stdlib: Add RFC 3339 functions to module calendar

Functions for converting between RFC 3339 strings and system time
are added.

Options are lists, but we are considering using maps instead. If we
change, it will happen after Erlang/OTP 21.0-rc1 is released.

1 files changed, 160 insertions, 6 deletions

diff --git a/lib/stdlib/src/calendar.erl b/lib/stdlib/src/calendar.erl
index 2e24e8c133..9a600c1972 100644
--- a/lib/stdlib/src/calendar.erl
+++ b/lib/stdlib/src/calendar.erl
@@ -39,10 +39,14 @@
 	 now_to_datetime/1,			% = now_to_universal_time/1
 	 now_to_local_time/1,
 	 now_to_universal_time/1,
+         rfc3339_to_system_time/1,
+         rfc3339_to_system_time/2,
 	 seconds_to_daystime/1,
 	 seconds_to_time/1,
          system_time_to_local_time/2,
          system_time_to_universal_time/2,
+         system_time_to_rfc3339/1,
+         system_time_to_rfc3339/2,
 	 time_difference/2,
 	 time_to_seconds/1,
 	 universal_time/0,
@@ -57,11 +61,13 @@
 -define(SECONDS_PER_DAY, 86400).
 -define(DAYS_PER_YEAR, 365).
 -define(DAYS_PER_LEAP_YEAR, 366).
--define(DAYS_PER_4YEARS, 1461).
--define(DAYS_PER_100YEARS, 36524).
--define(DAYS_PER_400YEARS, 146097).
+%% -define(DAYS_PER_4YEARS, 1461).
+%% -define(DAYS_PER_100YEARS, 36524).
+%% -define(DAYS_PER_400YEARS, 146097).
 -define(DAYS_FROM_0_TO_1970, 719528).
+-define(DAYS_FROM_0_TO_10000, 2932897).
 -define(SECONDS_FROM_0_TO_1970, (?DAYS_FROM_0_TO_1970*?SECONDS_PER_DAY)).
+-define(SECONDS_FROM_0_TO_10000, (?DAYS_FROM_0_TO_10000*?SECONDS_PER_DAY)).
 
 %%----------------------------------------------------------------------
 %% Types
@@ -86,6 +92,13 @@
 -type datetime1970()   :: {{year1970(),month(),day()},time()}.
 -type yearweeknum()    :: {year(),weeknum()}.
 
+-type rfc3339_string() :: [byte(), ...].
+%% By design 'native' is not supported:
+-type rfc3339_time_unit() :: 'microsecond'
+                           | 'millisecond'
+                           | 'nanosecond'
+                           | 'second'.
+
 %%----------------------------------------------------------------------
 
 %% All dates are according the the Gregorian calendar. In this module
@@ -312,8 +325,7 @@ local_time_to_universal_time_dst(DateTime) ->
 -spec now_to_datetime(Now) -> datetime1970() when
       Now :: erlang:timestamp().
 now_to_datetime({MSec, Sec, _uSec}) ->
-    Sec0 = MSec*1000000 + Sec + ?SECONDS_FROM_0_TO_1970,
-    gregorian_seconds_to_datetime(Sec0).
+    system_time_to_datetime(MSec*1000000 + Sec).
 
 -spec now_to_universal_time(Now) -> datetime1970() when
       Now :: erlang:timestamp().
@@ -331,6 +343,33 @@ now_to_local_time({MSec, Sec, _uSec}) ->
     erlang:universaltime_to_localtime(
       now_to_universal_time({MSec, Sec, _uSec})).
 
+-spec rfc3339_to_system_time(DateTimeString) -> integer() when
+      DateTimeString :: rfc3339_string().
+
+rfc3339_to_system_time(DateTimeString) ->
+    rfc3339_to_system_time(DateTimeString, []).
+
+-spec rfc3339_to_system_time(DateTimeString, Options) -> integer() when
+      DateTimeString :: rfc3339_string(),
+      Options :: [Option],
+      Option :: {'unit', rfc3339_time_unit()}.
+
+rfc3339_to_system_time(DateTimeString, Options) ->
+    Unit = proplists:get_value(unit, Options, second),
+    %% _T is the character separating the date and the time:
+    {DateStr, [_T|TimeStr]} = lists:split(10, DateTimeString),
+    {TimeStr2, TimeStr3} = lists:split(8, TimeStr),
+    {ok, [Hour, Min, Sec], []} = io_lib:fread("~d:~d:~d", TimeStr2),
+    {ok, [Year, Month, Day], []} = io_lib:fread("~d-~d-~d", DateStr),
+    DateTime = {{Year, Month, Day}, {Hour, Min, Sec}},
+    IsFractionChar = fun(C) -> C >= $0 andalso C =< $9 orelse C =:= $. end,
+    {FractionStr, UtcOffset} = lists:splitwith(IsFractionChar, TimeStr3),
+    Time = datetime_to_system_time(DateTime),
+    Secs = Time - offset_adjustment(Time, second, UtcOffset),
+    check(DateTimeString, Options, Secs),
+    ScaledEpoch = erlang:convert_time_unit(Secs, second, Unit),
+    ScaledEpoch + copy_sign(fraction(Unit, FractionStr), ScaledEpoch).
+
 
