fiedl/your_platform

# This is a parser that converts a localized datetime String
# into a Time.
#
# Use like this:
#
#     LocalizedDateTimeParser.parse("Montag, 25. April 2015, 14:36 Uhr", Time)
#     # => Sat, 25 Apr 2015 14:36:00 UTC +00:00
#
# This file is extracted from:
# https://github.com/clemens/delocalize/blob/master/lib/delocalize/localized_date_time_parser.rb
#
class LocalizedDateTimeParser
  # extend/change this according to your needs by merging your custom regexps
  REGEXPS = {
    '%B' => "(#{Date::MONTHNAMES.compact.join('|')})",      # long month name
    '%b' => "(#{Date::ABBR_MONTHNAMES.compact.join('|')})", # short month name
    '%m' => "(\\d{2})",                                     # numeric month
    '%A' => "(#{Date::DAYNAMES.join('|')})",                # full day name
    '%a' => "(#{Date::ABBR_DAYNAMES.join('|')})",           # short day name
    '%Y' => "(\\d{4})",                                     # long year
    '%y' => "(\\d{2})",                                     # short year
    '%e' => "(\\s\\d|\\d{2})",                              # short day
    '%d' => "(\\d{2})",                                     # full day
    '%H' => "(\\d{2})",                                     # hour (24)
    '%M' => "(\\d{2})",                                     # minute
    '%S' => "(\\d{2})"                                      # second
  }

  class << self
    def parse(datetime, type)
      return unless datetime
      return datetime if datetime.respond_to?(:strftime) # already a Date/Time object -> no need to parse it

      translate_month_and_day_names(datetime)
      input_formats(type).each do |original_format|
        next unless datetime =~ /^#{apply_regex(original_format)}$/

        datetime = DateTime.strptime(datetime, original_format)
        return Date == type ?
          datetime.to_date :
          Time.zone.local(datetime.year, datetime.mon, datetime.mday, datetime.hour, datetime.min, datetime.sec)
      end
      default_parse(datetime, type)
    end

    private
    def default_parse(datetime, type)
      return if datetime.blank?
      begin
        today = Date.current
        parsed = Date._parse(datetime)
        return if parsed.empty? # the datetime value is invalid
        # set default year, month and day if not found
        parsed.reverse_merge!(:year => today.year, :mon => today.mon, :mday => today.mday)
        datetime = Time.zone.local(*parsed.values_at(:year, :mon, :mday, :hour, :min, :sec))
        Date == type ? datetime.to_date : datetime
      rescue
        datetime
      end
    end

    def translate_month_and_day_names(datetime)
      # Note: This should be a bulk lookup but due to a bug in i18n it doesn't work properly with fallbacks.
      # See https://github.com/svenfuchs/i18n/issues/104.
      # TODO Make it a bulk lookup again at some point in the future when the bug is fixed in i18n.
      translated = [:month_names, :abbr_month_names, :day_names, :abbr_day_names].map do |key|
        I18n.t(key, :scope => :date)
      end.flatten.compact

      original = (Date::MONTHNAMES + Date::ABBR_MONTHNAMES + Date::DAYNAMES + Date::ABBR_DAYNAMES).compact
      translated.each_with_index { |name, i| datetime.gsub!(/\b#{name}\b/, original[i]) }
    end

    def input_formats(type)
      # Date uses date formats, all others use time formats
      type = type == Date ? :date : :time
      I18n.t(:"#{type}.formats").slice(*I18n.t(:"#{type}.input.formats")).values
    end

    def apply_regex(format)
      format.gsub(/(#{REGEXPS.keys.join('|')})/) { |s| REGEXPS[$1] }
    end
  end
end