/**
 * @Homework:  Assignment 3
 * @Exercise:  6.3 in textbook, page 342
 * @Author:    Richard Parry
 * @Version:   1.0 - July 20, 1998
 * @Filename:  Rational.java
 * @School:    UCSD, Summer 98 Java 1 class
 *
 * Description:
 * This program <code>Rational<code> accepts two rational numbers given
 * by the user and performs aritmetic operations: add, substract, multiply,
 * and divide.
 *
 * Usage:
 *         r1 = new Ration(numerator, denominator); // create object
 *         r2 = new Ration(numerator, denominator); // create object
 *
 *         Ration result = Rational.add(r1, r2);    // to add
 *         Ration result = Rational.sub(r1, r2);    // to subtract
 *         Ration result = Rational.mul(r1, r2);    // to multiply
 *         Ration result = Rational.div(r1, r2);    // to divide
 *         r1.toString();                           // convert to string
 **/

// declare class
public class Rational {

  // private instance variable
  private int numerator, denominator;


  /** This is a "no-argument" Constructor Method with default values
   * in case no initialzers are provided.  This ensure that each Rational
   * object starts in a consistent state (the default state).
   * @param none
   * @return none
   * @exception none
   **/
  public Rational() {
    this.numerator = 1;
    this.denominator = 2;
  }


  /**
   * This is the constructor.  It initializes the numerator and
   * denominator variables.
   **/
  public Rational(int numerator, int denominator) {
    this.numerator = numerator;
    this.denominator = denominator;
  }


  /**
   * An accessor method. Returns the numerator part of the rational number.
   * Note that there is no setNumerator() method to set the numerator part.
   * This means that the Rational class is "immutable".
   **/
  public int getNumerator() {
    return numerator;
  }

  /**
   * An accessor method. Returns the demoninator part of the rational number.
   **/
  public int getDenominator() {
    return denominator;
  }


  /**
   * This method converts a Ration number to a string.  This is a method of
   * Object that we override so that rational numbers can be meaningfully
   * converted to strings, and so they can conveniently be printed out with
   * System.out.println() and related methods.
   **/
  public String toString() {
    return numerator + "/" + denominator;
  }


  /**
   * This method accepts a rational number and converts a float (decimal)
   * If the numerator is zero, then force results to zero.  This solves
   * the problem of divide by zero AND the special case problem of
   * 0/0.  This is not an elegant solution, but is straight forward.
   **/
  public static float rational2Decimal( Rational rationalNum ) {
    float floatNumerator = rationalNum.getNumerator();
    float floatDenominator = rationalNum.getDenominator();
    if ( floatNumerator == 0 ) {
      return 0;
    }
    else {
      return floatNumerator / floatDenominator;
    }
  }


  /**
   * Reduce method, is a method that accepts a rational number consisting
   * of a numerator and denominator and reduces it.
   **/
  private static Rational reduce( Rational ration ) {

    int smallest, largest;
    int gcd = 1; // need to initialize

    // use accessor, to get numerator and denominator
    int n = ration.getNumerator();
    int d = ration.getDenominator();

    /** to reduce find smallest number then modulus divide
     * if no remainder, then see it will also divide into
     * the larger number, if so it is a possible candidate as
     * a divisor so save it.  Continue looking and save the highest
     * value, since it will be the largest common denominator
     **/
    smallest = Math.abs( Math.min(n, d) ); // no negative values
    largest  = Math.max(n, d);
    
    for (int i = 2; i <= smallest; i++) {
      if( smallest % i == 0 ) {
	if( largest % i == 0 ) {
	  gcd = i; // save greatest common denominator
	}
      }
    }

    // return reduced rational number
    Rational reducedNumber = new Rational( n/gcd, d/gcd );
    return reducedNumber;
  }



  /**
   * This is a static method.  It takes two Rational numbers, adds them,
   * and returns the result as a third number.  Because it is static, there is
   * no "current instance" or "this" object.  use it like this:
   *
   *           Rational sum = Rational.add(r1, r2)
   *
   * where r1 and r2 are rational numbers consisting of a numerator
   * and denominator. Example above is for addition, similar
   * method calls are used for other arithmetic operations.
   **/
  public static Rational add(Rational rat1, Rational rat2) {
    // add rational numbers
    int denom = rat1.denominator * rat2.denominator;
    int numer = rat1.numerator * rat2.denominator +  rat2.numerator * rat1.denominator;

    // make new object for results, reduce, and return rational number
    Rational r3 = new Rational( numer, denom );
    return r3.reduce( r3 );
  }


  // Static method to substract
  public static Rational sub(Rational rat1, Rational rat2) {
    int denom = rat1.denominator * rat2.denominator;
    int numer = rat1.numerator * rat2.denominator - rat2.numerator * rat1.denominator;

    // for special case of zero numerator, force denominator to zero
    // I assume that 1/2 - 1/2 expressed as a rational number is 0/0
    if ( numer == 0 ) {
      denom = 0;
    }

    // make new object for results, reduce, and return rational number
    Rational r3 = new Rational( numer, denom );
    return r3.reduce( r3 );
  }


  // Static method to multiple
  public static Rational mul(Rational rat1, Rational rat2) {
    int denom = rat1.denominator * rat2.denominator;
    int numer = rat1.numerator * rat2.numerator;

    // make new object for results, reduce, and return rational number
    Rational r3 = new Rational( numer, denom );
    return r3.reduce( r3 );
  }


  // Static method to divide
  public static Rational div(Rational rat1, Rational rat2) {
    int numer = rat1.numerator * rat2.denominator;
    int denom = rat1.denominator * rat2.numerator;

    // make new object for results, reduce, and return rational number
    Rational r3 = new Rational( numer, denom );
    return r3.reduce( r3 );
  }

} // end class declaration