// fraction.py
// Walker M. White (wmw2)
// October 7, 2012
/** 
 *  Instance is a Fraction n/d
 *
 *  The purpose of this class is to illustrate the differences between
 *  Python and Java classes
 */
class Fraction {
    // ALL functions must be a method inside of a class.
    private int numerator   = 0;        // must be an int
    private int denominator = 1;        // must be an int > 0

    // PROPERTIES
    /** Fraction numerator (getter) */
    public int getNumerator() {
        return this.numerator;      // returns the field
    }
    
    /** Fraction numerator (setter) */
    public void setNumerator(int value) {
        // assign to field
        this.numerator = value;
    }

    /** 
     *  Fraction denominator (getter) 
     *  Invariant: Must be an int > 0. 
     */
    public int getDenominator() {
        return this.denominator;      // returns the field
    }
    
    /** 
     *  Fraction denominator (setter)
     *  Invariant: Must be an int > 0. 
     */
    public void setDenominator(int value) {
        // assign to field
        assert value > 0 : value+" is not positive";        // Types cannot catch everything.
        this.denominator = value;
    }

    /** 
     *  Constructor: Creates a new Fraction n/d 
     *  Precondition: d > 0 
     */
    public Fraction(int n,int d) { 
        this.setNumerator(n);
        this.setDenominator(d);
    }
    
    /** Returns: this Fraction as a string 'n/d' */
    public String toString() {
        return this.getNumerator()+"/"+this.getDenominator();
    }

    /** 
     *  Returns: Product of this and other as a new Fractions
     *  Does not modify contents of self or other 
     */
    public Fraction mul(Fraction other) {
        int top = this.getNumerator()*other.getNumerator();
        int bot = this.getDenominator()*other.getDenominator();
        return new Fraction(top,bot);
    }

    /** 
     *  Returns: Sum of this and other as a new Fraction 
     *  Does not modify contents of self or other 
     */
    public Fraction add(Fraction other) {
        int bot = this.getDenominator()*other.getDenominator();
        int top = (this.getNumerator()*other.getDenominator()+
                   this.getDenominator()*other.getNumerator());
        return new Fraction(top,bot);
    }

    /** 
     *  Returns: True if this, other are equal Fractions.
     *           False if not equal, or other not a Fraction 
     */
    public boolean equals(Object other) {
        if (!(other instanceof Fraction)) {
            return false;
        }
        
        // Must change static type to agree with dynamic type
        Fraction frac = (Fraction)other;
        
        // Cross multiply
        int left = this.getNumerator()*frac.getDenominator();
        int rght = this.getDenominator()*frac.getNumerator();
        return left == rght;
    }

    /** 
     *  Returns: a negative integer if this < other,
     *           zero if this == other,
     *           a positive integer if this > other
     *  
     *  Used to implement comparison operations. 
     */
    public int compareTo(Fraction other) {
        // Cross multiply
        int left = this.getNumerator()*other.getDenominator();
        int rght = this.getDenominator()*other.getNumerator();
        return left - rght;
    }
    
    /** 
     *  Normalizes this fraction so that numerator
     *  and denominator have no common divisors. 
     */
    public void reduce() {
        int g = this.gcd(this.getNumerator(),this.getDenominator());
        this.setNumerator(this.getNumerator()/g);
        this.setDenominator(this.getDenominator()/g);
    }
    
    /** 
     * Returns: Greatest common divisor of x and y.
     * This was a function; is now a hidden method.
     */
    private int gcd(int a, int b) {
        while (b != 0) {
            int t = b;
            b = a % b;
            a = t;
        }
        return a;
    }
}