agent-framework/dotnet/src/Microsoft.Agents.AI/FunctionInvocationDelegatingAgent.cs

// Copyright (c) Microsoft. All rights reserved.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.AI;

namespace Microsoft.Agents.AI;

/// <summary>
/// Internal agent decorator that adds function invocation middleware logic.
/// </summary>
internal sealed class FunctionInvocationDelegatingAgent : DelegatingAIAgent
{
    private readonly Func<AIAgent, FunctionInvocationContext, Func<FunctionInvocationContext, CancellationToken, ValueTask<object?>>, CancellationToken, ValueTask<object?>> _delegateFunc;

    internal FunctionInvocationDelegatingAgent(AIAgent innerAgent, Func<AIAgent, FunctionInvocationContext, Func<FunctionInvocationContext, CancellationToken, ValueTask<object?>>, CancellationToken, ValueTask<object?>> delegateFunc) : base(innerAgent)
    {
        this._delegateFunc = delegateFunc;
    }

    protected override Task<AgentResponse> RunCoreAsync(IEnumerable<ChatMessage> messages, AgentThread? thread = null, AgentRunOptions? options = null, CancellationToken cancellationToken = default)
        => this.InnerAgent.RunAsync(messages, thread, this.AgentRunOptionsWithFunctionMiddleware(options), cancellationToken);

    protected override IAsyncEnumerable<AgentResponseUpdate> RunCoreStreamingAsync(IEnumerable<ChatMessage> messages, AgentThread? thread = null, AgentRunOptions? options = null, CancellationToken cancellationToken = default)
        => this.InnerAgent.RunStreamingAsync(messages, thread, this.AgentRunOptionsWithFunctionMiddleware(options), cancellationToken);

    // Decorate options to add the middleware function
    private AgentRunOptions? AgentRunOptionsWithFunctionMiddleware(AgentRunOptions? options)
    {
        if (options is null || options.GetType() == typeof(AgentRunOptions))
        {
            options = new ChatClientAgentRunOptions();
        }

        if (options is not ChatClientAgentRunOptions aco)
        {
            throw new NotSupportedException($"Function Invocation Middleware is only supported without options or with {nameof(ChatClientAgentRunOptions)}.");
        }

        var originalFactory = aco.ChatClientFactory;
        aco.ChatClientFactory = chatClient =>
        {
            var builder = chatClient.AsBuilder();

            if (originalFactory is not null)
            {
                builder.Use(originalFactory);
            }

            return builder.ConfigureOptions(co
                => co.Tools = co.Tools?.Select(tool => tool is AIFunction aiFunction
                        ? new MiddlewareEnabledFunction(this.InnerAgent, aiFunction, this._delegateFunc)
                        : tool)
                    .ToList())
                .Build();
        };

        return options;
    }

    private sealed class MiddlewareEnabledFunction(AIAgent innerAgent, AIFunction innerFunction, Func<AIAgent, FunctionInvocationContext, Func<FunctionInvocationContext, CancellationToken, ValueTask<object?>>, CancellationToken, ValueTask<object?>> next) : DelegatingAIFunction(innerFunction)
    {
        protected override async ValueTask<object?> InvokeCoreAsync(AIFunctionArguments arguments, CancellationToken cancellationToken)
        {
            var context = FunctionInvokingChatClient.CurrentContext
                ?? new FunctionInvocationContext() // When there is no ambient context, create a new one to hold the arguments
                {
                    Arguments = arguments,
                    Function = this.InnerFunction,
                    CallContent = new(string.Empty, this.InnerFunction.Name, new Dictionary<string, object?>(arguments)),
                };

            return await next(innerAgent, context, CoreLogicAsync, cancellationToken).ConfigureAwait(false);

            ValueTask<object?> CoreLogicAsync(FunctionInvocationContext ctx, CancellationToken cancellationToken)
                => base.InvokeCoreAsync(ctx.Arguments, cancellationToken);
        }
    }
}