namespace NATS.Server.Raft;

public sealed class RaftLog
{
    private readonly List<RaftLogEntry> _entries = [];
    private long _baseIndex;

    public IReadOnlyList<RaftLogEntry> Entries => _entries;

    public RaftLogEntry Append(int term, string command)
    {
        var entry = new RaftLogEntry(_baseIndex + _entries.Count + 1, term, command);
        _entries.Add(entry);
        return entry;
    }

    public void AppendReplicated(RaftLogEntry entry)
    {
        if (_entries.Any(e => e.Index == entry.Index))
            return;

        _entries.Add(entry);
    }

    public void ReplaceWithSnapshot(RaftSnapshot snapshot)
    {
        _entries.Clear();
        _baseIndex = snapshot.LastIncludedIndex;
    }

    public async Task PersistAsync(string path, CancellationToken ct)
    {
        Directory.CreateDirectory(Path.GetDirectoryName(path)!);
        var model = new PersistedLog
        {
            BaseIndex = _baseIndex,
            Entries = [.. _entries],
        };
        await File.WriteAllTextAsync(path, System.Text.Json.JsonSerializer.Serialize(model), ct);
    }

    public static async Task<RaftLog> LoadAsync(string path, CancellationToken ct)
    {
        var log = new RaftLog();
        if (!File.Exists(path))
            return log;

        var json = await File.ReadAllTextAsync(path, ct);
        var model = System.Text.Json.JsonSerializer.Deserialize<PersistedLog>(json) ?? new PersistedLog();
        log._baseIndex = model.BaseIndex;
        log._entries.AddRange(model.Entries);
        return log;
    }

    private sealed class PersistedLog
    {
        public long BaseIndex { get; set; }
        public List<RaftLogEntry> Entries { get; set; } = [];
    }
}

public sealed record RaftLogEntry(long Index, int Term, string Command);