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

namespace ClawdDotNet.Core.Tests.Engine;

/// <summary>
/// Test A13 of the test strategy — regression tests for B8 (#206).
///
/// <para><c>send_message</c> is a synchronous call: A holds its gate while it
/// waits for B. If B then called A, B waited for a gate that A only releases once B
/// has answered. Both stood still until the timeout of the outer run resolved it.</para>
///
/// <para>The tests check the three promises from <see cref="DelegationChain"/>: no
/// agent twice in a chain, at most <c>MaxDelegationDepth</c> hand-offs, and
/// the chain belongs to the call instead of to the agent.</para>
///
/// <para>A time limit is deliberately on every test that could deadlock: without the
/// check it would not turn red, but not continue at all.</para>
/// </summary>
public sealed class DelegationDepthTests
{
    private static readonly TimeSpan Deadline = TimeSpan.FromSeconds(20);

    /// <summary>Waits for the run, but fails instead of hanging.</summary>
    private static async Task<AgentRunResult> WithDeadline(Task<AgentRunResult> run)
    {
        var done = await Task.WhenAny(run, Task.Delay(Deadline));
        done.ShouldBe(run, "Der Lauf ist nicht zurückgekommen — das ist die Verklemmung aus B8.");
        return await run;
    }

    // ═══════════════════════════════════════════════════════════
    //  A13 — the reported case
    // ═══════════════════════════════════════════════════════════

    [Fact]
    public async Task A_to_B_to_A_is_aborted_instead_of_deadlocking()
    {
        var tool = new DelegatingTool(new Dictionary<string, string>
        {
            ["agent-a"] = "agent-b",
            ["agent-b"] = "agent-a"     // back to A — the cycle
        });

        var fixture = new EngineFixture().WithTool(tool);
        var a = fixture.AddAgent("agent-a", "TestTool");
        fixture.AddAgent("agent-b", "TestTool");

        fixture.Client.RespondsContextually();

        var result = await WithDeadline(
            fixture.Engine.ChatAsync(a, "Bitte klären", "test-instance", default));

        result.Status.ShouldBe(AgentRunStatus.Completed);

        // The way back B → A was rejected, the way there A → B was not.
        var wayBack = tool.Handoffs.Single(h => h is { From: "agent-b", To: "agent-a" });
        wayBack.Delivered.ShouldBeFalse();
        wayBack.Error.ShouldNotBeNull().ShouldContain("Zyklus");
        wayBack.Error.ShouldNotBeNull().ShouldContain("agent-a -> agent-b -> agent-a");

        tool.Handoffs.Single(h => h is { From: "agent-a", To: "agent-b" }).Delivered.ShouldBeTrue();
    }

    [Fact]
    public async Task The_rejection_comes_back_as_a_result_not_as_a_throw()
    {
        // The rejected agent should be able to continue working — it gets a reason,
        // not an abort. Otherwise the cycle check would only lead to a different failure.
        var tool = new DelegatingTool(new Dictionary<string, string>
        {
            ["agent-a"] = "agent-b",
            ["agent-b"] = "agent-a"
        });

        var fixture = new EngineFixture().WithTool(tool);
        var a = fixture.AddAgent("agent-a", "TestTool");
        fixture.AddAgent("agent-b", "TestTool");

        fixture.Client.RespondsContextually();

        var result = await WithDeadline(
            fixture.Engine.ChatAsync(a, "Bitte klären", "test-instance", default));

        result.Status.ShouldBe(AgentRunStatus.Completed);
        result.FinalMessage.ShouldBe("Fertig");
    }

    // ═══════════════════════════════════════════════════════════
    //  The relay that does not form a cycle
    // ═══════════════════════════════════════════════════════════

    [Fact]
    public async Task A_relay_ends_at_the_depth_limit()
    {
        // A → B → C → D would be depth 3. With MaxDelegationDepth = 2 it stops at C.
        var tool = new DelegatingTool(new Dictionary<string, string>
        {
            ["agent-a"] = "agent-b",
            ["agent-b"] = "agent-c",
            ["agent-c"] = "agent-d"
        });

        var fixture = new EngineFixture().WithTool(tool);
        fixture.Engine.MaxDelegationDepth = 2;

