:- use_module(library(time)).

main :-
    % We'll start by getting the current time.
    get_time(Now),
    format_time(atom(NowStr), '%Y-%m-%d %H:%M:%S', Now),
    writeln(NowStr),

    % You can create a timestamp by providing the date and time components.
    date_time_stamp(date(2009, 11, 17, 20, 34, 58.651387237), Then),
    format_time(atom(ThenStr), '%Y-%m-%d %H:%M:%S', Then),
    writeln(ThenStr),

    % You can extract the various components of the time value as expected.
    stamp_date_time(Then, DateTime, 'UTC'),
    date_time_value(year, DateTime, Year),
    date_time_value(month, DateTime, Month),
    date_time_value(day, DateTime, Day),
    date_time_value(hour, DateTime, Hour),
    date_time_value(minute, DateTime, Minute),
    date_time_value(second, DateTime, Second),
    writeln(Year), writeln(Month), writeln(Day),
    writeln(Hour), writeln(Minute), writeln(Second),

    % The day of the week is also available.
    day_of_the_week(date(2009, 11, 17), DayOfWeek),
    writeln(DayOfWeek),

    % These predicates compare two times, testing if the first occurs before,
    % after, or at the same time as the second, respectively.
    (Then @< Now -> writeln(true) ; writeln(false)),
    (Then @> Now -> writeln(true) ; writeln(false)),
    (Then =:= Now -> writeln(true) ; writeln(false)),

    % We can compute the difference between two timestamps.
    Diff is Now - Then,
    format('~3f~n', [Diff]),

    % We can compute the length of the duration in various units.
    Hours is Diff / 3600,
    Minutes is Diff / 60,
    Seconds is Diff,
    format('~3f~n', [Hours]),
    format('~3f~n', [Minutes]),
    format('~3f~n', [Seconds]),

    % You can use arithmetic to advance a time by a given duration,
    % or subtract to move backwards.
    Advanced is Then + Diff,
    format_time(atom(AdvancedStr), '%Y-%m-%d %H:%M:%S', Advanced),
    writeln(AdvancedStr),
    
    Backward is Then - Diff,
    format_time(atom(BackwardStr), '%Y-%m-%d %H:%M:%S', Backward),
    writeln(BackwardStr).