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

using System.Collections.Concurrent;

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 ConcurrentDictionary<string, HlcTimestamp> _states = new(StringComparer.Ordinal);

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

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

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

        _states.AddOrUpdate(
            timestamp.NodeId,
            timestamp,
            (_, existing) =>
            {
                // Only update if new timestamp is greater (maintain monotonicity)
                return timestamp > existing ? timestamp : existing;
            });

        return Task.CompletedTask;
    }

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

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