;;; spam-stat.el --- detecting spam based on statistics

;; Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.

;; Author: Alex Schroeder <alex@gnu.org>
;; Keywords: network
;; URL: http://www.emacswiki.org/cgi-bin/wiki.pl?SpamStat

;; This file is part of GNU Emacs.

;; This is free software; you can redistribute it and/or modify it
;; under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 3, or (at your option)
;; any later version.

;; This is distributed in the hope that it will be useful, but WITHOUT
;; ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
;; or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
;; License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; Commentary:

;; This implements spam analysis according to Paul Graham in "A Plan
;; for Spam".  The basis for all this is a statistical distribution of
;; words for your spam and non-spam mails.  We need this information
;; in a hash-table so that the analysis can use the information when
;; looking at your mails.  Therefore, before you begin, you need tons
;; of mails (Graham uses 4000 non-spam and 4000 spam mails for his
;; experiments).
;;
;; The main interface to using spam-stat, are the following functions:
;;
;; `spam-stat-buffer-is-spam' -- called in a buffer, that buffer is
;; considered to be a new spam mail; use this for new mail that has
;; not been processed before
;;
;; `spam-stat-buffer-is-non-spam' -- called in a buffer, that buffer
;; is considered to be a new non-spam mail; use this for new mail that
;; has not been processed before
;;
;; `spam-stat-buffer-change-to-spam' -- called in a buffer, that
;; buffer is no longer considered to be normal mail but spam; use this
;; to change the status of a mail that has already been processed as
;; non-spam
;;
;; `spam-stat-buffer-change-to-non-spam' -- called in a buffer, that
;; buffer is no longer considered to be spam but normal mail; use this
;; to change the status of a mail that has already been processed as
;; spam
;;
;; `spam-stat-save' -- save the hash table to the file; the filename
;; used is stored in the variable `spam-stat-file'
;;
;; `spam-stat-load' -- load the hash table from a file; the filename
;; used is stored in the variable `spam-stat-file'
;;
;; `spam-stat-score-word' -- return the spam score for a word
;;
;; `spam-stat-score-buffer' -- return the spam score for a buffer
;;
;; `spam-stat-split-fancy' -- for fancy mail splitting; add
;; the rule (: spam-stat-split-fancy) to `nnmail-split-fancy'
;;
;; This requires the following in your ~/.gnus file:
;;
;; (require 'spam-stat)
;; (spam-stat-load)

;;; Testing:

;; Typical test will involve calls to the following functions:
;;
;; Reset: (spam-stat-reset)
;; Learn spam: (spam-stat-process-spam-directory "~/Mail/mail/spam")
;; Learn non-spam: (spam-stat-process-non-spam-directory "~/Mail/mail/misc")
;; Save table: (spam-stat-save)
;; File size: (nth 7 (file-attributes spam-stat-file))
;; Number of words: (hash-table-count spam-stat)
;; Test spam: (spam-stat-test-directory "~/Mail/mail/spam")
;; Test non-spam: (spam-stat-test-directory "~/Mail/mail/misc")
;; Reduce table size: (spam-stat-reduce-size)
;; Save table: (spam-stat-save)
;; File size: (nth 7 (file-attributes spam-stat-file))
;; Number of words: (hash-table-count spam-stat)
;; Test spam: (spam-stat-test-directory "~/Mail/mail/spam")
;; Test non-spam: (spam-stat-test-directory "~/Mail/mail/misc")

;;; Dictionary Creation:

;; Typically, you will filter away mailing lists etc. using specific
;; rules in `nnmail-split-fancy'.  Somewhere among these rules, you
;; will filter spam.  Here is how you would create your dictionary:

;; Reset: (spam-stat-reset)
;; Learn spam: (spam-stat-process-spam-directory "~/Mail/mail/spam")
;; Learn non-spam: (spam-stat-process-non-spam-directory "~/Mail/mail/misc")
;; Repeat for any other non-spam group you need...
;; Reduce table size: (spam-stat-reduce-size)
;; Save table: (spam-stat-save)

;;; Todo:

;; Speed it up.  Integrate with Gnus such that it uses spam and expiry
;; marks to call the appropriate functions when leaving the summary
;; buffer and saves the hash table when leaving Gnus.  More testing:
;; More mails, disabling SpamAssassin, double checking algorithm, find
;; improved algorithm.

