module Logging::Appenders

  # The Buffering module is used to implement buffering of the log messages
  # in a given appender. The size of the buffer can be specified, and the
  # buffer can be configured to auto-flush at a given threshold. The
  # threshold can be a single message or a very large number of messages.
  #
  # Log messages of a certain level can cause the buffer to be flushed
  # immediately. If an error occurs, all previous messages and the error
  # message will be written immediately to the logging destination if the
  # buffer is configured to do so.
  #
  module Buffering

    # Default buffer size
    DEFAULT_BUFFER_SIZE = 500;

    # The buffer holding the log messages
    attr_reader :buffer

    # The auto-flushing setting. When the buffer reaches this size, all
    # messages will be be flushed automatically.
    attr_reader :auto_flushing

    # When set, the buffer will be flushed at regular intervals defined by the
    # flush_period.
    attr_reader :flush_period

    # When set, the buffer will be flushed using an asynchronous Thread. That
    # is, the main program thread will not be blocked during writes.
    attr_reader :async

    # Messages will be written in chunks. This controls the number of messages
    # to pull from the buffer for each write operation. The default is to pull
    # all messages from the buffer at once.
    attr_accessor :write_size

    # Setup the message buffer and other variables for automatically and
    # periodically flushing the buffer.
    #
    def initialize( *args, &block )
      @buffer = []
      @immediate = []
      @auto_flushing = 1
      @async = false
      @flush_period = @async_flusher = nil

      super(*args, &block)
    end

    # Close the message buffer by flushing all log events to the appender. If an
    # async flusher thread is running, shut it down and allow it to exit.
    #
    def close( *args )
      flush

      if @async_flusher
        @async_flusher.stop
        @async_flusher = nil
        Thread.pass
      end

      super(*args)
    end

    # Reopen the connection to the underlying logging destination. In addition
    # if the appender is configured for asynchronous flushing, then the flushing
    # thread will be stopped and restarted.
    #
    def reopen
      _setup_async_flusher
      super
    end

    # Call `flush` to force an appender to write out any buffered log events.
    # Similar to `IO#flush`, so use in a similar fashion.
    def flush
      return self if @buffer.empty?

      ary = nil
      sync {
        ary = @buffer.dup
        @buffer.clear
      }

      if ary.length <= write_size
        str = ary.join
        canonical_write str unless str.empty?
      else
        ary.each_slice(write_size) do |a|
          str = a.join
          canonical_write str unless str.empty?
        end
      end

      self
    end

    # Clear the underlying buffer of all log events. These events will not be
    # appended to the logging destination; they will be lost.
    def clear!
      sync { @buffer.clear }
    end

    # Configure the levels that will trigger an immediate flush of the
    # logging buffer. When a log event of the given level is seen, the
    # buffer will be flushed immediately. Only the levels explicitly given
    # in this assignment will flush the buffer; if an "error" message is
    # configured to immediately flush the buffer, a "fatal" message will not
    # even though it is a higher level. Both must be explicitly passed to
    # this assignment.
    #
    # You can pass in a single level name or number, an array of level
    # names or numbers, or a string containing a comma separated list of level
    # names or numbers.
    #
    #   immediate_at = :error
    #   immediate_at = [:error, :fatal]
    #   immediate_at = "warn, error"
    #
    def immediate_at=( level )
      @immediate.clear

      # get the immediate levels -- no buffering occurs at these levels, and
      # a log message is written to the logging destination immediately
      immediate_at =
        case level
        when String; level.split(',').map {|x| x.strip}
        when Array; level
        else Array(level) end

      immediate_at.each do |lvl|
        num = ::Logging.level_num(lvl)
        next if num.nil?
        @immediate[num] = true
      end
    end

    # Configure the auto-flushing threshold. Auto-flushing is used to flush
    # the contents of the logging buffer to the logging destination
    # automatically when the buffer reaches a certain threshold.
    #
    # By default, the auto-flushing will be configured to flush after each
    # log message.
    #
    # The allowed settings are as follows:
    #
    #   N      : flush after every N messages (N is an integer)
    #   true   : flush after each log message
    #   false  OR
    #   nil    OR
    #   0      : only flush when the buffer is full (500 messages)
    #
    # If the default buffer size of 500 is too small, then you can manually
    # configure it to be as large as you want. This will consume more memory.
    #
    #   auto_flushing = 42_000
    #
    def auto_flushing=( period )
      @auto_flushing =
        case period
        when true;             1
        when false, nil, 0;    DEFAULT_BUFFER_SIZE
        when Integer;          period
        when String;           Integer(period)
        else
          raise ArgumentError,
                "unrecognized auto_flushing period: #{period.inspect}"
        end

      if @auto_flushing <= 0
        raise ArgumentError,
          "auto_flushing period must be greater than zero: #{period.inspect}"
      end

