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+;;; org-id.el --- Global identifier for Org-mode entries
+;; Copyright (C) 2008 Free Software Foundation, Inc.
+;;
+;; Author: Carsten Dominik <carsten at orgmode dot org>
+;; Keywords: outlines, hypermedia, calendar, wp
+;; Homepage: http://orgmode.org
+;; Version: 6.05a
+;;
+;; 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 3 of the License, 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.  If not, see <http://www.gnu.org/licenses/>.
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;
+;;; Commentary:
+
+;; This file implements globally unique identifiers for Org-mode entries.
+;; Identifiers are stored in the entry as an :ID: property.  Functions
+;; are provided that create and retrieve such identifiers, and that find
+;; entries based on the identifier.
+
+;; Identifiers consist of a prefix (default "Org") and a compact encoding
+;; of the creation time of the ID, with microsecond accuracy.  This virtually
+;; guarantees globally unique identifiers, even if several people are
+;; creating ID's at the same time in files that will eventually be used
+;; together.  Even higher security can be achieved by using different
+;; prefix values for each collaborator or file.
+;;
+;; This file defines the following API:
+;;
+;; org-id-get-create
+;;        Create an ID for the entry at point if it does not yet have one.
+;;        Returns the ID (old or new).  This function can be used
+;;        interactively, with prefix argument the creation of a new ID is
+;;        forced, even if there was an old one.
+;;
+;; org-id-get
+;;        Get the ID property of an entry.  Using appropriate arguments
+;;        to the function, it can also create the ID for this entry.
+;;
+;; org-id-goto
+;;        Command to go to a specific ID, this command can be used
+;;        interactively.
+;;
+;; org-id-get-with-outline-path-completion
+;;        Retrieve the ID of an entry, using outline path completion.
+;;        This function can work for multiple files.
+;;
+;; org-id-get-with-outline-drilling
+;;        Retrieve the ID of an entry, using outline path completion.
+;;        This function only works for the current file.
+;;
+;; org-id-find
+;;        Find the location of an entry with specific id.
+;;
+
+(require 'org)
+
+(declare-function message-make-fqdn "message" ())
+
+;;; Customization
+
+(defgroup org-id nil
+  "Options concerning global entry identifiers in Org-mode."
+  :tag "Org ID"
+  :group 'org)
+
+(defcustom org-id-prefix "Org"
+  "The prefix for IDs.
+
+This may be a string, or it can be nil to indicate that no prefix is required.
+When a string, the string should have no space characters as IDs are expected
+to have no space characters in them."
+  :group 'org-id
+  :type '(choice
+          (const :tag "No prefix")
+          (string :tag "Prefix")))
+
+(defcustom org-id-include-domain t
+  "Non-nil means, add the domain name to new IDs.
+This ensures global uniqueness of ID's, and is also suggested by
+RFC 2445 in combination with RFC 822."
+  :group 'org-id
+  :type 'boolean)
+
+(defcustom org-id-locations-file "~/.org-id-locations"
+  "The file for remembering the last ID number generated."
+  :group 'org-id
+  :type 'file)
+
+(defvar org-id-locations nil
+  "List of files with ID's in those files.")
+
+(defcustom org-id-extra-files 'org-agenda-text-search-extra-files
+  "Files to be searched for ID's, besides the agenda files."
+  :group 'org-id
+  :type
+  '(choice
+    (symbol :tag "Variable")
+    (repeat :tag "List of files"
+            (file))))
+
+;;; The API functions
+
+;;;###autoload
+(defun org-id-get-create (&optional force)
+  "Create an ID for the current entry and return it.
+If the entry already has an ID, just return it.
+With optional argument FORCE, force the creation of a new ID."
+  (interactive "P")
+  (when force
+    (org-entry-put (point) "ID" nil))
+  (org-id-get (point) 'create))
+  
+;;;###autoload
+(defun org-id-copy ()
+  "Copy the ID of the entry at point to the kill ring.
+Create an ID if necessary."
+  (interactive)
+  (kill-new (org-id-get nil 'create)))  
+
+;;;###autoload
+(defun org-id-get (&optional pom create prefix)
+  "Get the ID property of the entry at point-or-marker POM.
+If POM is nil, refer to the entry at point.
+If the entry does not have an ID, the function returns nil.
+However, when CREATE is non nil, create an ID if none is present already.
+PREFIX will be passed through to `org-id-new'.
+In any case, the ID of the entry is returned."
+  (let ((id (org-entry-get pom "ID")))
+    (cond
+     ((and id (stringp id) (string-match "\\S-" id))
+      id)
+     (create
+      (setq id (org-id-new prefix))
+      (org-entry-put pom "ID" id)
+      (org-id-add-location id (buffer-file-name (buffer-base-buffer)))
+      id)
+     (t nil))))
+
+;;;###autoload
+(defun org-id-get-with-outline-path-completion (&optional targets)
+  "Use outline-path-completion to retrieve the ID of an entry.
