emacs/lisp/emacs-lisp/ewoc.el

;;; ewoc.el -- Utility to maintain a view of a list of objects in a buffer

;; Copyright (C) 1991-2000   Free Software Foundation

;; Author: Per Cederqvist <ceder@lysator.liu.se>
;;	Inge Wallin <inge@lysator.liu.se>
;; Maintainer: monnier@gnu.org
;; Created: 3 Aug 1992
;; Keywords: extensions, lisp

;; This file is part of GNU Emacs.

;; GNU Emacs 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 2, or (at your option)
;; any later version.

;; GNU Emacs 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., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; Ewoc Was Once Cookie
;; But now it's Emacs' Widget for Object Collections

;; As the name implies this derives from the `cookie' package (part
;; of Elib).  The changes are mostly superficial:

;; - uses CL (and its `defstruct'
;; - separate from Elib.
;; - uses its own version of a doubly-linked list which allows us
;;   to merge the elib-wrapper and the elib-node structures into ewoc-node
;; - dropping functions not used by PCL-CVS (the only client of ewoc at the
;;   time of writing)
;; - removing unused arguments
;; - renaming:
;;   elib-node	==>  ewoc--node
;;   collection ==>  ewoc
;;   tin 	==>  ewoc--node
;;   cookie 	==>  data or element or elem

;;     Introduction
;;     ============
;;
;; Ewoc is a package that implements a connection between an
;; dll (a doubly linked list) and the contents of a buffer.
;; Possible uses are dired (have all files in a list, and show them),
;; buffer-list, kom-prioritize (in the LysKOM elisp client) and
;; others.  pcl-cvs.el uses ewoc.el.
;;
;; Ewoc can be considered as the `view' part of a model-view-controller.
;;
;; A `element' can be any lisp object.  When you use the ewoc
;; package you specify a pretty-printer, a function that inserts
;; a printable representation of the element in the buffer.  (The
;; pretty-printer should use "insert" and not
;; "insert-before-markers").
;;
;; A `ewoc' consists of a doubly linked list of elements, a
;; header, a footer and a pretty-printer.  It is displayed at a
;; certain point in a certain buffer.  (The buffer and point are
;; fixed when the ewoc is created).  The header and the footer
;; are constant strings.  They appear before and after the elements.
;;
;; Ewoc does not affect the mode of the buffer in any way. It
;; merely makes it easy to connect an underlying data representation
;; to the buffer contents.
;;
;; A `ewoc--node' is an object that contains one element.  There are
;; functions in this package that given an ewoc--node extracts the data, or
;; gives the next or previous ewoc--node.  (All ewoc--nodes are linked together
;; in a doubly linked list.  The 'previous' ewoc--node is the one that appears
;; before the other in the buffer.)  You should not do anything with
;; an ewoc--node except pass it to the functions in this package.
;;
;; An ewoc is a very dynamic thing.  You can easily add or delete elements.
;; You can apply a function to all elements in an ewoc, etc, etc.
;;
;; Remember that an element can be anything.  Your imagination is the
;; limit!  It is even possible to have another ewoc as an
;; element.  In that way some kind of tree hierarchy can be created.
;;
;; Full documentation will, God willing, soon be available in a
;; Texinfo manual.

;; In the mean time `grep '^(.*ewoc-[^-]' emacs-lisp/ewoc.el' can help
;; you find all the exported functions:
;; 
;; (defun ewoc-create (pretty-printer &optional header footer)
;; (defalias 'ewoc-data 'ewoc--node-data)
;; (defun ewoc-enter-first (ewoc data)
;; (defun ewoc-enter-last (ewoc data)
;; (defun ewoc-enter-after (ewoc node data)
;; (defun ewoc-enter-before (ewoc node data)
;; (defun ewoc-next (ewoc node)
;; (defun ewoc-prev (ewoc node)
;; (defun ewoc-nth (ewoc n)
;; (defun ewoc-map (map-function ewoc &rest args)
;; (defun ewoc-filter (ewoc predicate &rest args)
;; (defun ewoc-locate (ewoc pos &optional guess)
;; (defun ewoc-invalidate (ewoc &rest nodes)
;; (defun ewoc-goto-prev (ewoc pos arg)
;; (defun ewoc-goto-next (ewoc pos arg)
;; (defun ewoc-goto-node (ewoc node)
;; (defun ewoc-refresh (ewoc)
;; (defun ewoc-collect (ewoc predicate &rest args)
;; (defun ewoc-buffer (ewoc)
;; (defun ewoc-get-hf (ewoc)
;; (defun ewoc-set-hf (ewoc header footer)