      @auto_flushing = DEFAULT_BUFFER_SIZE if @flush_period && @auto_flushing <= 1
    end

    # Configure periodic flushing of the message buffer. Periodic flushing is
    # used to flush the contents of the logging buffer at some regular
    # interval. Periodic flushing is disabled by default.
    #
    # When enabling periodic flushing the flush period should be set using one
    # of the following formats: "HH:MM:SS" or seconds as an numeric or string.
    #
    #   "01:00:00"  : every hour
    #   "00:05:00"  : every 5 minutes
    #   "00:00:30"  : every 30 seconds
    #   60          : every 60 seconds (1 minute)
    #   "120"       : every 120 seconds (2 minutes)
    #
    # For the periodic flusher to work properly, the auto-flushing threshold
    # will be set to the default value of 500. The auto-flushing threshold can
    # be changed, but it must be greater than 1.
    #
    # To disable the periodic flusher simply set the flush period to +nil+.
    # The auto-flushing threshold will not be changed; it must be disabled
    # manually if so desired.
    #
    def flush_period=( period )
      @flush_period =
        case period
        when Integer, Float, nil; period
        when String
          num = _parse_hours_minutes_seconds(period) || _parse_numeric(period)
          raise ArgumentError.new("unrecognized flush period: #{period.inspect}") if num.nil?
          num
        else
          raise ArgumentError.new("unrecognized flush period: #{period.inspect}")
        end

      if !@flush_period.nil? && @flush_period <= 0
        raise ArgumentError,
          "flush_period must be greater than zero: #{period.inspect}"
      end

      _setup_async_flusher
    end

    # Returns `true` if an asynchronous flush period has been defined for the
    # appender.
    def flush_period?
      !@flush_period.nil?
    end

    # Enable or disable asynchronous logging via a dedicated logging Thread.
    # Pass in `true` to enable and `false` to disable.
    #
    # bool - A boolean value
    #
    def async=( bool )
      @async = bool ? true : false
      _setup_async_flusher
    end

    alias_method :async?, :async

  protected

    # Configure the buffering using the arguments found in the give options
    # hash. This method must be called in order to use the message buffer.
    # The supported options are "immediate_at" and "auto_flushing". Please
    # refer to the documentation for those methods to see the allowed
    # options.
    #
    def configure_buffering( opts )
      ::Logging.init unless ::Logging.initialized?

      self.immediate_at  = opts.fetch(:immediate_at, '')
      self.auto_flushing = opts.fetch(:auto_flushing, true)
      self.flush_period  = opts.fetch(:flush_period, nil)
      self.async         = opts.fetch(:async, false)
      self.write_size    = opts.fetch(:write_size, DEFAULT_BUFFER_SIZE)
    end

    # Returns `true` if the `event` level matches one of the configured
    # immediate logging levels. Otherwise returns `false`.
    def immediate?( event )
      return false unless event.respond_to? :level
      @immediate[event.level]
    end


  private

    # call-seq:
    #    write( event )
    #
    # Writes the given `event` to the logging destination. The `event` can
    # be either a LogEvent or a String. If a LogEvent, then it will be
    # formatted using the layout given to the appender when it was created.
    #
    # The `event` will be formatted and then buffered until the
    # "auto_flushing" level has been reached. At this time the canonical_write
    # method will be used to log all events stored in the buffer.
    #
    # Returns this appender instance
    def write( event )
      str = event.instance_of?(::Logging::LogEvent) ?
            layout.format(event) : event.to_s
      return if str.empty?

      if @auto_flushing == 1
        canonical_write(str)
      else
        str = str.force_encoding(encoding) if encoding && str.encoding != encoding
        sync {
          @buffer << str
        }
        flush_now = @buffer.length >= @auto_flushing || immediate?(event)

        if flush_now
          if async?
            @async_flusher.signal(flush_now)
          else
            self.flush
          end
        elsif @async_flusher && flush_period?
          @async_flusher.signal
        end
      end

      self
    end

    # Attempt to parse an hours/minutes/seconds value from the string and return
    # an integer number of seconds.
    #
    # str - The input String to parse for time values.
    #
    # Examples
    #
    #   _parse_hours_minutes_seconds("14:12:42")  #=> 51162
    #   _parse_hours_minutes_seconds("foo")       #=> nil
    #
    # Returns a Numeric or `nil`
    def _parse_hours_minutes_seconds( str )
      m = %r/^\s*(\d{2,}):(\d{2}):(\d{2}(?:\.\d+)?)\s*$/.match(str)
      return if m.nil?

