Chessistics/chessistics-engine/Rules/TransferResolver.cs

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

namespace Chessistics.Engine.Rules;

public static class TransferResolver
{
    public static List<IWorldEvent> ResolveTransfers(BoardState state)
    {
        var events = new List<IWorldEvent>();
        var participated = new HashSet<int>(); // piece IDs that already gave or received
        var productionGave = new HashSet<Coords>(); // productions that already gave

        // Phase A: Productions give to adjacent pieces
        ResolveProductionTransfers(state, events, participated, productionGave);

        // Phase A2: Transformer outputs give to adjacent pieces (like productions)
        ResolveTransformerOutputTransfers(state, events, participated);

        // Phase B: Pieces give to demands, transformers, or other pieces
        ResolvePieceTransfers(state, events, participated);

        return events;
    }

    private static void ResolveProductionTransfers(
        BoardState state, List<IWorldEvent> events,
        HashSet<int> participated, HashSet<Coords> productionGave)
    {
        // Sort productions deterministically (by position)
        var productions = state.Productions.Values
            .Where(p => state.ProductionBuffers[p.Position] > 0)
            .OrderBy(p => p.Position.Col).ThenBy(p => p.Position.Row)
            .ToList();

        foreach (var prod in productions)
        {
            var cargoType = prod.Cargo;

            // Find adjacent pieces without cargo that accept this cargo type
            var receivers = GetAdjacentPiecesWithoutCargo(state, prod.Position, participated,
                cargoType: cargoType);

            foreach (var receiver in receivers)
            {
                if (state.ProductionBuffers[prod.Position] <= 0) break;

                receiver.Cargo = cargoType;
                state.ProductionBuffers[prod.Position]--;
                participated.Add(receiver.Id);

                events.Add(new CargoTransferredEvent(
                    state.TurnNumber, prod.Position, receiver.CurrentCell, cargoType,
                    GivingPieceId: null, ReceivingPieceId: receiver.Id));
            }

            if (state.ProductionBuffers[prod.Position] < prod.Amount)
                productionGave.Add(prod.Position);
        }
    }

    private static void ResolveTransformerOutputTransfers(
        BoardState state, List<IWorldEvent> events, HashSet<int> participated)
    {
        var transformers = state.Transformers.Values
            .Where(t => state.TransformerOutputBuffers[t.Position] > 0)
            .OrderBy(t => t.Position.Col).ThenBy(t => t.Position.Row)
            .ToList();

        foreach (var transformer in transformers)
        {
            var cargoType = transformer.OutputCargo;
            var receivers = GetAdjacentPiecesWithoutCargo(state, transformer.Position, participated,
                cargoType: cargoType);

            foreach (var receiver in receivers)
            {
                if (state.TransformerOutputBuffers[transformer.Position] <= 0) break;

                receiver.Cargo = cargoType;
                state.TransformerOutputBuffers[transformer.Position]--;
                participated.Add(receiver.Id);

                events.Add(new CargoTransferredEvent(
                    state.TurnNumber, transformer.Position, receiver.CurrentCell, cargoType,
                    GivingPieceId: null, ReceivingPieceId: receiver.Id));
            }
        }
    }

    private static void ResolvePieceTransfers(
        BoardState state, List<IWorldEvent> events, HashSet<int> participated)
    {
        // Get all pieces with cargo that haven't participated, sorted by giver priority
        var givers = state.Pieces
            .Where(p => p.Cargo != null && !participated.Contains(p.Id))
            .OrderByDescending(p => p.SocialStatus)
            .ThenByDescending(p => p.Level)
            .ToList();

        foreach (var giver in givers)
        {
            if (participated.Contains(giver.Id)) continue;

            var cargoType = giver.Cargo!.Value;

