AdventOfCode/AdventOfCode.Core/Shared/A-Star/AStarGrid.cs

namespace AdventOfCode.Core.Shared.A_Star
{
    public class AStarGrid<T>(T[] data) : Grid<T>(data) where T : AStarNode
    {
        public int TileMoveCost { get; set; }

        public int MinimalSteps(T start, T destination)
        {
            List<T> openNodes = [start];
            List<T> closedNodes = [];

            while(openNodes.Count != 0)
            {
                // get the lowest F-cost node
                T current = openNodes.OrderBy(n => n.FCost).First();
                openNodes.Remove(current);
                closedNodes.Add(current);

                if (current == destination)
                {
                    //done
                    return 1;
                }

                var neighbors = GetNeighbors(current, false)
                    .Where(n => current.CanMoveTo(current));

                // calc costs
                foreach(T neighbor in neighbors)
                {
                    long g = current.GCost + GetMoveCost(current, neighbor);
                    long h = neighbor.GetManhattanDistance(destination) * GetMoveCost(current, neighbor);
                    long f = g + h;

                    int openNodeIndex = openNodes.IndexOf(neighbor),
                        closedNodeIndex = closedNodes.IndexOf(neighbor);

                    if (openNodeIndex > 0 && openNodes[openNodeIndex].FCost > f)
                    {
                        openNodes[openNodeIndex].ParentNode = neighbor;
                        openNodes[openNodeIndex].GCost = g;
                        openNodes[openNodeIndex].HCost = h;
                    }

                    openNodes.Add(neighbor);
                }
            }

            return -1;
        }

        public virtual int GetMoveCost(T current, T neighbor) => TileMoveCost;
    }
}