Support adding a random number to computer names.

Addresses #33.

Author: SvenGroot

README.md

@@ -292,6 +292,21 @@ To provision a domain account for the computer, you can use the following comman
 djoin.exe /provision /domain domainname /machine machinename /savefile filename
 ```
 
+### Specifying a computer name
+
+When you provide a computer name using the [`-ComputerName`][] argument, the Answer File Generator
+does not check whether that computer name is valid. Specifying an invalid computer name will cause
+Windows setup to fail when applying the answer file. Make sure you follow the
+[rules for computer names](https://learn.microsoft.com/windows-hardware/customize/desktop/unattend/microsoft-windows-shell-setup-computername)
+when choosing a name.
+
+If you do not specify a computer name, Windows will automatically choose one during installation.
+In addition, you can also use the `#` character to generate a name containing a random number.
+
+Every occurrence of `#` in the provided computer name will be replaced with a digit between 0 and 9
+when generating the answer file. For example `PC-###` would be replaced with `PC-123` (or some
+other random number).
+
 ## Using JSON to provide options
 
 Because the large number of command line arguments may get unwieldy, the Answer File Generator
@@ -338,6 +353,7 @@ any other adverse effects caused by the use of answer files generated by this to
 [`-AutoLogonUser`]: doc/CommandLine.md#-autologonuser
 [`-AutoLogonCount`]: doc/CommandLine.md#-autologoncount
 [`-Feature`]: doc/CommandLine.md#-feature
+[`-ComputerName`]: doc/CommandLine.md#-computername
 [`-FirstLogonCommand`]: doc/CommandLine.md#-firstlogoncommand
 [`-Install`]: doc/CommandLine.md#-install
 [`-InstallToDisk`]: doc/CommandLine.md#-installtodisk

doc/CommandLine.md

@@ -404,10 +404,14 @@ Required argument: -JoinDomain
 
 ### `-ComputerName`
 
-The network name for the computer. If not specified, Windows will generate a default name.
+The network name for the computer. If not specified, Windows will generate a default name. Any `#`
+characters in the name will be replaced with a random digit between 0 and 9. For example, `PC-###`
+would be replaced with `PC-123` (or some other random number).
 
 Must not be blank.
 
+See [specifying a computer name](../README.md/#specifying-a-computer-name).
+
 ```yaml
 Value: <String>
 Alias: -n

src/GenerateAnswerFile/Properties/Resources.Designer.cs

@@ -142,7 +142,7 @@
     <value>User account options:</value>
   </data>
   <data name="ComputerNameDescription" xml:space="preserve">
-    <value>The network name for the computer. If not specified, Windows will generate a default name.</value>
+    <value>The network name for the computer. If not specified, Windows will generate a default name. Any '#' characters in the name will be replaced with a random digit between 0 and 9. For example, 'PC-###' would be replaced with 'PC-123' (or some other random number).</value>
   </data>
   <data name="DisableCloudDescription" xml:space="preserve">
     <value>Disable Windows cloud consumer features. This prevents auto-installation of recommended store apps.</value>

src/GenerateAnswerFile/Properties/Resources.resx

@@ -3,6 +3,7 @@
     "Override": true,
     "Text": "Displays a help message."
   },
+  "ComputerName": "See [specifying a computer name](../README.md/#specifying-a-computer-name).",
   "Feature": "See [optional features](../README.md#optional-features).",
   "ImageIndex": "See [selecting the edition to install](../README.md#selecting-the-edition-to-install).",
   "Install": "See [installation method](../README.md#installation-method).",

src/GenerateAnswerFile/Properties/launchSettings.json

@@ -1,5 +1,6 @@
 using System.Drawing;
 using System.Text.Json;
+using System.Text.RegularExpressions;
 
 namespace Ookii.AnswerFile.Tests;
 
