;;; ltx-help.el --- Lookup latex commands in info pages.

;; Authors: Peter Galbraith <[email protected]> or <[email protected]>
;;      Christian Lynbech <[email protected]>
;;      Martin Sjolin <[email protected]>
;;      Boris Goldowsky <[email protected]>
;; Maintainer: as part of latexrefman, http://home.gna.org/latexrefman/
;; Updated: 25 April 2013
;; Keywords: help, latex, info


;;; Commentary:

;; Use the function latex-help to look up a latex command or
;; environment in the latex online manual.  If point is at such a
;; command, this will be the default.

;; The Texinfo document that this code works with is at
;; http://ctan.org/pkg/latex2e-help-texinfo.

;; Installation:
;;
;; Add the following piece of code to your .emacs
;;  (define-key help-map "\C-l" 'latex-help)
;;
;; to bind latex-help to C-h C-l. To load latex-help when loading AUC-TeX or
;; some other LaTeX/TeX mode and bind the it to C-C i key, add the the following
;; to you .emacs:
;;
;; (add-hook 'Latex-mode-hook
;;           (function (lambda ()
;;                        (define-key LaTeX-mode-map "\C-ci" 'latex-help))))
;;
;; or if you do not have add-hook (a very nice package):
;;
;; (setq Latex-mode-hook
;;      (function (lambda ()
;;                  (define-key LaTeX-mode-map "\C-ci" 'latex-help))))
;;
;;

;;; Change Log:

;;Mar  4, 1994 <[email protected]>:
;;    Changed to my personal preferences.  I have changed the function
;;    names.  I have changed it to take a parameter, rather than just
;;    taking the current word. I am also basing it on the index rather
;;    than the node names.
;;
;;Mar 10, 1994 <[email protected]>:
;;    Added definition of current-word if not present.
;;    Made default value pick up a leading \ if apropriate
;;
;;Mar 11, 1994 <[email protected]>:
;;    Changed the name of current-word into latex-help-guess. This
;;    eliminates the need for the embedded defun.
;;    Also made describe-latex work more like describe-function in its
;;    way of using default values. Now you must press return at an
;;    empty prompt to get the listed default (if any).
;;
;;Mar 10, 1994 <[email protected]>:
;;    Rewrote part of the describe-latex command to use the prefix
;;    argument, changed latex-help-get-cmd-obarray to return the
;;    the new array and test if it is empty or not. Add information
;;    concerning where to find the latex.texi file and emacs 18 info.el
;;
;;Mar 28, 1994 <[email protected]>:
;;    * rewrote describe-latex's command-reading code; it did not
;;      default correctly on my system.
;;    * Added latex-help-hist, for completion history.
;;    * Modified it to use show-temp-buffer, if defined, so that it will
;;      display the help buffer in accord with user preferences.
;;    * Renamed describe-latex to latex-help, for consistency with other names.
;;    * Removed unneeded (interactive) specs for latex-help-guess and
;;      latex-help-get-cmd-obarray.
;;    * Added autoload cookies.
;;    * Doc fix.
;;
;;Mar 29, 1994 <[email protected]>:
;;    * made it working under epoch/emacs-18 by calling
;;      completion-read without the last argument.
;;    * made prompting similar to emacs help
;;    * moved add-hook and define keys to installation section, since
;;      the settings conflict with my own keybindings. Also, the key
;;      binding should be chosen by the end user.
;;
;; Wed Mar 30 08:45:50 1994     LYNBECH
;;      * Changed file layout to conform to FSF's standards
;;      * Tweaked latex-help-guess to include any leading backslashes
;;      * Inversed the meaning of the prefix argument. Now default is
;;        to switch buffers. Also added new variable `latex-help-split-window'
;;        to allow window splitting always.
;;      * Minor doc fixes
;;
;; Wed Apr  6 08:34:08 1994     LYNBECH
;;      * fixed latex-help-guess to be more faithful to the lexical rules
;;        of  TeX. The result is not especially elegant.
;;
;;Apr 16, 1994 <[email protected]>:
;;    Changed the name to `ltx-help.el'.
;;
;; Sat Apr  1 1995  Torsten Martinsen  ([email protected])
;;    Changed obarray to an alist where the car of each cons cell is the
;;    command name, and the cdr is the Info node describing that
;;    command. This implementation has the following advantages:
;;     - we don't need to have a lot of small redundant Info nodes; instead,
;;       we can use the Texinfo function index mechanism.
;;     - the alist is dynamically sized, so this version will work regardless
;;       of how many LaTeX commands the Info file contains.
;;    Added info on LaTeX2e Info file.
;;
;; Mon Apr 15 1996  Torsten Martinsen ([email protected])
;;    Changed node 'List of Commands' to 'Command Index' as suggested by
;;    Ralf Fassel <[email protected]>.
;;
;; Mon Apr 22 1996  Torsten Martinsen ([email protected])
;;    When running under FSF Emacs, use (buffer-substring-no-properties)
;;    instead of (buffer-substring) as suggested by Kurt Hornik
;;    <[email protected]>. Also removed Emacs 18 support.
;;
;; Thu Jun 12 2008  Karl Berry ([email protected])
;;    Change latex-help-file to "(latex2e)", so our names are consistent.
;;    Doc updates.
;;
;; Thu Apr 25 2013  Karl Berry ([email protected])
;;    Doc updates, and install these changes:
;;
;; Thu Apr 25 2013  Mandar Mitra ([email protected])
;;    Using with (for example) "array" goes to the top node
;;    of latex2e.info instead of the intended node.
;;
;; Thu Dec 3 2015  Kevin Ryde ([email protected])
;;    * latex-help-get-cmd-alist don't take \:: as double-colon style index,
;;      and allow "(line 123)" at the end of recent makeinfo output.
;;    * Use buffer-substring-no-properties when exists (does in XEmacs 21.4).

