/* An instance of this class represents a temperature (reading).
** It supports both Celsius and Fahrenheit scales.
*/
public class Temperature {

   // class constants
   // ---------------
   public final int CEL_MODE = 0;  // Celsius mode
   public final int FAH_MODE = 1;  // Fahrenheit mode
   //RWM: using boolean values would be better (assuming that there would
   //     never be reason to expand the set of modes to more than two).
   
   // instance variables
   // ------------------
   private int mode;       // value is either CEL_MODE or FAH_MODE
   private double degrees; // on scale corresponding to current mode
   
   // constructor
   // -----------
   
   /* Initializes this Temperature to be in the specified mode and to
   ** have the specified value in degrees on the corresponding scale.
   ** If initMode is equal to neither CEL_MODE nor FAH_MODE, an 
   ** IllegalArgumentException is thrown.
   */
   public Temperature(double initDegrees, int initMode) {
      if (initMode == CEL_MODE  ||  initMode == FAH_MODE) {   
         this.mode = initMode;
         this.degrees = initDegrees;
      }
      else {
         throw new IllegalArgumentException("initMode value invalid");
      }
   }
   //RWM: Had the mode been of type boolean, it would be impossible for
   //     the client to pass an "invalid" value via the second parameter.
   

   // observers
   // ---------
   
   /* Reports whether or not this temperature is in Celsius mode.
   */
   public boolean inCelsiusMode() { return mode == CEL_MODE; }
   
   /* Returns this temperature's value/reading on the scale corresponding
   ** to its current mode.
   */
   public double getDegrees() { return this.degrees; } 
   
   // mutators
   // --------

   /* Sets this temperature to the specified number of degrees,
   ** interpreted to be a measure on the scale corresponding to
   ** the current mode.
   */
   public void setToDegrees(double numDegrees) {
      this.degrees = numDegrees;
   }
   
   /* Changes this temperature by the specified # of degrees.
   ** The parameter's value is interpreted to be a # of degrees on the
   ** scale corresponding to this temperature's current mode.
   */
   public void change(double delta) {
      this.setToDegrees(this.degrees + delta);
   }

   /* Sets this temperature to Fahrenheit mode.
   */
   public void setToFahMode() { 
      if (this.inCelsiusMode()) {
         this.mode = FAH_MODE;
         this.degrees = celToFah(this.degrees);
      }
   }
   
   /* Sets this temperature to Celsius mode.
   */
   public void setToCelMode() {
      if (!this.inCelsiusMode()) {
         this.mode = CEL_MODE;
         this.degrees = fahToCel(this.degrees);
      }
   }

   // utility methods
   // ---------------
   
   /* Given a temperature reading on the Celsius scale, returns the
   ** corresponding temperature reading on the Fahrenheit scale.
   */
   private double celToFah(double deg) {
      return (9.0 / 5.0) * deg  +  32.0;
   }
   
   /* Given a temperature reading on the Fahrenheit scale, returns 
   ** the corresponding temperature reading on the Celsius scale.
   */
   private double fahToCel(double deg) {
      return (deg - 32.0) * (5.0 / 9.0);
   }
}