@@ -193,4 +194,25 @@ public void TestJsonSerializationManual()
         Assert.AreEqual(new Version(10, 0, 22000, 1), install.OptionalFeatures.WindowsVersion);
         CollectionAssert.AreEqual(new[] { "Microsoft-Windows-Subsystem-Linux", "VirtualMachinePlatform" }, install.OptionalFeatures.Features);
     }
+
+    [TestMethod]
+    public void TestRandomComputerName()
+    {
+        var options = new AnswerFileOptions()
+        {
+            ComputerName = "test-####",
+        };
+
+        Assert.IsTrue(Regex.IsMatch(options.ComputerName, @"^test-\d{4}$"));
+        options.ComputerName = "foo#bar";
+        Assert.IsTrue(Regex.IsMatch(options.ComputerName, @"^foo\dbar$"));
+        options.ComputerName = "####################";
+        Assert.IsTrue(Regex.IsMatch(options.ComputerName, @"^\d{20}$"));
+        options.ComputerName = "test-###-#####";
+        Assert.IsTrue(Regex.IsMatch(options.ComputerName, @"^test-\d{3}-\d{5}$"));
+
+        var json = "{\"ComputerName\": \"test-####\"}";
+        options = AnswerFileOptions.FromJson(json);
+        Assert.IsTrue(Regex.IsMatch(options!.ComputerName!, @"^test-\d{4}$"));
+    }
 }

src/GenerateAnswerFile/mdhelp.json

@@ -1,7 +1,9 @@
 using System.Collections.ObjectModel;
 using System.Drawing;
+using System.Text;
 using System.Text.Json;
 using System.Text.Json.Serialization;
+using System.Text.RegularExpressions;
 
 namespace Ookii.AnswerFile;
 
@@ -10,14 +12,13 @@ namespace Ookii.AnswerFile;
 /// <see cref="AnswerFileGenerator"/> class.
 /// </summary>
 /// <threadsafety instance="false" static="true"/>
-public class AnswerFileOptions
+public partial class AnswerFileOptions
 {
+    private string? _computerName;
     private Collection<LocalCredential>? _localAccounts;
     private Collection<string>? _firstLogonCommands;
     private Collection<string>? _firstLogonScripts;
 
-#pragma warning disable CA1822 // Mark members as static
-
     /// <summary>
     /// Gets the schema that can be used for validation of the JSON representation of this object.
     /// </summary>
@@ -29,8 +30,6 @@ public class AnswerFileOptions
     [JsonPropertyName("$schema")]
     public string JsonSchema => "https://www.ookii.org/Link/AnswerFileJsonSchema-2.0";
 
-#pragma warning restore CA1822 // Mark members as static
-
     /// <summary>
     /// Gets or sets the installation method to use, along with the options for that method.
     /// </summary>
@@ -66,7 +65,31 @@ public class AnswerFileOptions
     /// The computer name, or <see langword="null"/> to let Windows pick a computer name. The
     /// default value is <see langword="null"/>.
     /// </value>
-    public string? ComputerName { get; set; }
+    /// <remarks>
+    /// <para>
+    ///   If this property is set to a value containing the # character, each # will be replaced
+    ///   with a random digit between 0 and 9. For example, the value "PC-###" will be replaced with
+    ///   "PC-123" (or any other random number).
+    /// </para>
+    /// <note type="note">
+    ///   While random numbers can be used to generate a distinct computer name, it is not
+    ///   necessarily guaranteed to be a unique name on the network.
+    /// </note>
+    /// </remarks>
+    public string? ComputerName
+    {
+        get => _computerName;
+        set
+        {
+            if (value != null)
+            {
+                // Replace # with random digits.
+                value = RandomNumberRegex().Replace(value, m => Random.Shared.Next().ToString(m.Value).Substring(0, m.Length));
+            }
+
+            _computerName = value;
+        }
+    }
 
     /// <summary>
     /// Gets or sets a value which indicates whether Windows Defender is enabled after installation.
@@ -286,4 +309,10 @@ public Collection<string> FirstLogonScripts
     /// <returns>A JSON representation of the current instance.</returns>
     public string ToJson()
         => JsonSerializer.Serialize(this, typeof(AnswerFileOptions), SourceGenerationContext.Default);
+
+    // This regex is used to replace the # characters in the computer name with random digits.
+    // It processes groups of # in batches of 9, to avoid exceeding the maximum value of an int
+    // for a single random number.
+    [GeneratedRegex("#{1,9}")]
+    private static partial Regex RandomNumberRegex();
 }