;;; Thanks:

;; Ted Zlatanov <tzz@lifelogs.com>
;; Jesper Harder <harder@myrealbox.com>
;; Dan Schmidt <dfan@dfan.org>
;; Lasse Rasinen <lrasinen@iki.fi>
;; Milan Zamazal <pdm@zamazal.org>



;;; Code:

(defvar gnus-original-article-buffer)

(defgroup spam-stat nil
  "Statistical spam detection for Emacs.
Use the functions to build a dictionary of words and their statistical
distribution in spam and non-spam mails.  Then use a function to determine
whether a buffer contains spam or not."
  :version "22.1"
  :group 'gnus)

(defcustom spam-stat-file "~/.spam-stat.el"
  "File used to save and load the dictionary.
See `spam-stat-to-hash-table' for the format of the file."
  :type 'file
  :group 'spam-stat)

(defcustom spam-stat-install-hooks t
  "Whether spam-stat should install its hooks in Gnus.
This is set to nil if you use spam-stat through spam.el."
  :type 'boolean
  :group 'spam-stat)

(defcustom spam-stat-unknown-word-score 0.2
  "The score to use for unknown words.
Also used for words that don't appear often enough."
  :type 'number
  :group 'spam-stat)

(defcustom spam-stat-max-word-length 15
  "Only words shorter than this will be considered."
  :type 'integer
  :group 'spam-stat)

(defcustom spam-stat-max-buffer-length 10240
  "Only the beginning of buffers will be analyzed.
This variable says how many characters this will be."
  :type 'integer
  :group 'spam-stat)

(defcustom spam-stat-split-fancy-spam-group "mail.spam"
  "Name of the group where spam should be stored, if
`spam-stat-split-fancy' is used in fancy splitting rules.  Has no
effect when spam-stat is invoked through spam.el."
  :type 'string
  :group 'spam-stat)

(defcustom spam-stat-split-fancy-spam-threshhold 0.9
  "Spam score threshhold in spam-stat-split-fancy."
  :type 'number
  :group 'spam-stat)

(defvar spam-stat-syntax-table
  (let ((table (copy-syntax-table text-mode-syntax-table)))
    (modify-syntax-entry ?- "w" table)
    (modify-syntax-entry ?_ "w" table)
    (modify-syntax-entry ?. "w" table)
    (modify-syntax-entry ?! "w" table)
    (modify-syntax-entry ?? "w" table)
    (modify-syntax-entry ?+ "w" table)
    table)
  "Syntax table used when processing mails for statistical analysis.
The important part is which characters are word constituents.")

(defvar spam-stat-dirty nil
  "Whether the spam-stat database needs saving.")

(defvar spam-stat-buffer nil
  "Buffer to use for scoring while splitting.
This is set by hooking into Gnus.")

(defvar spam-stat-buffer-name " *spam stat buffer*"
  "Name of the `spam-stat-buffer'.")

;; Functions missing in Emacs 20

(when (memq nil (mapcar 'fboundp
			'(gethash hash-table-count make-hash-table
				  mapc puthash)))
  (require 'cl)
  (unless (fboundp 'puthash)
    ;; alias puthash is missing from Emacs 20 cl-extra.el
    (defalias 'puthash 'cl-puthash)))

(eval-when-compile
  (unless (fboundp 'with-syntax-table)
    ;; Imported from Emacs 21.2
    (defmacro with-syntax-table (table &rest body) "\
Evaluate BODY with syntax table of current buffer set to a copy of TABLE.
The syntax table of the current buffer is saved, BODY is evaluated, and the
saved table is restored, even in case of an abnormal exit.
Value is what BODY returns."
      (let ((old-table (make-symbol "table"))
	    (old-buffer (make-symbol "buffer")))
	`(let ((,old-table (syntax-table))
	       (,old-buffer (current-buffer)))
	   (unwind-protect
	       (progn
		 (set-syntax-table (copy-syntax-table ,table))
		 ,@body)
	     (save-current-buffer
	       (set-buffer ,old-buffer)
	       (set-syntax-table ,old-table))))))))

;; Hooking into Gnus

(defun spam-stat-store-current-buffer ()
  "Store a copy of the current buffer in `spam-stat-buffer'."
  (save-excursion
    (let ((str (buffer-string)))
      (set-buffer (get-buffer-create spam-stat-buffer-name))
      (erase-buffer)
      (insert str)
      (setq spam-stat-buffer (current-buffer)))))

(defun spam-stat-store-gnus-article-buffer ()
  "Store a copy of the current article in `spam-stat-buffer'.
This uses `gnus-article-buffer'."
  (save-excursion
    (set-buffer gnus-original-article-buffer)
    (spam-stat-store-current-buffer)))

;; Data -- not using defstruct in order to save space and time

(defvar spam-stat (make-hash-table :test 'equal)
  "Hash table used to store the statistics.
Use `spam-stat-load' to load the file.
Every word is used as a key in this table.  The value is a vector.
Use `spam-stat-ngood', `spam-stat-nbad', `spam-stat-good',
`spam-stat-bad', and `spam-stat-score' to access this vector.")

