tart export: make export path optional (#454)

Sources/tart/Commands/Export.swift

@@ -1,16 +1,44 @@
 import ArgumentParser
+import Foundation
 
 struct Export: AsyncParsableCommand {
-  static var configuration = CommandConfiguration(abstract: "Export VM to a file")
+  static var configuration = CommandConfiguration(abstract: "Export VM to a compressed .tvm file")
 
   @Argument(help: "Source VM name.")
   var name: String
 
   @Argument(help: "Path to the destination file.")
-  var path: String
+  var path: String?
 
   func run() async throws {
+    let correctedPath: String
+
+    if let path = path {
+      correctedPath = path
+    } else {
+      correctedPath = "\(name).tvm"
+
+      if FileManager.default.fileExists(atPath: correctedPath) {
+        while true {
+          if userWantsOverwrite(correctedPath) {
+            break
+          } else {
+            return
+          }
+        }
+      }
+    }
+
     print("exporting...")
-    try VMStorageHelper.open(name).exportToArchive(path: path)
+
+    try VMStorageHelper.open(name).exportToArchive(path: correctedPath)
+  }
+
+  func userWantsOverwrite(_ filename: String) -> Bool {
+    print("file \(filename) already exists, are you sure you want to overwrite it? (yes, [no])? ", terminator: "")
+
+    let answer = readLine()!
+
+    return answer == "yes"
   }
 }

Sources/tart/Commands/Import.swift

@@ -2,7 +2,7 @@ import ArgumentParser
 import Foundation
 
 struct Import: AsyncParsableCommand {
-  static var configuration = CommandConfiguration(abstract: "Import VM from a file")
+  static var configuration = CommandConfiguration(abstract: "Import VM from a compressed .tvm file")
 
   @Argument(help: "Path to a file created with \"tart export\".")
   var path: String