module Vedeu

  # Allows the creation of a lock-less log device.
  #
  # @api private
  class MonoLogger < Logger

    # Create a trappable Logger instance.
    #
    # @param logdev [String|IO] The filename (String) or IO object (typically
    #   STDOUT, STDERR or an open file).
    #
    def initialize(logdev)
      @level             = DEBUG
      @default_formatter = Formatter.new
      @formatter         = nil
      @logdev            = nil
      @logdev            = LocklessLogDevice.new(logdev) if logdev
    end

    # Ensures we can always write to the log file by creating a lock-less
    # log device.
    #
    class LocklessLogDevice < LogDevice

      # Returns a new instance of Vedeu::LocklessLogDevice.
      #
      # @param log []
      # @return []
      def initialize(log = nil)
        @dev      = nil
        @filename = nil

        if log.respond_to?(:write) && log.respond_to?(:close)
          @dev = log

        else
          @dev      = open_logfile(log)
          @dev.sync = true
          @filename = log

        end
      end

      # @param message []
      # @return []
      def write(message)
        @dev.write(message)

      rescue StandardError => exception
        warn("log writing failed. #{exception}")
      end

      # @return []
      def close
        @dev.close rescue nil
      end

      private

      # @param filename []
      # @return []
      def open_logfile(filename)
        if FileTest.exist?(filename)
          open(filename, (File::WRONLY | File::APPEND))

        else
          logdev = open(filename, (File::WRONLY | File::APPEND | File::CREAT))
          logdev.sync = true
          logdev

        end
      end

    end # LocklessLogDevice

  end # MonoLogger

  # Provides the ability to log anything to the Vedeu log file.
  #
  # @api public
  class Log

    class << self

      # Write a message to the Vedeu log file.
      #
      # @example
      #   Vedeu.log(type: :debug, message: 'A useful debugging message: Error!')
      #
      # @param message [String] The message you wish to emit to the log file,
      #   useful for debugging.
      # @param force [Boolean] When evaluates to true will attempt to write to
      #   the log file regardless of the Configuration setting.
      # @param type [Symbol] Colour code messages in the log file depending
      #   on their source. See {message_types}
      #
      # @return [TrueClass]
      def log(message:, force: false, type: :info)
        output = [message_type(type), message_body(type, message)]

        logger.debug(output) if enabled? || force

        output
      end

      # Write a message to STDOUT.
      #
      # @return [TrueClass]
      def log_stdout(type: :info, message:)
        $stdout.puts [message_type(type), message_body(type, message)].join
      end

      # Write a message to STDERR.
      #
      # @return [TrueClass]
      def log_stderr(type: :info, message:)
        $stderr.puts [message_type(type), message_body(type, message)].join
      end

      private

      # @return [TrueClass]
      def logger
        MonoLogger.new(log_file).tap do |log|
          log.formatter = proc do |_, _, _, message|
            formatted_message(message)
          end
        end
      end

      # Returns the message with timestamp.
      #
      #    [ 0.0987] [debug]  Something happened.
      #
      # @param message [String] The message type and message coloured and
      #   combined.
      # @return [String]
      def formatted_message(message)
        [timestamp, message, "\n"].join
      end

      # Fetches the filename from the configuration.
      #
      # @return [String]
      def log_file
        Vedeu::Configuration.log
      end
      alias_method :enabled?, :log_file

      # Displays the message body using the colour specified in the last element
      # of {message_types}.
      #
      # @param type [Symbol] The type of log message.
      # @param body [String] The log message itself.
      # @return [String]
      def message_body(type, body)
        Vedeu::Esc.send(message_types.fetch(type, :default).last) do
          body
        end
      end

      # Displays the message type using the colour specified in the first
      # element of {message_types}.
      #
      # @param type [Symbol] The type of log message.
      # @return [String]
      def message_type(type)
        Vedeu::Esc.send(message_types.fetch(type, :default).first) do
          "[#{type}]".ljust(9)
        end
      end

      # The defined message types for Vedeu with their respective colours.
      # When used, produces a log entry of the format:
      #
      #     [type] message
      #
      # The 'type' will be shown as the first colour defined in the value
      # array, whilst the 'message' will be shown using the last colour.
      # Valid types are available by viewing the source for this method.
      #
      # @return [Hash<Symbol => Array<Symbol>>]
      def message_types
        {
          config: [:light_yellow,  :yellow],
          create: [:light_green,   :green],
          debug:  [:light_red,     :red],
          drb:    [:light_blue,    :blue],
          event:  [:light_magenta, :magenta],
          info:   [:white,         :default],
          input:  [:light_yellow,  :yellow],
          output: [:light_green,   :green],
          reset:  [:light_cyan,    :cyan],
          store:  [:light_cyan,    :cyan],
          test:   [:light_white,   :white],
          timer:  [:light_yellow,  :yellow],
          update: [:light_cyan,    :cyan],
        }
      end

      # Returns a formatted timestamp.
      # eg. [137.7824]
      #
      # @return [String]
      def timestamp
        @now  = Time.now.to_f
        @time = 0.0  unless @time
        @last = @now unless @last

        unless @last == @time
          @time += (@now - @last).round(4)
          @last = @now
        end

        "[#{format('%7.4f', @time.to_s)}] ".rjust(7)
      end

    end # Eigenclass

  end # Log

end # Vedeu