      (3600 * m[1].to_i) + (60 * m[2].to_i) + (m[3].to_f)
    end

    # Convert the string into a numeric value. If the string does not
    # represent a valid Integer or Float then `nil` is returned.
    #
    # str - The input String to parse for Numeric values.
    #
    # Examples
    #
    #   _parse_numeric("10")   #=> 10
    #   _parse_numeric("1.0")  #=> 1.0
    #   _parse_numeric("foo")  #=> nil
    #
    # Returns a Numeric or `nil`
    def _parse_numeric( str )
      Integer(str) rescue (Float(str) rescue nil)
    end

    # Using the flush_period, create a new AsyncFlusher attached to this
    # appender. If the flush_period is nil, then no action will be taken. If a
    # AsyncFlusher already exists, it will be stopped and a new one will be
    # created.
    #
    # Returns `nil`
    def _setup_async_flusher
      # stop and remove any existing async flusher instance
      if @async_flusher
        @async_flusher.stop
        @async_flusher = nil
        Thread.pass
      end

      # create a new async flusher if we have a valid flush period
      if @flush_period || async?
        @auto_flushing = DEFAULT_BUFFER_SIZE unless @auto_flushing > 1
        @async_flusher = AsyncFlusher.new(self, @flush_period)
        @async_flusher.start
        Thread.pass
      end

      nil
    end

    # :stopdoc:

    # The AsyncFlusher contains an internal run loop that will periodically
    # wake up and flush any log events contained in the message buffer of the
    # owning appender instance. The AsyncFlusher relies on a `signal` from
    # the appender in order to wakeup and perform the flush on the appender.
    class AsyncFlusher

      # Create a new AsyncFlusher instance that will call the `flush`
      # method on the given `appender`. The `flush` method will be called
      # every `period` seconds, but only when the message buffer is non-empty.
      #
      # appender - The Appender instance to periodically `flush`
      # period   - The Numeric sleep period or `nil`
      #
      def initialize( appender, period )
        @appender = appender
        @period = period

        @mutex = Mutex.new
        @cv = ConditionVariable.new
        @thread = nil
        @waiting = nil
        @signaled = false
        @immediate = 0
      end

      # Start the periodic flusher's internal run loop.
      #
      # Returns this flusher instance
      def start
        return if @thread

        @thread = Thread.new { loop {
          begin
            break if Thread.current[:stop]
            _wait_for_signal
            _try_to_sleep
            @appender.flush
          rescue => err
            ::Logging.log_internal {"AsyncFlusher for appender #{@appender.inspect} encountered an error"}
            ::Logging.log_internal_error(err)
          end
        }}

        self
      end

      # Stop the async flusher's internal run loop.
      #
      # Returns this flusher instance
      def stop
        return if @thread.nil?
        @thread[:stop] = true
        signal if waiting?
        @thread = nil
        self
      end

      # Signal the async flusher. This will wake up the run loop if it is
      # currently waiting for something to do. If the signal method is never
      # called, the async flusher will never perform the flush action on
      # the appender.
      #
      # immediate - Set to `true` if the sleep period should be skipped
      #
      # Returns this flusher instance
      def signal( immediate = nil )
        return if Thread.current == @thread   # don't signal ourselves
        return if @signaled                   # don't need to signal again

        @mutex.synchronize {
          @signaled = true
          @immediate += 1 if immediate
          @cv.signal
        }
        self
      end

      # Returns `true` if the flusher is waiting for a signal. Returns `false`
      # if the flusher is somewhere in the processing loop.
      def waiting?
        @waiting
      end

      # Returns `true` if the flusher should immeidately write the buffer to the
      # IO destination.
      def immediate?
        @immediate > 0
      end

    private

      def _try_to_sleep
        return if Thread.current[:stop]
        return if immediate?
        sleep @period unless @period.nil?
      end

      def _wait_for_signal
        @mutex.synchronize {
          begin
            # wait on the condition variable only if we have NOT been signaled
            unless @signaled
              @waiting = true
              @immediate -= 1 if immediate?
              @cv.wait(@mutex)
              @waiting = false
            end
          ensure
            @signaled = false
          end
        }
      ensure
        @waiting = false
      end
    end
    # :startdoc:
  end
end