Chessistics/chessistics-engine/Simulation/TurnExecutor.cs

using Chessistics.Engine.Events;
using Chessistics.Engine.Model;
using Chessistics.Engine.Rules;

namespace Chessistics.Engine.Simulation;

public static class TurnExecutor
{
    public static void ExecuteTurn(BoardState state, List<IWorldEvent> changeList)
    {
        state.TurnNumber++;
        changeList.Add(new TurnStartedEvent(state.TurnNumber));

        // Sub-phase 1: PRODUCTION
        ExecuteProduction(state, changeList);

        // Sub-phase 2: TRANSFORMATION (convert accumulated input → output)
        ExecuteTransformation(state, changeList);

        // Sub-phase 3: TRANSFERS
        var transferEvents = TransferResolver.ResolveTransfers(state);
        changeList.AddRange(transferEvents);

        // Sub-phase 4: MOVEMENT
        ExecuteMovement(state, changeList);

        // Sub-phase 5: COLLISION RESOLUTION
        var collisions = CollisionResolver.ResolveCollisions(state.Pieces);
        foreach (var (survivor, destroyed, cell) in collisions)
        {
            foreach (var victim in destroyed)
            {
                state.Pieces.Remove(victim);
                victim.Cargo = null;

                // Return piece to stock instead of destroying permanently
                state.RemainingStock[victim.Kind] = state.RemainingStock.GetValueOrDefault(victim.Kind) + 1;
                changeList.Add(new PieceReturnedToStockEvent(
                    state.TurnNumber, victim.Id, victim.Kind, survivor?.Id, cell));
            }
        }

        // Auto-pause on collision
        if (collisions.Count > 0)
        {
            state.Phase = SimPhase.Paused;
            changeList.Add(new SimulationPausedEvent());
        }

        // Check mission completion
        if (MissionChecker.AllCurrentDemandsMet(state) && state.Demands.Count > 0)
        {
            var campaign = state.Campaign;
            var missionIndex = campaign?.CurrentMissionIndex ?? 0;
            campaign?.CompletedMissions.Add(missionIndex);
            changeList.Add(new MissionCompleteEvent(state.TurnNumber, missionIndex));

            // Auto-advance to next mission if available (campaign mode)
            if (campaign != null && !campaign.IsLastMission)
            {
                AdvanceToNextMission(state, campaign, changeList);
                // Phase stays Running — simulation continues
            }
            else
            {
                // Last mission or legacy mode — pause
                state.Phase = SimPhase.MissionComplete;
            }
        }

        changeList.Add(new TurnEndedEvent(state.TurnNumber));
    }

    private static void AdvanceToNextMission(BoardState state, CampaignState campaign, List<IWorldEvent> changeList)
    {
        campaign.CurrentMissionIndex++;
        var mission = campaign.CurrentMission;

        var oldWidth = state.Width;
        var oldHeight = state.Height;
        state.ApplyTerrainPatch(mission.TerrainPatch, campaign.CurrentMissionIndex);

        if (state.Width != oldWidth || state.Height != oldHeight)
            changeList.Add(new TerrainExpandedEvent(state.Width, state.Height, mission.TerrainPatch.Cells));

        state.AddStock(mission.Stock);

        foreach (var kind in mission.UnlockedPieces)
        {
            campaign.AvailablePieceKinds.Add(kind);
            changeList.Add(new PieceUnlockedEvent(kind, 1));
        }
        foreach (var upgrade in mission.UnlockedLevels)
        {
            campaign.AvailableLevels.Add(upgrade);
            changeList.Add(new PieceUnlockedEvent(upgrade.Kind, upgrade.Level));
        }

        changeList.Add(new MissionStartedEvent(campaign.CurrentMissionIndex, state.Width, state.Height));
    }

    private static void ExecuteMovement(BoardState state, List<IWorldEvent> changeList)
    {
        var moves = state.Pieces.Select(p => (piece: p, from: p.CurrentCell, to: p.TargetCell)).ToList();

        foreach (var (piece, from, to) in moves)
        {
            piece.CurrentCell = to;
            state.OccupiedCells.Add(to);
            changeList.Add(new PieceMovedEvent(state.TurnNumber, piece.Id, from, to));
        }
    }

    private static void ExecuteTransformation(BoardState state, List<IWorldEvent> changeList)
    {
        foreach (var (pos, transformer) in state.Transformers)
        {
            var inputBuffer = state.TransformerInputBuffers[pos];
            if (inputBuffer >= transformer.InputRequired)
            {
                state.TransformerInputBuffers[pos] = inputBuffer - transformer.InputRequired;
                state.TransformerOutputBuffers[pos] += transformer.OutputAmount;
                changeList.Add(new CargoConvertedEvent(
                    state.TurnNumber, pos, transformer.InputCargo, transformer.OutputCargo, transformer.OutputAmount));
            }
        }
    }

    private static void ExecuteProduction(BoardState state, List<IWorldEvent> changeList)
    {
        foreach (var (pos, prod) in state.Productions)
        {
            state.ProductionBuffers[pos] = prod.Amount;
            changeList.Add(new CargoProducedEvent(state.TurnNumber, pos, prod.Cargo));
        }
    }

    private static Metrics ComputeMetrics(BoardState state)
    {
        return new Metrics(
            PiecesUsed: state.Pieces.Count + state.DestroyedPieces.Count,
            TurnsTaken: state.TurnNumber,
            CellsOccupied: state.OccupiedCells.Count
        );
    }
}