%--------------------------------------------------%
% vim: ft=mercury ts=4 sw=4 et
%--------------------------------------------------%
% Originally written in 1999 by Tomas By <T.By@dcs.shef.ac.uk>
% "Feel free to use this code or parts of it any way you want."
%
% Some portions are Copyright (C) 1999-2007,2009-2012 The University of Melbourne.
% Copyright (C) 2014-2021 The Mercury team.
% This file is distributed under the terms specified in COPYING.LIB.
%--------------------------------------------------%
%
% File: time.m.
% Main authors: Tomas By <T.By@dcs.shef.ac.uk>, fjh.
% Stability: medium.
%
% Time functions.
%
%--------------------------------------------------%
%--------------------------------------------------%

:- module time.
:- interface.

:- import_module io.
:- import_module maybe.

%--------------------------------------------------%

    % The `clock_t' type represents times measured in clock ticks.
    % NOTE: the unit used for a value of this type depends on whether it was
    % returned by `clock' or `times'. See the comments on these
    % predicates below.
    %
:- type clock_t == int.

    % The `tms' type holds information about the amount of processor time
    % that a process and its child processes have consumed.
    %
:- type tms
    --->    tms(
                clock_t,    % tms_utime: user time
                clock_t,    % tms_stime: system time
                clock_t,    % tms_cutime: user time of children
                clock_t     % tms_cstime: system time of children
            ).

    % The `time_t' type is an abstract type that represents
    % calendar times.
    %
:- type time_t.

    % The `tm' type is a concrete type that represents calendar times,
    % broken down into their constituent components. Comparison (via compare/3)
    % of `tm' values is equivalent to comparison of the times those `tm'
    % values represent IF AND ONLY IF their `tm_dst' components are identical.
    %
    % Whether leap seconds are supported depends on the target language.
    % Currently, only C supports leap seconds, while Java and C# do not.
    % For target languages that do not support leap seconds:
    %
    % - predicates in this module that produce a `tm' value as an output
    %   will never set its `tm_sec' component to a value beyond 59;
    %
    % - predicates in this module that take a `tm_sec' value as an input
    %   will throw a time_error/1 exception if the value of the `tm_sec'
    %   component is beyond 59.
    %
:- type tm
    --->    tm(
                tm_year :: int,         % Year (number since 1900)
                tm_mon  :: int,         % Month (number since January, 0-11)
                tm_mday :: int,         % MonthDay (1-31)
                tm_hour :: int,         % Hours (after midnight, 0-23)
                tm_min  :: int,         % Minutes (0-59)
                tm_sec  :: int,         % Seconds (0-61)
                                        % (60 and 61 are for leap seconds)
                tm_yday :: int,         % YearDay (number since Jan 1st, 0-365)
                tm_wday :: int,         % WeekDay (number since Sunday, 0-6)
                tm_dst  :: maybe(dst)   % IsDST (is DST applicable, and if so,
                                        % is it in effect?)
            ).

:- type dst
    --->    standard_time   % no, DST is not in effect
    ;       daylight_time.  % yes, DST is in effect

    % Some of the procedures in this module throw this type
    % as an exception if they can't obtain a result.
    %
:- type time_error
    --->    time_error(string). % Error message

%--------------------------------------------------%

    % clock(Result, !IO):
    %
    % Returns the elapsed processor time (number of clock ticks). The base time
    % is arbitrary but doesn't change within a single process. If the time
    % cannot be obtained, this procedure will throw a time_error exception.
    % To obtain a time in seconds, divide Result by `clocks_per_sec'.
    %
    % On Java the elapsed time for the calling thread is returned.
    %
:- pred clock(clock_t::out, io::di, io::uo) is det.

    % clocks_per_sec:
    %
    % Returns the number of "clocks" per second as defined by CLOCKS_PER_SEC.
    % A `clock_t' value returned by `clock' can be divided by this value
    % to obtain a time in seconds. Note that the value of this function does
    % not necessarily reflect the actual clock precision; it just indicates the
    % scaling factor for the results of `clock'.
    %
:- func clocks_per_sec = int.

%--------------------------------------------------%

    % time(Result, !IO):
    %
    % Returns the current (simple) calendar time. If the time cannot be
    % obtained, this procedure will throw a time_error exception.
    %
:- pred time(time_t::out, io::di, io::uo) is det.

%--------------------------------------------------%

    % times(ProcessorTime, ElapsedRealTime, !IO):
    %
    % (POSIX)
    %
    % Returns the processor time information in the `tms' value, and the
    % elapsed real time relative to an arbitrary base in the `clock_t' value.
    % To obtain a time in seconds, divide the result by `clk_tck'.
    % If the time cannot be obtained, this procedure will throw a time_error
    % exception.
    %
    % On non-POSIX systems that do not support this functionality,
    % this procedure may simply always throw an exception.
    %
    % On Java the times for the calling thread are returned.
    % On Win32 and Java the child part of 'tms' is always zero.
    %
:- pred times(tms::out, clock_t::out, io::di, io::uo) is det.

    % clk_tck:
    %
    % Returns the number of "clock ticks" per second as defined by
    % sysconf(_SC_CLK_TCK). A `clock_t' value returned by `times'
    % can be divided by this value to obtain a time in seconds.
    %
    % On non-POSIX systems that do not support this functionality,
    % this procedure may simply always throw an exception.
    %
:- func clk_tck = int.

%--------------------------------------------------%

    % difftime(Time1, Time0) = Diff:
    %
    % Computes the number of seconds elapsed between `Time1' and `Time0'.
    %
:- func difftime(time_t, time_t) = float.

    % localtime(Time, TM, !IO):
    %
    % Converts the (simple) calendar time `Time' to a broken-down
    % representation `TM', expressed relative to the current time zone.
    %
:- pred localtime(time_t::in, tm::out, io::di, io::uo) is det.

    % gmtime(Time) = TM:
    %
    % Converts the (simple) calendar time `Time' to a broken-down
    % representation `TM', expressed as UTC (Universal Coordinated Time).
    %
:- func gmtime(time_t) = tm.

    % mktime(TM, Time, !IO):
    %
    % Converts the broken-down time value `TM' to a (simple) calendar time
    % `Time'. That is, `TM' is relative to the current time zone.
    % The `tm_wday' and `tm_yday' fields of `TM' are ignored.
    %
:- pred mktime(tm::in, time_t::out, io::di, io::uo) is det.

%--------------------------------------------------%

    % asctime(TM) = String:
    %
    % Converts the broken-down time value `TM' to a string in a standard
    % format.
    %
:- func asctime(tm) = string.

%--------------------------------------------------%
%--------------------------------------------------%