Implement 'change-url' command

Author: juho05

README.md

@@ -21,6 +21,11 @@ Update event definitions, wrappers and libraries to match the latest game versio
 codegame update
 ```
 
+Permanently switch to a different game URL:
+```sh
+codegame change-url <new_url>
+```
+
 Run a project:
 ```sh
 codegame run

commands/change_url.go

@@ -0,0 +1,60 @@
+package commands
+
+import (
+	"os"
+	"strings"
+
+	"github.com/Bananenpro/cli"
+	"github.com/code-game-project/codegame-cli/util/cgfile"
+)
+
+func ChangeURL() error {
+	root, err := cgfile.FindProjectRoot()
+	if err != nil {
+		return err
+	}
+
+	var url string
+	if len(os.Args) >= 3 {
+		url = strings.ToLower(os.Args[2])
+	} else {
+		var err error
+		url, err = cli.Input("New game URL:")
+		if err != nil {
+			return err
+		}
+	}
+
+	config, err := cgfile.LoadCodeGameFile(root)
+	if err != nil {
+		return err
+	}
+
+	if config.Type != "client" {
+		return cli.Error("Project is not a client.")
+	}
+
+	name, _, err := getCodeGameInfo(baseURL(url))
+	if err != nil {
+		return err
+	}
+	if name != config.Game {
+		return cli.Error("The URL points to a different game.")
+	}
+
+	prevURL := config.URL
+
+	config.URL = url
+	err = config.Write(root)
+	if err != nil {
+		return err
+	}
+
+	err = Update()
+	if err != nil {
+		config.URL = prevURL
+		config.Write(root)
+		return err
+	}
+	return nil
+}

main.go

@@ -24,12 +24,13 @@ func main() {
 		fmt.Fprintln(os.Stderr, "\nDescription:")
 		fmt.Fprintln(os.Stderr, "The official CodeGame CLI.")
 		fmt.Fprintln(os.Stderr, "\nCommands:")
-		fmt.Fprintln(os.Stderr, "\tnew \tCreate a new project.")
-		fmt.Fprintln(os.Stderr, "\tupdate \tUpdate the current project.")
-		fmt.Fprintln(os.Stderr, "\trun \tRun the current project.")
-		fmt.Fprintln(os.Stderr, "\tbuild \tBuild the current project.")
-		fmt.Fprintln(os.Stderr, "\tinfo \tDisplay some info about a game server.")
-		fmt.Fprintln(os.Stderr, "\tdocs \tOpen the CodeGame documentation in a web browser.")
+		fmt.Fprintln(os.Stderr, "  new         Create a new project.")
+		fmt.Fprintln(os.Stderr, "  update      Update the current project.")
+		fmt.Fprintln(os.Stderr, "  change-url  Permanently switch to a different game URL.")
+		fmt.Fprintln(os.Stderr, "  run         Run the current project.")
+		fmt.Fprintln(os.Stderr, "  build       Build the current project.")
+		fmt.Fprintln(os.Stderr, "  info        Display some info about a game server.")
+		fmt.Fprintln(os.Stderr, "  docs        Open the CodeGame documentation in a web browser.")
 		fmt.Fprintln(os.Stderr, "\nAbout: https://code-game.org")
 		fmt.Fprintln(os.Stderr, "Copyright (c) 2022 CodeGame Contributors (https://code-game.org/contributors)")
 		pflag.PrintDefaults()
@@ -50,6 +51,8 @@ func main() {
 		err = commands.New()
 	case "update":
 		err = commands.Update()
+	case "change-url":
+		err = commands.ChangeURL()
 	case "info":
 		err = commands.Info()
 	case "docs":