!! Module to manage date and time
!|author:  <a href="mailto:giovanni.ravazzani@polimi.it">Giovanni Ravazzani</a>
! license: <a href="http://www.gnu.org/licenses/">GPL</a>
!    
!### History
!
! current version 1.3 - 31st May 2023  
!
! | version  |  date       |  comment |
! |----------|-------------|----------|
! | 1.0      | 09/Nov/2008 | Original code |
! | 1.1      | 12/Jun/2011 | Add function to DateTimeIsDefault |
! | 1.2      | 30/Mar/2018 | date transformed to UTC in TimeDifference before computing difference |
! | 1.3      | 31/May/2023 | new function GetDayOfWeek |
!   
!
!### License  
! license: GNU GPL <http://www.gnu.org/licenses/>
!
! This file is part of 
!
!   MOSAICO -- MOdular library for raSter bAsed hydrologIcal appliCatiOn.
! 
!   Copyright (C) 2011 Giovanni Ravazzani
!
!### Code Description 
!   Language:           Fortran 90. 
!
!   Software Standards: "European Standards for Writing and  
!   Documenting Exchangeable Fortran 90 Code". 
! 
!### Module Description: 
!   set of fortran routines to manage date and time.
!   The module adhers to the International Standard ISO 8601 specifications.
!   Date and time is expressed in the form `YYYY-MM-DDThh:mm:ssTZD`
!   where:
!
! `YYYY` = four-digit year
!
! `MM`   = two-digit month (01=January, etc.)
!
! `DD`   = two-digit day of month (01 through 31)
!
! `hh`   = two digits of hour (00 through 23) (am/pm NOT allowed)
!
! `mm`   = two digits of minute (00 through 59)
!
! `ss`   = two digits of second (00 through 59)
!
! `TZD`  = time zone designator (+hh:mm or -hh:mm)
!
!   A time zone offset of "+hh:mm" indicates that the date/time uses a local 
!   time zone which is `hh` hours and `mm` minutes ahead of UTC 
!   (Coordinated Universal Time). A time zone offset of "-hh:mm" 
!   indicates that the date/time uses a local time zone which is 
!   `hh` hours and `mm` minutes behind UTC. 
!
!   Example: `2007-03-05T01:00:00+02:00`
!
!   This standard notation helps to avoid confusion in international 
!   communication caused by the many different national notations and 
!   increases the portability of computer user interfaces. 
!   In addition, these formats have several important advantages for 
!   computer usage compared to other traditional date and time notations. 
!
! References:
!   http://www.w3.org/TR/NOTE-datetime
!
!   http://en.wikipedia.org/wiki/ISO_8601
!
!   http://www.probabilityof.com/iso/8601v2000.pdf  
!
MODULE Chronos         
			

! 
! Modules used: 
! 
         
USE DataTypeSizes ,ONLY: & 
! Imported Parameters:  
short,long,float,double

USE LogLib, ONLY : &          
! Imported Routines:
Catch

USE ErrorCodes, ONLY : &
! Imported parameters:
DateTimeError, unknownOption

USE StringManipulation, ONLY : &
    !imported routines:
    StringToLong, ToString
         
! Declarations must be of the form: 
! [type]   [VariableName]      ! Description/ purpose of variable 
     
IMPLICIT NONE 
! Global (i.e. public) Declarations: 
! Global Procedures:
PUBLIC :: IsLeapYear
PUBLIC :: DayOfYear
PUBLIC :: AddSeconds
PUBLIC :: AddMinutes
PUBLIC :: AddHours
PUBLIC :: AddDays
PUBLIC :: IsUTC
PUBLIC :: ToUTC
PUBLIC :: Now
PUBLIC :: UtcNow
PUBLIC :: GetYear
PUBLIC :: GetMonth
PUBLIC :: GetDay
PUBLIC :: GetDayOfWeek
PUBLIC :: GetHour
PUBLIC :: GetMinute
PUBLIC :: GetSecond
PUBLIC :: GetTimeZone
PUBLIC :: SetYear
PUBLIC :: SetMonth
PUBLIC :: SetDay
PUBLIC :: SetHour
PUBLIC :: SetMinute
PUBLIC :: SetSecond
PUBLIC :: SetTimeZone
PUBLIC :: DateTimeIsDefault

! Global Type Definitions: 
TYPE:: DateTime
	INTEGER (KIND = short) :: year
	INTEGER (KIND = short) :: month
	INTEGER (KIND = short) :: day
	INTEGER (KIND = short) :: hour
	INTEGER (KIND = short) :: minute
	INTEGER (KIND = short) :: second
	!INTEGER (KIND = short) :: millisecond
	INTEGER (KIND = short) :: TZhour
	INTEGER (KIND = short) :: TZminute
	CHARACTER (LEN = 1)    :: TZsign
END TYPE DateTime


! Global Parameters: 
INTEGER, PARAMETER :: timeStringLength = 25
CHARACTER (LEN = timeStringLength) :: timeString
CHARACTER (LEN = timeStringLength), PARAMETER :: timeDefault = '0000-00-00T00:00:00+00:00'
         
! Global Scalars: 
         
! Global Arrays: 
         