+TARGETS may be a setting for `org-refile-targets' to define the eligible
+headlines.  When omitted, all headlines in all agenda files are
+eligible.
+It returns the ID of the entry.  If necessary, the ID is created."
+  (let* ((org-refile-targets (or targets '((nil . (:maxlevel . 10)))))
+         (org-refile-use-outline-path 
+          (if (caar org-refile-targets) 'file t))
+         (spos (org-refile-get-location "Entry: "))
+         (pom (and spos (move-marker (make-marker) (nth 3 spos) 
+                                     (get-file-buffer (nth 1 spos))))))
+    (prog1 (org-id-get pom 'create)
+      (move-marker pom nil))))
+
+;;;###autoload
+(defun org-id-get-with-outline-drilling (&optional targets)
+  "Use an outline-cycling interface to retrieve the ID of an entry.
+This only finds entries in the current buffer, using `org-get-location'.
+It returns the ID of the entry.  If necessary, the ID is created."
+  (let* ((spos (org-get-location (current-buffer) org-goto-help))
+         (pom (and spos (move-marker (make-marker) (car spos)))))
+    (prog1 (org-id-get pom 'create)
+      (move-marker pom nil))))
+
+;;;###autoload
+(defun org-id-goto (id)
+  "Switch to the buffer containing the entry with id ID.
+Move the cursor to that entry in that buffer."
+  (interactive)
+  (let ((m (org-id-find id 'marker)))
+    (unless m
+      (error "Cannot find entry with ID \"%s\"" id))
+    (switch-to-buffer (marker-buffer m))
+    (goto-char m)
+    (move-marker m nil)
+    (org-show-context)))    
+
+;;;###autoload
+(defun org-id-find (id &optional markerp)
+  "Return the location of the entry with the id ID.
+The return value is a cons cell (file-name . position), or nil
+if there is no entry with that ID.
+With optional argument MARKERP, return the position as a new marker."
+  (let ((file (org-id-find-id-file id))
+        org-agenda-new-buffers where)
+    (when file
+      (setq where (org-id-find-id-in-file id file markerp)))
+    (unless where
+      (org-id-update-id-locations)
+      (setq file (org-id-find-id-file id))
+      (when file
+        (setq where (org-id-find-id-in-file id file markerp))))
+    where))
+
+;;; Internal functions
+
+;; Creating new IDs
+
+(defun org-id-new (&optional prefix)
+  "Create a new globally unique ID.
+
+An ID consists of two parts separated by a colon:
+- a prefix
+- an encoding of the current time to micro-second accuracy
+
+PREFIX can specify the prefix, the default is given by the variable
+`org-id-prefix'.  However, if PREFIX is the symbol `none', don't use any
+prefix even if `org-id-prefix' specifies one.
+
+So a typical ID could look like \"Org:4nd91V40HI\"."
+  (let* ((prefix (if (eq prefix 'none)
+                     nil
+                   (or prefix org-id-prefix)))
+         (etime (org-id-time-to-b62))
+         (postfix (if org-id-include-domain
+                      (progn
+                        (require 'message)
+                        (concat "@" (message-make-fqdn))))))
+    (if prefix
+        (concat prefix ":" etime postfix)
+      (concat etime postfix))))
+
+(defun org-id-int-to-b62-one-digit (i)
+  "Turn an integer between 0 and 61 into a single character 0..9, A..Z, a..z."
+  (cond
+   ((< i 10) (+ ?0 i))
+   ((< i 36) (+ ?A i -10))
+   ((< i 62) (+ ?a i -36))
+   (t (error "Larger that 61"))))
+
+(defun org-id-b62-to-int-one-digit (i)
+  "Turn a character 0..9, A..Z, a..z into a number 0..61.
+The input I may be a character, or a single-letter string."
+  (and (stringp i) (setq i (string-to-char i)))
+  (cond
+   ((and (>= i ?0) (<= i ?9)) (- i ?0))
+   ((and (>= i ?A) (<= i ?Z)) (+ (- i ?A) 10))
+   ((and (>= i ?a) (<= i ?z)) (+ (- i ?a) 36))
+   (t (error "Invalid b62 letter"))))
+
+(defun org-id-int-to-b62 (i &optional length)
+  "Convert an integer to a base-62 number represented as a string."
+  (let ((s ""))
+    (while (> i 0)
+      (setq s (concat (char-to-string
+                       (org-id-int-to-b62-one-digit (mod i 62))) s)
+            i (/ i 62)))
+    (setq length (max 1 (or length 1)))
+    (if (< (length s) length)
+        (setq s (concat (make-string (- length (length s)) ?0) s)))
+    s))
+
+(defun org-id-b62-to-int (s)
+  "Convert a base-62 string into the corresponding integer."
