package com.onaro.util.jfc.date;

import java.util.concurrent.TimeUnit;

/**
 * Immutable class that computes an age (duration since
 * an event) and provides methods to display
 * the age. The age is not dynamic; it is determined
 * when an instance of the class is created.
 */
public class Age implements Comparable<Age> {
    private static final long TWO_DAYS = TimeUnit.DAYS.toMillis (2);
    private static final long TWO_HOURS = TimeUnit.HOURS.toMillis (2);
    private static final long TWO_MINUTES = TimeUnit.MINUTES.toMillis (2);
    private static final long TWO_SECONDS = TimeUnit.SECONDS.toMillis (2);
    private final long age;
    
    /**
     * Create {@link Age} whose value is the time
     * since the specified birth time.
     * @param birth time that should be considered age 0
     */
    public Age (long birth) {
        age = System.currentTimeMillis() - birth;
    }

    /**
     * Gets the age in milliseconds.
     * @return the age
     */
    public long getAge() {
        return age;
    }
    
    /**
     * Gets the age in the given time unit.
     * @param unit time unit enumerator
     * @return the age converted to the specified unit
     */
    public long getAge (TimeUnit unit) {
        return unit.convert (age, TimeUnit.MILLISECONDS);
    }

    /**
     * Gets the age as a displayable string. The format is:
     * <ul><li>
     * <b><i>n</i> days</b> if the age is >= 2 days, or
     * </li><li>
     * <b><i>n</i> hours</b> if the age is >= 2 hours, or
     * </li><li>
     * <b><i>n</i> minutes</b> if the age is >= 2 minutes, or
     * </li><li>
     * <b><i>n</i> seconds</b> if the age is >= 2 seconds, or
     * </li><li>
     * <b><i>n</i> milliseconds</b>
     * </li></ul>
     */
    public String getDisplayText() {
        if (age >= TWO_DAYS) {
            return Messages.INSTANCE.getDays (getAge (TimeUnit.DAYS));
        }
        if (age >= TWO_HOURS) {
            return Messages.INSTANCE.getHours (getAge (TimeUnit.HOURS));
        }
        if (age >= TWO_MINUTES) {
            return Messages.INSTANCE.getMinutes (getAge (TimeUnit.MINUTES));
        }
        if (age >= TWO_SECONDS) {
            return Messages.INSTANCE.getSeconds (getAge (TimeUnit.SECONDS));
        }
        return Messages.INSTANCE.getMillis (age);
    }
    
    
    @Override
    public boolean equals (Object that) {
        return that instanceof Age && this.age == ((Age)that).age;
    }

    @Override
    public int hashCode() {
        return Long.valueOf(age).hashCode();
    }

    @Override
    public String toString() {
        return Long.toString (age);
    }

    @Override
    public int compareTo (Age that) {
        return (int)(this.age - that.age);
    }
}