -52,6 +49,9 @@ func CheckGithubForReleases() {
 		if !v.Prerelease && len(latestStableRelease.TagName) == 0 {
 			latestStableRelease = v
 		}
+		if v.TagName == Version && v.Prerelease {
+			isPreRelease = true
+		}
 	}
 	if Version == latest.TagName {
 		return
@@ -60,15 +60,24 @@ func CheckGithubForReleases() {
 		return
 	}
 	if !latest.Prerelease {
-		printUpgradeMessage(Version, latest.TagName)
-		return
+		return latest.TagName
 	}
 	if isPreRelease {
-		printUpgradeMessage(Version, latest.TagName)
-		return
+		return latest.TagName
 	}
 	if !isPreRelease && latestStableRelease.TagName != Version {
-		printUpgradeMessage(Version, latestStableRelease.TagName)
+		return latestStableRelease.TagName
+	}
+	return
+}
+
+func CheckGithubForReleases() {
+	if Version == "development" {
+		return
+	}
+	newRelease := GetNewRelease()
+	if len(newRelease) > 0 {
+		printUpgradeMessage(Version, newRelease)
 	}
 }
 

update.go

@@ -0,0 +1,108 @@
+package main
+
+import (
+	"archive/tar"
+	"compress/gzip"
+	"fmt"
+	"github.com/fatih/color"
+	"github.com/urfave/cli/v2"
+	"io"
+	"net/http"
+	"os"
+	"path"
+	"path/filepath"
+	"runtime"
+)
+
+func Update(*cli.Context) (err error) {
+	newVersion := GetNewRelease()
+	if len(newVersion) == 0 {
+		fmt.Println("Already on latest version. Skipping update")
+		return
+	}
+	blue := color.New(color.FgHiBlue).SprintFunc()
+	yellow := color.New(color.FgYellow).SprintFunc()
+	green := color.New(color.FgGreen).SprintFunc()
+	fmt.Printf("New version %s is available.\n", green(newVersion))
+	confirm := ConfirmInput("Do you want to update?")
+	if !confirm {
+		return nil
+	}
+	extension := "tar.gz"
+	const GOOS = runtime.GOOS
+	const GOARCH = runtime.GOARCH
+	if GOOS == "windows" {
+		extension = "zip"
+	}
+	url := fmt.Sprintf("https://github.com/harness/migrator/releases/download/%s/harness-upgrade-%s-%s-%s.%s", newVersion, newVersion, GOOS, GOARCH, extension)
+
+	if GOOS != "darwin" {
+		fmt.Printf("%s\n", yellow("Auto update support is only available for MacOS right now"))
+		fmt.Printf("Download the following release - %s\n", blue(url))
+		return nil
+	}
+
+	ex, err := os.Executable()
+	if err != nil {
+		return err
+	}
+	dir, err := filepath.Abs(path.Dir(ex))
+	if err != nil {
+		return err
+	}
+
+	// Download the file
+	fmt.Printf("Downloading the following - %s\n", blue(url))
+	resp, err := http.Get(url)
+	if err != nil {
+		return err
+	}
+	defer func(Body io.ReadCloser) {
+		err := Body.Close()
+		if err != nil {
+			return
+		}
+	}(resp.Body)
+
+	fmt.Printf("Unpacking the contents and extracting to - %s\n", blue(dir))
+	err = readTar(resp.Body, dir)
+	if err == nil {
+		fmt.Printf("Successfully upgraded to - %s\n", green(newVersion))
+	}
+	return err
+}
+
+func readTar(body io.ReadCloser, dest string) error {
+	gzRead, err := gzip.NewReader(body)
+	if err != nil {
+		return err
+	}
+	reader := tar.NewReader(gzRead)
+	for true {
+		header, err := reader.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return err
+		}
+		if header.Typeflag == tar.TypeReg && header.Name == "harness-upgrade" {
+			execFile := path.Join(dest, header.Name)
+			green := color.New(color.FgGreen).SprintFunc()
+			fmt.Printf("Extracking harness-upgrade to - %s\n", green(execFile))
+			outFile, err := os.Create(execFile)
+			if err != nil {
+				return err
+			}
+			if _, err = io.Copy(outFile, reader); err != nil {
+				return err
+			}
+			err = outFile.Close()
+			if err != nil {
+				return err
+			}
+			return nil
+		}
+	}
+	return nil
+}