// -----------------------------------------------------------------------------
// InMemoryHlcStateStore.cs
// Sprint: SPRINT_20260105_002_001_LB_hlc_core_library
// Task: HLC-004 - Implement IHlcStateStore interface and InMemoryHlcStateStore
// -----------------------------------------------------------------------------

namespace StellaOps.HybridLogicalClock;

/// <summary>
/// In-memory implementation of HLC state store for testing and development.
/// </summary>
/// <remarks>
/// This implementation does not survive process restarts. Use PostgresHlcStateStore
/// for production deployments requiring persistence.
/// </remarks>
public sealed class InMemoryHlcStateStore : IHlcStateStore
{
    private readonly Dictionary<string, HlcTimestamp> _states = new(StringComparer.Ordinal);
    private readonly object _lock = new();

    /// <inheritdoc/>
    public Task<HlcTimestamp?> LoadAsync(string nodeId, CancellationToken ct = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(nodeId);
        ct.ThrowIfCancellationRequested();

        lock (_lock)
        {
            return Task.FromResult(
                _states.TryGetValue(nodeId, out var timestamp)
                    ? timestamp
                    : (HlcTimestamp?)null);
        }
    }

    /// <inheritdoc/>
    public Task SaveAsync(HlcTimestamp timestamp, CancellationToken ct = default)
    {
        ct.ThrowIfCancellationRequested();

        lock (_lock)
        {
            if (_states.TryGetValue(timestamp.NodeId, out var existing))
            {
                // Only update if new timestamp is greater (maintain monotonicity)
                if (timestamp > existing)
                {
                    _states[timestamp.NodeId] = timestamp;
                }
            }
            else
            {
                _states[timestamp.NodeId] = timestamp;
            }
        }

        return Task.CompletedTask;
    }

    /// <summary>
    /// Gets all stored states (for testing/debugging).
    /// </summary>
    public IReadOnlyDictionary<string, HlcTimestamp> GetAllStates() =>
        GetAllStatesSnapshot();

    /// <summary>
    /// Clears all stored states (for testing).
    /// </summary>
    public void Clear()
    {
        lock (_lock)
        {
            _states.Clear();
        }
    }

    private IReadOnlyDictionary<string, HlcTimestamp> GetAllStatesSnapshot()
    {
        lock (_lock)
        {
            return new Dictionary<string, HlcTimestamp>(_states);
        }
    }
}