using System;

namespace Netron.Diagramming.Core.Layout.Force {

  /// <summary>
  ///  Force function that computes the force acting on ForceItems due to a  given Spring.
  /// </summary>
  public class SpringForce : AbstractForce {

    #region Fields
    Random rnd = new Random();
    private static String[] pnames = new String[] { "SpringCoefficient", "DefaultSpringLength" };
    public static float DefaultSpriongCoeff = 1E-4f;
    public static float DefaultMaxSpringCoeff = 1E-3f;
    public static float DefaultMinSpringCoeff = 1E-5f;
    public static float DefaultSpringLength = 50;
    public static float DefaultMinSpringLength = 0;
    public static float DefaultMaxSpringLength = 200;
    public static int SpringCoeff = 0;
    public static int SpringLength = 1;

    #endregion

    #region Properties
    /// <summary>
    /// Gets a value indicating whether [spring force].
    /// </summary>
    /// <value><c>true</c> if [spring force]; otherwise, <c>false</c>.</value>
    public override bool IsSpringForce {
      get {
        return true;
      }
    }
    /// <summary>
    /// Gets the parameter names.
    /// </summary>
    /// <value></value>
    /// <returns></returns>
    protected override String[] ParameterNames {
      get {
        return pnames;
      }
    }
    #endregion

    #region Constructor
    /// <summary>
    ///  Create a new SpringForce.
    /// </summary>
    /// <param name="springCoeff"> the default spring co-efficient to use. This will be used if the spring's own co-efficient is less than zero..</param>
    /// <param name="defaultLength">the default spring length to use. This will be used if the spring's own length is less than zero.</param>
    public SpringForce(float springCoeff, float defaultLength) {
      parms = new float[] { springCoeff, defaultLength };
      minValues = new float[] { DefaultMinSpringCoeff, DefaultMinSpringLength };
      maxValues = new float[] { DefaultMaxSpringCoeff, DefaultMaxSpringLength };
    }

    /// <summary>
    /// Constructs a new SpringForce instance with default parameters.
    /// </summary>
    public SpringForce()
      : this(DefaultSpriongCoeff, DefaultSpringLength) {
    }
    #endregion

    #region Methdos
    /// <summary>
    /// Gets the force.
    /// </summary>
    /// <param name="s">The s.</param>
    public override void GetForce(Spring s) {
      ForceItem item1 = s.Item1;
      ForceItem item2 = s.Item2;
      float length = (s.Length < 0 ? parms[SpringLength] : s.Length);
      float x1 = item1.Location[0], y1 = item1.Location[1];
      float x2 = item2.Location[0], y2 = item2.Location[1];
      float dx = x2 - x1, dy = y2 - y1;
      float r = (float)Math.Sqrt(dx * dx + dy * dy);
      if (r == 0.0) {
        dx = ((float)rnd.NextDouble() - 0.5f) / 50.0f;
        dy = ((float)rnd.NextDouble() - 0.5f) / 50.0f;
        r = (float)Math.Sqrt(dx * dx + dy * dy);
      }
      float d = r - length;
      float coeff = (s.Coeff < 0 ? parms[SpringCoeff] : s.Coeff) * d / r;
      item1.Force[0] += coeff * dx;
      item1.Force[1] += coeff * dy;
      item2.Force[0] += -coeff * dx;
      item2.Force[1] += -coeff * dy;
    }

    #endregion

  }
}