package src;


public class MyDate {

    private static final int MIN_YEAR  = 1;
    private static final int MAX_YEAR  = 9999;

    private static final int MIN_MONTH = 1;  // human friendly
    private static final int MAX_MONTH = 12; // human friendly

    private int year;
    private int month;
    private int day;

    private String[] strMonths    = {"Jan", "Feb", "Mar", "Apr", "May", "Jun"
                                    ,"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};

    private String[] strDays      = {"Sunday", "Monday", "Tuesday", "Wednesday"
                                    ,"Thursday", "Friday", "Saturday"};

    private static final int[] daysInMonths            = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    private static final int[] nonLeapYearMonthNumbers = {0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5};    
    private static final int[] leapYearMonthNumbers    = {6, 2, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5};

    private boolean isPreviousDayOperation   = false;
    private boolean isPreviousMonthOperation = false;


    public MyDate(int year, int month, int day) {
        setDate(year, month, day);
    }

    /**
     * A year is a leap year if it is divisible by 4 but not by 100,
     * or it is divisible by 400.
     * 
     * @param  year [description]
     * @return      [description]
     */
    public static boolean isLeapYear(int year) {
        return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
    }


    public static int getMonthLastDay(int year, int month) {
        return daysInMonths[month-1] + (isLeapYear(year) && month == 2 ? 1 : 0 );
    }

    public static boolean isValidDate(int year, int month, int day) {
        // int dayMax = daysInMonths[month-1] + (isLeapYear(year) && month == 2 ? 1 : 0 );
        return (MIN_YEAR  <= year   && year  <= MAX_YEAR)
            && (MIN_MONTH <= month  && month <= MAX_MONTH)
            && (1         <= day    && day   <= getMonthLastDay(year, month));
    }

    /**
     * Returns the day of the week, where 0 for Sun, 1 for Mon, ..., 6 for Sat,
     * for the given date. Assume that the date is valid.
     * 
     * @param  year  [description]
     * @param  month [description]
     * @param  day   [description]
     * @return       [description]
     */
    public static int getDayOfWeek(int year, int month, int day)
    {
        if (! isValidDate(year, month, day)) {
            return -1;
        }

        // 1. Based on the first two digit of the year, get the number from the "century" table.
        int magicCenturyNumber = 6 - 2*((year / 100) % 4);
        
        // 2. Add to the last two digit of the year.
        int lastTwoDigitsOfYear = year % 100;
        
        // 3. Add to "the last two digit of the year divide by 4, truncate the fractional part".
        int magicYearNumber = lastTwoDigitsOfYear / 4;
        
        // 4. Add to the number obtained from the month table.
        int magicMonthNumber = isLeapYear(year) ? leapYearMonthNumbers[month-1] : nonLeapYearMonthNumbers[month-1];
        
        // 5. Add to the day.
        int magicDayNumber = day;
        
        // 6. The sum modulus 7 gives the day of the week, where 0 for SUN, 1 for MON, ..., 6 for SAT.
        return (  magicCenturyNumber + lastTwoDigitsOfYear 
                + magicYearNumber    + magicMonthNumber + magicDayNumber) % 7; 
    }

    public void setDate(int year, int month, int day)
    {
        if (! isValidDate(year, month, day)) {
            throw new IllegalArgumentException("Invalid year, month, or day!");
        }
        this.year  = year;
        this.month = month;
        this.day   = day;
    }

    public int getYear() {
        return this.year;
    }

    public int getMonth() {
        return this.month;
    }

    public int getDay() {
        return this.day;
    }

    public void setYear(int year)
    {
        if (year < MIN_YEAR || year > MAX_YEAR) {
            throw new IllegalArgumentException("Invalid year!");
        }
        this.year = year;
    }

    public void setMonth(int month)
    {
        if (month < MIN_MONTH || month > MAX_MONTH) {
            throw new IllegalArgumentException("Invalid month!");
        }
        this.month = month;
    }

    public void setDay(int day) 
    {
        // int dayMax = daysInMonths[month-1] + (isLeapYear(year) && month == 2 ? 1 : 0 );
        if (1 > day || day > getMonthLastDay(this.year, this.month)) {
            throw new IllegalArgumentException("Invalid day!");
        }
        this.day = day;
    }