;;     Coding conventions
;;     ==================
;;
;; All functions of course start with `ewoc'.  Functions and macros
;; starting with the prefix `ewoc--' are meant for internal use,
;; while those starting with `ewoc-' are exported for public use.
;; There are currently no global or buffer-local variables used.


;;; Code:

(eval-when-compile (require 'cl))	;because of CL compiler macros

;; The doubly linked list is implemented as a circular list
;; with a dummy node first and last. The dummy node is used as
;; "the dll" (or rather is the dll handle passed around).

(defstruct (ewoc--node
	    (:type vector)		;required for ewoc--node-branch hack
	    (:constructor ewoc--node-create (start-marker data)))
  left right data start-marker)

(defalias 'ewoc--node-branch 'aref)

(defun ewoc--dll-create ()
  "Create an empty doubly linked list."
  (let ((dummy-node (ewoc--node-create 'DL-LIST 'DL-LIST)))
    (setf (ewoc--node-right dummy-node) dummy-node)
    (setf (ewoc--node-left dummy-node) dummy-node)
    dummy-node))

(defun ewoc--node-enter-before (node elemnode)
  "Insert ELEMNODE before NODE in a DLL."
  (assert (and (null (ewoc--node-left elemnode)) (null (ewoc--node-right elemnode))))
  (setf (ewoc--node-left elemnode) (ewoc--node-left node))
  (setf (ewoc--node-right elemnode) node)
  (setf (ewoc--node-right (ewoc--node-left node)) elemnode)
  (setf (ewoc--node-left node) elemnode))

(defun ewoc--node-enter-first (dll node)
  "Add a free floating NODE first in DLL."
  (ewoc--node-enter-before (ewoc--node-right dll) node))

(defun ewoc--node-enter-last (dll node)
  "Add a free floating NODE last in DLL."
  (ewoc--node-enter-before dll node))

(defun ewoc--node-next (dll node)
  "Return the node after NODE, or nil if NODE is the last node."
  (unless (eq (ewoc--node-right node) dll) (ewoc--node-right node)))

(defun ewoc--node-prev (dll node)
  "Return the node before NODE, or nil if NODE is the first node."
  (unless (eq (ewoc--node-left node) dll) (ewoc--node-left node)))

(defun ewoc--node-delete (node)
  "Unbind NODE from its doubly linked list and return it."
  ;; This is a no-op when applied to the dummy node. This will return
  ;; nil if applied to the dummy node since it always contains nil.
  (setf (ewoc--node-right (ewoc--node-left node)) (ewoc--node-right node))
  (setf (ewoc--node-left (ewoc--node-right node)) (ewoc--node-left node))
  (setf (ewoc--node-left node) nil)
  (setf (ewoc--node-right node) nil)
  node)

(defun ewoc--node-nth (dll n)
  "Return the Nth node from the doubly linked list DLL.
N counts from zero. If DLL is not that long, nil is returned.
If N is negative, return the -(N+1)th last element.
Thus, (ewoc--node-nth dll 0) returns the first node,
and (ewoc--node-nth dll -1) returns the last node."
  ;; Branch 0 ("follow left pointer") is used when n is negative.
  ;; Branch 1 ("follow right pointer") is used otherwise.
  (let* ((branch (if (< n 0) 0 1))
	 (node   (ewoc--node-branch dll branch)))
    (if (< n 0) (setq n (- -1 n)))
    (while (and (not (eq dll node)) (> n 0))
      (setq node (ewoc--node-branch node branch))
      (setq n (1- n)))
    (unless (eq dll node) node)))


;;; The ewoc data type

(defstruct (ewoc
	    (:constructor nil)
	    (:constructor ewoc--create
			  (buffer pretty-printer header footer dll))
	    (:conc-name ewoc--))
  buffer pretty-printer header footer dll last-node)

