//  Date.java (c) 2004-2005 Kari Laitinen

//  http://www.naturalprogramming.com

//  2002-01-07  File created.
//  2005-07-25  DateDistance class was moved to its own .java file.
//  2005-07-25  Last modification.

/*  This file contains the definition of class Date.

    When this file is compiled, the file DateDistance.java
    must exist in the same folder (directory) with this file.
    The DateDistance class is used by method get_distance_to()
    of Date to return distance information to its caller.

    Because the Java class library already
    has a class named Date, there is a possiblity of
    a name collision. However, the Date class in
    the java.util package is largely deprecated and
    it is not used in this book. This reduces the
    likelihood of a name collision.

    To avoid name collisions between this Date class and
    java.util.Date, it is better not to have import
    statements like
        import java.util.* ;
    Instead, when you use this Date class, you can import
    single classes from the java.util package with statements
    such as
        import java.util.ArrayList ;
        import java.util.Calendar ;

    I avoid the statement
        import java.util.* ;
    in those programs which use this Date class, but it seems
    that although the statement were used, this Date class
    is selected instead of the java.util.Date class.

    Thus, it seems that the compiler first looks for classes
    from the default package and after that from the imported
    packages.

*/


class  Date
{
   protected int this_day    =  1 ;
   protected int this_month  =  1 ;
   protected int this_year   =  1970 ;

   protected char  date_print_format  =  'E' ;

   public Date() {}

   public Date( int  given_day,
                int  given_month,
                int  given_year,
                char given_print_format )
   {
      this_day           =  given_day ;
      this_month         =  given_month ;
      this_year          =  given_year ;
      date_print_format  =  given_print_format ;
   }

   public Date( int  given_day,
                int  given_month,
                int  given_year )
   {
      this_day     =  given_day ;
      this_month   =  given_month ;
      this_year    =  given_year ;
   }

   public Date( String  date_as_string )
   {
      //  This constructor accepts date strings in two formats:
      //
      //    MM/DD/YYYY  is the American format.
      //    DD.MM.YYYY  is the format used in Europe.
      //
      //  Member variable date_print_format will be set either
      //  to value 'A' or 'E'. This value will be used to select
      //  correct print format when this date object is converted
      //  to a string with the toString() method.

      if ( date_as_string.charAt( 2 )  ==  '/' )
      {
         date_print_format  =  'A' ;  // American format
         this_day   = Integer.parseInt( date_as_string.substring( 3, 5 ) ) ;
         this_month = Integer.parseInt( date_as_string.substring( 0, 2 ) ) ;
      }
      else
      {
         date_print_format  =  'E' ;  //  European format
         this_day   = Integer.parseInt( date_as_string.substring( 0, 2 ) ) ;
         this_month = Integer.parseInt( date_as_string.substring( 3, 5 ) ) ;
      }

      this_year  = Integer.parseInt( date_as_string.substring( 6, 10 ) ) ;
   }

   public int   day()    {  return  this_day   ; }
   public int   month()  {  return  this_month ; }
   public int   year()   {  return  this_year  ; }
   public char  get_date_print_format()  { return date_print_format ; }

   public boolean is_last_day_of_month()
   {
      boolean  it_is_last_day_of_month  =  false ;

      if  (  this_day  >  27  )
      {
         if  (  this_day  ==  31 )
         {
            it_is_last_day_of_month  =  true ;
         }
         else if  ( ( this_day  ==  30 ) &&
                    ( this_month  ==  2  ||  this_month  ==  4  ||
                      this_month  ==  6  ||  this_month  ==  9  ||
                      this_month  ==  11 ) )
         {
            it_is_last_day_of_month  =  true ;
         }
         else if  ( this_day  ==  29  &&  this_month  ==  2 )
         {
            it_is_last_day_of_month  =  true ;
         }
         else if  ( this_day    ==  28  &&
                    this_month  ==   2  &&
                    ! this_is_a_leap_year() )
         {
            it_is_last_day_of_month  =  true ;
         }
      }

      return  it_is_last_day_of_month ;
   }

   public boolean this_is_a_leap_year()
   {
      boolean  return_code  =  false ;

      if  ( this_year  %  4   ==  0 )
      {
         //  Years which are equally divisible by 4 and which
         //  are not full centuries are leap years. Centuries
         //  equally divisible by 4 are, however, leap years.

