/// <summary>
/// Returns the game to the state it was in after the specified number of turns.
/// </summary>
/// <param name="turnCount">The number of turns.</param>
/// <returns>A list of the spaces affected by the last move, starting with the space
/// of the move and including the spaces of all the pieces captured by the move.</returns>
private IAsyncOperation <IList <ISpace> > ResetAsync(int turnCount)
{
if (turnCount < 0 || turnCount > MoveStack.Count)
{
throw new ArgumentException("must be 0 or greater and " +
"no higher than MoveStack.Count.", "turnCount");
}
if (turnCount == Moves.Count)
{
throw new ArgumentException("must be different than " +
"Moves.Count.", "turnCount");
}
// Use a lock to prevent this method from modifying the game state at
// the same time a different thread is in the locked MoveAsync method.
lock (_lockObject)
{
IList <ISpace> newMoves;
if (turnCount < Moves.Count)
{
// Backward navigation resets the board to its initial state in
// preparation for replaying all moves up to the indicated move.
SetUpEmptyBoard();
newMoves = Moves.Take(turnCount).ToList();
Moves.Clear();
}
else
{
// Forward navigation retrieves previously-undone moves in
// preparation for their replay from the current board state.
newMoves = MoveStack.Skip(Moves.Count)
.Take(turnCount - Moves.Count).ToList();
}
return(MoveAsync(newMoves));
}
}
