/// <summary>
/// Checks if <paramref name="player"/> is currently under check.
/// </summary>
/// <typeparam name="TChess">Derived type. <paramref name="chess"/>
/// must be <typeparamref name="TChess"/>.</typeparam>
/// <param name="chess">A <see cref="Chess"/> board.</param>
/// <param name="player"><see langword="true"/> for player with white pieces. Otherwise, black.</param>
/// <returns><see langword="true"/> if <paramref name="player"/> is checked.
/// Otherwise, <see langword="false"/>.</returns>
public static bool IsChecked <TChess>(this IChess chess, bool player) where TChess : Chess
{
// Types of movements that might threaten a king.
// A pawn may promote while threatening.
var threateningMoves = new MoveType[] {
MoveType.Capture,
MoveType.PromoteToKnight,
MoveType.PromoteToBishop,
MoveType.PromoteToRook,
MoveType.PromoteToQueen
}.ToList();
// List of opponent's moves that might threaten the king.
var enemyMoves = ((TChess)chess)
.AllMoves(!player)
.Where(m => threateningMoves.Contains(m.Type))
.Where(m => chess.Position.ContainsKey(m.ToSquare))
.Where(m => chess.Position[m.ToSquare] is King).ToList();
// Case enemy moves is an empty list, no piece threatens the king.
return(enemyMoves.Count > 0);
}