Replace AIFunctionParameterMetadata with MethodInfo (#5886)

* Replace AIFunctionParemeterMetadata with MethodInfo

* Update src/Libraries/Microsoft.Extensions.AI.Abstractions/Functions/AIFunctionMetadata.cs

Co-authored-by: Stephen Toub <[email protected]>

* Update src/Libraries/Microsoft.Extensions.AI.Abstractions/Functions/AIFunctionMetadata.cs

Co-authored-by: Stephen Toub <[email protected]>

* Address feedback,

* Update src/Libraries/Microsoft.Extensions.AI.Abstractions/Utilities/AIJsonUtilities.Schema.cs

Co-authored-by: Steve Sanderson <[email protected]>

* Flatten AIFunctionMetadata properties into AIFunction.

* Address feedback.

* Mark JSO as virtual

---------

Co-authored-by: Stephen Toub <[email protected]>
Co-authored-by: Steve Sanderson <[email protected]>

src/Libraries/Microsoft.Extensions.AI.Abstractions/Functions/AIFunction.cs

@@ -3,6 +3,8 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Reflection;
+using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Shared.Collections;
@@ -13,8 +15,52 @@ namespace Microsoft.Extensions.AI;
 [DebuggerDisplay("{DebuggerDisplay,nq}")]
 public abstract class AIFunction : AITool
 {
-    /// <summary>Gets metadata describing the function.</summary>
-    public abstract AIFunctionMetadata Metadata { get; }
+    /// <summary>Gets the name of the function.</summary>
+    public abstract string Name { get; }
+
+    /// <summary>Gets a description of the function, suitable for use in describing the purpose to a model.</summary>
+    public abstract string Description { get; }
+
+    /// <summary>Gets a JSON Schema describing the function and its input parameters.</summary>
+    /// <remarks>
+    /// <para>
+    /// When specified, declares a self-contained JSON schema document that describes the function and its input parameters.
+    /// A simple example of a JSON schema for a function that adds two numbers together is shown below:
+    /// </para>
+    /// <code>
+    /// {
+    ///   "title" : "addNumbers",
+    ///   "description": "A simple function that adds two numbers together.",
+    ///   "type": "object",
+    ///   "properties": {
+    ///     "a" : { "type": "number" },
+    ///     "b" : { "type": "number", "default": 1 }
+    ///   }, 
+    ///   "required" : ["a"]
+    /// }
+    /// </code>
+    /// <para>
+    /// The metadata present in the schema document plays an important role in guiding AI function invocation.
+    /// </para>
+    /// <para>
+    /// When no schema is specified, consuming chat clients should assume the "{}" or "true" schema, indicating that any JSON input is admissible.
+    /// </para>
+    /// </remarks>
+    public virtual JsonElement JsonSchema => AIJsonUtilities.DefaultJsonSchema;
+
+    /// <summary>
+    /// Gets the underlying <see cref="MethodInfo"/> that this <see cref="AIFunction"/> might be wrapping.
+    /// </summary>
+    /// <remarks>
+    /// Provides additional metadata on the function and its signature. Implementations not wrapping .NET methods may return <see langword="null"/>.
+    /// </remarks>
+    public virtual MethodInfo? UnderlyingMethod => null;
+
+    /// <summary>Gets any additional properties associated with the function.</summary>
+    public virtual IReadOnlyDictionary<string, object?> AdditionalProperties => EmptyReadOnlyDictionary<string, object?>.Instance;
+
+    /// <summary>Gets a <see cref="JsonSerializerOptions"/> that can be used to marshal function parameters.</summary>
+    public virtual JsonSerializerOptions? JsonSerializerOptions => AIJsonUtilities.DefaultOptions;
 
     /// <summary>Invokes the <see cref="AIFunction"/> and returns its result.</summary>
     /// <param name="arguments">The arguments to pass to the function's invocation.</param>
@@ -30,7 +76,7 @@ public abstract class AIFunction : AITool
     }
 
     /// <inheritdoc/>
-    public override string ToString() => Metadata.Name;
+    public override string ToString() => Name;
 
     /// <summary>Invokes the <see cref="AIFunction"/> and returns its result.</summary>
     /// <param name="arguments">The arguments to pass to the function's invocation.</param>
@@ -42,8 +88,5 @@ public abstract class AIFunction : AITool
 
     /// <summary>Gets the string to display in the debugger for this instance.</summary>
     [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-    private string DebuggerDisplay =>
-        string.IsNullOrWhiteSpace(Metadata.Description) ?
-            Metadata.Name :
-            $"{Metadata.Name} ({Metadata.Description})";
+    private string DebuggerDisplay => string.IsNullOrWhiteSpace(Description) ? Name : $"{Name} ({Description})";
 }