using System.Diagnostics;

namespace Gameboard.ShogiUI.BoardState
{
  /// <summary>
  /// Provides normalized BoardVectors relative to player. 
  /// "Up" for player 1 is "Down" for player 2; that sort of thing.
  /// </summary>
  public class Direction
  {
    private static readonly BoardVector PositiveX = new BoardVector(1, 0);
    private static readonly BoardVector NegativeX = new BoardVector(-1, 0);
    private static readonly BoardVector PositiveY = new BoardVector(0, 1);
    private static readonly BoardVector NegativeY = new BoardVector(0, -1);
    private static readonly BoardVector PositiveYX = new BoardVector(1, 1);
    private static readonly BoardVector NegativeYX = new BoardVector(-1, -1);
    private static readonly BoardVector NegativeYPositiveX = new BoardVector(1, -1);
    private static readonly BoardVector PositiveYNegativeX = new BoardVector(-1, 1);

    private readonly WhichPlayer whichPlayer;
    public Direction(WhichPlayer whichPlayer)
    {
      this.whichPlayer = whichPlayer;
    }

    public BoardVector Up => whichPlayer == WhichPlayer.Player1 ? PositiveY : NegativeY;
    public BoardVector Down => whichPlayer == WhichPlayer.Player1 ? NegativeY : PositiveY;
    public BoardVector Left => whichPlayer == WhichPlayer.Player1 ? NegativeX : PositiveX;
    public BoardVector Right => whichPlayer == WhichPlayer.Player1 ? PositiveX : NegativeX;
    public BoardVector UpLeft => whichPlayer == WhichPlayer.Player1 ? PositiveYNegativeX : NegativeYPositiveX;
    public BoardVector UpRight => whichPlayer == WhichPlayer.Player1 ? PositiveYX : NegativeYX;
    public BoardVector DownLeft => whichPlayer == WhichPlayer.Player1 ? NegativeYX : PositiveYX;
    public BoardVector DownRight => whichPlayer == WhichPlayer.Player1 ? NegativeYPositiveX : PositiveYNegativeX;
    public BoardVector KnightLeft => whichPlayer == WhichPlayer.Player1 ? new BoardVector(-1, 2) : new BoardVector(1, -2);
    public BoardVector KnightRight => whichPlayer == WhichPlayer.Player1 ? new BoardVector(1, 2) : new BoardVector(-1, -2);

  }

  [DebuggerDisplay("[{X}, {Y}]")]
  public class BoardVector
  {
    public int X { get; set; }
    public int Y { get; set; }
    public bool IsValidBoardPosition => X > -1 && X < 9 && Y > -1 && Y < 9;
    public bool IsHand => X < 0 && Y < 0; // TODO: Find a better way to distinguish positions vs hand.
    public BoardVector(int x, int y)
    {
      X = x;
      Y = y;
    }

    public BoardVector Add(BoardVector other) => new BoardVector(X + other.X, Y + other.Y);
    public override bool Equals(object obj) => (obj is BoardVector other) && other.X == X && other.Y == Y;
    public override int GetHashCode()
    {
      // [0,3] should hash different than [3,0]
      return X.GetHashCode() * 3 + Y.GetHashCode() * 5;
    }
    public static bool operator ==(BoardVector a, BoardVector b) => a.Equals(b);
    public static bool operator !=(BoardVector a, BoardVector b) => !a.Equals(b);
  }
}