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

        fixture.Client.RespondsContextually();

        await WithDeadline(fixture.Engine.ChatAsync(a, "Bitte klären", "test-instance", default));

        tool.Handoffs.Single(h => h.To == "agent-b").Delivered.ShouldBeTrue();
        tool.Handoffs.Single(h => h.To == "agent-c").Delivered.ShouldBeTrue();

        var tooDeep = tool.Handoffs.Single(h => h.To == "agent-d");
        tooDeep.Delivered.ShouldBeFalse();
        tooDeep.Error.ShouldNotBeNull().ShouldContain("Delegationstiefe");
    }

    [Fact]
    public async Task Within_the_limit_the_relay_goes_through()
    {
        var tool = new DelegatingTool(new Dictionary<string, string>
        {
            ["agent-a"] = "agent-b",
            ["agent-b"] = "agent-c"
        });

        var fixture = new EngineFixture().WithTool(tool);
        fixture.Engine.MaxDelegationDepth = 2;

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

        fixture.Client.RespondsContextually();

        var result = await WithDeadline(
            fixture.Engine.ChatAsync(a, "Bitte klären", "test-instance", default));

        result.Status.ShouldBe(AgentRunStatus.Completed);
        tool.Handoffs.ShouldAllBe(h => h.Delivered);
    }

    // ═══════════════════════════════════════════════════════════
    //  The chain belongs to the call, not to the agent
    // ═══════════════════════════════════════════════════════════

    [Fact]
    public async Task Two_consecutive_runs_do_not_inherit_each_others_chain()
    {
        // Otherwise an agent could be permanently "used up" after a deep chain.
        var tool = new DelegatingTool(new Dictionary<string, string> { ["agent-a"] = "agent-b" });

        var fixture = new EngineFixture().WithTool(tool);
        var a = fixture.AddAgent("agent-a", "TestTool");
        fixture.AddAgent("agent-b", "TestTool");

        fixture.Client.RespondsContextually();

        await WithDeadline(fixture.Engine.ChatAsync(a, "Erste Frage", "test-instance", default));
        await WithDeadline(fixture.Engine.ChatAsync(a, "Zweite Frage", "test-instance", default));

        tool.Handoffs.Count(h => h.To == "agent-b").ShouldBe(2);
        tool.Handoffs.ShouldAllBe(h => h.Delivered);
    }

    // ═══════════════════════════════════════════════════════════
    //  spawn counts too
    // ═══════════════════════════════════════════════════════════

    [Fact]
    public async Task The_chain_cannot_be_bypassed_via_spawn_either()
    {
        var tool = new DelegatingTool(new Dictionary<string, string>
        {
            ["agent-a"] = "agent-b",
            ["agent-b"] = "agent-a"
        }, spawn: true);

        var fixture = new EngineFixture().WithTool(tool);
        var a = fixture.AddAgent("agent-a", "TestTool");
        fixture.AddAgent("agent-b", "TestTool");

        fixture.Client.RespondsContextually();

        await WithDeadline(fixture.Engine.ChatAsync(a, "Bitte klären", "test-instance", default));

        var wayBack = tool.Handoffs.Single(h => h is { From: "agent-b", To: "agent-a" });
        wayBack.Delivered.ShouldBeFalse();
        wayBack.Error.ShouldNotBeNull().ShouldContain("Zyklus");
    }

    // ═══════════════════════════════════════════════════════════
    //  #461 — what the chain fundamentally cannot see
    // ═══════════════════════════════════════════════════════════