! Local (i.e. private) Declarations: 
! Local Procedures:
PRIVATE :: Equality
PRIVATE :: GreaterThan
PRIVATE :: GreaterThanOrEqual
PRIVATE :: LessThan
PRIVATE :: LessThanOrEqual
PRIVATE :: Inequality
PRIVATE :: Parse
PRIVATE :: TimeToString
PRIVATE :: DateCheck
PRIVATE :: DaysInMonth
PRIVATE :: Copy
PRIVATE :: SecondOfYear
PRIVATE :: SecondsToEnd
PRIVATE :: TimeDifference

! Local Type Definitions: 
         
! Local Parameters: 
         
! Local Scalars: 
         
! Local Arrays: 
         
! Operator definitions: 
!   Define new operators or overload existing ones. 
INTERFACE ASSIGNMENT( = )
	MODULE PROCEDURE  TimeToString
	MODULE PROCEDURE  Parse
	MODULE PROCEDURE  Copy
END INTERFACE

INTERFACE OPERATOR ( == )
	MODULE PROCEDURE  Equality
END INTERFACE

INTERFACE OPERATOR ( + )
	MODULE PROCEDURE  AddSeconds
END INTERFACE

INTERFACE OPERATOR ( - )
	MODULE PROCEDURE  TimeDifference
END INTERFACE

INTERFACE OPERATOR ( > )
	MODULE PROCEDURE  GreaterThan
END INTERFACE

INTERFACE OPERATOR ( >= )
	MODULE PROCEDURE  GreaterThanOrEqual
END INTERFACE

INTERFACE OPERATOR ( < )
	MODULE PROCEDURE  LessThan
END INTERFACE

INTERFACE OPERATOR ( <= )
	MODULE PROCEDURE  LessThanOrEqual
END INTERFACE

INTERFACE OPERATOR ( /= )
	MODULE PROCEDURE  Inequality
END INTERFACE



!=======         
CONTAINS
!======= 
! Define procedures contained in this module. 

!==============================================================================
!| Description:
!   return `true` if time1 is equal to time2. Before comparison, dates are 
!   converted to UTC
FUNCTION Equality &
!
(time1, time2) &
!
RESULT (isEqual)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1, time2

! Local declarations:
LOGICAL :: isEqual
TYPE (DateTime) :: tempTime1, tempTime2

!------------end of declaration------------------------------------------------

!converto to utc
tempTime1 = ToUtc (time1)
tempTime2 = ToUtc (time2)

!perform comparison
IF(  tempTime1 % year   == tempTime2 % year   .AND. &
     tempTime1 % month  == tempTime2 % month  .AND. &
     tempTime1 % day    == tempTime2 % day    .AND. &
     tempTime1 % hour   == tempTime2 % hour   .AND. &
     tempTime1 % minute == tempTime2 % minute .AND. &
     tempTime1 % second == tempTime2 % second       ) THEN
  isEqual = .TRUE.
ELSE
  isEqual = .FALSE.
END IF

END FUNCTION Equality

!==============================================================================
!| Description:
!   return `true` if time1 is greater than time2
FUNCTION GreaterThan &
!
(time1, time2) &
!
RESULT (greater)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1, time2

! Local declarations:
LOGICAL :: greater
TYPE (DateTime) :: tempTime1, tempTime2

!------------end of declaration------------------------------------------------

!converto to utc
tempTime1 = ToUtc (time1)
tempTime2 = ToUtc (time2)

!perform comparison
IF(tempTime1 % year > tempTime2 % year)           THEN
   greater = .TRUE.
ELSE IF(tempTime1 % year < tempTime2 % year)      THEN
   greater = .FALSE.
ELSE IF(tempTime1 % month > tempTime2 % month)    THEN
   greater = .TRUE.
ELSE IF(tempTime1 % month < tempTime2 % month)    THEN
   greater = .FALSE.
ELSE IF(tempTime1 % day > tempTime2 % day)        THEN
   greater = .TRUE.
ELSE IF(tempTime1 % day < tempTime2 % day)        THEN
   greater = .FALSE.
ELSE IF(tempTime1 % hour > tempTime2 % hour)      THEN
   greater = .TRUE.
ELSE IF(tempTime1 % hour < tempTime2 % hour)      THEN
   greater = .FALSE.
ELSE IF(tempTime1 % minute > tempTime2 % minute)  THEN
   greater = .TRUE.
ELSE IF(tempTime1 % minute < tempTime2 % minute)  THEN
   greater = .FALSE.
ELSE IF(tempTime1 % second > tempTime2 % second)  THEN
   greater = .TRUE.
ELSE
   greater = .FALSE.
END IF

END FUNCTION GreaterThan

!==============================================================================
!| Description:
!   return `true` if time1 is greater than time2
!   or time1 is equal to time2
FUNCTION GreaterThanOrEqual &
!
(time1, time2) &
!
RESULT (greatequal)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1, time2

! Local scalars:
LOGICAL :: greatequal
TYPE (DateTime) :: tempTime1, tempTime2

!------------end of declaration------------------------------------------------

!converto to utc
tempTime1 = ToUtc (time1)
tempTime2 = ToUtc (time2)


IF ( tempTime1 > tempTime2 .OR. tempTime1 == tempTime2 ) THEN
  greatequal = .TRUE.
ELSE
  greatequal = .FALSE.
END IF

