time ambiguity

gistfile1.txt

# frozen_string_literal: true

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", "5.1.4"
  gem "activerecord", "5.1.4"
  gem "sqlite3"
end

require "active_support/railtie"
require "action_controller/railtie"
require "active_record"

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :events, force: true do |t|
    t.timestamp :start_datetime
  end
end

class Event < ActiveRecord::Base
end

class TestApp < Rails::Application
  config.root = __dir__
  secrets.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger
  config.time_zone = "Europe/London"

  routes.draw do
    put "/events/:id" => "events#update"
  end
end

class EventsController < ActionController::Base
  include Rails.application.routes.url_helpers

  def update
    @event = Event.find(params[:id])
    if @event.update(params.require(:event).permit(:start_datetime))
      render plain: "Event was successfully updated."
    else
      render plain: "Event was failed to update."
    end
    
  end

end

require "minitest/autorun"
require "rack/test"

Time.zone_default = Time.find_zone!("Europe/London")
ActiveRecord::Base.time_zone_aware_attributes = true

class BugTest < Minitest::Test
  include Rack::Test::Methods


  def test_update_at_ambiguous_time
    # this date is 2017/10/29 1:00 Europe/London
    # however, 2017/10/29 1:00 Europe/London happens at two times
    #  2017/10/29 1:00 UTC
    #  2017/10/29 0:00 UTC
    #  When rails converts back from local->UTC it always chooses
    #  the first one
    time = ActiveSupport::TimeZone["UTC"].parse("2017/10/29 1:00")
    event = Event.new(start_datetime: time)
    event.save(validate: false)
    event.reload


    year = event.start_datetime.year
    assert_equal(2017, year)
    month = event.start_datetime.month
    assert_equal(10, month)
    day = event.start_datetime.day
    assert_equal(29, day)
    hour = event.start_datetime.hour
    assert_equal(1, hour)
    minute = event.start_datetime.min
    assert_equal(0, minute)

    put "/events/#{event.id}",
      "event"=>{"start_datetime(1i)"=> year.to_s, 
      "start_datetime(2i)"=> month.to_s, 
      "start_datetime(3i)"=>day.to_s, 
      "start_datetime(4i)"=>hour.to_s, 
      "start_datetime(5i)"=>minute.to_s}
      
    assert last_response.ok?

    event.reload

    assert_equal(time, event.start_datetime)

  end

  def test_update_in_ambiguous_time_zone
    time = ActiveSupport::TimeZone["UTC"].parse("2017/10/29 3:00")
    event = Event.new(start_datetime: time)
    event.save(validate: false)

    year = event.start_datetime.year
    assert_equal(2017, year)
    month = event.start_datetime.month
    assert_equal(10, month)
    day = event.start_datetime.day
    assert_equal(29, day)
    hour = event.start_datetime.hour
    assert_equal(3, hour)
    minute = event.start_datetime.min
    assert_equal(0, minute)

    put "/events/#{event.id}",
      "event"=>{"start_datetime(1i)"=> year.to_s, 
      "start_datetime(2i)"=> month.to_s, 
      "start_datetime(3i)"=>day.to_s, 
      "start_datetime(4i)"=>hour.to_s, 
      "start_datetime(5i)"=>minute.to_s}

    assert last_response.ok?

    event.reload

    assert_equal(time, event.start_datetime)

  end

  private
    def app
      Rails.application
    end
end