using ClawdDotNet.Core.Engine;
using ClawdDotNet.Core.Tests.Infrastructure;
using Shouldly;

namespace ClawdDotNet.Core.Tests.Engine;

/// <summary>
/// Regression tests for bug B2: _chatContexts[agentId] is a shared
/// List&lt;ChatMessage&gt;. Only the lookup runs under lock — all Add calls in the
/// loop body are unprotected.
///
/// The same agent can be triggered from several sides at the same time:
/// Telegram/mail tool job, the user's WebView message, send_message of
/// another agent. Result: corrupt list, interleaved tool sequences and
/// thus HTTP 400 errors.
/// </summary>
public sealed class AgentEngineConcurrencyTests
{
    // ═══════════════════════════════════════════════════════════
    //  E1 — two parallel chats on the same agent
    // ═══════════════════════════════════════════════════════════

    [Theory]
    [Repeat(15)]
    public async Task Zwei_parallele_Chats_hinterlassen_einen_gueltigen_Kontext(int iteration)
    {
        _ = iteration;

        var fixture = new EngineFixture()
            .WithTool(FakeTool.Slow(TimeSpan.FromMilliseconds(15)));
        var agent = fixture.AddAgent("agent-a", "TestTool");

        // Every run: one tool step, then a text answer — regardless of
        // how the two conversations get interleaved.
        fixture.Client.RespondsContextually();

        await Task.WhenAll(
            fixture.Engine.ChatAsync(agent, "Anfrage A", "test-instance", default),
            fixture.Engine.ChatAsync(agent, "Anfrage B", "test-instance", default));

        var context = fixture.Engine.GetChatContext(agent.AgentId);
        ContextInvariants.AssertValid(context);
    }

    // ═══════════════════════════════════════════════════════════
    //  E2 — stress test
    // ═══════════════════════════════════════════════════════════

    [Fact]
    public async Task Viele_parallele_Chats_korrumpieren_den_Kontext_nicht()
    {
        var fixture = new EngineFixture()
            .WithTool(FakeTool.Slow(TimeSpan.FromMilliseconds(2)));
        var agent = fixture.AddAgent("agent-stress", "TestTool");

        fixture.Client.RespondsContextually();

        var tasks = Enumerable.Range(0, 30)
            .Select(i => fixture.Engine.ChatAsync(agent, $"Anfrage {i}", "test-instance", default));

        var results = await Task.WhenAll(tasks);

        results.ShouldAllBe(r => r.Status == AgentRunStatus.Completed);

        var context = fixture.Engine.GetChatContext(agent.AgentId);
        ContextInvariants.AssertValid(context);

        // Each of the 30 requests must be in the context exactly once — nothing lost,
        // nothing doubled through lost writes to the list.
        var userMessages = context.Count(m => m.Role == "user");
        userMessages.ShouldBe(30);
    }

    // ═══════════════════════════════════════════════════════════
    //  E3 — AbortChat
    // ═══════════════════════════════════════════════════════════

    [Fact]
    public async Task AbortChat_bricht_alle_laufenden_Chats_des_Agenten_ab()
    {
        var fixture = new EngineFixture()
            .WithTool(FakeTool.Slow(TimeSpan.FromSeconds(10)));
        var agent = fixture.AddAgent("agent-abort", "TestTool");

        fixture.Client.AlwaysRespondsWithToolCall();

        var first = fixture.Engine.ChatAsync(agent, "Erste", "test-instance", default);
        var second = fixture.Engine.ChatAsync(agent, "Zweite", "test-instance", default);

        // Wait until both have actually started.
        await WaitUntilAsync(() => fixture.Engine.IsRunning(agent.AgentId));
        await Task.Delay(50);

        var sw = System.Diagnostics.Stopwatch.StartNew();
        fixture.Engine.AbortChat(agent.AgentId);

        var results = await Task.WhenAll(first, second);
        sw.Stop();

        results.ShouldAllBe(r => r.Status == AgentRunStatus.Cancelled);

        // Crucial: _runningChats[agentId] used to hold only ONE CancellationTokenSource —
        // the second run overwrote the first. AbortChat then only aborted one, the
        // other ran until the run timeout. Without this time check the test would be green
        // although the abort did not take effect at all.
        sw.Elapsed.ShouldBeLessThan(TimeSpan.FromSeconds(5),
            "AbortChat muss beide Läufe sofort beenden, nicht erst über das Timeout");
    }

    // ═══════════════════════════════════════════════════════════
    //  E4 — counter-check: different agents may run in parallel
    // ═══════════════════════════════════════════════════════════

    [Fact]
    public async Task Verschiedene_Agenten_laufen_wirklich_parallel()
    {
        // Important counter-check: the fix for B2 must not accidentally lock all agents
        // against each other.
        //
        // Until 2026-09-24 the fake here only answered with text: the slow
        // tool never ran, the runs were finished immediately, and all that was checked was whether three
        // empty runs stay below 450 ms. That passed even with agents locking each other
        // - and failed under load, because it measured the machine instead of the engine.
        // Now every agent really calls the tool, and the overlap is proven.
        var tool = FakeTool.Slow(TimeSpan.FromMilliseconds(500));
        var fixture = new EngineFixture().WithTool(tool);

        var a = fixture.AddAgent("agent-1", "TestTool");
        var b = fixture.AddAgent("agent-2", "TestTool");
        var c = fixture.AddAgent("agent-3", "TestTool");

        fixture.Client.RespondsContextually("TestTool");

        await Task.WhenAll(
            fixture.Engine.ChatAsync(a, "x", "test-instance", default),
            fixture.Engine.ChatAsync(b, "x", "test-instance", default),
            fixture.Engine.ChatAsync(c, "x", "test-instance", default));

        tool.MaxConcurrent.ShouldBeGreaterThan(1, "Agenten dürfen sich nicht gegenseitig blockieren");
    }

    private static async Task WaitUntilAsync(Func<bool> condition, int timeoutMs = 2_000)
    {
        var sw = System.Diagnostics.Stopwatch.StartNew();
        while (!condition() && sw.ElapsedMilliseconds < timeoutMs)
            await Task.Delay(10);
    }
}