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Fix add_month(-12, January). Add more tests. Fixes #35

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This commit is contained in:
Jesse Gumm 2018-01-06 12:03:26 -06:00
parent 4c91fc4c01
commit 99e55979dc
1 changed files with 35 additions and 5 deletions
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40
src/qdate.erl
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@ -131,6 +131,10 @@
parse/1
]).
-export([
fix_year_month/1
]).
%% This the value in gregorian seconds for jan 1st 1970, 12am
%% It's used to convert to and from unixtime, since unixtime starts
%% 1970-01-01 12:00am
@ -621,6 +625,7 @@ add_weeks(Weeks) ->
add_months(Months, Date) ->
{{Y,M,D}, Time} = to_date(Date),
io:format("~p,~p~n",[Y, M+Months]),
{TargetYear, TargetMonth} = fix_year_month({Y,M+Months}),
DaysInMonth = calendar:last_day_of_the_month(TargetYear, TargetMonth),
NewD = lists:min([DaysInMonth, D]),
@ -692,15 +697,22 @@ fix_maybe_improper_date({Date0, Time}) ->
Date = fmid(Date0),
{Date, Time}.
fix_year_month({Y, M}) when M > 12, M rem 12==0 ->
YearsOver = (M div 12) - 1,
{Y + YearsOver, 12};
%% Originally, this function didn't recurse. Here's the story. Some numbers,
%% like M = 12 (December) or M = -11 (January) would trigger an overflow or
%% underflow, resulting in fix_year_month returning something nonsensical like
%% {2018, 13}. I added some extra clauses to special treat those "overflow but
%% shouldn't" situations, but realized it was just cleaner to recurse, calling
%% fix_year_month on the calculated result, knowing that the numbers will
%% normalize on their own. So for all the clauses of fix_year_month, we recurse
%% as a sanity check, eventually only returning the result of the "Everything
%% Looks good" clause at the bottom.
fix_year_month({Y, M}) when M > 12 ->
YearsOver = M div 12,
{Y + YearsOver, M-(YearsOver*12)};
fix_year_month({Y + YearsOver, M-(YearsOver*12)});
fix_year_month({Y, M}) when M < 1 ->
YearsUnder = (abs(M-1) div 12) + 1,
{Y - YearsUnder, M+(YearsUnder*12)};
fix_year_month({Y - YearsUnder, M+(YearsUnder*12)});
fix_year_month({Y, M}) ->
{Y, M}.
@ -1277,6 +1289,24 @@ arith_tests(_) ->
?_assertEqual({{2015,1,31},{23,59,59}}, to_date(add_months(1, {{2014,12,31},{23,59,59}}))),
?_assertEqual({{2015,2,28},{0,0,0}}, to_date(add_months(2, {{2014,12,31},{0,0,0}}))),
?_assertEqual({{2016,2,28},{0,0,0}}, to_date(add_years(1, {{2015,2,28},{0,0,0}}))),
?_assertEqual({{2017,2,1},{0,0,0}}, to_date(add_months(-11, {{2018,1,1},{0,0,0}}))),
?_assertEqual({{2017,1,1},{0,0,0}}, to_date(add_months(-12, {{2018,1,1},{0,0,0}}))),
?_assertEqual({{2016,12,1},{0,0,0}}, to_date(add_months(-13, {{2018,1,1},{0,0,0}}))),
?_assertEqual({{2018,12,1},{0,0,0}}, to_date(add_months(11, {{2018,1,1},{0,0,0}}))),
?_assertEqual({{2019,1,1},{0,0,0}}, to_date(add_months(12, {{2018,1,1},{0,0,0}}))),
?_assertEqual({{2019,2,1},{0,0,0}}, to_date(add_months(13, {{2018,1,1},{0,0,0}}))),
?_assertEqual({{2018,1,1},{0,0,0}}, to_date(add_months(-11, {{2018,12,1},{0,0,0}}))),
?_assertEqual({{2017,12,1},{0,0,0}}, to_date(add_months(-12, {{2018,12,1},{0,0,0}}))),
?_assertEqual({{2017,11,1},{0,0,0}}, to_date(add_months(-13, {{2018,12,1},{0,0,0}}))),
?_assertEqual({{2019,11,1},{0,0,0}}, to_date(add_months(11, {{2018,12,1},{0,0,0}}))),
?_assertEqual({{2019,12,1},{0,0,0}}, to_date(add_months(12, {{2018,12,1},{0,0,0}}))),
?_assertEqual({{2020,1,1},{0,0,0}}, to_date(add_months(13, {{2018,12,1},{0,0,0}}))),
?_assertEqual({{2014,2,28},{0,0,0}}, to_date(add_months(-24, {{2016,2,29},{0,0,0}}))),
?_assertEqual({{2018,12,15},{0,0,0}}, to_date(add_months(24, {{2016,12,15},{0,0,0}}))),
?_assertEqual({{2012,2,29},{0,0,0}}, to_date(add_months(-48, {{2016,2,29},{0,0,0}}))),