Fix string handling edge cases and case-insensitive URL/file detection (#290)

* Initial plan

* Fix CapitalizeFirstCharacter for empty string and single char edge cases

Co-authored-by: christianhelle <710400+christianhelle@users.noreply.github.com>

* Fix case-insensitive URL handling and refactor ParseOpenApi

Co-authored-by: christianhelle <710400+christianhelle@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: christianhelle <710400+christianhelle@users.noreply.github.com>

Author: Copilot

src/HttpGenerator.Core/OpenApiDocumentFactory.cs

@@ -81,7 +81,8 @@ private static async Task<string> GetHttpContent(string openApiPath)
     /// <returns>True if the path is an HTTP URL, otherwise false.</returns>
     private static bool IsHttp(string path)
     {
-        return path.StartsWith("http://") || path.StartsWith("https://");
+        return path.StartsWith("http://", StringComparison.OrdinalIgnoreCase) || 
+               path.StartsWith("https://", StringComparison.OrdinalIgnoreCase);
     }
 
     /// <summary>
@@ -91,6 +92,7 @@ private static bool IsHttp(string path)
     /// <returns>True if the path is a YAML file, otherwise false.</returns>
     private static bool IsYaml(string path)
     {
-        return path.EndsWith("yaml") || path.EndsWith("yml");
+        return path.EndsWith(".yaml", StringComparison.OrdinalIgnoreCase) || 
+               path.EndsWith(".yml", StringComparison.OrdinalIgnoreCase);
     }
 }

src/HttpGenerator.Core/StringExtensions.cs

@@ -28,6 +28,12 @@ public static string ConvertRouteToCamelCase(this string str)
 
     public static string CapitalizeFirstCharacter(this string str)
     {
+        if (string.IsNullOrEmpty(str))
+            return str;
+        
+        if (str.Length == 1)
+            return str.ToUpperInvariant();
+            
         return str.Substring(0, 1).ToUpperInvariant() +
                str.Substring(1, str.Length - 1);
     }

src/HttpGenerator.Tests/StringExtensionsTests.cs

@@ -26,6 +26,8 @@ public void ConvertRouteToCamelCase_ShouldConvert(string input, string expected)
     [Theory]
     [InlineData("string", "String")]
     [InlineData("anotherString", "AnotherString")]
+    [InlineData("a", "A")]
+    [InlineData("", "")]
     public void CapitalizeFirstCharacter_ShouldCapitalize(string input, string expected)
     {
         var result = input.CapitalizeFirstCharacter();

src/HttpGenerator/Validation/OpenApiValidator.cs

@@ -24,7 +24,7 @@ private static async Task<Stream> GetStream(
         string input,
         CancellationToken cancellationToken)
     {
-        if (input.StartsWith("http"))
+        if (input.StartsWith("http", StringComparison.OrdinalIgnoreCase))
         {
             try
             {
@@ -63,12 +63,20 @@ ex is SecurityException ||
 
     private static async Task<ReadResult> ParseOpenApi(string openApiFile)
     {
-        var directoryName = new FileInfo(openApiFile).DirectoryName;
+        Uri baseUrl;
+        if (openApiFile.StartsWith("http", StringComparison.OrdinalIgnoreCase))
+        {
+            baseUrl = new Uri(openApiFile);
+        }
+        else
+        {
+            var directoryName = new FileInfo(openApiFile).DirectoryName;
+            baseUrl = new Uri($"file://{directoryName}{Path.DirectorySeparatorChar}");
+        }
+        
         var openApiReaderSettings = new OpenApiReaderSettings
         {
-            BaseUrl = openApiFile.StartsWith("http", StringComparison.OrdinalIgnoreCase)
-                ? new Uri(openApiFile)
-                : new Uri($"file://{directoryName}{Path.DirectorySeparatorChar}")
+            BaseUrl = baseUrl
         };
 
         await using var stream = await GetStream(openApiFile, CancellationToken.None);