require 'thread'
require 'active_support/core_ext/class/attribute_accessors'

module ActiveSupport
  # Inspired by the buffered logger idea by Ezra
  class BufferedLogger
    module Severity
      DEBUG   = 0
      INFO    = 1
      WARN    = 2
      ERROR   = 3
      FATAL   = 4
      UNKNOWN = 5
    end
    include Severity

    MAX_BUFFER_SIZE = 1000

    ##
    # :singleton-method:
    # Set to false to disable the silencer
    cattr_accessor :silencer
    self.silencer = true

    # Silences the logger for the duration of the block.
    def silence(temporary_level = ERROR)
      if silencer
        old_logger_level = @tmp_levels[Thread.current]
        begin
          @tmp_levels[Thread.current] = temporary_level
          yield self
        ensure
          if old_logger_level
            @tmp_levels[Thread.current] = old_logger_level
          else
            @tmp_levels.delete(Thread.current)
          end
        end
      else
        yield self
      end
    end

    attr_writer :level
    attr_reader :auto_flushing

    def initialize(log, level = DEBUG)
      @level         = level
      @tmp_levels    = {}
      @buffer        = Hash.new { |h,k| h[k] = [] }
      @auto_flushing = 1
      @guard = Mutex.new

      if log.respond_to?(:write)
        @log = log
      elsif File.exist?(log)
        @log = open_log(log, (File::WRONLY | File::APPEND))
      else
        FileUtils.mkdir_p(File.dirname(log))
        @log = open_log(log, (File::WRONLY | File::APPEND | File::CREAT))
      end
    end

    def open_log(log, mode)
      open(log, mode).tap do |open_log|
        open_log.set_encoding(Encoding::BINARY) if open_log.respond_to?(:set_encoding)
        open_log.sync = true
      end
    end

    def level
      @tmp_levels[Thread.current] || @level
    end

    def add(severity, message = nil, progname = nil, &block)
      return if level > severity
      message = (message || (block && block.call) || progname).to_s
      # If a newline is necessary then create a new message ending with a newline.
      # Ensures that the original message is not mutated.
      message = "#{message}\n" unless message[-1] == ?\n
      buffer << message
      auto_flush
      message
    end

    # Dynamically add methods such as:
    # def info
    # def warn
    # def debug
    Severity.constants.each do |severity|
      class_eval <<-EOT, __FILE__, __LINE__ + 1
        def #{severity.downcase}(message = nil, progname = nil, &block) # def debug(message = nil, progname = nil, &block)
          add(#{severity}, message, progname, &block)                   #   add(DEBUG, message, progname, &block)
        end                                                             # end

        def #{severity.downcase}?                                       # def debug?
          #{severity} >= level                                         #   DEBUG >= @level
        end                                                             # end
      EOT
    end

    # Set the auto-flush period. Set to true to flush after every log message,
    # to an integer to flush every N messages, or to false, nil, or zero to
    # never auto-flush. If you turn auto-flushing off, be sure to regularly
    # flush the log yourself -- it will eat up memory until you do.
    def auto_flushing=(period)
      @auto_flushing =
        case period
        when true;                1
        when false, nil, 0;       MAX_BUFFER_SIZE
        when Integer;             period
        else raise ArgumentError, "Unrecognized auto_flushing period: #{period.inspect}"
        end
    end

    def flush
      @guard.synchronize do
        write_buffer(buffer)

        # Important to do this even if buffer was empty or else @buffer will
        # accumulate empty arrays for each request where nothing was logged.
        clear_buffer

        # Clear buffers associated with dead threads or else spawned threads
        # that don't call flush will result in a memory leak.
        flush_dead_buffers
      end
    end

    def close
      flush
      @log.close if @log.respond_to?(:close)
      @log = nil
    end

    protected
      def auto_flush
        flush if buffer.size >= @auto_flushing
      end

      def buffer
        @buffer[Thread.current]
      end

      def clear_buffer
        @buffer.delete(Thread.current)
      end

      # Find buffers created by threads that are no longer alive and flush them to the log
      # in order to prevent memory leaks from spawned threads.
      def flush_dead_buffers #:nodoc:
        @buffer.keys.reject{|thread| thread.alive?}.each do |thread|
          buffer = @buffer[thread]
          write_buffer(buffer)
          @buffer.delete(thread)
        end
      end

      def write_buffer(buffer)
        buffer.each do |content|
          @log.write(content)
        end
      end
  end
end