cedar/lib/transports/base.js

User-friendly logger.

var doNothing = function () {}


/**
 * The `Base` log defines methods that transports will share.
 */
var Base = module.exports = function (config, defaults) {

  var cedar = require('../../cedar')

  // A log is a shorthand for `log.log`, among other things.
  var log = function () {
    log.log.apply(log, arguments)
  }

  // Don't run `setMethods` until all config properties are set.
  var setMethods = doNothing

  // Define properties that trigger `setMethods`.
  Base.resetters.forEach(function (property) {
    var value
    Object.defineProperty(log, property, {
      get: function () {
        return value
      },
      set: function (newValue) {
        value = newValue
        setMethods.apply(log)
      }
    })
  })

  // Copy `config` properties to the `log`.
  Base.decorate(log, config, true)

  // Apply default properties.
  Base.decorate(log, defaults || Base.defaults)

  // Set up logging methods.
  Base.setMethods.apply(log)

  // Re-run `setMethods` if `resetters` change.
  setMethods = Base.setMethods

  // Return the fully-decorated log function.
  return log

}


/**
 * Some properties will reset methods if changed.
 */
Base.resetters = ['level', 'prefixes', 'format', 'showTrace']

/**
 * Cedar supports 7 levels of logging.
 */
Base.levels = ['trace', 'debug', 'log', 'info', 'warn', 'error', 'fatal']

/**
 * Share defaults between log objects.
 */
Base.defaults = {

  // Show all log messages by default.
  level: 'trace',

  // Stream to `stdout` (using `write`).
  stream: process.stdout,

  // Don't add any space to JSON.
  space: '',

  // Stringify with `JSON.stringify`.
  stringify: JSON.stringify,

  // Join arguments together as an array.
  join: function (args) {
    var list = []
    for (var index = 0, length = args.length; index < length; index++) {
      var arg = args[index]
      if (arg instanceof Error) {
        arg = '"' + (arg.stack || arg.toString()).replace(/\n/, '\\n') + '"'
      } else {
        arg = JSON.stringify(arg, null, this.space)
      }
      list.push(arg)
    }
    return '[' + list.join(',') + ']'
  },

  // Start messages with a prefix for each log method.
  prefixes: {
    trace: 'TRACE ',
    debug: 'DEBUG ',
    log: 'LOG ',
    info: 'INFO ',
    warn: 'WARN ',
    error: 'ERROR ',
    fatal: 'FATAL '
  },

  // Format a log message.
  format: function (message, type, prefix) {
    return prefix + message + '\n'
  }

}


/**
 * Decorate an object with the properties of another.
 */
Base.decorate = function (object, defaults, shouldOverwrite) {
  object = object || {}
  for (var key in defaults) {
    if (shouldOverwrite || (typeof object[key] === 'undefined')) {
      object[key] = defaults[key]
    }
  }
  return object
}

/**
 * Create logging methods based on the configured `level`.
 */
Base.setMethods = function () {
  var self = this
  var found = false
  if ((Base.levels.indexOf(self.level) < 0) && self.level !== 'nothing') {
    self.error('Unknown log level: "' + self.level + '".')
  } else {
    Base.levels.forEach(function (methodName, index) {
      if (methodName === self.level) {
        found = true
      }
      var prefix = self.prefixes[methodName] || ''
      var format = self.format
      // If this log is an Emitter, we can catch and emit errors.
      if (self.emit) {
        self[methodName] = found ? function () {
          var message = self.join(arguments)
          message = format.call(self, message, methodName, prefix)
          try {
            self.stream.write(message)
          } catch (e) {
            self.emit('error', e)
          }
        } : doNothing

      // Otherwise, they'll just throw.
      } else {
        self[methodName] = found ? function () {
          var message = self.join(arguments)
          message = format.call(self, message, methodName, prefix)
          self.stream.write(message)
        } : doNothing
      }
    })
    // Wrap the trace method with a stack tracer.
    if (self.trace !== doNothing) {
      var traceMethod = self.trace
      self.trace = function () {
        var e = new Error('')
        Error.captureStackTrace(e, self.trace)
        var l = arguments.length
        arguments[l] = e.stack.split('\n').splice(2).join('\n')
        arguments.length = ++l
        traceMethod.apply(self, arguments)
      }
    }
  }
}