         if  ( this_year  %  100  ==  0 )
         {
            int  century  =  this_year  /  100  ;

            if  ( century  %  4   ==   0 )
            { 
               return_code  =  true ;
            }
         }
         else
         {
            return_code  =  true ;
         }
      }

      return  return_code ;
   }

   public boolean is_within_dates( Date earlier_date,
                                   Date later_date   ) 
   {
      return (( equals( earlier_date )  )  ||
              ( equals(  later_date )   )  ||
              ( is_later_than( earlier_date ) &&
                is_earlier_than( later_date ) ) ) ;
   }

   public int index_for_day_of_week() 
   {
      //  day_index will get a value in the range from 0 to 6,
      //  0 meaning Monday and 6 meaning Sunday.

      int  day_index  =  0 ;
      Date  known_date  =  new  Date( 6, 10, 1997 ) ;
      // Oct. 6, 1997 is Monday.

      if  ( known_date.is_later_than( this ) )
      {
         while ( known_date.is_not_equal_to( this ) )
         {
            if ( day_index  >  0 )
            {
               day_index  --  ;
            }
            else
            {
               day_index  =  6 ;
            }

            known_date.decrement() ;
         }
      }
      else
      {
         while ( known_date.is_not_equal_to( this ) )
         {
            if ( day_index  <  6  )
            {
               day_index  ++  ;
            }
            else
            {
               day_index  =  0 ;
            }

            known_date.increment() ;
         }
      }

      return  day_index ;
   }

   public String get_day_of_week()
   {
      String[]  days_of_week  =  { "Monday", "Tuesday", "Wednesday",
                       "Thursday", "Friday", "Saturday", "Sunday" } ;

      return  days_of_week[ index_for_day_of_week() ] ;
   }

   public void increment()
   {
      if  (  is_last_day_of_month() )
      {
         this_day   =  1 ;

         if  (  this_month  <  12  )
         {
            this_month  ++  ;
         }
         else
         {
            this_month  =  1  ;
            this_year  ++ ;
         }
      }
      else
      {
         this_day  ++  ;
      }
   }

   public void decrement()
   {
      if ( this_day  >  1  )
      {
         this_day  --  ;
      }
      else
      {
         if ( this_month  ==   5  ||  this_month  ==   7  ||
              this_month  ==  10  ||  this_month  ==  12  )
         {
            this_day    =  30 ;
            this_month  -- ;
         }
         else if ( this_month  ==   2  ||  this_month  ==   4  ||
                   this_month  ==   6  ||  this_month  ==   8  ||
                   this_month  ==   9  ||  this_month  ==  11  )
         {
            this_day    =  31 ;
            this_month  -- ;
         }
         else if (  this_month  ==  1  )
         {
            this_day    =  31  ;
            this_month  =  12  ;
            this_year   -- ;
         }
         else if (  this_month  ==  3  )
         {
            this_month  =  2  ;

            if ( this_is_a_leap_year() )
            {
               this_day  =  29  ;
            }
            else
            {
               this_day  =  28  ;
            }
         }
      }
   }


   public DateDistance  get_distance_to( Date  another_date )
   {
      DateDistance  distance_to_return  =  new DateDistance() ;
      Date  start_date, end_date ;
      int   start_day, end_day ;

      if ( this.is_earlier_than( another_date ) )
      {
         start_date  =  this ;
         end_date    =  another_date ;  
      }
      else
      {
         start_date  =  another_date ;
         end_date    =  this ;
      }

      //  We will suppose that day 30 is the last day of every
      //  month. This way we minimize calculation errors.

