"use strict";
var zlib = require('zlib');
var layouts = require('../layouts');
var levels = require('../levels');
var dgram = require('dgram');
var util = require('util');
var debug = require('../debug')('GELF Appender');

var LOG_EMERG=0;    // system is unusable
var LOG_ALERT=1;    // action must be taken immediately
var LOG_CRIT=2;     // critical conditions
var LOG_ERR=3;      // error conditions
var LOG_ERROR=3;    // because people WILL typo
var LOG_WARNING=4;  // warning conditions
var LOG_NOTICE=5;   // normal, but significant, condition
var LOG_INFO=6;     // informational message
var LOG_DEBUG=7;    // debug-level message

var levelMapping = {};
levelMapping[levels.ALL] = LOG_DEBUG;
levelMapping[levels.TRACE] = LOG_DEBUG;
levelMapping[levels.DEBUG] = LOG_DEBUG;
levelMapping[levels.INFO] = LOG_INFO;
levelMapping[levels.WARN] = LOG_WARNING;
levelMapping[levels.ERROR] = LOG_ERR;
levelMapping[levels.FATAL] = LOG_CRIT;

/**
 * GELF appender that supports sending UDP packets to a GELF compatible server such as Graylog
 *
 * @param layout a function that takes a logevent and returns a string (defaults to none).
 * @param host - host to which to send logs (default:localhost)
 * @param port - port at which to send logs to (default:12201)
 * @param hostname - hostname of the current host (default:os hostname)
 * @param facility - facility to log to (default:nodejs-server)
 */
function gelfAppender (layout, host, port, hostname, facility) {
  
  host = host || 'localhost';
  port = port || 12201;
  hostname = hostname || require('os').hostname();
  facility = facility || 'nodejs-server';
  layout = layout || layouts.messagePassThroughLayout;
  
  var client = dgram.createSocket("udp4");
  
  process.on('exit', function() {
    if (client) client.close();
  });

  /**
   * Add custom fields (start with underscore ) 
   * - if the first object passed to the logger contains 'GELF' field, add copy the underscore fields to the message
   * @param loggingEvent
   * @param msg
   */
  function addCustomFields(loggingEvent, msg){
      var data = loggingEvent.data;
      if (!Array.isArray(data) || data.length === 0) return;
      var firstData = data[0];
      if (!firstData['GELF']) return; // identify with GELF field defined
      var keys = Object.keys(firstData);
      for (var i in keys){
          var key = keys[i];
          // skip _id field for graylog2, skip keys not starts with UNDERSCORE
          if (!key.match(/^_/) || key === "_id") continue; 
          msg[key] = firstData[key];
      }
      loggingEvent.data.shift(); // remove the first object
      //console.log('=== msg ===');
      //console.log(msg);
  }
 
  function preparePacket(loggingEvent) {
    var msg = {};
    addCustomFields(loggingEvent, msg);
    msg.full_message = layout(loggingEvent);
    msg.short_message = msg.full_message;
    
    msg.version="1.0";
    msg.timestamp = msg.timestamp || new Date().getTime() / 1000 >> 0;
    msg.host = hostname;
    msg.level = levelMapping[loggingEvent.level || levels.DEBUG];
    msg.facility = facility;
    return msg;
  }
  
  function sendPacket(packet) {
    try {
      client.send(packet, 0, packet.length, port, host);
    } catch(e) {}
  }

  return function(loggingEvent) {
    var message = preparePacket(loggingEvent);
    zlib.gzip(new Buffer(JSON.stringify(message)), function(err, packet) {
      if (err) {
        console.error(err.stack);
      } else {
        if (packet.length > 8192) {
          debug("Message packet length (" + packet.length + ") is larger than 8k. Not sending");
        } else {
          sendPacket(packet);
        }
      }
    });
  };
}

function configure(config) {
  var layout;
  if (config.layout) {
    layout = layouts.layout(config.layout.type, config.layout);
  }
  return gelfAppender(layout, config.host, config.port, config.hostname, config.facility);
}

exports.appender = gelfAppender;
exports.configure = configure;