(defvar spam-stat-ngood 0
  "The number of good mails in the dictionary.")

(defvar spam-stat-nbad 0
  "The number of bad mails in the dictionary.")

(defsubst spam-stat-good (entry)
  "Return the number of times this word belongs to good mails."
  (aref entry 0))

(defsubst spam-stat-bad (entry)
  "Return the number of times this word belongs to bad mails."
  (aref entry 1))

(defsubst spam-stat-score (entry)
  "Set the score of this word."
  (if entry
      (aref entry 2)
    spam-stat-unknown-word-score))

(defsubst spam-stat-set-good (entry value)
  "Set the number of times this word belongs to good mails."
  (aset entry 0 value))

(defsubst spam-stat-set-bad (entry value)
  "Set the number of times this word belongs to bad mails."
  (aset entry 1 value))

(defsubst spam-stat-set-score (entry value)
  "Set the score of this word."
  (aset entry 2 value))

(defsubst spam-stat-make-entry (good bad)
  "Return a vector with the given properties."
  (let ((entry (vector good bad nil)))
    (spam-stat-set-score entry (spam-stat-compute-score entry))
    entry))

;; Computing

(defun spam-stat-compute-score (entry)
  "Compute the score of this word.  1.0 means spam."
   ;; promote all numbers to floats for the divisions
   (let* ((g (* 2.0 (spam-stat-good entry)))
	  (b (float (spam-stat-bad entry))))
     (cond ((< (+ g b) 5)
	    .2)
	   ((= 0 spam-stat-ngood)
	    .99)
	   ((= 0 spam-stat-nbad)
	    .01)
	   (t
	    (max .01
		 (min .99 (/ (/ b spam-stat-nbad)
			     (+ (/ g spam-stat-ngood)
				(/ b spam-stat-nbad)))))))))

;; Parsing

(defmacro with-spam-stat-max-buffer-size (&rest body)
  "Narrows the buffer down to the first 4k characters, then evaluates BODY."
  `(save-restriction
     (when (> (- (point-max)
		 (point-min))
	      spam-stat-max-buffer-length)
       (narrow-to-region (point-min)
			 (+ (point-min) spam-stat-max-buffer-length)))
     ,@body))

(defun spam-stat-buffer-words ()
  "Return a hash table of words and number of occurrences in the buffer."
  (with-spam-stat-max-buffer-size
   (with-syntax-table spam-stat-syntax-table
     (goto-char (point-min))
     (let ((result (make-hash-table :test 'equal))
	   word count)
       (while (re-search-forward "\\w+" nil t)
	 (setq word (match-string-no-properties 0)
	       count (1+ (gethash word result 0)))
	 (when (< (length word) spam-stat-max-word-length)
	   (puthash word count result)))
       result))))

(defun spam-stat-buffer-is-spam ()
  "Consider current buffer to be a new spam mail."
  (setq spam-stat-nbad (1+ spam-stat-nbad))
  (maphash
   (lambda (word count)
     (let ((entry (gethash word spam-stat)))
       (if entry
	   (spam-stat-set-bad entry (+ count (spam-stat-bad entry)))
	 (setq entry (spam-stat-make-entry 0 count)))
       (spam-stat-set-score entry (spam-stat-compute-score entry))
       (puthash word entry spam-stat)))
   (spam-stat-buffer-words))
  (setq spam-stat-dirty t))

(defun spam-stat-buffer-is-non-spam ()
  "Consider current buffer to be a new non-spam mail."
  (setq spam-stat-ngood (1+ spam-stat-ngood))
  (maphash
   (lambda (word count)
     (let ((entry (gethash word spam-stat)))
       (if entry
	   (spam-stat-set-good entry (+ count (spam-stat-good entry)))
	 (setq entry (spam-stat-make-entry count 0)))
       (spam-stat-set-score entry (spam-stat-compute-score entry))
       (puthash word entry spam-stat)))
   (spam-stat-buffer-words))
  (setq spam-stat-dirty t))

