# logger.rb - simple logging utility
# Copyright (C) 2000-2003, 2005, 2008, 2011  NAKAMURA, Hiroshi <nahi@ruby-lang.org>.
#
# Documentation:: NAKAMURA, Hiroshi and Gavin Sinclair
# License::
#   You can redistribute it and/or modify it under the same terms of Ruby's
#   license; either the dual license version in 2003, or any later version.
# Revision:: $Id$
#
# A simple system for logging messages.  See Logger for more documentation.

require 'monitor'

# == Description
#
# The Logger class provides a simple but sophisticated logging utility that
# you can use to output messages.
#
# The messages have associated levels, such as +INFO+ or +ERROR+ that indicate
# their importance.  You can then give the Logger a level, and only messages
# at that level of higher will be printed.
#
# The levels are:
#
# +FATAL+:: an unhandleable error that results in a program crash
# +ERROR+:: a handleable error condition
# +WARN+::  a warning
# +INFO+::  generic (useful) information about system operation
# +DEBUG+:: low-level information for developers
#
# For instance, in a production system, you may have your Logger set to
# +INFO+ or even +WARN+
# When you are developing the system, however, you probably
# want to know about the program's internal state, and would set the Logger to
# +DEBUG+.
#
# *Note*: Logger does not escape or sanitize any messages passed to it.
# Developers should be aware of when potentially malicious data (user-input)
# is passed to Logger, and manually escape the untrusted data:
#
#   logger.info("User-input: #{input.dump}")
#   logger.info("User-input: %p" % input)
#
# You can use #formatter= for escaping all data.
#
#   original_formatter = Logger::Formatter.new
#   logger.formatter = proc { |severity, datetime, progname, msg|
#     original_formatter.call(severity, datetime, progname, msg.dump)
#   }
#   logger.info(input)
#
# === Example
#
# This creates a logger to the standard output stream, with a level of +WARN+
#
#   log = Logger.new(STDOUT)
#   log.level = Logger::WARN
#
#   log.debug("Created logger")
#   log.info("Program started")
#   log.warn("Nothing to do!")
#
#   begin
#     File.each_line(path) do |line|
#       unless line =~ /^(\w+) = (.*)$/
#         log.error("Line in wrong format: #{line}")
#       end
#     end
#   rescue => err
#     log.fatal("Caught exception; exiting")
#     log.fatal(err)
#   end
#
# Because the Logger's level is set to +WARN+, only the warning, error, and
# fatal messages are recorded.  The debug and info messages are silently
# discarded.
#
# === Features
#
# There are several interesting features that Logger provides, like
# auto-rolling of log files, setting the format of log messages, and
# specifying a program name in conjunction with the message.  The next section
# shows you how to achieve these things.
#
#
# == HOWTOs
#
# === How to create a logger
#
# The options below give you various choices, in more or less increasing
# complexity.
#
# 1. Create a logger which logs messages to STDERR/STDOUT.
#
#      logger = Logger.new(STDERR)
#      logger = Logger.new(STDOUT)
#
# 2. Create a logger for the file which has the specified name.
#
#      logger = Logger.new('logfile.log')
#
# 3. Create a logger for the specified file.
#
#      file = File.open('foo.log', File::WRONLY | File::APPEND)
#      # To create new (and to remove old) logfile, add File::CREAT like;
#      #   file = open('foo.log', File::WRONLY | File::APPEND | File::CREAT)
#      logger = Logger.new(file)
#
# 4. Create a logger which ages logfile once it reaches a certain size.  Leave
#    10 "old log files" and each file is about 1,024,000 bytes.
#
#      logger = Logger.new('foo.log', 10, 1024000)
#
# 5. Create a logger which ages logfile daily/weekly/monthly.
#
#      logger = Logger.new('foo.log', 'daily')
#      logger = Logger.new('foo.log', 'weekly')
#      logger = Logger.new('foo.log', 'monthly')
#
# === How to log a message
#
# Notice the different methods (+fatal+, +error+, +info+) being used to log
# messages of various levels?  Other methods in this family are +warn+ and
# +debug+.  +add+ is used below to log a message of an arbitrary (perhaps
# dynamic) level.
#
# 1. Message in block.
#
#      logger.fatal { "Argument 'foo' not given." }
#
# 2. Message as a string.
#
#      logger.error "Argument #{ @foo } mismatch."
#
# 3. With progname.
#
#      logger.info('initialize') { "Initializing..." }
#
# 4. With severity.
#
#      logger.add(Logger::FATAL) { 'Fatal error!' }
#
# The block form allows you to create potentially complex log messages,
# but to delay their evaluation until and unless the message is
# logged.  For example, if we have the following:
#
#     logger.debug { "This is a " + potentially + " expensive operation" }
#
# If the logger's level is +INFO+ or higher, no debug messages will be logged,
# and the entire block will not even be evaluated.  Compare to this:
#
#     logger.debug("This is a " + potentially + " expensive operation")
#
# Here, the string concatenation is done every time, even if the log
# level is not set to show the debug message.
#
# === How to close a logger
#
#      logger.close
#
# === Setting severity threshold
#
# 1. Original interface.
#
#      logger.sev_threshold = Logger::WARN
#
# 2. Log4r (somewhat) compatible interface.
#
#      logger.level = Logger::INFO
#
#      DEBUG < INFO < WARN < ERROR < FATAL < UNKNOWN
#
#
# == Format
#
# Log messages are rendered in the output stream in a certain format by
# default.  The default format and a sample are shown below:
#
# Log format:
#   SeverityID, [Date Time mSec #pid] SeverityLabel -- ProgName: message
#
# Log sample:
#   I, [Wed Mar 03 02:34:24 JST 1999 895701 #19074]  INFO -- Main: info.
#
# You may change the date and time format via #datetime_format=
#
#   logger.datetime_format = "%Y-%m-%d %H:%M:%S"
#         # e.g. "2004-01-03 00:54:26"
#
# Or, you may change the overall format with #formatter= method.
#
#   logger.formatter = proc do |severity, datetime, progname, msg|
#     "#{datetime}: #{msg}\n"
#   end
#   # e.g. "Thu Sep 22 08:51:08 GMT+9:00 2005: hello world"
#
class Logger
  VERSION = "1.2.7"
  _, name, rev = %w$Id$
  if name
    name = name.chomp(",v")
  else
    name = File.basename(__FILE__)
  end
  rev ||= "v#{VERSION}"
  ProgName = "#{name}/#{rev}"

