Chessistics/chessistics-engine/Model/Coords.cs

namespace Chessistics.Engine.Model;

public readonly struct Coords : IEquatable<Coords>
{
    public int Col { get; }
    public int Row { get; }

    public Coords(int col, int row)
    {
        Col = col;
        Row = row;
    }

    public bool IsOnBoard(int width, int height)
        => Col >= 0 && Col < width && Row >= 0 && Row < height;

    public int ManhattanDistance(Coords other)
        => Math.Abs(Col - other.Col) + Math.Abs(Row - other.Row);

    public bool IsAdjacent4(Coords other)
        => ManhattanDistance(other) == 1;

    public IReadOnlyList<Coords> GetAdjacent4(int width, int height)
    {
        var result = new List<Coords>(4);
        Coords[] offsets = [new(0, 1), new(0, -1), new(1, 0), new(-1, 0)];
        foreach (var offset in offsets)
        {
            var neighbor = new Coords(Col + offset.Col, Row + offset.Row);
            if (neighbor.IsOnBoard(width, height))
                result.Add(neighbor);
        }
        return result;
    }

    /// <summary>
    /// Checkerboard parity: true if (Col + Row) is even (light square).
    /// </summary>
    public bool IsLight => (Col + Row) % 2 == 0;

    public bool Equals(Coords other) => Col == other.Col && Row == other.Row;
    public override bool Equals(object? obj) => obj is Coords other && Equals(other);
    public override int GetHashCode() => HashCode.Combine(Col, Row);
    public override string ToString() => $"({Col},{Row})";

    public static bool operator ==(Coords left, Coords right) => left.Equals(right);
    public static bool operator !=(Coords left, Coords right) => !left.Equals(right);
}