using System.Collections.Concurrent;

namespace StellaOps.Policy.Engine.Snapshots;

internal interface ISnapshotStore
{
    Task SaveAsync(SnapshotDetail snapshot, CancellationToken cancellationToken = default);
    Task<SnapshotDetail?> GetAsync(string snapshotId, CancellationToken cancellationToken = default);
    Task<IReadOnlyList<SnapshotDetail>> ListAsync(string? tenantId = null, CancellationToken cancellationToken = default);
}

internal sealed class InMemorySnapshotStore : ISnapshotStore
{
    private readonly ConcurrentDictionary<string, SnapshotDetail> _snapshots = new(StringComparer.Ordinal);

    public Task SaveAsync(SnapshotDetail snapshot, CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(snapshot);
        _snapshots[snapshot.SnapshotId] = snapshot;
        return Task.CompletedTask;
    }

    public Task<SnapshotDetail?> GetAsync(string snapshotId, CancellationToken cancellationToken = default)
    {
        _snapshots.TryGetValue(snapshotId, out var value);
        return Task.FromResult(value);
    }

    public Task<IReadOnlyList<SnapshotDetail>> ListAsync(string? tenantId = null, CancellationToken cancellationToken = default)
    {
        IEnumerable<SnapshotDetail> items = _snapshots.Values;
        if (!string.IsNullOrWhiteSpace(tenantId))
        {
            items = items.Where(s => string.Equals(s.TenantId, tenantId, StringComparison.Ordinal));
        }

        var ordered = items
            .OrderBy(s => s.GeneratedAt, StringComparer.Ordinal)
            .ThenBy(s => s.SnapshotId, StringComparer.Ordinal)
            .ToList();

        return Task.FromResult<IReadOnlyList<SnapshotDetail>>(ordered);
    }
}