END FUNCTION GreaterThanOrEqual

!==============================================================================
!| Description:
!   return `true` if time1 is less than time2
FUNCTION LessThan &
!
(time1, time2) &
!
RESULT (less)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1, time2

! Local declarations:
LOGICAL :: less
TYPE (DateTime) :: tempTime1, tempTime2

!------------end of declaration------------------------------------------------

!converto to utc
tempTime1 = ToUtc (time1)
tempTime2 = ToUtc (time2)

IF(tempTime1 % year < tempTime2 % year)           THEN
   less = .TRUE.
ELSE IF(tempTime1 % year > tempTime2 % year)      THEN
   less = .FALSE.
ELSE IF(tempTime1 % month < tempTime2 % month)    THEN
   less = .TRUE.
ELSE IF(tempTime1 % month > tempTime2 % month)    THEN
   less = .FALSE.
ELSE IF(tempTime1 % day < tempTime2 % day)        THEN
   less = .TRUE.
ELSE IF(tempTime1 % day > tempTime2 % day)        THEN
   less = .FALSE.
ELSE IF(tempTime1 % hour < tempTime2 % hour)      THEN
   less = .TRUE.
ELSE IF(tempTime1 % hour > tempTime2 % hour)      THEN
   less = .FALSE.
ELSE IF(tempTime1 % minute < tempTime2 % minute)  THEN
   less = .TRUE.
ELSE IF(tempTime1 % minute > tempTime2 % minute)  THEN
   less = .FALSE.
ELSE IF(tempTime1 % second < tempTime2 % second)  THEN
   less = .TRUE.
ELSE
   less = .FALSE.
END IF

END FUNCTION LessThan

!==============================================================================
!| Description:
!   return `true` if time1 is less than time2
!   or time1 is equal to time2
FUNCTION LessThanOrEqual &
!
(time1, time2) &
!
RESULT (lessequal)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1, time2

! Local declarations:
LOGICAL :: lessequal
TYPE (DateTime) :: tempTime1, tempTime2

!------------end of declaration------------------------------------------------

!converto to utc
tempTime1 = ToUtc (time1)
tempTime2 = ToUtc (time2)

IF ( tempTime1 < tempTime2 .OR. tempTime1 == tempTime2 ) THEN
  lessequal = .TRUE.
ELSE
  lessequal = .FALSE.
END IF

END FUNCTION LessThanOrEqual

!==============================================================================
!| Description:
!   return `true` if time1 is different from time2
FUNCTION Inequality &
!
(time1, time2) &
!
RESULT (isInequal)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1, time2

! Local declarations:
LOGICAL :: isInequal
TYPE (DateTime) :: tempTime1, tempTime2

!------------end of declaration------------------------------------------------

!converto to utc
tempTime1 = ToUtc (time1)
tempTime2 = ToUtc (time2)

IF(  tempTime1 % year   /= tempTime2 % year   .OR. &
     tempTime1 % month  /= tempTime2 % month  .OR. &
     tempTime1 % day    /= tempTime2 % day    .OR. &
     tempTime1 % hour   /= tempTime2 % hour   .OR. &
     tempTime1 % minute /= tempTime2 % minute .OR. &
     tempTime1 % second /= tempTime2 % second       ) THEN
  isInequal = .TRUE.
ELSE
  isInequal = .FALSE.
END IF

END FUNCTION Inequality

!==============================================================================
!| Description:
! Converts the specified string representation of a 
! date and time to its `DateTime` equivalent.
SUBROUTINE  Parse &
!
(time, string)

USE StringManipulation, ONLY : &
! Imported routines:
StringToShort

IMPLICIT NONE

! Arguments with intent(in):
CHARACTER (LEN = timeStringLength), INTENT(IN) :: string 


! Arguments with intent(out):
TYPE (DateTime), INTENT(OUT) :: time

!------------end of declaration------------------------------------------------
!1234567890123456789012345
!2007-03-05T01:00:00+02:00

time % year     = StringToShort ( string (1:4) )
time % month    = StringToShort ( string (6:7) )
time % day      = StringToShort ( string (9:10) )
time % hour     = StringToShort ( string (12:13) )
time % minute   = StringToShort ( string (15:16) )
time % second   = StringToShort ( string (18:19) )
time % TZhour   = StringToShort ( string (21:22) )
time % TZminute = StringToShort ( string (24:25) )
time % TZsign   = string (20:20) 
CALL DateCheck ( time )
END SUBROUTINE Parse

!==============================================================================
!| Description:
! Converts the value of the current `DateTime` object to its equivalent 
! string representation
SUBROUTINE  TimeToString &
!
(string, time)

USE StringManipulation, ONLY: &
! Imported routines:
ToString

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Arguments with intent(out):
CHARACTER(LEN = timeStringLength), INTENT(OUT) :: string
!------------end of declaration------------------------------------------------
string = TRIM ( ToString ( time % year, fmt = '(I4.4)' ) )   // '-' // &
         TRIM ( ToString ( time % month, fmt = '(I2.2)' ) )  // '-' // &
         TRIM ( ToString ( time % day, fmt = '(I2.2)' ) )    // 'T' // &
         TRIM ( ToString ( time % hour, fmt = '(I2.2)' ) )   // ':' // &
         TRIM ( ToString ( time % minute, fmt = '(I2.2)' ) ) // ':' // &
         TRIM ( ToString ( time % second, fmt = '(I2.2)' ) ) //        &
         time % TZsign                                       //        &
         TRIM ( ToString ( time % TZhour, fmt = '(I2.2)' ) ) // ':' // &
         TRIM ( ToString ( time % TZminute, fmt = '(I2.2)' ) )
END SUBROUTINE TimeToString