+  (let ((r 0))
+    (mapc (lambda (i) (setq r (+ (* r 62) (org-id-b62-to-int-one-digit i))))
+          s)
+    r))
+
+(defun org-id-time-to-b62 (&optional time)
+  "Encode TIME as a 10-digit string.
+This string holds the time to micro-second accuracy, and can be decoded
+using `org-id-decode'."
+  (setq time (or time (current-time)))
+  (concat (org-id-int-to-b62 (nth 0 time) 3)
+          (org-id-int-to-b62 (nth 1 time) 3)
+          (org-id-int-to-b62 (or (nth 2 time) 0) 4)))
+
+(defun org-id-decode (id)
+  "Split ID into the prefix and the time value that was used to create it.
+The return value is (prefix . time) where PREFIX is nil or a string,
+and time is the usual three-integer representation of time."
+  (let (prefix time parts)
+    (setq parts (org-split-string id ":"))
+    (if (= 2 (length parts))
+        (setq prefix (car parts) time (nth 1 parts))
+      (setq prefix nil time (nth 0 parts)))
+    (setq time (list (org-id-b62-to-int (substring time 0 3))
+                     (org-id-b62-to-int (substring time 3 6))
+                     (org-id-b62-to-int (substring time 6 10))))
+    (cons prefix time)))
+
+;; Storing ID locations (files)
+
+(defun org-id-update-id-locations ()
+  "Scan relevant files for ID's.
+Store the relation between files and corresponding ID's."
+  (interactive)
+  (let ((files (append (org-agenda-files)
+                       (if (symbolp org-id-extra-files)
+                           (symbol-value org-id-extra-files)
+                         org-id-extra-files)))
+        org-agenda-new-buffers
+        file ids reg found id)
+    (while (setq file (pop files))
+      (setq ids nil)
+      (with-current-buffer (org-get-agenda-file-buffer file)
+        (save-excursion
+          (save-restriction
+            (widen)
+            (goto-char (point-min))
+            (while (re-search-forward "^[ \t]*:ID:[ \t]+\\(\\S-+\\)[ \t]*$"
+                                      nil t)
+              (setq id (org-match-string-no-properties 1))
+              (if (member id found)
+                  (error "Duplicate ID \"%s\"" id))
+              (push id found)
+              (push id ids))
+            (push (cons file ids) reg)))))
+    (org-release-buffers org-agenda-new-buffers)
+    (setq org-agenda-new-buffers nil)
+    (setq org-id-locations reg)
+    (org-id-locations-save)))
+
+(defun org-id-locations-save ()
+  "Save `org-id-locations' in `org-id-locations-file'."
+  (with-temp-file org-id-locations-file
+    (print org-id-locations (current-buffer))))
+
+(defun org-id-locations-load ()
+  "Read the data from `org-id-locations-file'."
+  (setq org-id-locations nil)
+  (with-temp-buffer
+    (condition-case nil
+        (progn
+          (insert-file-contents-literally org-id-locations-file)
+          (goto-char (point-min))
+          (setq org-id-locations (read (current-buffer))))
+      (error
+       (message "Could not read org-id-values from %s. Setting it to nil."
+                org-id-locations-file)))))
+
+(defun org-id-add-location (id file)
+  "Add the ID with location FILE to the database of ID loations."
+  (unless org-id-locations (org-id-locations-load))
+  (catch 'exit
+    (let ((locs org-id-locations) list)
+      (while (setq list (pop locs))
+        (when (equal (file-truename file) (file-truename (car list)))
+          (setcdr list (cons id (cdr list)))
+          (throw 'exit t))))
+    (push (list file id) org-id-locations))
+  (org-id-locations-save))
+
+;; Finding entries with specified id
+
+(defun org-id-find-id-file (id)
+  "Query the id database for the file in which this ID is located."
+  (unless org-id-locations (org-id-locations-load))
+  (catch 'found
+    (mapc (lambda (x) (if (member id (cdr x))
+                          (throw 'found (car x))))
+          org-id-locations)
+    nil))
+
+(defun org-id-find-id-in-file (id file &optional markerp)
+  "Return the position of the entry ID in FILE.
+If that files does not exist, or if it does not contain this ID,
+return nil.
+The position is returned as a cons cell (file-name . position).  With
+optional argument MARKERP, return the position as a new marker."
+  (let (org-agenda-new-buffers m buf pos)
+    (cond
+     ((not file) nil)
+     ((not (file-exists-p file)) nil)
+     (t (with-current-buffer (setq buf (org-get-agenda-file-buffer file))
+          (setq pos (org-find-entry-with-id id))
+          (when pos
+            (if markerp
+                (move-marker (make-marker) pos buf)
+              (cons file pos))))))))
+
+(provide 'org-id)
+
+;;; org-id.el ends here
+