#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2012 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
 *
 * This file is part of HeuristicLab.
 *
 * HeuristicLab is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * HeuristicLab is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
 */
#endregion

using System.Collections.Generic;
using System.Linq;
using HeuristicLab.Core;

namespace HeuristicLab.Problems.GeneralizedQuadraticAssignment.Common {
  public static class ExtensionMethods {
    #region Graph walk
    /// <summary>
    /// Walks an operator graph in that it jumps from one operator to all its operator parameters and yields each operator it touches.
    /// Cycles are detected and not walked twice.
    /// </summary>
    /// <param name="initial">The operator where the walk starts (is also yielded).</param>
    /// <returns>An enumeration of all the operators that could be found.</returns>
    public static IEnumerable<IOperator> Walk(this IOperator initial) {
      var open = new Stack<IOperator>();
      var visited = new HashSet<IOperator>();
      open.Push(initial);

      while (open.Any()) {
        IOperator current = open.Pop();
        if (visited.Contains(current)) continue;
        visited.Add(current);

        foreach (var parameter in current.Parameters.OfType<IValueParameter>()) {
          if (typeof(IOperator).IsAssignableFrom(parameter.DataType)) {
            if (parameter.Value != null)
              open.Push((IOperator)parameter.Value);
          }
        }

        yield return current;
      }
    }
    #endregion
  }
}