Make try terminate process more graceful

src/DiffEngine.Tests/WindowsProcessTests.cs

@@ -53,4 +53,115 @@ public void FindAll_ReturnsProcessCommands()
             Debug.WriteLine($"{cmd.Process}: {cmd.Command}");
         }
     }
+
+    [Fact]
+    public void TryTerminateProcess_WithWindowedProcess_GracefullyCloses()
+    {
+        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            return;
+        }
+
+        // Start FakeDiffTool in windowed mode (has a main window)
+        var process = Process.Start(new ProcessStartInfo
+        {
+            FileName = FakeDiffTool.Exe,
+            Arguments = "--windowed",
+            UseShellExecute = false,
+            CreateNoWindow = true
+        });
+
+        Assert.NotNull(process);
+
+        try
+        {
+            // Wait for the process to fully start and create its window
+            Thread.Sleep(1000);
+
+            // Attempt graceful termination via CloseMainWindow
+            var result = WindowsProcess.TryTerminateProcess(process.Id);
+
+            Assert.True(result);
+
+            // Verify process exited gracefully
+            Assert.True(process.WaitForExit(1000));
+        }
+        finally
+        {
+            // Cleanup: ensure process is killed if test fails
+            try
+            {
+                if (!process.HasExited)
+                {
+                    process.Kill();
+                }
+            }
+            catch
+            {
+                // Ignore cleanup errors
+            }
+        }
+    }
+
+    [Fact]
+    public void TryTerminateProcess_WithNonWindowedProcess_ForcefullyTerminates()
+    {
+        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            return;
+        }
+
+        // Start FakeDiffTool - a console process without a main window
+        var process = Process.Start(new ProcessStartInfo
+        {
+            FileName = FakeDiffTool.Exe,
+            UseShellExecute = false,
+            CreateNoWindow = true
+        });
+
+        Assert.NotNull(process);
+
+        try
+        {
+            // Wait for the process to fully start
+            Thread.Sleep(500);
+
+            // Attempt termination (should fall back to forceful kill since no main window)
+            var result = WindowsProcess.TryTerminateProcess(process.Id);
+
+            Assert.True(result);
+
+            // Verify process was terminated (should be immediate with forceful kill)
+            Assert.True(process.WaitForExit(1000));
+        }
+        finally
+        {
+            // Cleanup: ensure process is killed if test fails
+            try
+            {
+                if (!process.HasExited)
+                {
+                    process.Kill();
+                }
+            }
+            catch
+            {
+                // Ignore cleanup errors
+            }
+        }
+    }
+
+    [Fact]
+    public void TryTerminateProcess_WithInvalidProcessId_ReturnsFalse()
+    {
+        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            return;
+        }
+
+        // Use a very unlikely process ID
+        var result = WindowsProcess.TryTerminateProcess(999999);
+
+        Assert.False(result);
+    }
 }

src/DiffEngine/Process/WindowsProcess.cs

@@ -127,6 +127,28 @@ struct PROCESS_BASIC_INFORMATION
 
     public static bool TryTerminateProcess(int processId)
     {
+        // First, try graceful shutdown by closing the main window
+        try
+        {
+            using var process = System.Diagnostics.Process.GetProcessById(processId);
+
+            // Try to close the main window gracefully
+            if (process.CloseMainWindow())
+            {
+                // Wait up to 5 seconds for graceful exit
+                if (process.WaitForExit(5000))
+                {
+                    return true;
+                }
+            }
+            // If no main window or still running, fall through to force kill
+        }
+        catch
+        {
+            // Process may have already exited or be inaccessible, fall through to force kill
+        }
+
+        // Fall back to forceful termination
         using var processHandle = OpenProcess(PROCESS_TERMINATE, false, processId);
         if (processHandle.IsInvalid)
         {

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649;NU1608;NU1109</NoWarn>
-    <Version>18.0.0</Version>
+    <Version>18.0.1</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <PackageTags>Testing, Snapshot, Diff, Compare</PackageTags>
     <Description>Launches diff tools based on file extensions. Designed to be consumed by snapshot testing libraries.</Description>

src/FakeDiffTool/FakeDiffTool.csproj

@@ -2,12 +2,13 @@
 
   <PropertyGroup>
     <OutputType>WinExe</OutputType>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net10.0-windows</TargetFramework>
+    <UseWindowsForms>true</UseWindowsForms>
     <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
     <OutputPath>bin</OutputPath>
     <RuntimeIdentifier Condition=" '$(OS)' == 'Windows_NT' ">win-x64</RuntimeIdentifier>
     <RuntimeIdentifier Condition=" '$(OS)' != 'Windows_NT' ">osx-x64</RuntimeIdentifier>
-    <PublishTrimmed>true</PublishTrimmed>
+    <PublishTrimmed>false</PublishTrimmed>
     <PublishReadyToRun>true</PublishReadyToRun>
     <PublishSingleFile>true</PublishSingleFile>
   </PropertyGroup>

src/FakeDiffTool/Program.cs

@@ -1,7 +1,28 @@
-using System.Threading;
+using System;
+using System.Threading;
+using System.Windows.Forms;
 
 class Program
 {
-    static void Main() =>
-        Thread.Sleep(5000);
+    [STAThread]
+    static void Main(string[] args)
+    {
+        // If --windowed is passed, create a simple form that can be closed gracefully
+        if (args.Length > 0 && args[0] == "--windowed")
+        {
+            Application.EnableVisualStyles();
+            Application.SetCompatibleTextRenderingDefault(false);
+            Application.Run(new Form
+            {
+                Text = "FakeDiffTool",
+                WindowState = FormWindowState.Minimized,
+                ShowInTaskbar = false
+            });
+        }
+        else
+        {
+            // Default behavior: just sleep (no main window)
+            Thread.Sleep(5000);
+        }
+    }
 }