feat(headless): complete portable single-session host

src/AcDream.Headless/Configuration/HeadlessCommandLine.cs

@@ -0,0 +1,83 @@
+namespace AcDream.Headless.Configuration;
+
+internal sealed record HeadlessCommandLine(
+    string Command,
+    string ConfigurationPath,
+    HeadlessPathOverrides Paths)
+{
+    internal static HeadlessCommandLine Parse(
+        IReadOnlyList<string> arguments)
+    {
+        ArgumentNullException.ThrowIfNull(arguments);
+        if (arguments.Count < 3)
+            throw new HeadlessCommandLineException("Missing command options.");
+
+        string command = arguments[0];
+        if (command is not ("validate" or "run"))
+            throw new HeadlessCommandLineException("Unknown command.");
+
+        string? configurationPath = null;
+        string? configDirectory = null;
+        string? dataDirectory = null;
+        string? cacheDirectory = null;
+        for (int index = 1; index < arguments.Count; index += 2)
+        {
+            if (index + 1 >= arguments.Count)
+            {
+                throw new HeadlessCommandLineException(
+                    "Every command option requires a value.");
+            }
+
+            string name = arguments[index];
+            string value = arguments[index + 1];
+            if (string.IsNullOrWhiteSpace(value))
+            {
+                throw new HeadlessCommandLineException(
+                    "Command option values cannot be empty.");
+            }
+
+            switch (name)
+            {
+                case "--config":
+                    SetOnce(ref configurationPath, value);
+                    break;
+                case "--config-dir":
+                    SetOnce(ref configDirectory, value);
+                    break;
+                case "--data-dir":
+                    SetOnce(ref dataDirectory, value);
+                    break;
+                case "--cache-dir":
+                    SetOnce(ref cacheDirectory, value);
+                    break;
+                default:
+                    throw new HeadlessCommandLineException(
+                        "Unknown command option.");
+            }
+        }
+
+        if (configurationPath is null)
+        {
+            throw new HeadlessCommandLineException(
+                "The --config option is required.");
+        }
+
+        return new HeadlessCommandLine(
+            command,
+            configurationPath,
+            new HeadlessPathOverrides(
+                configDirectory,
+                dataDirectory,
+                cacheDirectory));
+    }
+
+    private static void SetOnce(ref string? destination, string value)
+    {
+        if (destination is not null)
+        {
+            throw new HeadlessCommandLineException(
+                "Command options cannot be repeated.");
+        }
+        destination = value;
+    }
+}