using System.Collections;
using System.Collections.Generic;
namespace Netron.Diagramming.Core {
  /// <summary>
  /// This <see cref="IComparer"/> compares two diagram entities with respect to their scene index.
  /// A diagram entity is 'less' than another if the scene index is smaller. Note that two distinct entities can never
  /// have the same scene index. Since this comparer is used in the first place to re-order the <see cref="IPaintable"/> collection
  /// it will throw an exception if two indices are found to be the same.
  /// </summary>
  /// <typeparam name="T"></typeparam>
  class SceneIndexComparer<T> : IComparer<T> where T : IDiagramEntity {
    /// <summary>
    /// Compares two objects and returns a value indicating whether one is less than, equal to, or greater than the other.
    /// </summary>
    /// <param name="x">The first object to compare.</param>
    /// <param name="y">The second object to compare.</param>
    /// <returns>
    /// Value Condition Less than zerox is less than y.Zerox equals y.Greater than zerox is greater than y.
    /// </returns>
    public int Compare(T x, T y) {
      if (x.SceneIndex == y.SceneIndex)
        throw new InconsistencyException("Inconsistent stack: two entities had the same scene index.");

      if (x.SceneIndex < y.SceneIndex)
        return -1;
      else
        return +1;
    }


  }
}