  class Error < RuntimeError # :nodoc:
  end
  # not used after 1.2.7. just for compat.
  class ShiftingError < Error # :nodoc:
  end

  # Logging severity.
  module Severity
    # Low-level information, mostly for developers
    DEBUG = 0
    # generic, useful information about system operation
    INFO = 1
    # a warning
    WARN = 2
    # a handleable error condition
    ERROR = 3
    # an unhandleable error that results in a program crash
    FATAL = 4
    # an unknown message that should always be logged
    UNKNOWN = 5
  end
  include Severity

  # Logging severity threshold (e.g. <tt>Logger::INFO</tt>).
  attr_accessor :level

  # program name to include in log messages.
  attr_accessor :progname

  # Set date-time format.
  #
  # +datetime_format+:: A string suitable for passing to +strftime+.
  def datetime_format=(datetime_format)
    @default_formatter.datetime_format = datetime_format
  end

  # Returns the date format being used.  See #datetime_format=
  def datetime_format
    @default_formatter.datetime_format
  end

  # Logging formatter, as a +Proc+ that will take four arguments and
  # return the formatted message. The arguments are:
  #
  # +severity+:: The Severity of the log message
  # +time+:: A Time instance representing when the message was logged
  # +progname+:: The #progname configured, or passed to the logger method
  # +msg+:: The _Object_ the user passed to the log message; not necessarily a
  #         String.
  #
  # The block should return an Object that can be written to the logging
  # device via +write+.  The default formatter is used when no formatter is
  # set.
  attr_accessor :formatter

  alias sev_threshold level
  alias sev_threshold= level=

  # Returns +true+ iff the current severity level allows for the printing of
  # +DEBUG+ messages.
  def debug?; @level <= DEBUG; end

  # Returns +true+ iff the current severity level allows for the printing of
  # +INFO+ messages.
  def info?; @level <= INFO; end

  # Returns +true+ iff the current severity level allows for the printing of
  # +WARN+ messages.
  def warn?; @level <= WARN; end

  # Returns +true+ iff the current severity level allows for the printing of
  # +ERROR+ messages.
  def error?; @level <= ERROR; end

  # Returns +true+ iff the current severity level allows for the printing of
  # +FATAL+ messages.
  def fatal?; @level <= FATAL; end

  #
  # === Synopsis
  #
  #   Logger.new(name, shift_age = 7, shift_size = 1048576)
  #   Logger.new(name, shift_age = 'weekly')
  #
  # === Args
  #
  # +logdev+::
  #   The log device.  This is a filename (String) or IO object (typically
  #   +STDOUT+, +STDERR+, or an open file).
  # +shift_age+::
  #   Number of old log files to keep, *or* frequency of rotation (+daily+,
  #   +weekly+ or +monthly+).
  # +shift_size+::
  #   Maximum logfile size (only applies when +shift_age+ is a number).
  #
  # === Description
  #
  # Create an instance.
  #
  def initialize(logdev, shift_age = 0, shift_size = 1048576)
    @progname = nil
    @level = DEBUG
    @default_formatter = Formatter.new
    @formatter = nil
    @logdev = nil
    if logdev
      @logdev = LogDevice.new(logdev, :shift_age => shift_age,
        :shift_size => shift_size)
    end
  end

  #
  # === Synopsis
  #
  #   Logger#add(severity, message = nil, progname = nil) { ... }
  #
  # === Args
  #
  # +severity+::
  #   Severity.  Constants are defined in Logger namespace: +DEBUG+, +INFO+,
  #   +WARN+, +ERROR+, +FATAL+, or +UNKNOWN+.
  # +message+::
  #   The log message.  A String or Exception.
  # +progname+::
  #   Program name string.  Can be omitted.  Treated as a message if no
  #   +message+ and +block+ are given.
  # +block+::
  #   Can be omitted.  Called to get a message string if +message+ is nil.
  #
  # === Return
  #
  # +true+ if successful, +false+ otherwise.
  #
  # When the given severity is not high enough (for this particular logger), log
  # no message, and return +true+.
  #
  # === Description
  #