Filter tart list by source (#349)

* Adds Option to filter VMs by 'source'

* Tidy up columns for table on some Terminals

* Don't show headers if there's an error.

* Fixes linting errors.

* Update Sources/tart/Commands/List.swift

- removing the short name for now, as we don't know if we may need -s in the future
- removing the capitalization for the word "source" and adding an example instead

Co-authored-by: Nikolay Edigaryev <edigaryev@gmail.com>

* source should be an Optional flag. Reverts header change.

Co-authored-by: Nikolay Edigaryev <edigaryev@gmail.com>

Sources/tart/Commands/List.swift

@@ -5,17 +5,35 @@ import SwiftUI
 struct List: AsyncParsableCommand {
   static var configuration = CommandConfiguration(abstract: "List created VMs")
 
-  @Flag(name: [.short, .long], help: ArgumentHelp("Only display VM names"))
+  @Flag(name: [.short, .long], help: ArgumentHelp("Only display VM names."))
   var quiet: Bool = false
 
+  @Option(help: ArgumentHelp("Only display VMs from the specified source (e.g. --source local, --source oci)."))
+  var source: String?
+
+  func validate() throws {
+    guard let source = source else {
+      return
+    }
+
+    if !["local", "oci"].contains(source) {
+      throw ValidationError("'\(source)' is not a valid <source>")
+    }
+  }
+
   func run() async throws {
     do {
       if !quiet {
         print("Source\tName")
       }
 
-      displayTable("local", try VMStorageLocal().list())
-      displayTable("oci", try VMStorageOCI().list().map { (name, vmDir, _) in (name, vmDir) })
+      if source == nil || source == "local" {
+        displayTable("local", try VMStorageLocal().list())
+      }
+
+      if source == nil || source == "oci" {
+        displayTable("oci", try VMStorageOCI().list().map { (name, vmDir, _) in (name, vmDir) })
+      }
 
       Foundation.exit(0)
     } catch {
@@ -30,6 +48,7 @@ struct List: AsyncParsableCommand {
       if quiet {
         print(name)
       } else {
+        let source = source.padding(toLength: "Source".count, withPad: " ", startingAt: 0)
         print("\(source)\t\(name)")
       }
     }