package fractions;

import java.util.Scanner;

/**
 * Class for working with fractions
 *
 */
public class Fraction {

    /**
     * Read in input
     */
    private Scanner scan;

    /**
     * Numerator
     */
    private int num;

    /**
     * Denominator
     */
    private int denom;

    /**
     * Constructor
     */
    public Fraction() {
        scan = new Scanner(System.in);
    }

    /**
     * Sets values and reduces
     * @param n
     * @param d
     */
    public void setFraction(int n, int d) {
        this.num = n;
        this.denom = d;
        reduce();
    }

    /**
     * Adds the fraction and returns
     * @param op
     * @return
     */
    public Fraction add(Fraction op) {
        //null check
        if(op == null) {
            return this;
        }

        //general case -- get a common denominator by getting product of denominators and then adding numerators
        int previousDenom = this.denom;
        this.denom *= op.denom;
        this.num *=op.denom;
        this.num += op.num * previousDenom;

        reduce();

        return this;
    }

    /**
     * Subtracts fractions
     * @param op
     * @return
     */
    public Fraction subtract(Fraction op) {
        //null check
        if(op == null) {
            return this;
        }

        //subtracting is the same as adding the opposite:)
        op.setFraction(op.num * -1, op.denom);
        return add(op);
    }

    /**
     * Multiply and return
     * @param op
     * @return
     */
    public Fraction multiply(Fraction op) {
        //null check
        if(op == null) {
            return this;
        }

        //multiplying is easy -- multiply straight across and we are good:)
        this.num *= op.num;
        this.denom *= op.denom;

        reduce();

        return this;
    }

    /**
     * Divides fractions
     * @param op
     * @return
     */
    public Fraction divide(Fraction op) {
        //null check
        if(op == null) {
            return this;
        }

        //division is the same as multiplying by reciprocal
        int oldNum = op.num;
        op.setFraction(op.denom, oldNum);
        multiply(op);

        reduce();

        return this;
    }

    /**
     * Override equals method.  Is true if both num and denom are the same
     * assumes both are already reduced.
     */
    @Override
    public boolean equals(Object other) {
        //null
        if(other == null) {
            return false;
        }

        //instance of check
        if(!(other instanceof Fraction)) {
            return false;
        }

        //all fields match
        return ((Fraction)other).num == num && ((Fraction)other).denom == denom;
    }


    /**
     * Override to string
     */
    @Override
    public String toString() {
        return num + "/" + denom;
    }

    /**
     * Read in fraction
     * @param label
     */
    public void readin(String label) {
        while (true) // Keep trying if bad input is received
        {
            System.out.print(label);
            String temp = scan.next();
            temp = temp.trim(); // get rid of white space at the beginning and end
            int index = temp.indexOf('/');
            if (index >= 0)             {
                String numStr = temp.substring(0, index);
                String denomStr = temp.substring(index+1);
                int n = Integer.parseInt(numStr);
                int d = Integer.parseInt(denomStr);
                setFraction(n,d);
                return;
            }
            else
                System.out.println("Input Fraction missing / ");
        }//Keep trying until you get it right
    }


    /**
     * Reduces this representation of a fraction
     */
    private void reduce() {
        //find the gcd
        int gcd = findGreatestCommonFactor(num, denom);

        //divide both numerator and denominator by gcd
        num /=gcd;
        denom /=gcd;
    }

    /**
     * Recursively find the greatest common denominator of two numbers.
     * @param a
     * @param b
     * @return
     */
    private int findGreatestCommonFactor(int a, int b) {
        return (b == 0)? a: findGreatestCommonFactor(b,  a % b);
    }

    /**
     * Entry point.
     * @param args command line args
     */
    public static void main(String[] args) {
        Fraction f1= new Fraction();
        Fraction f2= new Fraction();
        Fraction f3=null;
        Scanner scan = new Scanner(System.in);
        while(true)         {
            System.out.println();  // Add a blank line
            System.out.print("Enter operation: + - * / q (q ==> quit) : ");
            String input = scan.next();
            if (input.charAt(0) == 'q')
                break; // All done
            f1.readin("Enter Fraction 1: ");
            f2.readin("Enter Fraction 2: ");
            System.out.println("f1 = " + f1);
            System.out.println("f2 = " + f2);
            if (f1.equals(f2))
                System.out.println("f1 and f2 are equal");
            else
                System.out.println("f1 and f2 are not equal");
            switch (input.charAt(0))             {
            case '+':
                f3 = f1.add(f2);
                System.out.println("f1+f2=" + f3);
                break;
            case '-':
                f3 = f1.subtract(f2);
                System.out.println("f1-f2=" + f3);
                break;
            case '*':
                f3 = f1.multiply(f2);
                System.out.println("f1*f2="+f3);
                break;
            case '/':
                f3 = f1.divide(f2);
                System.out.println("f1/f2="+f3);
                break;
            default:
                System.out.println("Illegal command: "  + input );
                break;

            }
        }// end of while loop
        System.out.println("Bye");

        //don't forget to close our scan resource :)
        if(scan != null) {
            scan.close();
        }
    }

}