using LiteDB;

namespace ZB.MOM.WW.OtOpcUa.Configuration.LocalCache;

/// <summary>
///     LiteDB-backed <see cref="ILocalConfigCache"/>. One file per node (default
///     <c>config_cache.db</c>), one collection per snapshot. Corruption surfaces as
///     <see cref="LocalConfigCacheCorruptException"/> on construction or read — callers should
///     delete and re-fetch from the central DB (decision #80).
/// </summary>
public sealed class LiteDbConfigCache : ILocalConfigCache, IDisposable
{
    private const string CollectionName = "generations";
    private readonly LiteDatabase _db;
    private readonly ILiteCollection<GenerationSnapshot> _col;

    public LiteDbConfigCache(string dbPath)
    {
        // LiteDB can be tolerant of header-only corruption at construction time (it may overwrite
        // the header and "recover"), so we force a write + read probe to fail fast on real corruption.
        try
        {
            _db = new LiteDatabase(new ConnectionString { Filename = dbPath, Upgrade = true });
            _col = _db.GetCollection<GenerationSnapshot>(CollectionName);
            _col.EnsureIndex(s => s.ClusterId);
            _col.EnsureIndex(s => s.GenerationId);
            _ = _col.Count();
        }
        catch (Exception ex) when (ex is LiteException or InvalidDataException or IOException
                                      or NotSupportedException or UnauthorizedAccessException
                                      or ArgumentOutOfRangeException or FormatException)
        {
            _db?.Dispose();
            throw new LocalConfigCacheCorruptException(
                $"LiteDB cache at '{dbPath}' is corrupt or unreadable — delete the file and refetch from the central DB.",
                ex);
        }
    }

    public Task<GenerationSnapshot?> GetMostRecentAsync(string clusterId, CancellationToken ct = default)
    {
        ct.ThrowIfCancellationRequested();
        var snapshot = _col
            .Find(s => s.ClusterId == clusterId)
            .OrderByDescending(s => s.GenerationId)
            .FirstOrDefault();
        return Task.FromResult<GenerationSnapshot?>(snapshot);
    }

    public Task PutAsync(GenerationSnapshot snapshot, CancellationToken ct = default)
    {
        ct.ThrowIfCancellationRequested();
        // upsert by (ClusterId, GenerationId) — replace in place if already cached
        var existing = _col
            .Find(s => s.ClusterId == snapshot.ClusterId && s.GenerationId == snapshot.GenerationId)
            .FirstOrDefault();

        if (existing is null)
            _col.Insert(snapshot);
        else
        {
            snapshot.Id = existing.Id;
            _col.Update(snapshot);
        }

        return Task.CompletedTask;
    }

    public Task PruneOldGenerationsAsync(string clusterId, int keepLatest = 10, CancellationToken ct = default)
    {
        ct.ThrowIfCancellationRequested();
        var doomed = _col
            .Find(s => s.ClusterId == clusterId)
            .OrderByDescending(s => s.GenerationId)
            .Skip(keepLatest)
            .Select(s => s.Id)
            .ToList();

        foreach (var id in doomed)
            _col.Delete(id);

        return Task.CompletedTask;
    }

    public void Dispose() => _db.Dispose();
}

public sealed class LocalConfigCacheCorruptException(string message, Exception inner)
    : Exception(message, inner);