(defun spam-stat-buffer-change-to-spam ()
  "Consider current buffer no longer normal mail but spam."
  (setq spam-stat-nbad (1+ spam-stat-nbad)
	spam-stat-ngood (1- spam-stat-ngood))
  (maphash
   (lambda (word count)
     (let ((entry (gethash word spam-stat)))
       (if (not entry)
	   (error "This buffer has unknown words in it")
	 (spam-stat-set-good entry (- (spam-stat-good entry) count))
	 (spam-stat-set-bad entry (+ (spam-stat-bad entry) count))
	 (spam-stat-set-score entry (spam-stat-compute-score entry))
	 (puthash word entry spam-stat))))
   (spam-stat-buffer-words))
  (setq spam-stat-dirty t))

(defun spam-stat-buffer-change-to-non-spam ()
  "Consider current buffer no longer spam but normal mail."
  (setq spam-stat-nbad (1- spam-stat-nbad)
	spam-stat-ngood (1+ spam-stat-ngood))
  (maphash
   (lambda (word count)
     (let ((entry (gethash word spam-stat)))
       (if (not entry)
	   (error "This buffer has unknown words in it")
	 (spam-stat-set-good entry (+ (spam-stat-good entry) count))
	 (spam-stat-set-bad entry (- (spam-stat-bad entry) count))
	 (spam-stat-set-score entry (spam-stat-compute-score entry))
	 (puthash word entry spam-stat))))
   (spam-stat-buffer-words))
  (setq spam-stat-dirty t))

;; Saving and Loading

(defun spam-stat-save (&optional force)
  "Save the `spam-stat' hash table as lisp file.
With a prefix argument save unconditionally."
  (interactive "P")
  (when (or force spam-stat-dirty)
    (with-temp-buffer
      (let ((standard-output (current-buffer))
	    (font-lock-maximum-size 0))
	(insert "(setq spam-stat-ngood "
		(number-to-string spam-stat-ngood)
		" spam-stat-nbad "
		(number-to-string spam-stat-nbad)
		" spam-stat (spam-stat-to-hash-table '(")
	(maphash (lambda (word entry)
		   (prin1 (list word
				(spam-stat-good entry)
				(spam-stat-bad entry))))
		 spam-stat)
	(insert ")))")
	(write-file spam-stat-file)))
    (setq spam-stat-dirty nil)))

(defun spam-stat-load ()
  "Read the `spam-stat' hash table from disk."
  ;; TODO: maybe we should warn the user if spam-stat-dirty is t?
  (load-file spam-stat-file)
  (setq spam-stat-dirty nil))

(defun spam-stat-to-hash-table (entries)
  "Turn list ENTRIES into a hash table and store as `spam-stat'.
Every element in ENTRIES has the form \(WORD GOOD BAD) where WORD is
the word string, NGOOD is the number of good mails it has appeared in,
NBAD is the number of bad mails it has appeared in, GOOD is the number
of times it appeared in good mails, and BAD is the number of times it
has appeared in bad mails."
  (let ((table (make-hash-table :test 'equal)))
    (mapc (lambda (l)
	    (puthash (car l)
		     (spam-stat-make-entry (nth 1 l) (nth 2 l))
		     table))
	  entries)
    table))

(defun spam-stat-reset ()
  "Reset `spam-stat' to an empty hash-table.
This deletes all the statistics."
  (interactive)
  (setq spam-stat (make-hash-table :test 'equal)
	spam-stat-ngood 0
	spam-stat-nbad 0)
  (setq spam-stat-dirty t))

;; Scoring buffers

(defvar spam-stat-score-data nil
  "Raw data used in the last run of `spam-stat-score-buffer'.")

(defsubst spam-stat-score-word (word)
  "Return score for WORD.
The default score for unknown words is stored in
`spam-stat-unknown-word-score'."
  (spam-stat-score (gethash word spam-stat)))

(defun spam-stat-buffer-words-with-scores ()
  "Process current buffer, return the 15 most conspicuous words.
These are the words whose spam-stat differs the most from 0.5.
The list returned contains elements of the form \(WORD SCORE DIFF),
where DIFF is the difference between SCORE and 0.5."
  (with-spam-stat-max-buffer-size
   (with-syntax-table spam-stat-syntax-table
     (let (result word score)
       (maphash	(lambda (word ignore)
		  (setq score (spam-stat-score-word word)
			result (cons (list word score (abs (- score 0.5)))
				     result)))
		(spam-stat-buffer-words))
       (setq result (sort result (lambda (a b) (< (nth 2 b) (nth 2 a)))))
       (setcdr (nthcdr 14 result) nil)
       result))))

(defun spam-stat-score-buffer ()
  "Return a score describing the spam-probability for this buffer."
  (setq spam-stat-score-data (spam-stat-buffer-words-with-scores))
  (let* ((probs (mapcar (lambda (e) (cadr e)) spam-stat-score-data))
	 (prod (apply #'* probs)))
    (/ prod (+ prod (apply #'* (mapcar #'(lambda (x) (- 1 x))
				       probs))))))