      if ( start_date.is_last_day_of_month() ||
           ( start_date.day()    ==  28  &&
             start_date.month()  ==  2  )    )
      {
         start_day   =  30  ;
      }
      else
      {
         start_day   =  start_date.day() ;
      }

      if ( end_date.is_last_day_of_month() ||
           ( end_date.day()    ==  28  &&
             end_date.month()  ==  2  )    )
      {
         end_day   =  30  ;
      }
      else
      {
         end_day   =  end_date.day() ;
      }

      distance_to_return.years  =  end_date.year()  - start_date.year() ;
      distance_to_return.months =  end_date.month() - start_date.month() ;
      distance_to_return.days   =  end_day  -  start_day ;

      if ( distance_to_return.days  <  0 )
      {
         distance_to_return.months  --  ;
         distance_to_return.days  =  distance_to_return.days  +  30 ;
      }

      if ( distance_to_return.months  <  0 )
      {
         distance_to_return.years   --  ;
         distance_to_return.months  =  distance_to_return.months +  12 ;
      }

      return  distance_to_return ;
   }


   public int get_week_number()
   {
      // January 1, 1883 was a Monday with week number 1.
      // January 1, 1990 was a Monday with week number 1.

      Date  date_to_increment  =  new  Date( 1, 1, 1883 ) ;
      int    week_number  =  1 ;
      int    local_index_for_day_of_week  =  0 ; // 0 means Monday

      while ( date_to_increment.is_earlier_than( this ) )
      {
         date_to_increment.increment() ;
 
         if ( local_index_for_day_of_week  ==  6  ) // 6 means Sunday
         {
            local_index_for_day_of_week  =  0 ; // back to Monday

            if  ( week_number  <   52 )
            {
               week_number  ++  ;
            }
            else  if  ( week_number  ==  52 )
            {
               if ( date_to_increment.day()    <=  28  &&
                    date_to_increment.month()  ==  12  )
               {
                  week_number  =  53 ;
               }
               else
               {
                  week_number  =  1  ;
               }
            }
            else  // must be week_number  53 
            {
               week_number  =  1 ;
            }
         }
         else
         {
            local_index_for_day_of_week  ++  ;
         }
      }

      return  week_number  ;
   }


   public boolean is_equal_to( Date another_date )
   {
      return ( this_day    ==  another_date.day()    &&
               this_month  ==  another_date.month()  &&
               this_year   ==  another_date.year()  ) ;
   }

   public boolean is_not_equal_to( Date another_date )
   {
      return ( this_day    !=  another_date.day()    ||
               this_month  !=  another_date.month()  ||
               this_year   !=  another_date.year()  ) ;
   }

   public boolean is_earlier_than( Date another_date )
   {
      return ( (   this_year  <   another_date.year()     )  ||
               ( ( this_year  ==  another_date.year() )  &&
                 ( this_month <   another_date.month() )  )  ||
               ( ( this_year  ==  another_date.year() )  &&
                 ( this_month ==  another_date.month() ) &&
                 ( this_day   <   another_date.day() )   )    ) ;
   }

   public boolean is_later_than( Date another_date )
   {
      return ( (   this_year  >   another_date.year()     )  ||
               ( ( this_year  ==  another_date.year() )  &&
                 ( this_month >   another_date.month() )  )  ||
               ( ( this_year  ==  another_date.year() )  &&
                 ( this_month ==  another_date.month() ) &&
                 ( this_day   >   another_date.day() )   )    ) ;
   }

   public String toString()
   {
      String day_as_string    =  String.format( "%02d", this_day ) ;

      String month_as_string  =  String.format( "%02d", this_month ) ;

      String year_as_string   =  ""  +  this_year ;

      String string_to_caller ;

      if ( date_print_format  ==  'A' )
      {
         string_to_caller  =  month_as_string + "/" + day_as_string
                              + "/"  +  year_as_string  ;
      }
      else
      {
         string_to_caller  =  day_as_string + "." + month_as_string
                              + "."  +  year_as_string  ;
      }

      return  string_to_caller ;
   }
}