    public MyDate nextDay()
    {
        int maxDay = getMonthLastDay(year, month);
        if (maxDay == day && MAX_MONTH == month && MAX_YEAR == year) {
            return this;
        }

        if (maxDay == day && MAX_MONTH == month) {
            setDate(year+1, MIN_MONTH, 1);
            return this;
        }

        if (maxDay == day) {
            setDate(year, month+1, 1);
            return this;
        }
        
        setDate(year, month, day+1);
        return this;
    }

    public MyDate nextMonth()
    {
        if (MAX_MONTH == month && MAX_YEAR == year) {
            return this;
        }

        int maxDay = (MAX_MONTH == month)
                ?   getMonthLastDay(year+1, MIN_MONTH)
                :   getMonthLastDay(year, month+1);

        if (day == getMonthLastDay(year, month)) {
            maxDay = maxDay;
        }
        else if (day > maxDay) {
            maxDay = maxDay;
        }
        else if (day < maxDay) {
            maxDay = day;
        }

        if (MAX_MONTH == month) {
            setDate(year+1, MIN_MONTH, maxDay);
            return this;
        }

        setDate(year, month+1, maxDay);
        return this;
    }

    public MyDate nextYear()
    {
        if (MAX_YEAR == year) {
            return this;
        }

        int maxDay = getMonthLastDay(year+1, month);

        if (day == getMonthLastDay(year, month)) {
            maxDay = maxDay;
        }
        else if (day > maxDay) {
            maxDay = maxDay;
        }
        else if (day < maxDay) {
            maxDay = day;
        }

        setDate(year+1, month, maxDay);
        return this;
    }

    public MyDate previousDay()
    {
        if (1 == day && MIN_MONTH == month && MIN_YEAR == year) {
            return this;
        }

        if (1 == day && MIN_MONTH == month) {
            setDate(year-1, MAX_MONTH, getMonthLastDay(year-1, MAX_MONTH));
            return this;
        }

        if (1 == day) {
            setDate(year, month-1, getMonthLastDay(year, month-1));
            return this;
        }
        
        setDate(year, month, --day);
        return this;
    }

    public MyDate previousMonth()
    {
        if (MIN_MONTH == month && MIN_YEAR == year) {
            return this;
        }

        int maxDay = (MIN_MONTH == month)
                ?   getMonthLastDay(year-1, MAX_MONTH)
                :   getMonthLastDay(year, month-1);

        if (day == getMonthLastDay(year, month)) {
            maxDay = maxDay;
        }
        else if (day > maxDay) {
            maxDay = maxDay;
        }
        else if (day < maxDay) {
            maxDay = day;
        }

        if (MIN_MONTH == month) {
            setDate(year-1, MAX_MONTH, maxDay);
            return this;
        }

        setDate(year, month-1, maxDay);
        return this;
    }

    public MyDate previousYear()
    {
        if (MIN_YEAR == year) {
            return this;
        }

        int maxDay = getMonthLastDay(year-1, month);

        if (day == getMonthLastDay(year, month)) {
            maxDay = maxDay;
        }
        else if (day > maxDay) {
            maxDay = maxDay;
        }
        else if (day < maxDay) {
            maxDay = day;
        }

        setDate(year-1, month, maxDay);
        return this;
    }

    /**
     * @return date in "xxxday d mmm yyyy", e.g., "Tuesday 14 Feb 2012" format.
     */
    public String toString() {
        int weekDay = getDayOfWeek(year, month, day);
        return String.format("%1$s %2$d %3$s %4$d", strDays[weekDay], day, strMonths[month-1], year);
    }

    @Override
    public boolean equals(Object other)
    {
        if (other == null) return false;
        if (other == this) return true;
        if (!(other instanceof MyDate)) return false;
    
        MyDate otherMyDate = (MyDate) other;
        return (this.year  == otherMyDate.getYear())
            && (this.month == otherMyDate.getMonth())
            && (this.day   == otherMyDate.getDay());
    }
}