feat(startup): add configurable game root

engine/Age.Engine.Tests/GameRootSelectionTests.cs

@@ -0,0 +1,132 @@
+using Age.Engine.Sys4;
+
+public sealed class GameRootSelectionTests
+{
+    [Fact]
+    public void ExplicitRelativeOverrideWinsAndResolvesAgainstCurrentDirectory()
+    {
+        using var tree = new TempTree();
+        string executableDirectory = tree.CreateDirectory("exe", withCatalog: true);
+        string currentDirectory = tree.CreateDirectory("working", withCatalog: true);
+        string selectedDirectory = tree.CreateDirectory("selected", withCatalog: true);
+
+        GameRootSelection selection = GameRootSelection.Resolve(
+            ["--scene", "SYSTEM4", "--game-root", Path.Combine("..", "selected")],
+            Path.Combine(executableDirectory, "OpenMaidEngine.exe"),
+            currentDirectory);
+
+        Assert.Equal(selectedDirectory, selection.Root);
+        Assert.Equal(GameRootSource.LaunchArgument, selection.Source);
+        Assert.Equal("launch-argument", selection.SourceName);
+    }
+
+    [Fact]
+    public void DuplicateOverrideUsesLastDirectory()
+    {
+        using var tree = new TempTree();
+        string currentDirectory = tree.CreateDirectory("working");
+        tree.CreateDirectory("first", withCatalog: true);
+        string second = tree.CreateDirectory("second", withCatalog: true);
+
+        GameRootSelection selection = GameRootSelection.Resolve(
+            ["--game-root", Path.Combine("..", "first"),
+             "--game-root", Path.Combine("..", "second")],
+            null,
+            currentDirectory);
+
+        Assert.Equal(second, selection.Root);
+    }
+
+    [Fact]
+    public void DefaultsToExecutableDirectory()
+    {
+        using var tree = new TempTree();
+        string executableDirectory = tree.CreateDirectory("exe", withCatalog: true);
+        string currentDirectory = tree.CreateDirectory("working", withCatalog: true);
+
+        GameRootSelection selection = GameRootSelection.Resolve(
+            [], Path.Combine(executableDirectory, "OpenMaidEngine.exe"), currentDirectory);
+
+        Assert.Equal(executableDirectory, selection.Root);
+        Assert.Equal(GameRootSource.ExecutableDirectory, selection.Source);
+    }
+
+    [Fact]
+    public void FallsBackToCurrentDirectory()
+    {
+        using var tree = new TempTree();
+        string executableDirectory = tree.CreateDirectory("exe");
+        string currentDirectory = tree.CreateDirectory("working", withCatalog: true);
+
+        GameRootSelection selection = GameRootSelection.Resolve(
+            [], Path.Combine(executableDirectory, "OpenMaidEngine"), currentDirectory);
+
+        Assert.Equal(currentDirectory, selection.Root);
+        Assert.Equal(GameRootSource.CurrentDirectory, selection.Source);
+    }
+
+    [Theory]
+    [InlineData("--game-root")]
+    [InlineData("--game-root", "--scene", "SYSTEM4")]
+    public void MissingOverridePathIsRejected(params string[] arguments)
+    {
+        using var tree = new TempTree();
+
+        var error = Assert.Throws<ArgumentException>(
+            () => GameRootSelection.Resolve(arguments, null, tree.Root));
+
+        Assert.Contains("--game-root requires a directory path", error.Message);
+    }
+
+    [Fact]
+    public void ExplicitDirectoryWithoutCatalogIsRejectedWithoutFallback()
+    {
+        using var tree = new TempTree();
+        string executableDirectory = tree.CreateDirectory("exe", withCatalog: true);
+        string currentDirectory = tree.CreateDirectory("working");
+        tree.CreateDirectory("invalid");
+
+        var error = Assert.Throws<ArgumentException>(() => GameRootSelection.Resolve(
+            ["--game-root", Path.Combine("..", "invalid")],
+            Path.Combine(executableDirectory, "OpenMaidEngine.exe"),
+            currentDirectory));
+
+        Assert.Contains("does not contain SYS4INI.BIN", error.Message);
+    }
+
+    [Fact]
+    public void MissingDefaultsReportSearchedLocationsAndOverride()
+    {
+        using var tree = new TempTree();
+        string executableDirectory = tree.CreateDirectory("exe");
+        string currentDirectory = tree.CreateDirectory("working");
+
+        var error = Assert.Throws<ArgumentException>(() => GameRootSelection.Resolve(
+            [], Path.Combine(executableDirectory, "OpenMaidEngine"), currentDirectory));
+
+        Assert.Contains(executableDirectory, error.Message);
+        Assert.Contains(currentDirectory, error.Message);
+        Assert.Contains("--game-root <directory>", error.Message);
+    }
+
+    private sealed class TempTree : IDisposable
+    {
+        public string Root { get; } = Path.Combine(
+            Path.GetTempPath(), "age-game-root-tests", Guid.NewGuid().ToString("N"));
+
+        public TempTree() => Directory.CreateDirectory(Root);
+
+        public string CreateDirectory(string name, bool withCatalog = false)
+        {
+            string path = Path.Combine(Root, name);
+            Directory.CreateDirectory(path);
+            if (withCatalog) File.WriteAllBytes(Path.Combine(path, "SYS4INI.BIN"), []);
+            return Path.GetFullPath(path);
+        }
+
+        public void Dispose()
+        {
+            if (Directory.Exists(Root)) Directory.Delete(Root, recursive: true);
+        }
+    }
+}