using System;

namespace Netron.Diagramming.Core.Layout.Force {
  /// <summary>
  ///  Implements a viscosity/drag force to help stabilize items.
  /// </summary>
  public class DragForce : AbstractForce {
    #region Fields
    /// <summary>
    /// the parameter names
    /// </summary>
    private static String[] pnames = new String[] { "DragCoefficient" };
    /// <summary>
    /// dragging coefficient
    /// </summary>
    public static float DefaultDragCoeff = 0.01f;
    /// <summary>
    /// minimum dragging coefficient
    /// </summary>
    public static float DefaultMinDragCoeff = 0.0f;
    /// <summary>
    /// maximum drag coefficient
    /// </summary>
    public static float DefaultMaxDragCoeff = 0.1f;
    /// <summary>
    /// current dragging coefficient
    /// </summary>
    public static int DragCoeff = 0;
    #endregion

    #region Properties
    /// <summary>
    /// Returns true.
    /// </summary>
    /// <value></value>
    public override bool IsItemForce {
      get {
        return true;
      }
    }
    /// <summary>
    /// Gets the parameter names.
    /// </summary>
    /// <value></value>
    /// <returns></returns>
    protected override String[] ParameterNames {
      get {
        return pnames;
      }
    }
    #endregion

    #region Methods
    /// <summary>
    ///  Create a new DragForce.
    /// </summary>
    /// <param name="dragCoeff">The drag coefficient.</param>
    public DragForce(float dragCoeff) {
      parms = new float[] { dragCoeff };
      minValues = new float[] { DefaultMinDragCoeff };
      maxValues = new float[] { DefaultMaxDragCoeff };
    }

    /// <summary>
    /// Create a new DragForce with default drag co-efficient.
    /// </summary>
    public DragForce()
      : this(DefaultDragCoeff) {

    }

    /// <summary>
    /// Returns the force acting on the given item.
    /// </summary>
    /// <param name="item"></param>
    public override void GetForce(ForceItem item) {
      item.Force[0] -= parms[DragCoeff] * item.Velocity[0];
      item.Force[1] -= parms[DragCoeff] * item.Velocity[1];
    }
    #endregion


  }
}