require 'facter'

module Facter::Core::Logging

  extend self

  # @api private
  GREEN = ""
  # @api private
  RESET = ""

  # @api private
  @@debug = false
  # @api private
  @@timing = false
  # @api private
  @@trace = false

  # @api private
  @@warn_messages = {}
  # @api private
  @@debug_messages = {}

  # @api private
  @@message_callback = nil

  # Used to register a callback that is called when a message is logged.
  # If a block is given, Facter will not log messages.
  # If a block is not given, Facter will resume logging messages.
  # @param block [Proc] the callback to call when a message is logged.
  #   The first argument to the callback will be a symbol representing a level. The supported
  #   levels are: :trace, :debug, :info, :warn, :error, and :fatal.
  #   The second argument to the callback will be a string containing the message
  #   that was logged.
  # @api public
  def on_message(&block)
    @@message_callback = block
  end

  # Prints a debug message if debugging is turned on
  #
  # @param msg [String] the debug message
  # @return [void]
  def debug(msg)
    if self.debugging?
      if msg.nil? or msg.empty?
        invoker = caller[0].slice(/.*:\d+/)
        self.warn "#{self.class}#debug invoked with invalid message #{msg.inspect}:#{msg.class} at #{invoker}"
      elsif @@message_callback
        @@message_callback.call(:debug, msg)
      else
        puts GREEN + msg + RESET
      end
    end
  end

  # Prints a debug message only once.
  #
  # @note Uniqueness is based on the string, not the specific location
  #   of the method call.
  #
  # @param msg [String] the debug message
  # @return [void]
  def debugonce(msg)
    if msg and not msg.empty? and @@debug_messages[msg].nil?
      @@debug_messages[msg] = true
      debug(msg)
    end
  end

  # Prints a warning message. The message is only printed if debugging
  # is enabled.
  #
  # @param msg [String] the warning message to be printed
  #
  # @return [void]
  def warn(msg)
    if msg.nil? or msg.empty?
      invoker = caller[0].slice(/.*:\d+/)
      msg = "#{self.class}#debug invoked with invalid message #{msg.inspect}:#{msg.class} at #{invoker}"
    end
    if @@message_callback
      @@message_callback.call(:warn, msg)
    else
      Kernel.warn msg
    end
  end

  # Prints a warning message only once per process. Each unique string
  # is printed once.
  #
  # @note Unlike {warn} the message will be printed even if debugging is
  #   not turned on. This behavior is likely to change and should not be
  #   relied on.
  #
  # @param msg [String] the warning message to be printed
  #
  # @return [void]
  def warnonce(msg)
    if @@warn_messages[msg].nil?
      self.warn(msg)
      @@warn_messages[msg] = true
    end
  end

  def log_exception(exception, message = :default)
    self.warn(format_exception(exception, message, @@trace))
  end

  def format_exception(exception, message, trace)
    arr = []

    if message == :default
      arr << exception.message
    elsif message
      arr << message
    end

    if trace
      arr.concat(exception.backtrace)
    end

    arr.flatten.join("\n")
  end

  # Print an exception message, and optionally a backtrace if trace is set

  # Print timing information
  #
  # @param string [String] the time to print
  # @return [void]
  #
  # @api private
  def show_time(string)
    return unless string && self.timing?

    if @@message_callback
      @@message_callback.call(:info, string)
    else
      $stderr.puts "#{GREEN}#{string}#{RESET}"
    end
  end

  # Enable or disable logging of debug messages
  #
  # @param bool [true, false]
  # @return [void]
  #
  # @api private
  def debugging(bool)
    @@debug = bool
  end

  # Is debugging enabled?
  #
  # @return [true, false]
  #
  # @api private
  def debugging?
    @@debug
  end

  # Enable or disable logging of timing information
  #
  # @param bool [true, false]
  # @return [void]
  #
  # @api private
  def timing(bool)
    @@timing = bool
  end

  # Returns whether timing output is turned on
  #
  # @api private
  def timing?
    @@timing
  end

  def trace(bool)
    @@trace = bool
  end

  def trace?
    @@trace
  end

  # Clears the seen state of debug and warning messages. See {debugonce} and {warnonce}.
  #
  # @return [void]
  #
  # @api private
  def clear_messages
    @@debug_messages.clear
    @@warn_messages.clear
  end
end