Chessistics/chessistics-engine/Simulation/GameSim.cs

using Chessistics.Engine.Commands;
using Chessistics.Engine.Events;
using Chessistics.Engine.Model;

namespace Chessistics.Engine.Simulation;

public class GameSim
{
    private readonly BoardState _state;
    private readonly Dictionary<int, WorldSave> _saveSlots = new();
    private const int DefaultSlot = 0;

    public GameSim(LevelDef level)
    {
        _state = BoardState.FromLevel(level);
    }

    public GameSim(CampaignDef campaign)
    {
        _state = BoardState.FromCampaign(campaign);
    }

    public IReadOnlyList<IWorldEvent> ProcessCommand(IWorldCommand command)
    {
        var changeList = new List<IWorldEvent>();
        try
        {
            command.Apply(_state, changeList);
        }
        catch (CommandRejectedException ex)
        {
            return [ex.RejectionEvent];
        }
        return changeList;
    }

    public BoardSnapshot GetSnapshot() => new(_state);

    /// <summary>
    /// Capture a full deep-copy of the world into an in-memory slot.
    /// Returns a single StateSavedEvent — no state mutation.
    /// </summary>
    public IReadOnlyList<IWorldEvent> QuickSave(int slot = DefaultSlot)
    {
        _saveSlots[slot] = _state.CaptureSave();
        return [new StateSavedEvent(_state.TurnNumber, slot)];
    }

    /// <summary>
    /// Restore the world from a saved slot. Emits StateRestoredEvent with a
    /// fresh snapshot — the presentation layer must rebuild all visuals.
    /// Returns an empty list (no event) if the slot is empty.
    /// </summary>
    public IReadOnlyList<IWorldEvent> QuickLoad(int slot = DefaultSlot)
    {
        if (!_saveSlots.TryGetValue(slot, out var save))
            return [];

        _state.RestoreFromSave(save);
        return [new StateRestoredEvent(new BoardSnapshot(_state), slot)];
    }

    public bool HasSave(int slot = DefaultSlot) => _saveSlots.ContainsKey(slot);
}