!==============================================================================
!| Description:
! Create an exact copy of `DateTime`
SUBROUTINE  Copy &
!
(time2, time1)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1


! Arguments with intent(out):
TYPE (DateTime), INTENT(OUT) :: time2

!------------end of declaration------------------------------------------------

time2 % year     = time1 % year
time2 % month    = time1 % month
time2 % day      = time1 % day
time2 % hour     = time1 % hour
time2 % minute   = time1 % minute
time2 % second   = time1 % second
time2 % TZhour   = time1 % TZhour
time2 % TZminute = time1 % TZminute
time2 % TZsign   = time1 % TZsign
END SUBROUTINE Copy


!==============================================================================
!| Description:
!   check that date do not contain errors.
SUBROUTINE  DateCheck &
!
( time )

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
CHARACTER (LEN = timeStringLength) :: string
!------------end of declaration------------------------------------------------

IF (DateTimeIsDefault(time)) THEN
  RETURN !skip check
END IF

IF ( time % second < 0 .OR. time % second >= 60 ) THEN
   string = time
   CALL Catch ('error', 'Chronos', 'second ', &
               code = DateTimeError, argument = string )
END IF

IF ( time % minute < 0 .OR. time % minute >= 60 ) THEN
   string = time
   CALL Catch ('error', 'Chronos', 'minute ', &
               code = DateTimeError, argument = string )
END IF

IF ( time % hour < 0 .OR. time % hour >= 25 )  THEN
   string = time
   CALL Catch ('error', 'Chronos', 'hour ', &
               code = DateTimeError, argument = string )
END IF

IF ( time % year <= 0)  THEN
   string = time
   CALL Catch ('error', 'Chronos', 'year ', &
               code = DateTimeError, argument = string )
END IF

IF ( time % month <= 0 .OR. time % month > 12 )       THEN
   string = time
   CALL Catch ('error', 'Chronos', 'month ', &
               code = DateTimeError, argument = string )
ELSE IF ( time % day <= 0 .OR. time % day > &
         DaysInMonth (time % month, time % year)     ) THEN
   string = time      
   CALL Catch ('error', 'Chronos', 'day ', &
               code = DateTimeError, argument = string )
END IF
END SUBROUTINE DateCheck

!==============================================================================
!| Description:
!   Returns `true` if the specified year is a leap year
!
! Method:
!
!   In the _Gregorian_ calendar, a normal year consists of 365 days. 
!   Because the actual length of a sidereal year (the time required 
!   for the Earth to revolve once about the Sun) is actually 365.25635 days, 
!   a "leap year" of 366 days is used once every four years to eliminate the 
!   error caused by three normal (but short) years. Any year that is evenly 
!   divisible by 4 is a leap year: for example, 1988, 1992, and 1996 
!   are leap years.
!   However, there is still a small error that must be accounted for. 
!   To eliminate this error, the _Gregorian_ calendar stipulates that a year 
!   that is evenly divisible by 100 (for example, 1900) is a leap year only 
!   if it is also evenly divisible by 400.
!   For this reason, the following years are not leap years:
!   1700, 1800, 1900, 2100, 2200, 2300, 2500, 2600
!   This is because they are evenly divisible by 100 but not by 400.
!   The following years are leap years:
!   1600, 2000, 2400
!   This is because they are evenly divisible by both 100 and 400. 
FUNCTION IsLeapYear &
!
(year) &
!
RESULT (isLeap)

IMPLICIT NONE

! Arguments with intent(in):
INTEGER (KIND = short), INTENT(IN) :: year

! Local variables:
LOGICAL :: isLeap
!------------end of declaration------------------------------------------------

IF ( MOD ( year, 4 ) == 0 ) THEN
  IF ( MOD ( year, 400) > 0 .AND. MOD ( year, 100) == 0 ) THEN
     isLeap = .FALSE.
  ELSE
     isLeap = .TRUE.
  END IF
ELSE
  isLeap = .FALSE.
END IF 

END FUNCTION IsLeapYear


!==============================================================================
!| Description:
!   Returns the number of days in the specified month. It accounts
!   for leap years
FUNCTION DaysInMonth &
!
(month, year) &
!
RESULT (days)

IMPLICIT NONE

! Arguments with intent(in):
INTEGER (KIND = short), INTENT(IN) :: year, month

! Local variables:
INTEGER (KIND = short) :: days
!------------end of declaration------------------------------------------------

IF( (month == 1) .OR. (month == 3) .OR. (month == 5) .OR. (month == 7) .OR. &
    (month == 8) .OR. (month == 10) .OR. (month == 12) ) THEN
     days = 31
ELSE IF ( (month == 4) .OR. (month == 6) .OR. (month == 9) .OR. &
          (month == 11) ) THEN
     days = 30
ELSE IF (month == 2) THEN
     IF ( IsLeapYear (year) ) THEN
        days = 29
     ELSE
        days = 28
     END IF
END IF
END FUNCTION DaysInMonth