(defmacro ewoc--set-buffer-bind-dll-let* (ewoc varlist &rest forms)
  "Execute FORMS with ewoc--buffer selected as current buffer,
dll bound to ewoc--dll, and VARLIST bound as in a let*.
dll will be bound when VARLIST is initialized, but the current
buffer will *not* have been changed.
Return value of last form in FORMS."
  (let ((old-buffer (make-symbol "old-buffer"))
	(hnd (make-symbol "ewoc")))
    (` (let* (((, old-buffer) (current-buffer))
	      ((, hnd) (, ewoc))
	      (dll (ewoc--dll (, hnd)))
	      (,@ varlist))
	 (set-buffer (ewoc--buffer (, hnd)))
	 (unwind-protect
	     (progn (,@ forms))
	   (set-buffer (, old-buffer)))))))

(defmacro ewoc--set-buffer-bind-dll (ewoc &rest forms)
  `(ewoc--set-buffer-bind-dll-let* ,ewoc nil ,@forms))

(defsubst ewoc--filter-hf-nodes (ewoc node)
  "Evaluate NODE once and return it.
BUT if it is the header or the footer in EWOC return nil instead."
  (unless (or (eq node (ewoc--header ewoc))
	      (eq node (ewoc--footer ewoc)))
    node))


(defun ewoc--create-node (data pretty-printer pos)
  "Call PRETTY-PRINTER with point set at POS in current buffer.
Remember the start position. Create a wrapper containing that
start position and the element DATA."
  (save-excursion
    ;; Remember the position as a number so that it doesn't move
    ;; when we insert the string.
    (when (markerp pos) (setq pos (marker-position pos)))
    (goto-char pos)
    (let ((inhibit-read-only t))
      ;; Insert the trailing newline using insert-before-markers
      ;; so that the start position for the next element is updated.
      (insert-before-markers ?\n)
      ;; Move back, and call the pretty-printer.
      (backward-char 1)
      (funcall pretty-printer data)
      (ewoc--node-create (copy-marker pos) data))))


(defun ewoc--delete-node-internal (ewoc node)
  "Delete a data string from EWOC.
Can not be used on the footer. Returns the wrapper that is deleted.
The start-marker in the wrapper is set to nil, so that it doesn't
consume any more resources."
  (let ((dll (ewoc--dll ewoc))
	(inhibit-read-only t))
    ;; If we are about to delete the node pointed at by last-node,
    ;; set last-node to nil.
    (if (eq (ewoc--last-node ewoc) node)
	(setf (ewoc--last-node ewoc) nil))

    (delete-region (ewoc--node-start-marker node)
		   (ewoc--node-start-marker (ewoc--node-next dll node)))
    (set-marker (ewoc--node-start-marker node) nil)
    ;; Delete the node, and return the wrapper.
    (ewoc--node-delete node)))


(defun ewoc--refresh-node (pp node)
  "Redisplay the element represented by NODE using the pretty-printer PP."
  (let ((inhibit-read-only t))
    (save-excursion
      ;; First, remove the string from the buffer:
      (delete-region (ewoc--node-start-marker node)
		     (1- (marker-position
			  (ewoc--node-start-marker (ewoc--node-right node)))))
      ;; Calculate and insert the string.
      (goto-char (ewoc--node-start-marker node))
      (funcall pp (ewoc--node-data node)))))

;;; ===========================================================================
;;;                  Public members of the Ewoc package


(defun ewoc-create (pretty-printer &optional header footer)
  "Create an empty ewoc.

The ewoc will be inserted in the current buffer at the current position.

PRETTY-PRINTER should be a function that takes one argument, an
element, and inserts a string representing it in the buffer (at
point). The string PRETTY-PRINTER inserts may be empty or span
several linse. A trailing newline will always be inserted
automatically. The PRETTY-PRINTER should use insert, and not
insert-before-markers.

