using System.Collections.Concurrent;
using Microsoft.Extensions.Logging;

namespace IceImportBLL.IceImportRun;

// Singleton (registered explicitly in IceImportModule.Register(), same as
// AutomationSL.Hubs.AutomationRunNotifier's singleton registration) — a ConcurrentDictionary with
// disciplined eviction via Complete(), never left to grow unbounded, per CLAUDE.md's
// "Static Collections" anti-pattern guidance.
public class IceImportRunCancellationRegistry : IIceImportRunCancellationRegistry
{
    private readonly ConcurrentDictionary<long, CancellationTokenSource> _tokens = new();
    private readonly ILogger<IceImportRunCancellationRegistry> _logger;

    public IceImportRunCancellationRegistry(ILogger<IceImportRunCancellationRegistry> logger)
        => _logger = logger;

    public CancellationToken Register(long runId, CancellationToken callerToken)
    {
        var cts = CancellationTokenSource.CreateLinkedTokenSource(callerToken);
        // Replace-and-dispose any stale entry (shouldn't normally happen — one CTS per RunId for
        // its single background execution — but guards against a double-Register on retry paths).
        var previous = _tokens.AddOrUpdate(runId, cts, (_, old) => { old.Dispose(); return cts; });
        return previous.Token;
    }

    public bool TryCancel(long runId)
    {
        if (!_tokens.TryGetValue(runId, out var cts))
            return false;

        try
        {
            cts.Cancel();
            return true;
        }
        catch (ObjectDisposedException)
        {
            // Run completed and was disposed between TryGetValue and Cancel — benign race.
            return false;
        }
    }

    public void Complete(long runId)
    {
        if (_tokens.TryRemove(runId, out var cts))
        {
            try { cts.Dispose(); }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "IceImportRunCancellationRegistry: dispose failed for RunId {RunId}", runId);
            }
        }
    }
}