 
 %% seconds_to_daystime(Secs) = {Days, {Hour, Minute, Second}}
@@ -380,7 +419,40 @@ system_time_to_local_time(Time, TimeUnit) ->
 
 system_time_to_universal_time(Time, TimeUnit) ->
     Secs = erlang:convert_time_unit(Time, TimeUnit, second),
-    gregorian_seconds_to_datetime(Secs + ?SECONDS_FROM_0_TO_1970).
+    system_time_to_datetime(Secs).
+
+-spec system_time_to_rfc3339(Time) -> DateTimeString when
+      Time :: integer(),
+      DateTimeString :: rfc3339_string().
+
+system_time_to_rfc3339(Time) ->
+    system_time_to_rfc3339(Time, []).
+
+-type offset() :: [byte()] | (Time :: integer()).
+-spec system_time_to_rfc3339(Time, Options) -> DateTimeString when
+      Time :: integer(), % Since Epoch
+      Options :: [Option],
+      Option :: {'offset', offset()}
+              | {'time_designator', byte()}
+              | {'unit', rfc3339_time_unit()},
+      DateTimeString :: rfc3339_string().
+
+system_time_to_rfc3339(Time, Options) ->
+    Unit = proplists:get_value(unit, Options, second),
+    OffsetOption = proplists:get_value(offset, Options, ""),
+    T = proplists:get_value(time_designator, Options, $T),
+    AdjustmentSecs = offset_adjustment(Time, Unit, OffsetOption),
+    Offset = offset(OffsetOption, AdjustmentSecs),
+    Adjustment = erlang:convert_time_unit(AdjustmentSecs, second, Unit),
+    AdjustedTime = Time + Adjustment,
+    Factor = factor(Unit),
+    Secs = AdjustedTime div Factor,
+    check(Time, Options, Secs),
+    DateTime = system_time_to_datetime(Secs),
+    {{Year, Month, Day}, {Hour, Min, Sec}} = DateTime,
+    FractionStr = fraction_str(Factor, AdjustedTime),
+    flat_fwrite("~4.10.0B-~2.10.0B-~2.10.0B~c~2.10.0B:~2.10.0B:~2.10.0B~s~s",
+                [Year, Month, Day, T, Hour, Min, Sec, FractionStr, Offset]).
 
 %% time_difference(T1, T2) = Tdiff
 %%
@@ -569,3 +641,85 @@ df(Year, _) ->
 	true -> 1;
 	false  -> 0
     end.
+
+check(_Arg, _Options, Secs) when Secs >= - ?SECONDS_FROM_0_TO_1970,
+                                 Secs < ?SECONDS_FROM_0_TO_10000 ->
+    ok;
+check(Arg, Options, _Secs) ->
+    erlang:error({badarg, [Arg, Options]}).
+
+datetime_to_system_time(DateTime) ->
+    datetime_to_gregorian_seconds(DateTime) - ?SECONDS_FROM_0_TO_1970.
+
+system_time_to_datetime(Seconds) ->
+    gregorian_seconds_to_datetime(Seconds + ?SECONDS_FROM_0_TO_1970).
+
+offset(OffsetOption, Secs0) when OffsetOption =:= "";
+                                 is_integer(OffsetOption) ->
+    Sign = case Secs0 < 0 of
+               true -> $-;
+               false -> $+
+           end,
+    Secs = abs(Secs0),
+    Hour = Secs div 3600,
+    Min = (Secs rem 3600) div 60,
+    io_lib:fwrite("~c~2.10.0B:~2.10.0B", [Sign, Hour, Min]);
+offset(OffsetOption, _Secs) ->
+    OffsetOption.
+
+offset_adjustment(Time, Unit, OffsetString) when is_list(OffsetString) ->
+    offset_string_adjustment(Time, Unit, OffsetString);
+offset_adjustment(_Time, Unit, Offset) when is_integer(Offset) ->
+    erlang:convert_time_unit(Offset, Unit, second).
+
+offset_string_adjustment(Time, Unit, "") ->
+    local_offset(Time, Unit);
+offset_string_adjustment(_Time, _Unit, "Z") ->
+    0;
+offset_string_adjustment(_Time, _Unit, "z") ->
+    0;
+offset_string_adjustment(_Time, _Unit, [Sign|Tz]) ->
+    {ok, [Hour, Min], []} = io_lib:fread("~d:~d", Tz),
+    Adjustment = 3600 * Hour + 60 * Min,
+    case Sign of
+        $- -> -Adjustment;
+        $+ -> Adjustment
+    end.
+
+local_offset(SystemTime, Unit) ->
+    LocalTime = system_time_to_local_time(SystemTime, Unit),
+    UniversalTime = system_time_to_universal_time(SystemTime, Unit),
+    LocalSecs = datetime_to_gregorian_seconds(LocalTime),
+    UniversalSecs = datetime_to_gregorian_seconds(UniversalTime),
+    LocalSecs - UniversalSecs.
+
+fraction_str(Factor, Time) ->
+    case Time rem Factor of
+        0 ->
+            "";
+        Fraction ->
+            FS = io_lib:fwrite(".~*..0B", [log10(Factor), abs(Fraction)]),
+            string:trim(FS, trailing, "0")
+    end.
+
+fraction(second, _) ->
+    0;
+fraction(_, "") ->
+    0;
+fraction(Unit, FractionStr) ->
+    round(factor(Unit) * list_to_float([$0|FractionStr])).
+
+copy_sign(N1, N2) when N2 < 0 -> -N1;
+copy_sign(N1, _N2) -> N1.
+
+factor(second)      -> 1;
+factor(millisecond) -> 1000;
+factor(microsecond) -> 1000000;
+factor(nanosecond)  -> 1000000000.
+
+log10(1000) -> 3;
+log10(1000000) -> 6;
+log10(1000000000) -> 9.
+
+flat_fwrite(F, S) ->
+    lists:flatten(io_lib:fwrite(F, S)).