Add Sequel.tzinfo_disambiguator= to the named_timezones plugin for au…

…tomatically handling TZInfo::AmbiguousTime exceptions (Fixes #616)

CHANGELOG

@@ -1,5 +1,7 @@
 === HEAD
 
+* Add Sequel.tzinfo_disambiguator= to the named_timezones plugin for automatically handling TZInfo::AmbiguousTime exceptions (jeremyevans) (#616)
+
 * Add Dataset#escape_like, for escaping LIKE metacharacters (jeremyevans) (#614)
 
 * The LIKE operators now use an explicit ESCAPE '\' clause for similar behavior across databases (jeremyevans)

lib/sequel/extensions/named_timezones.rb

@@ -37,14 +37,21 @@ module Sequel
   self.datetime_class = DateTime
 
   module NamedTimezones
+    # Handles TZInfo::AmbiguousTime exceptions automatically by providing a
+    # proc called with both the datetime value being converted as well as
+    # the array of TZInfo::TimezonePeriod results. Example:
+    #
+    #   Sequel.tzinfo_disambiguator = proc{|datetime, periods| periods.first}
+    attr_accessor :tzinfo_disambiguator
+
     private 
 
     # Assume the given DateTime has a correct time but a wrong timezone.  It is
     # currently in UTC timezone, but it should be converted to the input_timzone.
     # Keep the time the same but convert the timezone to the input_timezone.
     # Expects the input_timezone to be a TZInfo::Timezone instance.
     def convert_input_datetime_other(v, input_timezone)
-      local_offset = input_timezone.period_for_local(v).utc_total_offset_rational
+      local_offset = input_timezone.period_for_local(v, &tzinfo_disambiguator_for(v)).utc_total_offset_rational
       (v - local_offset).new_offset(local_offset)
     end
 
@@ -54,7 +61,7 @@ def convert_output_datetime_other(v, output_timezone)
       # TZInfo converts times, but expects the given DateTime to have an offset
       # of 0 and always leaves the timezone offset as 0
       v = output_timezone.utc_to_local(v.new_offset(0))
-      local_offset = output_timezone.period_for_local(v).utc_total_offset_rational
+      local_offset = output_timezone.period_for_local(v, &tzinfo_disambiguator_for(v)).utc_total_offset_rational
       # Convert timezone offset from UTC to the offset for the output_timezone
       (v - local_offset).new_offset(local_offset)
     end
@@ -63,6 +70,15 @@ def convert_output_datetime_other(v, output_timezone)
     def convert_timezone_setter_arg(tz)
       tz.is_a?(String) ? TZInfo::Timezone.get(tz) : super
     end
+
+    # Return a disambiguation proc that provides both the datetime value
+    # and the periods, in order to allow the choice of period to depend
+    # on the datetime value.
+    def tzinfo_disambiguator_for(v)
+      if pr = @tzinfo_disambiguator
+        proc{|periods| pr.call(v, periods)}
+      end
+    end
   end
 
   extend NamedTimezones

spec/extensions/named_timezones_spec.rb

@@ -19,6 +19,7 @@
     Sequel.datetime_class = DateTime
   end
   after do
+    Sequel.tzinfo_disambiguator = nil
     Sequel.default_timezone = nil
     Sequel.datetime_class = Time
   end
@@ -53,6 +54,15 @@ def ds.supports_timestamp_usecs?; false; end
     dt.offset.should == -7/24.0
   end
 
+  it "should raise an error for ambiguous timezones by default" do
+    proc{Sequel.database_to_application_timestamp('2004-10-31T01:30:00')}.should raise_error(Sequel::InvalidValue)
+  end
+
+  it "should support tzinfo_disambiguator= to handle ambiguous timezones automatically" do
+    Sequel.tzinfo_disambiguator = proc{|datetime, periods| periods.first}
+    Sequel.database_to_application_timestamp('2004-10-31T01:30:00').should == DateTime.parse('2004-10-30T22:30:00-07:00')
+  end
+
   it "should assume datetimes coming out of the database that don't have an offset as coming from database_timezone" do
     dt = Sequel.database_to_application_timestamp('2009-06-01 06:20:30')
     dt.should == @dt