Log

class BasicLog
    # log-level constant
    FATAL, ERROR, WARN, INFO, DEBUG = 1, 2, 3, 4, 5

    attr_accessor :level

    def initialize(log_file=nil, level=nil)
      @level = level || INFO
      case log_file
      when String
        @log = open(log_file, "a+")
        @log.sync = true
        @opened = true
      when NilClass
        @log = $stderr
      else
        @log = log_file  # requires "<<". (see BasicLog#log)
      end
    end

    def close
      @log.close if @opened
      @log = nil
    end

    def log(level, data)
      if @log && level <= @level
        data += "\n" if /\n\Z/ !~ data
        @log << data
      end
    end

    def <<(obj)
      log(INFO, obj.to_s)
    end

    def fatal(msg) log(FATAL, "FATAL " << format(msg)); end
    def error(msg) log(ERROR, "ERROR " << format(msg)); end
    def warn(msg)  log(WARN,  "WARN  " << format(msg)); end
    def info(msg)  log(INFO,  "INFO  " << format(msg)); end
    def debug(msg) log(DEBUG, "DEBUG " << format(msg)); end

    def fatal?; @level >= FATAL; end
    def error?; @level >= ERROR; end
    def warn?;  @level >= WARN; end
    def info?;  @level >= INFO; end
    def debug?; @level >= DEBUG; end

    private

    def format(arg)
      str = if arg.is_a?(Exception)
        "#{arg.class}: #{arg.message}\n\t" <<
        arg.backtrace.join("\n\t") << "\n"
      elsif arg.respond_to?(:to_str)
        arg.to_str
      else
        arg.inspect
      end
    end
  end

  class Log < BasicLog
    attr_accessor :time_format 

    def initialize(log_file=nil, level=nil)
      super(log_file, level)
      @time_format = "[%Y-%m-%d %H:%M:%S]"
    end

    def log(level, data)
      tmp = Time.now.strftime(@time_format)
      tmp << " " << data
      super(level, tmp)
    end
  end