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: MOVEMENT
        ExecuteMovement(state, changeList);

        // Sub-phase 2: COLLISION DETECTION
        var collisions = CollisionDetector.DetectCollisions(state.Pieces);
        if (collisions.Count > 0)
        {
            foreach (var (idA, idB, cell) in collisions)
                changeList.Add(new CollisionDetectedEvent(idA, idB, cell));

            state.Phase = SimPhase.Collision;
            changeList.Add(new TurnEndedEvent(state.TurnNumber));
            return;
        }

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

        // Sub-phase 4: PRODUCTION
        ExecuteProduction(state, changeList);

        // Check victory / defeat
        if (VictoryChecker.AllDemandsMet(state))
        {
            state.Phase = SimPhase.Victory;
            changeList.Add(new VictoryEvent(ComputeMetrics(state)));
        }
        else if (VictoryChecker.AnyDeadlineExpired(state))
        {
            state.Phase = SimPhase.Defeat;
            foreach (var demand in VictoryChecker.GetExpiredDemands(state))
                changeList.Add(new DeadlineExpiredEvent(demand.Position, demand.Name));
        }

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

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

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

    private static void ExecuteProduction(BoardState state, List<IWorldEvent> changeList)
    {
        foreach (var (pos, prod) in state.Productions)
        {
            if (state.ProductionBuffers[pos] != null)
                continue; // buffer already full

            if (state.TurnNumber % prod.Interval == 0)
            {
                state.ProductionBuffers[pos] = prod.Cargo;
                changeList.Add(new CargoProducedEvent(pos, prod.Cargo));
            }
        }
    }

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