            // Priority 1: deliver to adjacent demand (always accepts matching cargo, even when satisfied)
            var adjacentDemand = GetAdjacentCompatibleDemand(state, giver.CurrentCell, cargoType);
            if (adjacentDemand != null)
            {
                giver.Cargo = null;
                adjacentDemand.ReceivedCount++;
                participated.Add(giver.Id);

                events.Add(new CargoTransferredEvent(
                    state.TurnNumber, giver.CurrentCell, adjacentDemand.Position, cargoType,
                    GivingPieceId: giver.Id, ReceivingPieceId: null));

                events.Add(new DemandProgressEvent(
                    state.TurnNumber, adjacentDemand.Position, adjacentDemand.Name,
                    adjacentDemand.ReceivedCount, adjacentDemand.Required));

                continue;
            }

            // Priority 2: deliver to adjacent transformer (input side)
            var adjacentTransformer = GetAdjacentCompatibleTransformer(state, giver.CurrentCell, cargoType);
            if (adjacentTransformer != null)
            {
                giver.Cargo = null;
                state.TransformerInputBuffers[adjacentTransformer.Position]++;
                participated.Add(giver.Id);

                events.Add(new CargoTransferredEvent(
                    state.TurnNumber, giver.CurrentCell, adjacentTransformer.Position, cargoType,
                    GivingPieceId: giver.Id, ReceivingPieceId: null));

                continue;
            }

            // Priority 3: transfer to adjacent piece without cargo
            var receivers = GetAdjacentPiecesWithoutCargo(state, giver.CurrentCell, participated,
                cargoType: cargoType);
            if (receivers.Count == 0) continue;

            var receiver = receivers[0];
            receiver.Cargo = cargoType;
            giver.Cargo = null;
            participated.Add(giver.Id);
            participated.Add(receiver.Id);

            events.Add(new CargoTransferredEvent(
                state.TurnNumber, giver.CurrentCell, receiver.CurrentCell, cargoType,
                GivingPieceId: giver.Id, ReceivingPieceId: receiver.Id));
        }
    }

    private static List<PieceState> GetAdjacentPiecesWithoutCargo(
        BoardState state, Coords position, HashSet<int> participated,
        CargoType? cargoType = null)
    {
        var adjacent = position.GetAdjacent4(state.Width, state.Height);

        return state.Pieces
            .Where(p => p.Cargo == null
                        && !participated.Contains(p.Id)
                        && adjacent.Contains(p.CurrentCell)
                        && (p.CargoFilter == null || cargoType == null || p.CargoFilter == cargoType))
            .OrderByDescending(p => p.SocialStatus)
            .ThenByDescending(p => p.Level)
            .ThenBy(p => ClockwiseOrder(p.CurrentCell, position, state.TurnNumber))
            .ToList();
    }

    private static DemandState? GetAdjacentCompatibleDemand(
        BoardState state, Coords position, CargoType cargoType)
    {
        var adjacent = position.GetAdjacent4(state.Width, state.Height);

        return state.Demands.Values
            .Where(d => d.Cargo == cargoType
                        && adjacent.Contains(d.Position))
            .FirstOrDefault();
    }

    private static TransformerDef? GetAdjacentCompatibleTransformer(
        BoardState state, Coords position, CargoType cargoType)
    {
        var adjacent = position.GetAdjacent4(state.Width, state.Height);

        return state.Transformers.Values
            .Where(t => t.InputCargo == cargoType
                        && adjacent.Contains(t.Position))
            .FirstOrDefault();
    }

    /// <summary>
    /// Returns a sort key (0-3) based on cardinal direction from center to piece.
    /// In y-up coordinates, clockwise from 0° (right):
    ///   right(1,0)=0, up(0,1)=1, left(-1,0)=2, down(0,-1)=3
    /// On even turns, start from right (0°). On odd turns, start from left (180°).
    /// </summary>
    private static int ClockwiseOrder(Coords pieceCell, Coords center, int turnNumber)
    {
        int dx = pieceCell.Col - center.Col;
        int dy = pieceCell.Row - center.Row;

        int baseOrder = (dx, dy) switch
        {
            (1, 0) => 0,   // right
            (0, 1) => 1,   // up (y-up)
            (-1, 0) => 2,  // left
            (0, -1) => 3,  // down (y-up)
            _ => 4         // non-adjacent, shouldn't happen
        };

        // Odd turns: rotate by 2 (start from left instead of right)
        if (turnNumber % 2 == 1)
            baseOrder = (baseOrder + 2) % 4;

        return baseOrder;
    }
}