package test2;

/**
 * A class that represents temperatures in degrees Celcius or degrees
 * Fahrenheit.
 * 
 *
 */
public class Temperature {

    /**
     * The abbreviation of Celcius.
     */
    public static final String CELCIUS = "C";

    /**
     * The abbreviation of Fahrenheit
     */
    public static final String FAHRENHEIT = "F";

    private double degC;
    private double degF;
    private String units;

    /**
     * Initializes the temperature to 0 degrees Celcius.
     */
    public Temperature() {
        this(0.0, Temperature.CELCIUS);
    }

    /**
     * Initializes the temperature by copying the numeric value and units of
     * another temperature.
     * 
     * @param other
     *            the temperature to copy
     */
    public Temperature(Temperature other) {
        this(other.getTemperature(), other.getUnits());
    }

    /**
     * Initializes the temperature to the given numeric value having the given
     * units.
     * 
     * @param temp
     *            the temperature
     * @param units
     *            the units (Temperature.CELCIUS or Temperature.FAHRENHEIT)
     * @throws IllegalArgumentException
     *             if units is not one of Temperature.CELCIUS or
     *             Temperature.FAHRENHEIT
     */
    public Temperature(double temp, String units) {
        this.setUnits(units);
        this.setTemperature(temp);
    }

    /**
     * Gets the numeric value of the temperature using the current units. For
     * instance, the value of <code>degC</code> is <code>0.0</code> and the
     * value of <code>degF</code> is <code>32.0</code> in the following example:
     * 
     * <pre>
     * Temperature t = new Temperature(0.0, Temperature.CELCIUS);
     * double degC = t.getTemperature();
     * 
     * Temperature u = new Temperature(32.0, Temperature.FAHRENHEIT);
     * double degF = u.getTemperature();
     * </pre>
     * 
     * @return the numeric value of the temperature using the current units
     */
    public double getTemperature() {
        if (this.units.equals(Temperature.CELCIUS)) {
            return this.degC;
        }
        return this.degF;
    }

    /**
     * Sets the numeric value of the temperature using the current units. For
     * instance, the final numeric value of <code>t</code> is <code>15.0</code>
     * degrees Celcius in the example below:
     * 
     * <pre>
     * Temperature t = new Temperature(0.0, Temperature.CELCIUS);
     * t.setTemperature(15.0);
     * </pre>
     * 
     * @param temp
     *            the numeric value of the temperature
     */
    public final void setTemperature(double temp) {
        if (this.units.equals(Temperature.CELCIUS)) {
            this.degC = temp;
            this.degF = Temperature.toFahrenheit(temp);
        } else {
            this.degF = temp;
            this.degC = Temperature.toCelcius(temp);
        }
    }

    /**
     * Gets the units of the temperature.
     * 
     * @return Temperature.CELCIUS if the temperature is in
     *         Celcius, or Temperature.FAHRENHEIT if the
     *         temperature is in Fahrenheit.
     */
    public String getUnits() {
        return this.units;
    }

    /**
     * Set the units of the temperature. This method has the side effect that
     * the numeric value of the temperature changes to reflect the change in
     * units. For instance, changing the units of <code>0</code> degrees Celcius
     * to Fahrenheit causes the value of <code>degF</code> to be
     * <code>32.0</code> (because 0C is equal to 32F):
     * 
     * <pre>
     * Temperature t = new Temperature(0, Temperature.CELCIUS);
     * t.setUnits(Temperature.FAHRENHEIT);
     * double degF = t.getTemperature();    // degF is equal to 32.0
     * String units = t.getUnits();         // units is equal to Temperature.FAHRENHEIT 
     * </pre>
     * 
     * @param units
     *            the units of the temperature (Temperature.CELCIUS
     *            or Temperature.FAHRENHEIT)
     * @throws IllegalArgumentException
     *             if units is not one of
     *             Temperature.CELCIUS or Temperature.FAHRENHEIT
     * 
     */
    public final void setUnits(String units) {
        if (!units.equals(Temperature.CELCIUS) && !units.equals(Temperature.FAHRENHEIT)) {
            throw new IllegalArgumentException();
        }
        this.units = units;
    }

    /**
     * Converts a value of degrees Fahrenheit to the equivalent value of degrees
     * Celcius. The formula to convert degrees Fahrenheit to degrees Celcius is:
     * 
     * <p>
     * <b>C = (F - 32) &times; (5 / 9)</b>
     * 
     * <p>
     * where <b>F</b> is degrees Fahrenheit and <b>C</b> is degrees Celcius.
     * 
     * @param degF
     *            a value of degrees Fahrenheit
     * @return the equivalent value in degrees Celcius
     */
    public static double toCelcius(double degF) {
        return (degF - 32.0) * 5.0 / 9.0;
    }

    /**
     * Converts a value of degrees Celcius to the equivalent value of degrees
     * Fahrenheit. The formula to convert degrees Celcius to degrees Fahrenheit
     * is:
     * 
     * <p>
     * <b>F = C &times; (9 / 5) + 32</b>
     * 
     * <p>
     * where <b>C</b> is degrees Celcius and <b>F</b> is degrees Fahrenheit.
     * 
     * @param degC
     *            a value of degrees Celcius
     * @return the equivalent value in degrees Fahrenheit
     */
    public static double toFahrenheit(double degC) {
        return degC * 9.0 / 5.0 + 32.0;
    }

    /**
     * Returns a string made up of the numeric value of the temperature followed
     * by its units. For example, the Strings
     * 
     * <pre>
     * -12.5C
     * 73.01234F
     * </pre>
     * 
     * <p>
     * are returned for temperatures of <code>-12.5</code> degrees Celcius and
     * <code>73.01234</code> degrees Fahrenheit, respectively.
     * 
     * @return a string representation of the temperature
     */
    @Override
    public String toString() {
        if (this.getUnits().equals(Temperature.CELCIUS)) {
            return this.getTemperature() + Temperature.CELCIUS;
        } else {
            return this.getTemperature() + Temperature.FAHRENHEIT;
        }
    }

    /**
     * Compares two temperatures for equality. Two temperatures are considered
     * equal if they represent the same temperature expressed in degrees
     * Celcius. For instance, the values of <code>eq1</code> and
     * <code>eq2</code> are <code>true</code> in the following example:
     * 
     * <pre>
     * Temperature t = new Temperature(0.0, Temperature.CELCIUS);
     * Temperature u = new Temperature(32.0, Temperature.FAHRENHEIT);
     * boolean eq1 = t.equals(u);
     * boolean eq2 = u.equals(t);
     * </pre>
     * 
     * <p>
     * because <code>32</code> degrees Fahrenheit is equivalent to
     * <code>0</code> degrees Celcius, and vice versa.
     * 
     * @param obj an object to compare with this Temperature
     * @return true if obj is a Temperature object with the same
     * temperature when expressed in degrees Celcius as this temperature
     * 
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Temperature other = (Temperature) obj;
        if (Double.doubleToLongBits(this.degC) != Double.doubleToLongBits(other.degC))
            return false;
        return true;
    }

}