!==============================================================================
!| Description:
!   Gets the day of the year represented by this instance. Returns
!   366 for leap years
FUNCTION DayOfYear &
!
(time, leap) &
!
RESULT (day)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time
CHARACTER (LEN = *), OPTIONAL, INTENT(IN) :: leap ! 'noleap' ignores 29th february of leap years

! Local variables:
INTEGER (KIND = short) :: day, i
TYPE (DateTime) :: february29
!------------end of declaration------------------------------------------------

day = 0
DO i = 1, time % month - 1
    day = day + DaysInMonth (i, time % year)
END DO
day = day + time % day

IF ( PRESENT (leap) ) THEN
  IF ( leap == 'noleap' ) THEN
    IF ( IsLeapYear (time % year) ) THEN
      !string = time
      !february29 = string
      february29 = time
      february29 % month = 2
      february29 % day = 29
      IF ( time >= february29 ) THEN
        day = day - 1
      END IF
    END IF
  ELSE
    CALL Catch ('warning', 'Chronos', 'unknown option in DayOfYear: ', &
               code = unknownOption, argument = leap )
  END IF
ELSE
  
END IF

END FUNCTION DayOfYear

!==============================================================================
!| Description:
!   Gets the second of the year represented by this instance.
FUNCTION SecondOfYear &
!
(time) &
!
RESULT (second)

USE Units, ONLY: &
! Imported parameters:
day, hour, minute

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
INTEGER (KIND = short) :: second
!------------end of declaration------------------------------------------------

second = (DayOfYear (time) - 1) * day

second = second + GetHour (time) * hour + GetMinute (time) * minute + &
         GetSecond (time)


END FUNCTION SecondOfYear

!==============================================================================
!| Description:
!   Gets the second to the end of the year represented by this instance.
FUNCTION SecondsToEnd &
!
(time) &
!
RESULT (second)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
INTEGER (KIND = short) :: second
!------------end of declaration------------------------------------------------

IF ( IsLeapYear (time % year) ) THEN
  second = 366 * 86400 - SecondOfYear (time) 
ELSE
  second = 365 * 86400 - SecondOfYear (time) 
END IF

END FUNCTION SecondsToEnd

!==============================================================================
!| Description:
!  Adds the specified number of seconds to the value of this instance.
!  If number of seconds is a negative number, the amount is subtracted     
FUNCTION AddSeconds &
!
(time1, step) &
!
RESULT (time2)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1
INTEGER, INTENT(IN) :: step

! Local variables:
TYPE (DateTime):: time2
INTEGER  :: maxDay
!------------end of declaration------------------------------------------------

time2 = time1
IF(step >= 0) THEN
  time2 % second = time2 % second + step
  IF(time2 % second >= 60) THEN
    time2 % minute = time2 % minute  + INT ( time2 % second / 60 )
    time2 % second = time2 % second   - INT ( time2 % second / 60 ) * 60
    IF(time2 % minute >= 60) THEN
      time2 % hour = time2 % hour  + INT ( time2 % minute / 60)
      time2 % minute = time2 % minute - INT(time2%minute / 60) * 60
      IF(time2 % hour >= 24) THEN
        time2 % day = time2 % day  + INT(time2 % hour / 24)
        time2 % hour = time2 % hour - INT(time2%hour / 24) * 24
        maxDay = DaysInMonth (time2 % month, time2 % year)
        DO WHILE (time2 % day > maxDay)
          time2 % month = time2 % month + 1
          time2 % day = time2 % day - maxDay
          IF ( time2 % month == 13) THEN
            time2 % year = time2 % year + 1
            time2 % month = 1
          END IF
          maxDay = DaysInMonth (time2 % month, time2 % year)
        END DO
      END IF
    END IF
  END IF
ELSE
  time2 % second = time2 % second + step
  IF(time2 % second < 0) THEN
    time2 % minute = time2 % minute + INT(time2 % second / 60) - 1
    time2 % second = time2 % second + (-INT(time2 % second / 60) + 1) * 60
    IF(time2 % second == 60) THEN
      time2 % second = 0
      time2 % minute = time2 % minute + 1
    END IF
    IF(time2 % minute < 0) THEN
      time2 % hour = time2 % hour + INT(time2 % minute / 60) - 1				
      time2 % minute = time2 % minute + (-INT(time2 % minute / 60) + 1) * 60
      IF(time2 % minute == 60) THEN
        time2 % minute = 0
        time2 % hour = time2 % hour + 1
      END IF
      IF(time2 % hour < 0) THEN
        time2 % day = time2 % day + INT(time2 % hour / 24) - 1
        time2 % hour = time2 % hour + (-INT(time2 % hour / 24) + 1) * 24
        IF(time2 % hour == 24) THEN
          time2 % hour = 0
          time2 % day = time2 % day + 1
        END IF
        DO WHILE (time2 % day <= 0)
          IF(time2 % month - 1 <= 0) time2 % month = 13
            maxDay = DaysInMonth(time2 % month - 1,time2 % year)
            time2 % month = time2 % month - 1
            time2 % day = time2 % day + maxDay
            IF(time2%month == 12) THEN
              time2 % year = time2 % year - 1
            END IF
            maxDay = DaysInMonth(time2 % month,time2 % year)
        END DO
      END IF
    END IF
  END IF
END IF

