(*

Class:      DateRange
Package:    com.waysysweb.util
Author:     W. Shaffer
Date:       13-Nov-2006
Description:

    This structure extends the set class to provide certain funtions specific
    to date sets.

Maintenance:

Date        Author  Description
----------- ------  -----------------------------------------------------------
13-Nov-2006 Shaffer File created

*)

structure DATERANGE = struct

    (*============  Exceptions ==============================================*)

    exception DateSetException of string;

    (*============  Imports     =============================================*)
    
    (* Set imports                                                           *)

    type ''a Set = ''a SET.Set;
    
    fun add(set : ''a Set, item : ''a) : ''a Set = SET.add(set, item);
    fun fetch(set : ''a Set) : ''a = SET.fetch(set);
    fun remove(set : ''a Set, item : ''a) : ''a Set = SET.remove(set, item);
    fun isEmpty(set : ''a Set) : bool = SET.isEmpty(set);
    val empty = SET.empty;
    
    (* Date imports                                                          *)
    
    type WayDate = WAYDATE.WayDate;
    
    fun increment(date1 : WayDate) : WayDate = WAYDATE.increment(date1);
    fun compare(date1 : WayDate, date2 : WayDate) : order =
        WAYDATE.compare(date1, date2);

    (*============  Types       =============================================*)

    type DateSet = WayDate Set;

    (*============  Constants  ==============================================*)



    (*============  Properties ==============================================*)



    (*============  Attributes  =============================================*)



    (*============  Invariant   =============================================*)



    (*============  Initialization ==========================================*)



    (*============  Operations  =============================================*)

    (* return a set of dates with every date starting at the from date to    *)
    (* the through date                                                      *)
    (* Precondition: true                                                    *)
    (* Postcondition: if compare(fromDate, date) != LESS andalso             *)
    (*                   compare(thruDate, date) != GREATER                  *)
    (*                then date inset range(fromDate, thruDate)              *)
    (*                else date notinset range(fromDate, thruDate)           *)
    fun range(fromDate : WayDate, thruDate : WayDate) : DateSet =
        if compare(fromDate, thruDate) = GREATER
        then empty
        else add(range(increment(fromDate), thruDate), fromDate);
        
    (* return the maximum date in a date set that satifies a predicate       *)
    fun maxInSet([] : DateSet, pred : WayDate -> bool, current : WayDate) :
        WayDate = current
      | maxInSet(set : DateSet, pred : WayDate -> bool, current : WayDate) :
        WayDate =
        let
            val nextDate = fetch(set);
            val rest = remove(set, nextDate);
        in
            if pred(nextDate) andalso (compare(nextDate, current) = GREATER)
            then maxInSet(rest, pred, nextDate)
            else maxInSet(rest, pred, current)
        end;
        
    (* return the maximum date in a date set that satifies a predicate       *)
    fun max(set : DateSet, pred : WayDate -> bool) : WayDate =
        if isEmpty(set) then raise DateSetException("max: set is empty")
        else
            let
                val date = fetch(set);
                val rest = remove(set, date)
            in
                maxInSet(rest, pred, date)
            end;

end (* DATERANGE *)