Change type of Tool.InputSchema to be JsonElement (#4)

* Change type of Tool.InputSchema to be JsonElement

* Add schema validation in the InputSchema property setter.

* Simplify AIFunction tool adapter.

---------

Co-authored-by: Eirik Tsarpalis <eirik.tsarpalis@gmail.com>

tests/ModelContextProtocol.Tests/Protocol/ProtocolTypeTests.cs

@@ -0,0 +1,52 @@
+using ModelContextProtocol.Protocol.Types;
+using System.Text.Json;
+
+namespace ModelContextProtocol.Tests.Protocol;
+
+public static class ProtocolTypeTests
+{
+    [Fact]
+    public static void ToolInputSchema_HasValidDefaultSchema()
+    {
+        var tool = new Tool();
+        JsonElement jsonElement = tool.InputSchema;
+
+        Assert.Equal(JsonValueKind.Object, jsonElement.ValueKind);
+        Assert.Single(jsonElement.EnumerateObject());
+        Assert.True(jsonElement.TryGetProperty("type", out JsonElement typeElement));
+        Assert.Equal(JsonValueKind.String, typeElement.ValueKind);
+        Assert.Equal("object", typeElement.GetString());
+    }
+
+    [Theory]
+    [InlineData("null")]
+    [InlineData("false")]
+    [InlineData("true")]
+    [InlineData("3.5e3")]
+    [InlineData("[]")]
+    [InlineData("{}")]
+    [InlineData("""{"properties":{}}""")]
+    [InlineData("""{"type":"number"}""")]
+    [InlineData("""{"type":"array"}""")]
+    [InlineData("""{"type":["object"]}""")]
+    public static void ToolInputSchema_RejectsInvalidSchemaDocuments(string invalidSchema)
+    {
+        using var document = JsonDocument.Parse(invalidSchema);
+        var tool = new Tool();
+
+        Assert.Throws<ArgumentException>(() => tool.InputSchema = document.RootElement);
+    }
+
+    [Theory]
+    [InlineData("""{"type":"object"}""")]
+    [InlineData("""{"type":"object", "properties": {}, "required" : [] }""")]
+    [InlineData("""{"type":"object", "title": "MyAwesomeTool", "description": "It's awesome!", "properties": {}, "required" : ["NotAParam"] }""")]
+    public static void ToolInputSchema_AcceptsValidSchemaDocuments(string validSchema)
+    {
+        using var document = JsonDocument.Parse(validSchema);
+        var tool = new Tool();
+
+        tool.InputSchema = document.RootElement;
+        Assert.True(JsonElement.DeepEquals(document.RootElement, tool.InputSchema));
+    }
+}