#ifndef DATE_TIME_PERIOD_HPP___

 #define DATE_TIME_PERIOD_HPP___

 /*    Copyright (c) 2002,2003 CrystalClear Software, Inc.

  *

  * Distributed under the Boost Software License, Version 1.0.

  *     (See accompanying file LICENSE_1_0.txt or copy at

  *           http://www.boost.org/LICENSE_1_0.txt)

  *

  *

  * Author: Jeff Garland, Bart Garst 

  * $Date: 2006/07/17 03:56:05 $

  */

 /*! \file period.hpp

   This file contain the implementation of the period abstraction. This is

   basically the same idea as a range.  Although this class is intended for

   use in the time library, it is pretty close to general enough for other

   numeric uses.

 */

 #include "boost/operators.hpp"

 namespace boost {

 namespace date_time {

   //!Provides generalized period type useful in date-time systems

   /*!This template uses a class to represent a time point within the period

     and another class to represent a duration.  As a result, this class is

     not appropriate for use when the number and duration representation 

     are the same (eg: in the regular number domain).

     A period can be specified by providing either the begining point and 

     a duration or the begining point and the end point( end is NOT part 

     of the period but 1 unit past it. A period will be "invalid" if either

     end_point <= begin_point or the given duration is <= 0. Any valid period 

     will return false for is_null().

     Zero length periods are also considered invalid. Zero length periods are

     periods where the begining and end points are the same, or, the given 

     duration is zero. For a zero length period, the last point will be one 

     unit less than the begining point.

     In the case that the begin and last are the same, the period has a 

     length of one unit.

     The best way to handle periods is usually to provide a begining point and

     a duration.  So, day1 + 7 days is a week period which includes all of the

     first day and 6 more days (eg: Sun to Sat).

    */

   template<class point_rep, class duration_rep>

   class period : private

       boost::less_than_comparable<period<point_rep, duration_rep> 

     , boost::equality_comparable< period<point_rep, duration_rep> 

     > >

   {

   public:

     typedef point_rep point_type;

     typedef duration_rep duration_type;

     period(point_rep first_point, point_rep end_point);

     period(point_rep first_point, duration_rep len);

     point_rep begin() const;

     point_rep end() const;

     point_rep last() const;

     duration_rep length() const;

     bool is_null() const;

     bool operator==(const period& rhs) const;

     bool operator<(const period& rhs) const;

     void shift(const duration_rep& d);

     bool contains(const point_rep& point) const;

     bool contains(const period& other) const;

     bool intersects(const period& other) const;

     bool is_adjacent(const period& other) const;

     bool is_before(const point_rep& point) const;

     bool is_after(const point_rep& point) const;

     period intersection(const period& other) const;

     period merge(const period& other) const;

     period span(const period& other) const;

   private:

     point_rep begin_;

     point_rep last_;

   };

   //! create a period from begin to last eg: [begin,end)

   /*! If end <= begin then the period will be invalid

    */

   template<class point_rep, class duration_rep>

   inline

   period<point_rep,duration_rep>::period(point_rep first_point, 

                                          point_rep end_point) : 

     begin_(first_point), 

     last_(end_point - duration_rep::unit())

   {}

   //! create a period as [begin, begin+len)

   /*! If len is <= 0 then the period will be invalid

    */

   template<class point_rep, class duration_rep>

   inline

   period<point_rep,duration_rep>::period(point_rep first_point, duration_rep len) :

     begin_(first_point), 

     last_(first_point + len-duration_rep::unit())

   { }

   //! Return the first element in the period

   template<class point_rep, class duration_rep>

   inline

   point_rep period<point_rep,duration_rep>::begin() const 

   {

     return begin_;

   }

   //! Return one past the last element 

   template<class point_rep, class duration_rep>

   inline

   point_rep period<point_rep,duration_rep>::end() const 

   {

     return last_ + duration_rep::unit();

   }

   //! Return the last item in the period

   template<class point_rep, class duration_rep>

   inline

   point_rep period<point_rep,duration_rep>::last() const 

   {

     return last_;

   }

   //! True if period is ill formed (length is zero or less)

   template<class point_rep, class duration_rep>

   inline

   bool period<point_rep,duration_rep>::is_null() const 

   {

     return end() <= begin_;

   }

   //! Return the length of the period

   template<class point_rep, class duration_rep>

   inline

   duration_rep period<point_rep,duration_rep>::length() const

   {

     if(last_ < begin_){ // invalid period

       return last_+duration_rep::unit() - begin_;

     }

     else{

       return end() - begin_; // normal case

     }

   }

   //! Equality operator

   template<class point_rep, class duration_rep>

   inline

   bool period<point_rep,duration_rep>::operator==(const period& rhs) const 

   {

     return  ((begin_ == rhs.begin_) && 

              (last_ == rhs.last_));

   }

   //! Strict as defined by rhs.last <= lhs.last

   template<class point_rep, class duration_rep>

   inline

   bool period<point_rep,duration_rep>::operator<(const period& rhs) const 

   {

     return (last_ < rhs.begin_);

