cli: unify cloudcmd create and upgrade code (#2513)

* Unify cloudcmd create and upgrade code
* Make libvirt runner code a bit more idempotent

---------

Signed-off-by: Daniel Weiße <dw@edgeless.systems>

cli/internal/cloudcmd/tfplan.go

@@ -0,0 +1,96 @@
+/*
+Copyright (c) Edgeless Systems GmbH
+
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+
+package cloudcmd
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/edgelesssys/constellation/v2/cli/internal/terraform"
+	"github.com/edgelesssys/constellation/v2/internal/file"
+)
+
+// plan prepares a workspace and plans the possible Terraform actions.
+// This will either create a new workspace or update an existing one.
+// In case of possible migrations, the diff is written to outWriter and this function returns true.
+func plan(
+	ctx context.Context, tfClient tfPlanner, fileHandler file.Handler,
+	outWriter io.Writer, logLevel terraform.LogLevel, vars terraform.Variables,
+	templateDir, existingWorkspace, backupDir string,
+) (bool, error) {
+	isNewWorkspace, err := fileHandler.IsEmpty(existingWorkspace)
+	if err != nil {
+		if !errors.Is(err, os.ErrNotExist) {
+			return false, fmt.Errorf("checking if workspace is empty: %w", err)
+		}
+		isNewWorkspace = true
+	}
+
+	// Backup old workspace if it exists
+	if !isNewWorkspace {
+		if err := ensureFileNotExist(fileHandler, backupDir); err != nil {
+			return false, fmt.Errorf("backup directory %s already exists: %w", backupDir, err)
+		}
+		if err := fileHandler.CopyDir(existingWorkspace, backupDir); err != nil {
+			return false, fmt.Errorf("backing up old workspace: %w", err)
+		}
+	}
+
+	// Move the new embedded Terraform files into the workspace.
+	if err := tfClient.PrepareWorkspace(templateDir, vars); err != nil {
+		return false, fmt.Errorf("preparing terraform workspace: %w", err)
+	}
+
+	hasDiff, err := tfClient.Plan(ctx, logLevel)
+	if err != nil {
+		return false, fmt.Errorf("terraform plan: %w", err)
+	}
+
+	// If we are planning in a new workspace, we don't want to show a diff
+	if isNewWorkspace {
+		return false, nil
+	}
+
+	if hasDiff {
+		if err := tfClient.ShowPlan(ctx, logLevel, outWriter); err != nil {
+			return false, fmt.Errorf("terraform show plan: %w", err)
+		}
+	}
+	return hasDiff, nil
+}
+
+// restoreBackup replaces the existing Terraform workspace with the backup.
+func restoreBackup(fileHandler file.Handler, workingDir, backupDir string) error {
+	if err := fileHandler.RemoveAll(workingDir); err != nil {
+		return fmt.Errorf("removing existing workspace: %w", err)
+	}
+	if err := fileHandler.CopyDir(
+		backupDir,
+		workingDir,
+	); err != nil {
+		return fmt.Errorf("replacing terraform workspace with backup: %w", err)
+	}
+
+	if err := fileHandler.RemoveAll(backupDir); err != nil {
+		return fmt.Errorf("removing backup directory: %w", err)
+	}
+	return nil
+}
+
+// ensureFileNotExist checks if a single file or directory does not exist, returning an error if it does.
+func ensureFileNotExist(fileHandler file.Handler, fileName string) error {
+	if _, err := fileHandler.Stat(fileName); err != nil {
+		if !os.IsNotExist(err) {
+			return fmt.Errorf("checking %q: %w", fileName, err)
+		}
+		return nil
+	}
+	return fmt.Errorf("%q already exists", fileName)
+}