    /// <summary>
    /// Two independent chains crossing over: run 1 starts at A and commissions B, run 2
    /// starts at the same time at B and commissions A. Neither chain contains the
    /// other's agent — both are cycle-free on their own, and yet run 1 holds
    /// gate(A) and waits for gate(B), while run 2 holds gate(B) and waits for gate(A).
    ///
    /// <para>The delegation chain fundamentally cannot recognize that; only a deadline
    /// resolves it. A delegated run therefore waits at most
    /// <c>DelegationGateTimeout</c> for a foreign gate and refuses afterwards.</para>
    ///
    /// <para>The pause before the hand-off is the core of the setup: the fake client
    /// answers synchronously; without it the first chat would run through completely before the
    /// second begins — the chains could not overlap at all, and the test
    /// would be green without showing anything.</para>
    /// </summary>
    [Fact]
    public async Task Two_independent_crossing_chains_do_not_deadlock()
    {
        var tool = new DelegatingTool(new Dictionary<string, string>
        {
            ["agent-a"] = "agent-b",
            ["agent-b"] = "agent-a"
        }, delayBeforeHandoff: TimeSpan.FromMilliseconds(300));

        var fixture = new EngineFixture().WithTool(tool);
        fixture.Engine.DelegationGateTimeout = TimeSpan.FromSeconds(1);

        var a = fixture.AddAgent("agent-a", "TestTool");
        var b = fixture.AddAgent("agent-b", "TestTool");

        fixture.Client.RespondsContextually();

        var runA = fixture.Engine.ChatAsync(a, "A fragt B", "test-instance", default);
        var runB = fixture.Engine.ChatAsync(b, "B fragt A", "test-instance", default);

        var both = Task.WhenAll(runA, runB);
        var done = await Task.WhenAny(both, Task.Delay(Deadline));

        done.ShouldBe(both, "Beide Laeufe warten auf das Gate des jeweils anderen (#461).");

        // Both outer runs come to an end. At least one hand-off failed at the
        // deadline — which one is decided by the order and is not
        // fixed; that both runs come back is.
        (await runA).Status.ShouldBe(AgentRunStatus.Completed);
        (await runB).Status.ShouldBe(AgentRunStatus.Completed);
        tool.Handoffs.ShouldContain(h => !h.Delivered && h.Error!.Contains("belegt"));
    }

    [Fact]
    public async Task A_chat_from_a_human_keeps_waiting_as_long_as_it_takes()
    {
        // The counter-check to the deadline: it only applies to delegated runs. A second
        // chat of the same agent queues up and is served, even if the first one
        // takes longer than the delegation deadline.
        var fixture = new EngineFixture().WithTool(FakeTool.Slow(TimeSpan.FromMilliseconds(600)));
        fixture.Engine.DelegationGateTimeout = TimeSpan.FromMilliseconds(50);

        var a = fixture.AddAgent("agent-a", "TestTool");

        fixture.Client.RespondsContextually();

        var firstOne = fixture.Engine.ChatAsync(a, "Erste Frage", "test-instance", default);
        var secondOne = fixture.Engine.ChatAsync(a, "Zweite Frage", "test-instance", default);

        (await WithDeadline(firstOne)).Status.ShouldBe(AgentRunStatus.Completed);
        (await WithDeadline(secondOne)).Status.ShouldBe(AgentRunStatus.Completed);
    }

    // ═══════════════════════════════════════════════════════════
    //  The chain itself
    // ═══════════════════════════════════════════════════════════

    [Fact]
    public void The_chain_counts_handoffs_not_agents()
    {
        var chain = DelegationChain.Root("a");
        chain.Depth.ShouldBe(0);
        chain.Append("b").Depth.ShouldBe(1);
        chain.Append("b").Append("c").Depth.ShouldBe(2);
    }

    [Fact]
    public void Append_does_not_change_the_callers_chain()
    {
        // Immutable: two hand-offs from the same run must not see
        // each other — otherwise the second would count the first as a predecessor.
        var chain = DelegationChain.Root("a");

        var toB = chain.Append("b");
        var toC = chain.Append("c");

        chain.Agents.ShouldBe(["a"]);
        toB.Agents.ShouldBe(["a", "b"]);
        toC.Agents.ShouldBe(["a", "c"]);
        toB.Contains("c").ShouldBeFalse();
    }

    [Fact]
    public void The_chain_reads_as_a_path()
    {
        DelegationChain.Root("a").Append("b").Append("c").ToString()
            .ShouldBe("a -> b -> c");
    }
}