class Fluent::TimeParser

def initialize(format = nil, localtime = true, timezone = nil)
  if format.nil? && (timezone || !localtime)
    raise Fluent::ConfigError, "specifying timezone requires time format"
  end
  @cache1_key = nil
  @cache1_time = nil
  @cache2_key = nil
  @cache2_time = nil
  format_with_timezone = format && (format.include?("%z") || format.include?("%Z"))
  # unixtime_in_expected_tz = unixtime_in_localtime + offset_diff
  offset_diff = case
                when format_with_timezone then nil
                when timezone  then
                  offset = Fluent::Timezone.utc_offset(timezone)
                  if offset.respond_to?(:call)
                    ->(t) { Time.now.localtime.utc_offset - offset.call(t) }
                  else
                    Time.now.localtime.utc_offset - offset
                  end
                when localtime then 0
                else Time.now.localtime.utc_offset # utc
                end
  strptime = format && (Strptime.new(format) rescue nil)
  @parse = case
           when format_with_timezone && strptime then ->(v){ Fluent::EventTime.from_time(strptime.exec(v)) }
           when format_with_timezone             then ->(v){ Fluent::EventTime.from_time(Time.strptime(v, format)) }
           when format == '%iso8601'             then ->(v){ Fluent::EventTime.from_time(Time.iso8601(v)) }
           when strptime then
             if offset_diff.respond_to?(:call)
               ->(v) { t = strptime.exec(v); Fluent::EventTime.new(t.to_i + offset_diff.call(t), t.nsec) }
             else
               ->(v) { t = strptime.exec(v); Fluent::EventTime.new(t.to_i + offset_diff, t.nsec) }
             end
           when format   then
             if offset_diff.respond_to?(:call)
               ->(v){ t = Time.strptime(v, format); Fluent::EventTime.new(t.to_i + offset_diff.call(t), t.nsec) }
             else
               ->(v){ t = Time.strptime(v, format); Fluent::EventTime.new(t.to_i + offset_diff, t.nsec) }
             end
           else ->(v){ Fluent::EventTime.parse(v) }
           end
end

def parse(value)
  unless value.is_a?(String)
    raise TimeParseError, "value must be string: #{value}"
  end
  if @cache1_key == value
    return @cache1_time
  elsif @cache2_key == value
    return @cache2_time
  else
    begin
      time = @parse.call(value)
    rescue => e
      raise TimeParseError, "invalid time format: value = #{value}, error_class = #{e.class.name}, error = #{e.message}"
    end
    @cache1_key = @cache2_key
    @cache1_time = @cache2_time
    @cache2_key = value
    @cache2_time = time
    return time
  end
end