Don't remove if there are zero or no reachable contexts

When run on start-up, if there is no WiFi available, we want to
preserve the clusters, or allow the user to --force the removal.

When there are zero changes to make, don't write out the file.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

README.md

@@ -9,7 +9,7 @@ Q&A:
 
 * What if I like doing things the long way?
 
-    You can combine `kubectl config get-clusters` with `kubectl config use-context` and `kubectl get nodes`, followed by `kubectl config delete-cluster` and `kubectl config delete-context` for each.
+    You can combine `kubectl config get-clusters` with `kubectl config use-context` and `kubectl get nodes`, followed by `kubectl config delete-cluster` and `kubectl config delete-context` for each. `kubectx -d` will remove a context, but leaves the cluster in your kubeconfig file, so requires additional steps.
 
 * Doesn't [my favourite tool] have an option to do this?
 
@@ -35,6 +35,10 @@ Q&A:
 
     Yes, you can add `kubetrim &` to your `.bashrc`, `.bash_profile` or `.zshrc` file, which will run in the background, and not slow down your terminal session from starting up.
 
+* What if my WiFi is down and I run this tool?
+
+    If all clusters show as unavailable, kubetrim will not delete any clusters, in this case add `--force` to the command.
+
 ## Usage
 
 ```bash
@@ -62,6 +66,20 @@ default
 kind-2
 ```
 
+What if the Internet is unavailable, and all clusters report as unavailable?
+
+```bash
+# Take down WiFi/Ethernet
+
+$ kubetrim
+
+No contexts are working, the Internet may be down, use --force to delete all contexts anyway.
+
+# Force the deletion, even if all clusters are unavailable.
+
+$ kubetrim --force
+```
+
 Try out kubetrim without writing changes to the kubeconfig file:
 
 ```bash

main.go

@@ -24,6 +24,7 @@ import (
 
 var (
 	writeFile bool
+	force     bool
 )
 
 func main() {
@@ -44,6 +45,7 @@ func main() {
 	}
 
 	flag.BoolVar(&writeFile, "write", true, "Write changes to the kubeconfig file")
+	flag.BoolVar(&force, "force", false, "Force delete all contexts, even if all are unreachable")
 	flag.Parse()
 
 	// Load the kubeconfig file
@@ -102,11 +104,18 @@ func main() {
 	}
 
 	if writeFile {
-		// Save the modified kubeconfig
-		if err = clientcmd.WriteToFile(*config, kubeconfig); err != nil {
-			fmt.Printf("Error saving updated kubeconfig: %v\n", err)
+
+		if len(contextsToDelete) == len(config.Contexts) && !force {
+			fmt.Println("No contexts are working, the Internet may be down, use --force to delete all contexts anyway.")
 			os.Exit(1)
 		}
+		if len(contextsToDelete) > 0 {
+			// Save the modified kubeconfig
+			if err = clientcmd.WriteToFile(*config, kubeconfig); err != nil {
+				fmt.Printf("Error saving updated kubeconfig: %v\n", err)
+				os.Exit(1)
+			}
+		}
 		fmt.Printf("Updated: %s (in %s).\n", kubeconfig, time.Since(st).Round(time.Millisecond))
 	}
 }