require 'oj'
require 'date'
require 'gelf'

module Fluent
  module GelfPluginUtil

    LEVEL_MAP = {
      '0' => GELF::UNKNOWN, '1' => GELF::UNKNOWN, 'a' => GELF::UNKNOWN,
      '2' => GELF::FATAL, 'c' => GELF::FATAL,
      '3' => GELF::ERROR,
      '4' => GELF::WARN, 'w' => GELF::WARN,
      '5' => GELF::INFO, 'n' => GELF::INFO,
      '6' => GELF::INFO, 'i' => GELF::INFO,
      '7' => GELF::DEBUG, 'd' => GELF::DEBUG,
      'e' => GELF::ERROR
    }.freeze

    def get_internal_json_out(record, key)
      json_data = parse_json_field(record[key])
      return record unless json_data

      record.delete(key)
      merge_record_with_json(record, json_data)
    rescue Oj::ParseError, EncodingError
      # Return original record if JSON parsing fails
      record
    end

    def make_gelfentry(tag, time, record, conf = {})
      record = get_internal_json_out(record, "message")
      record = get_internal_json_out(record, "log")
      gelfentry = {"_fluentd_tag" => tag, "timestamp" => calculate_timestamp(time)}

      record.each do |k, v|
        process_record_entry(k, v, conf, gelfentry)
      end

      ensure_short_message(gelfentry)
      gelfentry.compact
    end

    private

    def parse_json_field(json_field)
      return nil unless json_field
      json = Oj.load(json_field.strip)
      return nil unless json.is_a?(Hash)
      json
    end

    def calculate_timestamp(time)
      if defined?(Fluent::EventTime) && time.is_a?(Fluent::EventTime)
        time.sec + (time.nsec.to_f / 1_000_000_000).round(3)
      else
        time
      end
    end

    def process_record_entry(k, v, conf, gelfentry)
      case k
      when 'host', 'hostname'
        gelfentry['host'] = conf[:use_record_host] ? v : (gelfentry['_host'] = v)
      when 'timestamp', 'time'
        gelfentry['timestamp'] = parse_timestamp(v)
      when 'level'
        gelfentry['level'] = LEVEL_MAP[v.to_s.downcase[0]] || GELF::UNKNOWN
      when 'msec'
        gelfentry['timestamp'] = conf[:add_msec_time] ? "#{time.to_s}.#{v}".to_f : (gelfentry['_msec'] = v)
      when 'short_message', 'version', 'full_message', 'facility', 'file', 'line'
        gelfentry[k] = v
      else
        gelfentry[k.start_with?('_') ? k : "_#{k}"] = v
      end
    end

    def parse_timestamp(v)
      return v if v.is_a?(Integer) || v.is_a?(Float)

      DateTime.parse(v).strftime("%Q").to_f / 1_000 rescue v
    end

    def ensure_short_message(gelfentry)
      default_key = ['_message', '_msg', '_log', '_record'].find { |key| gelfentry[key]&.strip&.empty? == false }
      gelfentry['short_message'] = default_key ? gelfentry.delete(default_key) : '(no message)'
    end
  end
end