Optional third argument HEADER is a string that will always be
present at the top of the ewoc. HEADER should end with a
newline.  Optionaly fourth argument FOOTER is similar, and will
be inserted at the bottom of the ewoc."
  (let ((new-ewoc
	 (ewoc--create (current-buffer)
		       pretty-printer nil nil (ewoc--dll-create)))
	(pos (point)))
    (ewoc--set-buffer-bind-dll new-ewoc
      ;; Set default values
      (unless header (setq header ""))
      (unless footer (setq footer ""))
      (setf (ewoc--node-start-marker dll) (copy-marker pos))
      (let ((foot (ewoc--create-node footer (lambda (x) (insert footer)) pos))
	    (head (ewoc--create-node header (lambda (x) (insert header)) pos)))
	(ewoc--node-enter-first dll head)
	(ewoc--node-enter-last  dll foot)
	(setf (ewoc--header new-ewoc) head)
	(setf (ewoc--footer new-ewoc) foot)))
    ;; Return the ewoc
    new-ewoc))

(defalias 'ewoc-data 'ewoc--node-data)

(defun ewoc-enter-first (ewoc data)
  "Enter DATA first in EWOC."
  (ewoc--set-buffer-bind-dll ewoc
    (ewoc-enter-after ewoc (ewoc--node-nth dll 0) data)))

(defun ewoc-enter-last (ewoc data)
  "Enter DATA last in EWOC."
  (ewoc--set-buffer-bind-dll ewoc
    (ewoc-enter-before ewoc (ewoc--node-nth dll -1) data)))


(defun ewoc-enter-after (ewoc node data)
  "Enter a new element DATA after NODE in EWOC."
  (ewoc--set-buffer-bind-dll ewoc
    (ewoc-enter-before ewoc (ewoc--node-next dll node) data)))

(defun ewoc-enter-before (ewoc node data)
  "Enter a new element DATA before NODE in EWOC."
  (ewoc--set-buffer-bind-dll ewoc
    (ewoc--node-enter-before
     node
     (ewoc--create-node
      data
      (ewoc--pretty-printer ewoc)
      (ewoc--node-start-marker node)))))

(defun ewoc-next (ewoc node)
  "Get the next node.
Returns nil if NODE is nil or the last element."
  (when node
    (ewoc--filter-hf-nodes
     ewoc (ewoc--node-next (ewoc--dll ewoc) node))))

(defun ewoc-prev (ewoc node)
  "Get the previous node.
Returns nil if NODE is nil or the first element."
  (when node
    (ewoc--filter-hf-nodes
     ewoc
     (ewoc--node-prev (ewoc--dll ewoc) node))))


(defun ewoc-nth (ewoc n)
  "Return the Nth node.
N counts from zero. Nil is returned if there is less than N elements.
If N is negative, return the -(N+1)th last element.
Thus, (ewoc-nth dll 0) returns the first node,
and (ewoc-nth dll -1) returns the last node.
Use `ewoc--node-data' to extract the data from the node."
  ;; Skip the header (or footer, if n is negative).
  (setq n (if (< n 0) (1- n) (1+ n)))
  (ewoc--filter-hf-nodes ewoc
		  (ewoc--node-nth (ewoc--dll ewoc) n)))

(defun ewoc-map (map-function ewoc &rest args)
  "Apply MAP-FUNCTION to all elements in EWOC.
MAP-FUNCTION is applied to the first element first.
If MAP-FUNCTION returns non-nil the element will be refreshed (its
pretty-printer will be called once again).

Note that the buffer for EWOC will be current buffer when MAP-FUNCTION 
is called.  MAP-FUNCTION must restore the current buffer to BUFFER before 
it returns, if it changes it.

If more than two arguments are given, the remaining
arguments will be passed to MAP-FUNCTION."
  (ewoc--set-buffer-bind-dll-let* ewoc
      ((footer (ewoc--footer ewoc))
       (node (ewoc--node-nth dll 1)))
    (while (not (eq node footer))
      (if (apply map-function (ewoc--node-data node) args)
	  (ewoc--refresh-node (ewoc--pretty-printer ewoc) node))
      (setq node (ewoc--node-next dll node)))))