;;; Code:

(require 'info)

(defalias 'ltxh-buffer-substring
 (if (fboundp 'buffer-substring-no-properties)  ;; when available
     'buffer-substring-no-properties
   'buffer-substring))

(defcustom latex-help-file "(latex2e)"
 "Select the LaTeX2e non official reference manual translation."
 :type '(choice
         (string :tag "English" "(latex2e)")
         (string :tag "French" "(latex2e-fr)")
         (string :tag "Spanish" "(latex2e-es)") ))

(defvar latex-help-split-window nil
 "*When this is non-nil, `latex-help' will always pop up the info
buffer, rather than just switch to it.")

(defvar latex-help-hist nil
 "History for latex command help")

(defconst latex-help-cmd-alist nil
 "Alist of the commands in the index of the latex info manual,
used for validation and completion.")

;;;###autoload
(defun latex-help (cmd split)
 "Try to find info entry about LaTeX entity CMD.
CMD may be either a command or an environment.
If CMD is not a string, this function will prompt for it, eventually
with completion. If SPLIT (prefix arg.) is non-nil, latex-help will
pop up the Info buffer, rather than just switch to it. See also
variable `latex-help-split-window'."
 (interactive
  (list
   (let* ((cw (latex-help-guess))
          (cww (concat "\\" cw))
          (cmd-alist (latex-help-get-cmd-alist))
          (node (try-completion cw cmd-alist))
          ; try-completion returns actual string in case of partial match
          ; but returns t in case of exact match
          (nodename1 (if (equal node t) cw node))
          (nodename2 (if (equal nodename1 nil)
                         (try-completion cww cmd-alist) nodename1))
         (guess (cond ((equal nodename2 t) cww)
                       ((equal nodename2 nil) nil)
                       (t nodename2)))
          (val (completing-read (if guess
                                    (format "Describe LaTeX command (default %s): " guess)
                                  "Describe LaTeX command: ")
                                cmd-alist nil t nil
                                'latex-help-hist)))
     (cdr (assoc (if (equal val "")
                     guess
                   val) cmd-alist)))
   current-prefix-arg))
 (if (not (or split latex-help-split-window))
     (Info-goto-node (concat latex-help-file cmd))
   (save-excursion
     (let ((pop-up-windows t)
           (buffer (current-buffer)))
       (pop-to-buffer nil)
       (Info-goto-node (concat latex-help-file cmd))
       (if (fboundp 'show-temp-buffer)
           (show-temp-buffer (current-buffer) t)
         (pop-to-buffer buffer))))))

(defun latex-help-guess ()
 "Return the word point is on as a string, if it's between two
word-constituent characters. If not, but it immediately follows one,
move back first.  Otherwise, if point precedes a word constituent,
move forward first.  Otherwise, move backwards until a word constituent
is found and get that word; if you reach a newline first, move forward
instead.

This function has been tweaked to deal better with latex commands.

Return the LaTeX command point is on as a string.
"
 ;; cl: I am not claiming this to be neither elegant nor fast.
 (save-excursion
   (let ((oldpoint (point)) (start (point)) (end (point))
         (wc "A-Za-z") (nwc "^A-Za-z"))

     (cond
      ((looking-at "\\\\[^A-Za-z]")
       (setq start (point)
             end (+ 2 (point))))

      ((looking-at "\\\\[A-Za-z]+")
       (setq start (match-beginning 0)
             end (match-end 0)))

      (t
       (skip-chars-backward wc)
       (skip-chars-backward "\\\\" (1- (point)))
       (setq start (point))

       (goto-char oldpoint)

       (skip-chars-forward "\\\\" (1+ (point)))
       (skip-chars-forward wc)
       (setq end (point))

       (if (and (eq start oldpoint) (eq end oldpoint))
           (progn
             (skip-chars-backward nwc
                                  (save-excursion (beginning-of-line) (point)))
             (if (eq (preceding-char) ?\n)
                 (progn
                   (skip-chars-forward nwc)
                   (setq start (point))
                   (skip-chars-forward "\\\\" (1+ (point)))
                   (skip-chars-forward wc)
                   (setq end (point)))
               (setq end (point))
               (skip-chars-backward wc)
               (skip-chars-backward "\\\\" (1- (point)))
               (setq start (point)))))
       )
      )
     (ltxh-buffer-substring start end)))
 )

(defun latex-help-get-cmd-alist ()
 "Scoop up the commands in the index of the latex info manual.
The values are saved in `latex-help-cmd-alist' for speed."
 ;; mm, does it contain any cached entries
 (if (not (assoc "\\begin" latex-help-cmd-alist))
     (save-window-excursion
       (setq latex-help-cmd-alist nil)
       (Info-goto-node (concat latex-help-file "Command Index"))
       (if (re-search-forward "::$" nil t)
           (progn
             (end-of-buffer)
             (while (re-search-backward "^\\* \\(.+\\)::$" nil t)
               (setq key (ltxh-buffer-substring (match-beginning 1) (match-end 1)))
               (setq latex-help-cmd-alist
                     (cons (cons key key) latex-help-cmd-alist))))
         (end-of-buffer)
         (while (re-search-backward "^\\* \\(.+\\): *\\(.+\\)\\." nil t)
           (setq key (ltxh-buffer-substring (match-beginning 1) (match-end 1)))
           (setq value (ltxh-buffer-substring (match-beginning 2) (match-end 2)))
           (setq latex-help-cmd-alist
                 (cons (cons key value) latex-help-cmd-alist))))
       ))
 ;; and return the alist.
 latex-help-cmd-alist
 )

(provide 'ltx-help)

;;; ltx-help.el ends here

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