(defun spam-stat-split-fancy ()
  "Return the name of the spam group if the current mail is spam.
Use this function on `nnmail-split-fancy'.  If you are interested in
the raw data used for the last run of `spam-stat-score-buffer',
check the variable `spam-stat-score-data'."
  (condition-case var
      (progn
	(set-buffer spam-stat-buffer)
	(goto-char (point-min))
	(when (> (spam-stat-score-buffer) spam-stat-split-fancy-spam-threshhold)
	  (when (boundp 'nnmail-split-trace)
	    (mapc (lambda (entry)
		    (push entry nnmail-split-trace))
		  spam-stat-score-data))
	  spam-stat-split-fancy-spam-group))
    (error (message "Error in spam-stat-split-fancy: %S" var)
	   nil)))

;; Testing

(defun spam-stat-process-directory (dir func)
  "Process all the regular files in directory DIR using function FUNC."
  (let* ((files (directory-files dir t "^[^.]"))
	 (max (/ (length files) 100.0))
	 (count 0))
    (with-temp-buffer
      (dolist (f files)
	(when (and (file-readable-p f)
		   (file-regular-p f)
                   (> (nth 7 (file-attributes f)) 0))
	  (setq count (1+ count))
	  (message "Reading %s: %.2f%%" dir (/ count max))
	  (insert-file-contents f)
	  (funcall func)
	  (erase-buffer))))))

(defun spam-stat-process-spam-directory (dir)
  "Process all the regular files in directory DIR as spam."
  (interactive "D")
  (spam-stat-process-directory dir 'spam-stat-buffer-is-spam))

(defun spam-stat-process-non-spam-directory (dir)
  "Process all the regular files in directory DIR as non-spam."
  (interactive "D")
  (spam-stat-process-directory dir 'spam-stat-buffer-is-non-spam))

(defun spam-stat-count ()
  "Return size of `spam-stat'."
  (interactive)
  (hash-table-count spam-stat))

(defun spam-stat-test-directory (dir)
  "Test all the regular files in directory DIR for spam.
If the result is 1.0, then all files are considered spam.
If the result is 0.0, non of the files is considered spam.
You can use this to determine error rates."
  (interactive "D")
  (let* ((files (directory-files dir t "^[^.]"))
	 (total (length files))
	 (score 0.0); float
	 (max (/ total 100.0)); float
	 (count 0))
    (with-temp-buffer
      (dolist (f files)
	(when (and (file-readable-p f)
		   (file-regular-p f)
                   (> (nth 7 (file-attributes f)) 0))
	  (setq count (1+ count))
	  (message "Reading %.2f%%, score %.2f%%"
		   (/ count max) (/ score count))
	  (insert-file-contents f)
	  (when (> (spam-stat-score-buffer) 0.9)
	    (setq score (1+ score)))
	  (erase-buffer))))
    (message "Final score: %d / %d = %f" score total (/ score total))))

;; Shrinking the dictionary

(defun spam-stat-reduce-size (&optional count)
  "Reduce the size of `spam-stat'.
This removes all words that occur less than COUNT from the dictionary.
COUNT defaults to 5"
  (interactive)
  (setq count (or count 5))
  (maphash (lambda (key entry)
	     (when (< (+ (spam-stat-good entry)
			 (spam-stat-bad entry))
		      count)
	       (remhash key spam-stat)))
	   spam-stat)
  (setq spam-stat-dirty t))

(defun spam-stat-install-hooks-function ()
  "Install the spam-stat function hooks"
  (interactive)
  (add-hook 'nnmail-prepare-incoming-message-hook
	    'spam-stat-store-current-buffer)
  (add-hook 'gnus-select-article-hook
	    'spam-stat-store-gnus-article-buffer))

(when spam-stat-install-hooks
  (spam-stat-install-hooks-function))

(defun spam-stat-unload-hook ()
  "Uninstall the spam-stat function hooks"
  (interactive)
  (remove-hook 'nnmail-prepare-incoming-message-hook
	       'spam-stat-store-current-buffer)
  (remove-hook 'gnus-select-article-hook
	       'spam-stat-store-gnus-article-buffer))

(add-hook 'spam-stat-unload-hook 'spam-stat-unload-hook)

(provide 'spam-stat)

;;; arch-tag: ff1d2200-8ddb-42fb-bb7b-1b5e20448554
;;; spam-stat.el ends here