(defun ewoc-filter (ewoc predicate &rest args)
  "Remove all elements in EWOC for which PREDICATE returns nil.
Note that the buffer for EWOC will be current-buffer when PREDICATE 
is called. PREDICATE must restore the current buffer before it returns
if it changes it.
The PREDICATE is called with the element as its first argument. If any
ARGS are given they will be passed to the PREDICATE."
  (ewoc--set-buffer-bind-dll-let* ewoc
      ((node (ewoc--node-nth dll 1))
       (footer (ewoc--footer ewoc))
       (next nil))
    (while (not (eq node footer))
      (setq next (ewoc--node-next dll node))
      (unless (apply predicate (ewoc--node-data node) args)
	(ewoc--delete-node-internal ewoc node))
      (setq node next))))

(defun ewoc-locate (ewoc pos &optional guess)
  "Return the node that POS (a buffer position) is within.
POS may be a marker or an integer.
GUESS should be a node that it is likely that POS is near.

If POS points before the first element, the first node is returned.
If POS points after the last element, the last node is returned.
If the EWOC is empty, nil is returned."
  (ewoc--set-buffer-bind-dll-let* ewoc
      ((footer (ewoc--footer ewoc)))

    (cond
     ;; Nothing present?
     ((eq (ewoc--node-nth dll 1) (ewoc--node-nth dll -1))
      nil)

     ;; Before second elem?
     ((< pos (ewoc--node-start-marker (ewoc--node-nth dll 2)))
      (ewoc--node-nth dll 1))

     ;; After one-before-last elem?
     ((>= pos (ewoc--node-start-marker (ewoc--node-nth dll -2)))
      (ewoc--node-nth dll -2))

     ;; We now know that pos is within a elem.
     (t
      ;; Make an educated guess about which of the three known
      ;; node'es (the first, the last, or GUESS) is nearest.
      (let* ((best-guess (ewoc--node-nth dll 1))
	     (distance (abs (- pos (ewoc--node-start-marker best-guess)))))
	(when guess
	  (let ((d (abs (- pos (ewoc--node-start-marker guess)))))
	    (when (< d distance)
	      (setq distance d)
	      (setq best-guess guess))))

	(let* ((g (ewoc--node-nth dll -1))	;Check the last elem
	       (d (abs (- pos (ewoc--node-start-marker g)))))
	  (when (< d distance)
	    (setq distance d)
	    (setq best-guess g)))

	(when (ewoc--last-node ewoc) ;Check "previous".
	  (let* ((g (ewoc--last-node ewoc))
		 (d (abs (- pos (ewoc--node-start-marker g)))))
	    (when (< d distance)
	      (setq distance d)
	      (setq best-guess g))))

	;; best-guess is now a "best guess".
	;; Find the correct node. First determine in which direction
	;; it lies, and then move in that direction until it is found.
    
	(cond
	 ;; Is pos after the guess?
	 ((>= pos
	      (ewoc--node-start-marker best-guess))
	  ;; Loop until we are exactly one node too far down...
	  (while (>= pos (ewoc--node-start-marker best-guess))
	    (setq best-guess (ewoc--node-next dll best-guess)))
	  ;; ...and return the previous node.
	  (ewoc--node-prev dll best-guess))

	 ;; Pos is before best-guess
	 (t
	  (while (< pos (ewoc--node-start-marker best-guess))
	    (setq best-guess (ewoc--node-prev dll best-guess)))
	  best-guess)))))))

(defun ewoc-invalidate (ewoc &rest nodes)
  "Refresh some elements.
The pretty-printer that for EWOC will be called for all NODES."
  (ewoc--set-buffer-bind-dll ewoc
    (dolist (node nodes)
      (ewoc--refresh-node (ewoc--pretty-printer ewoc) node))))

(defun ewoc-goto-prev (ewoc pos arg)
  "Move point to the ARGth previous element.
Don't move if we are at the first element, or if EWOC is empty.
Returns the node we moved to."
  (ewoc--set-buffer-bind-dll-let* ewoc
      ((node (ewoc-locate ewoc pos (ewoc--last-node ewoc))))
    (when node
      (while (and node (> arg 0))
	(setq arg (1- arg))
	(setq node (ewoc--node-prev dll node)))
      ;; Never step above the first element.
      (unless (ewoc--filter-hf-nodes ewoc node)
	(setq node (ewoc--node-nth dll 1)))
      (ewoc-goto-node ewoc node))))