CALL DateCheck (time2)
	
END FUNCTION AddSeconds


!==============================================================================
!| Description:
!  Adds the specified number of days to the value of this instance.      
FUNCTION AddDays &
!
(time1, step) &
!
RESULT (time2)

USE Units, ONLY: &
! imported parameters:
day

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1
INTEGER, INTENT(IN) :: step

! Local variables:
TYPE (DateTime):: time2
!------------end of declaration------------------------------------------------

time2 = AddSeconds (time1, INT(step * day) )
	
END FUNCTION AddDays

!==============================================================================
!| Description:
!  Adds the specified number of hours to the value of this instance.      
FUNCTION AddHours &
!
(time1, step) &
!
RESULT (time2)

USE Units, ONLY: &
! Imported parameters:
hour

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1
INTEGER, INTENT(IN) :: step

! Local variables:
TYPE (DateTime):: time2
!------------end of declaration------------------------------------------------

time2 = AddSeconds (time1, INT(step * hour) )
	
END FUNCTION AddHours

!==============================================================================
!| Description:
!  Adds the specified number of minutes to the value of this instance.      
FUNCTION AddMinutes &
!
(time1, step) &
!
RESULT (time2)

USE Units, ONLY: &
! Imported parameters:
minute

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1
INTEGER, INTENT(IN) :: step

! Local variables:
TYPE (DateTime):: time2
!------------end of declaration------------------------------------------------

time2 = AddSeconds (time1, INT(step * minute) )
	
END FUNCTION AddMinutes

!==============================================================================
!| Description:
!   calculate the difference in seconds between two date: time1 - time2
FUNCTION TimeDifference &
!
(time1, time2) &
RESULT (seconds)

USE Units, ONLY: &
! Imported parameters:
day

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1, time2

! Local variables:
INTEGER (KIND = long) :: seconds, a, b, c
INTEGER (KIND = short) :: i
TYPE (DateTime) :: tempTime1, tempTime2
!------------end of declaration------------------------------------------------

!converto to utc
tempTime1 = ToUtc (time1)
tempTime2 = ToUtc (time2)

a = SecondOfYear (tempTime1)
b = SecondOfYear (tempTime2)

c = 0
DO i = tempTime2 % year, tempTime1 % year - 1
  IF (IsLeapYear (i)) THEN
    c = c + 366 * day
  ELSE
    c = c + 365 * day
  END IF
END DO

seconds = a + c - b

END FUNCTION TimeDifference

!==============================================================================
!| Description:
!   Returns true if datetime object is expressed in UTC      
FUNCTION IsUTC &
!
(time) &
!
RESULT (utc)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
LOGICAL :: utc
!------------end of declaration------------------------------------------------

IF (time % TZhour == 0 .AND. time % TZminute == 0) THEN
  utc = .TRUE.
ELSE
  utc = .FALSE.
END IF
	
END FUNCTION IsUTC


!==============================================================================
!| Description:
!   Converts the value of the current `DateTime` object to 
!   Coordinated Universal Time (UTC). 
FUNCTION  ToUTC &
!
(time1) &
!
RESULT (time2)

USE Units, ONLY: &
!Imported parameters
hour, minute

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time1

! Local variables:
TYPE (DateTime) :: time2
INTEGER :: variation

!------------end of declaration------------------------------------------------

!reset time2
time2 = timeDefault

!calculate variation in seconds
variation = time1 % TZhour * hour + time1 % TZminute * minute

!Apply variation to convert to UTC
IF (time1 % TZsign == '+' ) THEN !subtract variation
  time2 = AddSeconds (time1, - variation)
ELSE IF (time1 % TZsign == '-' ) THEN !add variation
  time2 = AddSeconds (time1, variation)
END IF
time2 % TZhour   = 0
time2 % TZminute = 0
time2 % TZsign   = '+'
END FUNCTION ToUTC

!==============================================================================
!| Description:
!   Gets a `DateTime` object that is set to the current date and time on 
!   this computer, expressed as the local time. 
FUNCTION  Now &
!
() &
!
RESULT (time)

USE StringManipulation, ONLY: &
!Imported routines
StringToShort

IMPLICIT NONE

! Local variables:
TYPE (DateTime) :: time

! Local scalars:
CHARACTER ( LEN = 8 )  :: systemDate
CHARACTER ( LEN = 10 ) :: systemTime
INTEGER (KIND = short) :: values(8)
CHARACTER ( LEN = 5 )  :: zone
!------------end of declaration------------------------------------------------
 
  CALL date_and_time ( systemDate, systemTime, zone, values )

  time % year = values(1)
  time % month = values(2)
  time % day = values(3)
  time % hour = values(5)
  time % minute = values(6)
  time % second = values(7)
  time % TZhour = StringToShort ( zone (2:3) )
  time % TZminute = StringToShort ( zone (4:5) )
  time % TZsign = zone (1:1)
  
