using System.Collections.Generic;

namespace Netron.Diagramming.Core.Layout.Force {
  /// <summary>
  /// Represents a spring in a force simulation.
  /// </summary>
  public class Spring {
    #region Fields
    private static SpringFactory mFactory = new SpringFactory();
    private ForceItem item1;
    private ForceItem item2;
    private float length;
    private float coeff;

    #endregion

    #region Properties
    /// <summary>
    /// Retrieve the SpringFactory instance, which serves as an object pool
    /// for Spring instances.
    /// </summary>
    /// <value>The spring factory.</value>
    public static SpringFactory Factory {
      get {
        return mFactory;
      }
    }
    /// <summary> 
    /// The first ForceItem endpoint 
    /// </summary>

    public ForceItem Item1 {
      get { return item1; }
      set { item1 = value; }
    }
    /// <summary>
    /// The second ForceItem endpoint 
    /// </summary> 
    public ForceItem Item2 {
      get { return item2; }
      set { item2 = value; }
    }
    /// <summary> 
    /// The spring's resting length 
    /// </summary>
    public float Length {
      get { return length; }
      set { length = value; }
    }
    /// <summary> 
    /// The spring tension co-efficient
    /// </summary>
    public float Coeff {
      get { return coeff; }
      set { coeff = value; }
    }
    #endregion

    #region Constructor
    /// <summary>
    /// Create a new Spring instance
    ///<param name="fi1">  the first ForceItem endpoint</param>
    /// <param name="fi2"> the second ForceItem endpoint          </param>
    ///  <param name="k">the spring tension co-efficient                             </param>
    ///  <param name="len">the spring's resting length                                               </param>
    /// </summary>
    public Spring(ForceItem fi1, ForceItem fi2, float k, float len) {
      item1 = fi1;
      item2 = fi2;
      coeff = k;
      length = len;
    }

    #endregion

    #region Classes
    /// <summary>
    /// The SpringFactory is responsible for generating Spring instances
    /// and maintaining an object pool of Springs to reduce garbage collection
    /// overheads while force simulations are running.
    /// </summary>
    public sealed class SpringFactory {
      public const int Capacity = 5000;
      private List<Spring> springs = new List<Spring>(Capacity);

      /// <summary>
      /// Get a Spring instance and set it to the given parameters.
      /// </summary>
      public Spring getSpring(ForceItem f1, ForceItem f2, float k, float length) {
        if (springs.Count > 0) {
          Spring s = springs[springs.Count - 1];
          springs.Remove(s);
          s.Item1 = f1;
          s.Item2 = f2;
          s.Coeff = k;
          s.Length = length;
          return s;
        } else {
          return new Spring(f1, f2, k, length);
        }
      }
      /// <summary>
      /// Reclaim a Spring into the object pool.
      /// </summary>
      public void reclaim(Spring s) {
        s.Item1 = null;
        s.Item2 = null;
        if (springs.Count < Capacity)
          springs.Add(s);
      }
    }
    #endregion
  }
}