(defun ewoc-goto-next (ewoc pos arg)
  "Move point to the ARGth next element.
Don't move if we are at the last element.
Returns the node."
  (ewoc--set-buffer-bind-dll-let* ewoc
      ((node (ewoc-locate ewoc pos (ewoc--last-node ewoc))))
    (while (and node (> arg 0))
      (setq arg (1- arg))
      (setq node (ewoc--node-next dll node)))
    ;; Never step below the first element.
    (unless (ewoc--filter-hf-nodes ewoc node)
      (setq node (ewoc--node-nth dll -2)))
    (ewoc-goto-node ewoc node)))

(defun ewoc-goto-node (ewoc node)
  "Move point to NODE."
  (ewoc--set-buffer-bind-dll ewoc
    (goto-char (ewoc--node-start-marker node))
    (if goal-column (move-to-column goal-column))
    (setf (ewoc--last-node ewoc) node)))

(defun ewoc-refresh (ewoc)
  "Refresh all data in EWOC.
The pretty-printer that was specified when the EWOC was created
will be called for all elements in EWOC.
Note that `ewoc-invalidate' is more efficient if only a small
number of elements needs to be refreshed."
  (ewoc--set-buffer-bind-dll-let* ewoc
      ((footer (ewoc--footer ewoc)))
    (let ((inhibit-read-only t))
      (delete-region (ewoc--node-start-marker (ewoc--node-nth dll 1))
		     (ewoc--node-start-marker footer))
      (goto-char (ewoc--node-start-marker footer))
      (let ((node (ewoc--node-nth dll 1)))
	(while (not (eq node footer))
	  (set-marker (ewoc--node-start-marker node) (point))
	  (funcall (ewoc--pretty-printer ewoc)
		   (ewoc--node-data node))
	  (insert "\n")
	  (setq node (ewoc--node-next dll node)))))
    (set-marker (ewoc--node-start-marker footer) (point))))

(defun ewoc-collect (ewoc predicate &rest args)
  "Select elements from EWOC using PREDICATE.
Return a list of all selected data elements.
PREDICATE is a function that takes a data element as its first argument.
The elements on the returned list will appear in the same order as in
the buffer.  You should not rely on in which order PREDICATE is
called.
Note that the buffer the EWOC is displayed in is current-buffer
when PREDICATE is called.  If PREDICATE must restore current-buffer if
it changes it.
If more than two arguments are given the
remaining arguments will be passed to PREDICATE."
  (ewoc--set-buffer-bind-dll-let* ewoc
      ((header (ewoc--header ewoc))
       (node (ewoc--node-nth dll -2))
       result)
    (while (not (eq node header))
      (if (apply predicate (ewoc--node-data node) args)
	  (push (ewoc--node-data node) result))
      (setq node (ewoc--node-prev dll node)))
    result))

(defun ewoc-buffer (ewoc)
  "Return the buffer that is associated with EWOC.
Returns nil if the buffer has been deleted."
  (let ((buf (ewoc--buffer ewoc)))
    (when (buffer-name buf) buf)))

(defun ewoc-get-hf (ewoc)
  "Return a cons cell containing the (HEADER . FOOTER) of EWOC."
  (cons (ewoc--node-data (ewoc--header ewoc))
	(ewoc--node-data (ewoc--footer ewoc))))

(defun ewoc-set-hf (ewoc header footer)
  "Set the HEADER and FOOTER of EWOC."
  (setf (ewoc--node-data (ewoc--header ewoc)) header)
  (setf (ewoc--node-data (ewoc--footer ewoc)) footer)
  (ewoc--refresh-node (lambda (x) (insert header)) (ewoc--header ewoc))
  (ewoc--refresh-node (lambda (x) (insert footer)) (ewoc--footer ewoc)))


(provide 'ewoc)

;;; Local Variables:
;;; eval: (put 'ewoc--set-buffer-bind-dll 'lisp-indent-hook 1)
;;; eval: (put 'ewoc--set-buffer-bind-dll-let* 'lisp-indent-hook 2)
;;; End:

;;; ewoc.el ends here