#3 Fix using replacement

Author: inyutin-maxim

System.IO.Abstractions.Analyzers.Tests/Analyzers/FileServiceInterfaceInjectionAnalyzerTests.cs

@@ -11,6 +11,7 @@ public class FileServiceInterfaceInjectionAnalyzerTests : CSharpDiagnosticAnalyz
 	{
 		[Theory]
 		[InlineData("Valid.txt")]
+		[InlineData("Valid2.txt")]
 		public void Analyzer_is_not_triggered(string filename)
 		{
 			var source = ReadFile(filename);

System.IO.Abstractions.Analyzers.Tests/CodeFixes/FileServiceInterfaceInjectionCodeFixTests.cs

@@ -13,6 +13,7 @@ public class FileServiceInterfaceInjectionCodeFixTests :
 		[Theory]
 		[InlineData("BeforeFix.txt", "AfterFix.txt")]
 		[InlineData("BeforeFixWithoutConstructor.txt", "AfterFix.txt")]
+		[InlineData("BeforeFixExistsAbstractionsUsing.txt", "AfterFix.txt")]
 		public void CodeFix(string sourceBefore, string sourceAfter)
 		{
 			var sourceBeforeFix = ReadFile(sourceBefore);

System.IO.Abstractions.Analyzers.Tests/TestData/Analyzer/FileServiceInterfaceInjectionAnalyzer/Valid2.txt

@@ -0,0 +1,15 @@
+using System.IO;
+using System.IO.Abstractions;
+
+namespace SomeNameSpace
+{
+	public class Valid
+	{
+		private readonly IFileSystem _fileSystem;
+
+		public Valid(IFileSystem fileSystem)
+		{
+			_fileSystem = fileSystem;
+		}
+	}
+}

System.IO.Abstractions.Analyzers.Tests/TestData/CodeFix/FileServiceInterfaceInjectionCodeFix/AfterFix.txt

@@ -1,3 +1,4 @@
+using System.IO;
 using System.IO.Abstractions;
 
 namespace SomeNameSpace

System.IO.Abstractions.Analyzers.Tests/TestData/CodeFix/FileServiceInterfaceInjectionCodeFix/BeforeFixExistsAbstractionsUsing.txt

@@ -0,0 +1,18 @@
+using System.IO;
+using System.IO.Abstractions;
+
+namespace SomeNameSpace
+{
+	public class WithOutFileSystem
+	{
+		public void SomeMethod()
+		{
+			const string filePath = "C:\\temp.txt";
+
+			if (File.Exists(filePath))
+			{
+				File.Delete(filePath);
+			}
+		}
+	}
+}

System.IO.Abstractions.Analyzers/Analyzers/FileServiceInterfaceInjectionAnalyzer.cs

@@ -66,7 +66,7 @@ protected override void AnalyzeCompilation(CompilationStartAnalysisContext compi
 
 					var fileSystem = classDeclarationSyntax.Members.OfType<FieldDeclarationSyntax>()
 						.FirstOrDefault(x =>
-							x.NormalizeWhitespace().ToFullString() == fileSystemContext.FileSystemType.Name);
+							x.Declaration.Type.NormalizeWhitespace().ToFullString() == fileSystemContext.FileSystemType.Name);
 
 					if (fileSystem == null)
 					{

System.IO.Abstractions.Analyzers/CodeActions/FileServiceInterfaceInjectionCodeAction.cs

@@ -48,9 +48,27 @@ protected override async Task<Document> GetChangedDocumentAsync(CancellationToke
 
 			var compilationUnitSyntax = RoslynClassFileSystem.GetCompilationUnit(_class);
 
-			if (compilationUnitSyntax.Usings.Any())
+			if (!compilationUnitSyntax.Usings.Any())
 			{
-				editor.ReplaceNode(RoslynClassFileSystem.GetSystemIoUsing(compilationUnitSyntax),
+				return editor.GetChangedDocument();
+			}
+
+			var fileSystem = RoslynClassFileSystem.GetUsing(compilationUnitSyntax, Constants.FileSystemNameSpace);
+
+			if (fileSystem != default(UsingDirectiveSyntax))
+			{
+				return editor.GetChangedDocument();
+			}
+
+			var systemIo = RoslynClassFileSystem.GetSystemIoUsing(compilationUnitSyntax);
+
+			if (systemIo == default(UsingDirectiveSyntax))
+			{
+				editor.InsertBefore(compilationUnitSyntax.Usings.FirstOrDefault(),
+					RoslynClassFileSystem.GetFileSystemUsing());
+			} else
+			{
+				editor.InsertAfter(compilationUnitSyntax.Usings.FirstOrDefault(),
 					RoslynClassFileSystem.GetFileSystemUsing());
 			}
 

System.IO.Abstractions.Analyzers/RoslynToken/RoslynClassFileSystem.cs

@@ -42,9 +42,14 @@ public static UsingDirectiveSyntax GetFileSystemUsing()
 		}
 
 		public static UsingDirectiveSyntax GetSystemIoUsing(CompilationUnitSyntax unit)
+		{
+			return GetUsing(unit, typeof(Path).Namespace);
+		}
+
+		public static UsingDirectiveSyntax GetUsing(CompilationUnitSyntax unit, string usingName)
 		{
 			return unit.Usings.FirstOrDefault(x =>
-				x.Name.NormalizeWhitespace().ToFullString().Equals(typeof(Path).Namespace));
+				x.Name.NormalizeWhitespace().ToFullString().Equals(usingName));
 		}
 
 		public static FieldDeclarationSyntax CreateFileSystemFieldDeclaration()