/**
  * Bounce Graph Class for Rob's
  * Difference Equation Iteration Demonstrator Applet
  * @author Robert J Morton UK-YE572246C
  * @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

  /* construct the bounce graph resources by passing
  the instance reference of the main applet class. */

  formula(difeqnap ap) { this.ap = ap; }

  // Set the instance reference of the setbutt class.
  void setSB(setbutt sb) {this.sb = sb;}

  // Set the instance reference of the bounce-graph class.
  void setBG(bouncegr bg) {this.bg = bg;}

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

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


  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 plotting
  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 the equation switch flag is set TRUE, use the square
      law equation; otherwise, use standard logistics equation. */

      if(EqnFlag) y = x * x + c; else y = c * x * (1 - x);

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


  void iterate() {  // DO ONE ITERATION OF THE SELECTED FORMULA

    /* If the equation switch flag is set TRUE, use the square
    law equation; otherwise, use standard logistics equation. */

    if(EqnFlag) x = x * x + c; else x = c * x * (1 - x);

    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
      ap.showStatus(
        "Stopped because x has gone out of range of the graph."
      );
    }
  }


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

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