using ClawdDotNet.Core.Tools;

namespace ClawdDotNet.Core.Activity;

/// <summary>A run that is in progress right now.</summary>
public sealed record ActiveRun(
    string RunId,
    string AgentId,
    string Source,
    string? TaskId,
    string? CalledBy,
    DateTime StartedAtUtc);

/// <summary>
/// One agent reaching another — for now a delegated run (<see cref="Kind"/> =
/// <c>delegation</c>). Meetings and escalations will add their own kinds.
/// </summary>
public sealed record AgentLink(string From, string To, string Kind, DateTime AtUtc);

/// <summary>
/// #711: Who is working right now, and who reached whom — the live side of the team overview.
///
/// <para><b>Why a component of its own.</b> The engine already tracked running chats, but
/// only those that went through <c>ChatAsync</c>; a fresh run (<c>@new</c>) was invisible to
/// <c>IsRunning</c>. And nothing recorded that agent A had called agent B — the delegation
/// chain knew it for the length of the call and then forgot. Here both are kept and
/// announced, independent of which engine path a run takes.</para>
///
/// <para><b>Memory only, and bounded.</b> This is the view of "now". What happened
/// yesterday is in the audit log; the time line (#711, later) replays it from there.</para>
/// </summary>
public sealed class AgentActivity
{
    /// <summary>How many recent links are kept for a page that connects late.</summary>
    public const int RecentLinkCapacity = 500;

    private readonly Lock _lock = new();
    private readonly Dictionary<string, ActiveRun> _active = new(StringComparer.Ordinal);
    private readonly Queue<AgentLink> _recentLinks = new();
    private readonly TimeProvider _clock;

    public AgentActivity(TimeProvider? clock = null) => _clock = clock ?? TimeProvider.System;

    public event Action<ActiveRun>? RunStarted;

    /// <summary>A run ended — with the <c>AgentRunStatus</c> name, or <c>Aborted</c>.</summary>
    public event Action<ActiveRun, string>? RunFinished;

    public event Action<AgentLink>? LinkObserved;

    /// <summary>
    /// Announces a run. Dispose the handle when it ends; call <see cref="RunHandle.Complete"/>
    /// first to report how. A delegated run (<paramref name="chain"/> deeper than its root)
    /// also records the link from the caller.
    /// </summary>
    public RunHandle Begin(string runId, string agentId, string source, string? taskId, DelegationChain? chain)
    {
        var now = _clock.GetUtcNow().UtcDateTime;
        var calledBy = chain is { Depth: > 0 } ? chain.Agents[^2] : null;
        var run = new ActiveRun(runId, agentId, source, taskId, calledBy, now);

        AgentLink? link = calledBy is null ? null : new AgentLink(calledBy, agentId, "delegation", now);

        lock (_lock)
        {
            _active[runId] = run;
            if (link is not null)
            {
                _recentLinks.Enqueue(link);
                while (_recentLinks.Count > RecentLinkCapacity)
                    _recentLinks.Dequeue();
            }
        }

        Raise(() => RunStarted?.Invoke(run));
        if (link is not null)
            Raise(() => LinkObserved?.Invoke(link));

        return new RunHandle(this, run);
    }

    /// <summary>#697: A run in progress, by its id.</summary>
    public ActiveRun? Find(string runId)
    {
        lock (_lock)
            return _active.GetValueOrDefault(runId);
    }

    /// <summary>The runs in progress right now.</summary>
    public IReadOnlyList<ActiveRun> ActiveRuns()
    {
        lock (_lock)
            return [.. _active.Values];
    }

    /// <summary>Links observed within <paramref name="window"/>, oldest first.</summary>
    public IReadOnlyList<AgentLink> RecentLinks(TimeSpan window)
    {
        var since = _clock.GetUtcNow().UtcDateTime - window;
        lock (_lock)
            return [.. _recentLinks.Where(l => l.AtUtc >= since)];
    }

    private void End(ActiveRun run, string status)
    {
        lock (_lock)
        {
            if (!_active.Remove(run.RunId))
                return;
        }

        Raise(() => RunFinished?.Invoke(run, status));
    }

    /// <summary>A subscriber that throws must not break the run it is watching.</summary>
    private static void Raise(Action raise)
    {
        try { raise(); }
        catch { /* observers are best effort */ }
    }

    public sealed class RunHandle : IDisposable
    {
        private readonly AgentActivity _owner;
        private readonly ActiveRun _run;
        private string _status = "Aborted";

        internal RunHandle(AgentActivity owner, ActiveRun run)
        {
            _owner = owner;
            _run = run;
        }

        /// <summary>How the run ended. Without it, disposal reports <c>Aborted</c>.</summary>
        public void Complete(string status) => _status = status;

        public void Dispose() => _owner.End(_run, _status);
    }
}