   } 

   //! Shift the start and end by the specified amount

   template<class point_rep, class duration_rep>

   inline

   void period<point_rep,duration_rep>::shift(const duration_rep& d)

   {

     begin_ = begin_ + d;

     last_  = last_  + d;

   }

   //! True if the point is inside the period, zero length periods contain no points

   template<class point_rep, class duration_rep>

   inline

   bool period<point_rep,duration_rep>::contains(const point_rep& point) const 

   {

     return ((point >= begin_) &&

             (point <= last_));

   }

   //! True if this period fully contains (or equals) the other period

   template<class point_rep, class duration_rep>

   inline

   bool period<point_rep,duration_rep>::contains(const period<point_rep,duration_rep>& other) const

   {

     return ((begin_ <= other.begin_) && (last_ >= other.last_));

   }

   //! True if periods are next to each other without a gap.

   /* In the example below, p1 and p2 are adjacent, but p3 is not adjacent

    * with either of p1 or p2.

    *@code

    *   [-p1-)

    *        [-p2-)

    *          [-p3-) 

    *@endcode

    */

   template<class point_rep, class duration_rep>

   inline

   bool 

   period<point_rep,duration_rep>::is_adjacent(const period<point_rep,duration_rep>& other) const 

   {

     return (other.begin() == end() ||

             begin_ == other.end());

   }

   //! True if all of the period is prior or t < start

   /* In the example below only point 1 would evaluate to true.

    *@code

    *     [---------])

    * ^   ^    ^     ^   ^

    * 1   2    3     4   5

    * 

    *@endcode

    */

   template<class point_rep, class duration_rep>

   inline

   bool 

   period<point_rep,duration_rep>::is_after(const point_rep& t) const 

   { 

     if (is_null()) 

     {

       return false; //null period isn't after

     }

     return t < begin_;

   }

   //! True if all of the period is prior to the passed point or end <= t

   /* In the example below points 4 and 5 return true.

    *@code

    *     [---------])

    * ^   ^    ^     ^   ^

    * 1   2    3     4   5

    * 

    *@endcode

    */

   template<class point_rep, class duration_rep>

   inline

   bool 

   period<point_rep,duration_rep>::is_before(const point_rep& t) const 

   { 

     if (is_null()) 

     {

       return false;  //null period isn't before anything

     }

     return last_ < t;

   }

   //! True if the periods overlap in any way

   /* In the example below p1 intersects with p2, p4, and p6.

    *@code

    *       [---p1---)

    *             [---p2---)

    *                [---p3---) 

    *  [---p4---) 

    * [-p5-) 

    *         [-p6-) 

    *@endcode

    */

   template<class point_rep, class duration_rep>

   inline

   bool period<point_rep,duration_rep>::intersects(const period<point_rep,duration_rep>& other) const 

   { 

     return ( contains(other.begin_) ||

              other.contains(begin_) ||

              ((other.begin_ < begin_) && (other.last_ >= begin_)));

   }

   //! Returns the period of intersection or invalid range no intersection

   template<class point_rep, class duration_rep>

   inline

   period<point_rep,duration_rep>

   period<point_rep,duration_rep>::intersection(const period<point_rep,duration_rep>& other) const 

   {

     if (begin_ > other.begin_) {

       if (last_ <= other.last_) { //case2

         return *this;  

       }

       //case 1

       return period<point_rep,duration_rep>(begin_, other.end());

     }

     else {

       if (last_ <= other.last_) { //case3

         return period<point_rep,duration_rep>(other.begin_, this->end());

       }

       //case4

       return other;

     }

     //unreachable

   }

   //! Returns the union of intersecting periods -- or null period

   /*! 

    */

   template<class point_rep, class duration_rep>

   inline

   period<point_rep,duration_rep>

   period<point_rep,duration_rep>::merge(const period<point_rep,duration_rep>& other) const 

   {

     if (this->intersects(other)) {      

       if (begin_ < other.begin_) {

         return period<point_rep,duration_rep>(begin_, last_ > other.last_ ? this->end() : other.end());

       }

       return period<point_rep,duration_rep>(other.begin_, last_ > other.last_ ? this->end() : other.end());

     }

     return period<point_rep,duration_rep>(begin_,begin_); // no intersect return null

   }

   //! Combine two periods with earliest start and latest end.

   /*! Combines two periods and any gap between them such that 

    *  start = minimum(p1.start, p2.start)

    *  end   = maximum(p1.end  , p2.end)

    *@code

    *        [---p1---)

    *                       [---p2---)

    * result:

    *        [-----------p3----------) 

    *@endcode

    */

   template<class point_rep, class duration_rep>

   inline

   period<point_rep,duration_rep>

   period<point_rep,duration_rep>::span(const period<point_rep,duration_rep>& other) const 

   {

     point_rep start((begin_ < other.begin_) ? begin() : other.begin());

     point_rep newend((last_  < other.last_)  ? other.end() : this->end());

     return period<point_rep,duration_rep>(start, newend);

   }

 } } //namespace date_time

 #endif