END FUNCTION Now

!==============================================================================
!| Description:
!   Gets a `DateTime` object that is set to the current date and time on 
!   this computer, expressed as the Coordinated Universal Time (UTC).  
FUNCTION  UtcNow &
!
() &
!
RESULT (time)

IMPLICIT NONE

! Local variables:
TYPE (DateTime) :: time

!------------end of declaration------------------------------------------------

time = ToUTC ( Now() )
 
END FUNCTION UtcNow

!==============================================================================
!| Description:
!   Gets the year of the datetime represented by this instance
FUNCTION  GetYear &
!
(time) &
!
RESULT (year)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
INTEGER (KIND = short) :: year

!------------end of declaration------------------------------------------------

year = time % year

END FUNCTION GetYear

!==============================================================================
!| Description:
!   Gets the month of the datetime represented by this instance
FUNCTION  GetMonth &
!
(time) &
!
RESULT (month)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
INTEGER (KIND = short) :: month

!------------end of declaration------------------------------------------------

month = time % month

END FUNCTION GetMonth

!==============================================================================
!| Description:
!   Gets the day of the datetime represented by this instance
FUNCTION  GetDay &
!
(time) &
!
RESULT (day)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
INTEGER (KIND = short) :: day

!------------end of declaration------------------------------------------------

day = time % day

END FUNCTION GetDay



!==============================================================================
!| Description:
!   Gets the day of week (0 - 6) (Sunday to Saturday
!   The formula is:
!
! `(yearCode + monthCode + centuryCode + dateNumber - leapYearCode) mod 7 `
! 
! To calculate the`yearCode`, use this formula:
!
!  `(YY + (YY div 4)) mod 7`
!
!  `YY` is the last two digits of the year.
!
! The `monthCode`:
!
! * January = 0
! * February = 3
! * March = 3
! * April = 6
! * May = 1
! * June = 4
! * July = 6
! * August = 2
! * September = 5
! * October = 0
! * November = 3
! * December = 5
!
! The `centuryCode` for the Gregorian Calendar:
!
! * 1700s = 4
! * 1800s = 2
! * 1900s = 0
! * 2000s = 6
! * 2100s = 4
! * 2200s = 2
! * 2300s = 0
!
! `dateNumber` is the day of Month

! `leapYearCode`: if the date is in a January or February of a leap year,
! you have to subtract one from your total before the final step.
!
! References:
!
! https://artofmemory.com/blog/how-to-calculate-the-day-of-the-week/
!
FUNCTION  GetDayOfWeek &
!
(time) &
!
RESULT (day)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
INTEGER (KIND = short) :: day !! returned value
INTEGER (KIND = short) :: yearCode !! year code
INTEGER (KIND = short) :: monthCode !! month code
INTEGER (KIND = short) :: centuryCode !! month code
INTEGER (KIND = short) :: leapYearCode !! leap year code
INTEGER (KIND = short) :: dateNumber !! the day of month
INTEGER (KIND = short) :: yy !! the last two digits of the year
INTEGER (KIND = short) :: yyyy !! year (four digits)
INTEGER (KIND = short) :: month !! month number
CHARACTER (LEN = 4) :: year

!------------end of declaration------------------------------------------------

!compute the yearCode (YY + (YY div 4)) mod 7
yyyy = GetYear (time)
year = ToString (yyyy )
yy = StringToLong ( year (3:4) )
yearCode = MOD ( yy + INT(yy/4), 7)

!set the monthCode
month = GetMonth (time)
SELECT CASE (month )
   CASE (1,10)
       monthCode = 0
   CASE (2,3,11)
       monthCode = 3
   CASE (4,7)
       monthCode = 6
   CASE (5)
       monthCode = 1
   CASE (6)
       monthCode = 4
   CASE (8)
       monthCode = 2
   CASE (9,12)
       monthCode = 5
   END SELECT
   
!set the centuryCode
SELECT CASE ( yyyy )
    CASE (1700:1799)
        centuryCode = 4
    CASE (1800:1899)
        centuryCode = 2
    CASE (1900:1999)
        centuryCode = 0
    CASE (2000:2099)
        centuryCode = 6
    CASE (2100:2199)
        centuryCode = 4
    CASE (2200:2299)
        centuryCode = 2
    CASE (2300:2399)
        centuryCode = 0
    END SELECT

! set leapYearCode
leapYearCode = 0
IF ( IsLeapYear (yyyy) ) THEN
    IF ( month <= 2) THEN
        leapYearCode = -1
    END IF
END IF

!dateNumber
dateNumber = GetDay (time)

! yearCode + monthCode + centuryCode + dateNumber - leapYearCode) mod 7 
day = MOD (yearCode + monthCode + centuryCode + dateNumber - leapYearCode, 7)

RETURN
END FUNCTION GetDayOfWeek



!==============================================================================
!| Description:
!   Gets the month of the datetime represented by this instance
FUNCTION  GetHour &
!
(time) &
!
RESULT (hour)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
INTEGER (KIND = short) :: hour

!------------end of declaration------------------------------------------------

hour = time % hour

END FUNCTION GetHour

!==============================================================================
!| Description:
!   Gets the minute of the datetime represented by this instance
FUNCTION  GetMinute &
!
(time) &
!
RESULT (minute)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
INTEGER (KIND = short) :: minute

