/**
  * Bounce Graph Class for Rob's
  * Difference Equation Iteration Demonstrator Applet
  * @author Robert J Morton
  * @version 27 November 1997 modified 07 August 2009, 18 April 2012 */

// FORMULA ITERATION CLASS

class formula {
  private double 
    x = 0.01,   // the iterated variable
    c = 3.68,   // the formula scaling constant
    P1 = 0,     // upper real range limit of graph area
    P2 = 1,     // lower real range limit of graph area
    δP = 0.01;  // real x-increment for drawing the parabola

  boolean
    InRange = true,   // indicates if x goes off the graph
    EqnFlag = false;  // which of the 2 equations is being used

  private difeqnap ap;   // instance reference to the main applet class
  private bouncegr bg;   // instance reference to the bounce-graph class
  private setbutt sb;    // instance reference to the setbutt class


  formula(difeqnap ap) {  // construct the bounce graph resources
    this.ap = ap;  // instance reference to the main applet class
  }


  void setSB(setbutt sb) {
    this.sb = sb;  // set instance reference to setbutt class
  }


  void setBG(bouncegr bg) {
    this.bg = bg;  // set instance reference to bounce-graph
  }


  void setEF(boolean b) {
    EqnFlag = b;  // set which equation is in force
  }


  void setC(double c) {
    this.c = c;  // current C-value set by the Cval panel
  }


  void reset() {   // PRIME/RESET THE BOUCE GRAPH FORMULA
    if(EqnFlag) {  // IF USING X = X**2 + C
      P1 = -2;     // upper real range limit of graph area
      P2 = +2;     // lower real range limit of graph area
      δP = .005;   // real x-increment for drawing the parabola 
      x = 0;       // initial value of x
    } else {       // IF USING X = CX(1 - X)
      P1 = 0;      // upper real range limit of graph area 
      P2 = 1;      // lower real range limit of graph area
      δP = .001;   // real x-increment for drawing the parabola
      x = 0.01;    // initial value of x
    }
    InRange = true;  // assume x is not out of range to start with
  }
 

  /* The following loop increments the real variables for plot-
  ting the parabola for the initial drawing of the bounce-graph.
  On each pass  of the loop it calls the plotParabola() method
  in the bounce-graph class to do each plot in pixel units. */

  void plotParabola() {  // DRAW THE PARABOLA
    double x, y;         // horizontal and vertical real variables

    // for each small step along the horizontal axis
    for(x = P1 ; x <= P2 ; x += δP) {

      if(EqnFlag)             // if equation switch flag set true
        y = x * x + c;        // use the square law EqnFlag
      else                    // else [equation switch flag set false]
        y = c * x * (1 - x);  // use standard logistics equation

      if(y >= P1 && y <= P2)    // provided y is within range of graph area
        bg.plotParabola(x, y);  // do plot in pixel units
    }
  }


  void iterate() {          // DO ONE ITERATION OF THE SELECTED FORMULA
    if(EqnFlag)             // if equation switch flag set true
      x = x * x + c;        // use the square law EqnFlag
    else                    // if equation switch flag set false
      x = c * x * (1 - x);  // use standard logistics equation
    if(x < P1 || x > P2) {  // if out of range of graph area
      InRange = false;      // set to 'out of range'
      sb.Stop();            // stop the iteration process
      System.out.println("formula.java: Stopped because x has");
      System.out.println("gone out of range of the graph.");
    }
  }


  double getX() {
    return x;  // get the [iterated i.e. updated] value of x
  }


  boolean inRange() {
    return InRange;  // is x still within the range of the graph area?
  }

}