Add deterministic_parsing env_var
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Jesse Gumm
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2 changed files with 128 additions and 6 deletions
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@ -144,6 +144,90 @@ be attempted before engaging the `ec_date` parser.
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+ `deregister_format(Key)` - Deregister the formatting string from the
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`qdate` server.
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## About backwards compatibility with `ec_date` and deterministic parsing
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`ec_date` and `dh_date` both have a quirk that bothers me with respect to the
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parsing of dates that causes some date parsing to be *non-deterministic*. That
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is, if parsing an incomplete date or time (ie, a text string that is missing a
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time or a date), `ec_date` will automatically insert the current values of
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those.
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For example, if the following lines are run a few seconds apart:
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```erlang
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1> ec_date:parse("2012-02-04").
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{{2012,2,4},{0,1,10}}
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2> ec_date:parse("2012-02-04").
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{{2012,2,4},{0,1,12}}
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3> ec_date:parse("2012-02-04").
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{{2012,2,4},{0,1,13}}
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```
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As you can see, even though the inputs are the same each time, the resulting
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parsed dates have the current time inferred. The same behavior can be observed
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if parsing a time without a date:
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```erlang
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4> ec_date:parse("7pm").
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{{2013,4,30},{19,0,0}}
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```
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As you can see, even though the time did not specify a date, the resulting
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parsed datetime has the date inferred from the current date. Admittedly,
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inferring the date bothers me less than inferring the time, but in the name of
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consistency, there should be options for enabling or disabling both.
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### The Solution For Both
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To solve this issue for users that are bothered by this, while preserving
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backwards compatibility for folks who prefer this, we're going to introduce a
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`qdate` application environment variable called `deterministic_parsing`.
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The value of `deterministic_parsing` can be a tuple of the following format:
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`{DatePref, TimePref}`
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Where `DatePref` and `TimePref` are either of the following atoms:
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+ `now` - Automatically fill in the missing date or time components with the
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current time (the is the behavior described above)
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+ `zero` - Fill in the missing date or time components with zeroed out
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values. This means that if a date is missing, it'll be set to the unix
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epoch (`{1970,1,1}`) and if a time is missing, it'll be set to midnight:
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`{0,0,0}`.
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So, the acceptable combinations can be the following:
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+ `{zero, zero}` - Any missing components will be replaced with zero-values.
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**(This is the qdate default behavior)**
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+ `{now, zero}` - If a date is missing, insert the current date, but if a
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time is missing, set it to midnight.
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+ `{zero, now}` - If a date is missing, set it to the unix epoch, and if a
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time is missing, set it to the current time of day.
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+ `{now, now}` - If either date or time are missing, set it to the current
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date or current time.
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**Note:** If this application value is not set, the default behavior for
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`qdate` is to avoid non-determinism and use `{zero, zero}`.
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To set this value, you can either set the value manually in code with:
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```erlang
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application:set_env(qdate, deterministic_parsing, {now, zero}).
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```
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or (and this is the preferred method) use a config file and load it with
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`erl -config path/to/file.config`
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Sample config file specifying this application variable:
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```erlang
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[{qdate, [
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{deterministic_parsing, {now, zero}}
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]}].
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```
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## Demonstration
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### Basic Conversion and Formatting
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@ -182,9 +182,17 @@ to_date(ToTZ, RawDate) ->
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{ParsedDate,ParsedTZ} ->
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{ParsedDate,ParsedTZ}
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end,
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Date = raw_to_date(RawDate3),
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try raw_to_date(RawDate3) of
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D={{_,_,_},{_,_,_}} ->
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date_tz_to_tz(D, FromTZ, ToTZ)
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catch
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_:_ ->
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case raw_to_date(RawDate) of
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D2={{_,_,_},{_,_,_}} ->
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date_tz_to_tz(D2, ?DETERMINE_TZ, ToTZ)
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end
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end.
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date_tz_to_tz(Date, FromTZ, ToTZ).
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extract_timezone(Unixtime) when is_integer(Unixtime) ->
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{Unixtime, "GMT"};
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@ -223,14 +231,16 @@ minutes_from_gmt_relative_timezone("-", HourStr, MinStr) ->
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extract_timezone_helper(RevDate, []) ->
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{lists:reverse(RevDate), ?DETERMINE_TZ};
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extract_timezone_helper(RevDate, [TZ | TZs]) ->
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extract_timezone_helper(RevDate, [TZ | TZs]) when length(RevDate) >= length(TZ) ->
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RevTZ = lists:reverse(TZ),
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case lists:split(length(TZ),RevDate) of
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{RevTZ," " ++ Remainder} ->
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{lists:reverse(Remainder), TZ};
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_ ->
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extract_timezone_helper(RevDate, TZs)
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end.
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end;
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extract_timezone_helper(RevDate, [_TZ | TZs]) ->
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extract_timezone_helper(RevDate, TZs).
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determine_timezone() ->
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case qdate_srv:get_timezone() of
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@ -243,12 +253,24 @@ determine_timezone() ->
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raw_to_date(Unixtime) when is_integer(Unixtime) ->
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unixtime_to_date(Unixtime);
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raw_to_date(DateString) when is_list(DateString) ->
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ec_date:parse(DateString);
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ec_date:parse(DateString, get_deterministic_datetime());
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raw_to_date(Now = {_,_,_}) ->
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calendar:now_to_datetime(Now);
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raw_to_date(Date = {{_,_,_},{_,_,_}}) ->
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Date.
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get_deterministic_datetime() ->
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DateZero = {1970,1,1},
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TimeZero = {0,0,0},
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case application:get_env(qdate, deterministic_parsing) of
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{ok, {zero, zero}} -> {DateZero, TimeZero};
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{ok, {zero, now}} -> {DateZero, time()};
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{ok, {now, zero}} -> {date(), TimeZero};
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{ok, {now, now}} -> {date(), time()};
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undefined -> {DateZero, TimeZero};
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{ok, Val} -> throw({invalid_env_var, {qdate, deterministic_parsing, Val}})
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end.
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%% If FromTZ is an integer, then it's an integer that represents the number of minutes
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%% relative to GMT. So we convert the date to GMT based on that number, then we can
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%% do the other timezone conversion.
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@ -389,11 +411,27 @@ tz_test_() ->
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simple_test(SetupData),
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tz_tests(SetupData),
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test_process_die(SetupData),
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parser_format_test(SetupData)
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parser_format_test(SetupData),
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test_deterministic_parser(SetupData)
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]}
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end
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}.
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test_deterministic_parser(_) ->
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{inorder, [
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?_assertEqual(ok, application:set_env(qdate, deterministic_parsing, {now, now})),
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?_assertEqual({date(), {7,0,0}}, qdate:to_date("7am")),
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?_assertEqual({{2012,5,10}, time()}, qdate:to_date("2012-5-10")),
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?_assertEqual(ok, application:set_env(qdate, deterministic_parsing, {zero, zero})),
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?_assertEqual({{1970,1,1}, {7,0,0}}, qdate:to_date("7am")),
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?_assertEqual({{2012,5,10}, {0,0,0}}, qdate:to_date("2012-5-10")),
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?_assertEqual(ok, application:unset_env(qdate, deterministic_parsing)),
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?_assertEqual({{1970,1,1}, {7,0,0}}, qdate:to_date("7am")),
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?_assertEqual({{2012,5,10}, {0,0,0}}, qdate:to_date("2012-5-10"))
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]}.
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tz_tests(_) ->
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{inorder,[
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?_assertEqual(ok,set_timezone(?SELF_TZ)),
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