!------------end of declaration------------------------------------------------

minute = time % minute

END FUNCTION GetMinute

!==============================================================================
!| Description:
!   Gets the second of the datetime represented by this instance
FUNCTION  GetSecond &
!
(time) &
!
RESULT (second)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
INTEGER (KIND = short) :: second

!------------end of declaration------------------------------------------------

second = time % second

END FUNCTION GetSecond

!==============================================================================
!| Description:
!   Gets the string representing time zone of the datetime
!   represented by this instance. Example: '+02:00'
FUNCTION  GetTimeZone &
!
(time) &
!
RESULT (timeZone)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local variables:
CHARACTER (LEN = 6) :: timeZone
CHARACTER (LEN = 25) :: string

!------------end of declaration------------------------------------------------

string = time
timeZone = string (20:25)

END FUNCTION GetTimeZone

!==============================================================================
!| Description:
!   Set the year of the datetime represented by this instance
SUBROUTINE  SetYear &
!
(year, time)

IMPLICIT NONE

! Arguments with intent(in):
INTEGER (KIND = short), INTENT(IN) :: year

! Arguments with intent(out):
TYPE (DateTime), INTENT(OUT) :: time

!------------end of declaration------------------------------------------------

time % year = year

CALL DateCheck (time)

END SUBROUTINE SetYear

!==============================================================================
!| Description:
!   Set the month of the datetime represented by this instance
SUBROUTINE  SetMonth &
!
(month, time)

IMPLICIT NONE

! Arguments with intent(in):
INTEGER (KIND = short), INTENT(IN) :: month

! Arguments with intent(out):
TYPE (DateTime), INTENT(OUT) :: time

!------------end of declaration------------------------------------------------

time % month = month

CALL DateCheck (time)

END SUBROUTINE SetMonth

!==============================================================================
!| Description:
!   Set the day of the datetime represented by this instance
SUBROUTINE  SetDay &
!
(day, time)

IMPLICIT NONE

! Arguments with intent(in):
INTEGER (KIND = short), INTENT(IN) :: day

! Arguments with intent(out):
TYPE (DateTime), INTENT(OUT) :: time

!------------end of declaration------------------------------------------------

time % day = day

CALL DateCheck (time)

END SUBROUTINE SetDay

!==============================================================================
!| Description:
!   Set the hour of the datetime represented by this instance
SUBROUTINE  SetHour &
!
(hour, time)

IMPLICIT NONE

! Arguments with intent(in):
INTEGER (KIND = short), INTENT(IN) :: hour

! Arguments with intent(out):
TYPE (DateTime), INTENT(OUT) :: time

!------------end of declaration------------------------------------------------

time % hour = hour

CALL DateCheck (time)

END SUBROUTINE SetHour

!==============================================================================
!| Description:
!   Set the minute of the datetime represented by this instance
SUBROUTINE  SetMinute &
!
(minute, time)

IMPLICIT NONE

! Arguments with intent(in):
INTEGER (KIND = short), INTENT(IN) :: minute

! Arguments with intent(out):
TYPE (DateTime), INTENT(OUT) :: time

!------------end of declaration------------------------------------------------

time % minute = minute

CALL DateCheck (time)

END SUBROUTINE SetMinute

!==============================================================================
!| Description:
!   Set the second of the datetime represented by this instance
SUBROUTINE  SetSecond &
!
(second, time)

IMPLICIT NONE

! Arguments with intent(in):
INTEGER (KIND = short), INTENT(IN) :: second

! Arguments with intent(out):
TYPE (DateTime), INTENT(OUT) :: time

!------------end of declaration------------------------------------------------

time % second = second

CALL DateCheck (time)

END SUBROUTINE SetSecond

!==============================================================================
!| Description:
!   Set the timezone of the datetime represented by this instance
SUBROUTINE  SetTimeZone &
!
(timeZone, time)

USE StringManipulation, ONLY : &
! Imported routines:
StringCompact

IMPLICIT NONE

! Arguments with intent(in):
CHARACTER (LEN = *), INTENT(IN) :: timeZone

! Arguments with intent(out):
TYPE (DateTime), INTENT(OUT) :: time

! Local variables:
CHARACTER (LEN = 25) :: string

!------------end of declaration------------------------------------------------

string = time
string (20:25) = timeZone
time = string
CALL DateCheck (time)

END SUBROUTINE SetTimeZone


!==============================================================================
!| Description:
!   Check if datetime is set to default
FUNCTION  DateTimeIsDefault &
!
(time) &
!
RESULT (isDefault)

IMPLICIT NONE

! Arguments with intent(in):
TYPE (DateTime), INTENT(IN) :: time

! Local declarations:
LOGICAL :: isDefault

!------------end of declaration------------------------------------------------

IF (time % year == 0 .AND. &
    time % month == 0 .AND. &
    time % day == 0 .AND. &
    time % hour == 0 .AND. &
    time % minute == 0 .AND. &
    time % second == 0 ) THEN
    
    isDefault = .TRUE.
ELSE
    isDefault = .FALSE.
END IF

RETURN

END FUNCTION DateTimeIsDefault





!http://msdn.microsoft.com/en-us/library/system.datetime_members.aspx
!AddHours, AddMinutes, AddSeconds,AddDays,AddYears, AddMonths

END MODULE Chronos