From 41b313d425883095fc8e41bf971452eefe87b2b7 Mon Sep 17 00:00:00 2001
From: Jesse Gumm <gumm@sigma-star.com>
Date: Sat, 5 Mar 2016 15:16:03 -0600
Subject: [PATCH] Add relative date/time parsing parser.

---
 src/qdate.erl | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 94 insertions(+), 1 deletion(-)

diff --git a/src/qdate.erl b/src/qdate.erl
index d43f637..8f9c5ea 100644
--- a/src/qdate.erl
+++ b/src/qdate.erl
@@ -61,6 +61,8 @@
     add_months/1,
     add_years/2,
     add_years/1,
+    add_unit/2,
+    add_unit/3,
     add_date/2
 ]).
 
@@ -94,6 +96,9 @@
     clear_timezone/1
 ]).
 
+-export([
+    parse_relative/1
+]).
 
 %% Exported for API compatibility with ec_date
 -export([
@@ -309,7 +314,8 @@ to_unixtime(Date) ->
 
 to_unixtime(_, Unixtime) when is_integer(Unixtime) ->
     Unixtime;
-to_unixtime(_, {MegaSecs,Secs,_}) ->
+
+to_unixtime(_, {MegaSecs,Secs,_}) when is_integer(MegaSecs), is_integer(Secs) ->
     MegaSecs*1000000 + Secs;
 to_unixtime(Disamb, ToParse) ->
     %% We want to treat all unixtimes as GMT
@@ -483,6 +489,39 @@ add_years(Years, Date) ->
 add_years(Years) ->
     add_years(Years, os:timestamp()).
 
+add_unit(second, Value, Date) ->
+    add_unit(seconds, Value, Date);
+add_unit(seconds, Value, Date) ->
+    add_seconds(Value, Date);
+add_unit(minute, Value, Date) ->
+    add_unit(minutes, Value, Date);
+add_unit(minutes, Value, Date) ->
+    add_minutes(Value, Date);
+add_unit(hour, Value, Date) ->
+    add_unit(hours, Value, Date);
+add_unit(hours, Value, Date) ->
+    add_hours(Value, Date);
+add_unit(day, Value, Date) ->
+    add_unit(days, Value, Date);
+add_unit(days, Value, Date) ->
+    add_days(Value, Date);
+add_unit(week, Value, Date) ->
+    add_unit(weeks, Value, Date);
+add_unit(weeks, Value, Date) ->
+    add_weeks(Value, Date);
+add_unit(month, Value, Date) ->
+    add_unit(months, Value, Date);
+add_unit(months, Value, Date) ->
+    add_months(Value, Date);
+add_unit(year, Value, Date) ->
+    add_unit(years, Value, Date);
+add_unit(years, Value, Date) ->
+    add_years(Value, Date).
+
+add_unit(Unit, Value) ->
+    add_unit(Unit, Value, os:timestamp()).
+
+
 add_date({{AddY, AddM, AddD}, {AddH, AddI, AddS}}, Date) ->
     {{Y, M, D}, {H, I, S}} = to_date(Date),
     Date1 = fix_maybe_improper_date({{Y+AddY, M+AddM, D+AddD}, {H, I, S}}),
@@ -610,6 +649,58 @@ range_years(Interval, Start, Finish) ->
     range(years, Interval, Start, Finish).
 
 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%  Relative Date Parsing  %%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+parse_relative({relative, Date, Relation}) when is_atom(Relation) ->
+    parse_relative({relative, Date, atom_to_list(Relation)});
+parse_relative({relative, Date, Relation})  ->
+    {OpStr, NumStr, UnitStr} = parse_actual_relation(Relation), 
+    {Num, Unit} = normalize_relative_matches(OpStr, NumStr, UnitStr),
+    add_unit(Unit, Num, Date);
+parse_relative(now) ->
+    unixtime();
+parse_relative("now") ->
+    unixtime();
+parse_relative(<<"now">>) ->
+    unixtime();
+parse_relative(Relation) ->
+    parse_relative({relative, unixtime(), Relation}).
+
+
+%% I would do this function recursively, but the return order of arguments
+%% inconsistent, so I just leave it like this. It's a little nasty to have the
+%% nested case expressions, but I can deal with it.
+parse_actual_relation(Relation) ->
+    PrefixRE = "^(\\-|\\+|in)\\s?(\\d+) (second|minute|hour|day|week|month|year)s?$",
+    SuffixRE = "^(\\d+) (second|minute|hour|day|week|month|year)s\\s?(ago|from now)?$",
+    case re:run(Relation, PrefixRE, [{capture, all_but_first, list}]) of
+        nomatch ->
+            case re:run(Relation, SuffixRE, [{capture, all_but_first, list}]) of
+                nomatch -> undefined;
+                {match, [NumStr, UnitStr, OpStr]} ->
+                    {OpStr, NumStr, UnitStr}
+            end;
+        {match, [OpStr, NumStr, UnitStr]} ->
+            {OpStr, NumStr, UnitStr}
+    end.
+
+normalize_relative_matches(OpStr, NumStr, UnitStr) ->
+    Op = normalize_relative_op(OpStr),
+    Num = list_to_integer(Op ++ NumStr),
+    Unit = list_to_existing_atom(UnitStr),
+    {Num, Unit}.
+
+normalize_relative_op(Op) ->
+    case Op of
+        "+"         -> "+";
+        "-"         -> "-";
+        "ago"       -> "-";
+        "from now"  -> "+";
+        "in"        -> "+"
+    end.
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%   Timezone Stuff   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -637,6 +728,8 @@ extract_timezone(DateString) when is_list(DateString) ->
     end;
 extract_timezone(Date={{_,_,_},{_,_,_}}) ->
     {Date, ?DETERMINE_TZ};
+extract_timezone(Rel={relative, _, _}) ->
+    {Rel, "GMT"};
 extract_timezone(Now={_,_,_}) ->
     {Now, "GMT"};
 extract_timezone({MiscDate,TZ}) ->