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-rw-r--r--lib/stdlib/src/calendar.erl53
1 files changed, 53 insertions, 0 deletions
diff --git a/lib/stdlib/src/calendar.erl b/lib/stdlib/src/calendar.erl
index ddc0666f77..57b7c28dee 100644
--- a/lib/stdlib/src/calendar.erl
+++ b/lib/stdlib/src/calendar.erl
@@ -28,6 +28,8 @@
gregorian_days_to_date/1,
gregorian_seconds_to_datetime/1,
is_leap_year/1,
+ iso_week_number/0,
+ iso_week_number/1,
last_day_of_the_month/2,
local_time/0,
local_time_to_universal_time/1,
@@ -70,6 +72,7 @@
-type second() :: 0..59.
-type daynum() :: 1..7.
-type ldom() :: 28 | 29 | 30 | 31. % last day of month
+-type weeknum() :: 1..53.
-type t_now() :: {non_neg_integer(),non_neg_integer(),non_neg_integer()}.
@@ -77,6 +80,7 @@
-type t_time() :: {hour(),minute(),second()}.
-type t_datetime() :: {t_date(),t_time()}.
-type t_datetime1970() :: {{year1970(),month(),day()},t_time()}.
+-type t_yearweeknum() :: {year(),weeknum()}.
%%----------------------------------------------------------------------
@@ -172,6 +176,42 @@ is_leap_year1(Year) when Year rem 400 =:= 0 ->
is_leap_year1(_) -> false.
+%%
+%% Calculates the iso week number for the current date.
+%%
+-spec iso_week_number() -> t_yearweeknum().
+iso_week_number() ->
+ {Date, _} = local_time(),
+ iso_week_number(Date).
+
+
+%%
+%% Calculates the iso week number for the given date.
+%%
+-spec iso_week_number(t_date()) -> t_yearweeknum().
+iso_week_number({Year, Month, Day}) ->
+ D = date_to_gregorian_days({Year, Month, Day}),
+ W01_1_Year = gregorian_days_of_iso_w01_1(Year),
+ W01_1_NextYear = gregorian_days_of_iso_w01_1(Year + 1),
+ if W01_1_Year =< D andalso D < W01_1_NextYear ->
+ % Current Year Week 01..52(,53)
+ {Year, (D - W01_1_Year) div 7 + 1};
+ D < W01_1_Year ->
+ % Previous Year 52 or 53
+ PWN = case day_of_the_week(Year - 1, 1, 1) of
+ 4 -> 53;
+ _ -> case day_of_the_week(Year - 1, 12, 31) of
+ 4 -> 53;
+ _ -> 52
+ end
+ end,
+ {Year - 1, PWN};
+ W01_1_NextYear =< D ->
+ % Next Year, Week 01
+ {Year + 1, 1}
+ end.
+
+
%% last_day_of_the_month(Year, Month)
%%
%% Returns the number of days in a month.
@@ -377,6 +417,19 @@ dty(Y, D1, D2) when D1 < D2 ->
dty(Y, _D1, D2) ->
{Y, D2}.
+%%
+%% The Gregorian days of the iso week 01 day 1 for a given year.
+%%
+-spec gregorian_days_of_iso_w01_1(year()) -> non_neg_integer().
+gregorian_days_of_iso_w01_1(Year) ->
+ D0101 = date_to_gregorian_days(Year, 1, 1),
+ DOW = day_of_the_week(Year, 1, 1),
+ if DOW =< 4 ->
+ D0101 - DOW + 1;
+ true ->
+ D0101 + 7 - DOW + 1
+ end.
+
%% year_day_to_date(Year, DayOfYear) = {Month, DayOfMonth}
%%
%% Note: 1 is the first day of the month.