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+;;; jupiter.el --- An implementation of the Jupiter algorithm
+;;
+;; Copyright (C) 2008, 2009 Jan Moringen
+;;
+;; Author: Jan Moringen <scymtym@users.sourceforge.net>
+;; Keywords: rudel, jupiter, algorithm, distributed, integrity
+;; X-RCS: $Id:$
+;;
+;; This file is part of Rudel.
+;;
+;; Rudel 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.
+;;
+;; Rudel 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 Rudel. If not, see <http://www.gnu.org/licenses>.
+
+
+;;; Commentary:
+;;
+;; This file contains an implementation of the jupiter algorithm,
+;; which ensures the synchronization of data shared between multiple
+;; peers despite differences in network latency.
+;;
+;; This implementation is partly based on the implementation used in
+;; the obby library <http://gobby.0x539.de/trac/>. Note, however, that
+;; the details of the implementations differ.
+
+
+;;; History:
+;;
+;; 0.1 - Initial revision.
+
+
+;;; Code:
+;;
+
+(eval-when-compile
+  (require 'cl))
+
+(require 'eieio)
+
+(require 'jupiter-operation)
+(require 'jupiter-insert)
+(require 'jupiter-delete)
+(require 'jupiter-compound)
+(require 'jupiter-nop)
+
+
+;;; Class jupiter-context
+;;
+
+(defclass jupiter-context ()
+  ((local-revision  :initarg  :local-revision
+		    :type     (integer 0)
+		    :initform 0
+		    :documentation
+		    "Revision number of the local data.")
+   (remote-revision :initarg  :remote-revision
+		    :type     (integer 0)
+		    :initform 0
+		    :documentation
+		    "Revision number of the remote data.")
+   (local-log       :initarg  :local-log
+		    :type     list
+		    :initform nil
+		    :documentation
+		    "List of local operations, that have not been
+acknowledged by the remote side."))
+  "Objects of this class store the state of one side of a
+concurrent modification activity, which is synchronized using the
+jupiter algorithm.")
+
+(defmethod jupiter-local-operation ((this jupiter-context) operation)
+  "Store OPERATION in the operation log of THIS and increase local revision count."
+  (with-slots (local-revision local-log) this
+    (push (cons local-revision operation) local-log)
+    (incf local-revision)))
+
+(defmethod jupiter-remote-operation ((this jupiter-context)
+				     local-revision remote-revision
+				     operation)
+  "Transform OPERATION with revisions LOCAL-REVISION and REMOTE-REVISION using the local operations stored in THIS.
+LOCAL-REVISION is the local revision of THIS context, the remote
+site is referring to."
+  (let ((transformed-operation operation))
+    (with-slots ((this-remote-revision :remote-revision)
+		 local-log) this
+
+      ;; Discard stored local operations which are older than the
+      ;; local revision to which the remote site refers.
+      (setq local-log (delete-if
+		       (lambda (revision) (< revision local-revision))
+		       local-log
+		       :key 'car))
+
+      ;; Transform the operation
+      (mapc
+       (lambda (log-operation)
+
+	 ;; Transform the remote operation using the stored operation.
+	 (setq transformed-operation
+	       (jupiter-transform (cdr log-operation)
+				  transformed-operation))
+
+	 ;; Transform the stored operation using the already
+	 ;; transformed remote operation.
+	 (setf (cdr log-operation)
+	       (jupiter-transform transformed-operation
+				  (cdr log-operation))))
+       (reverse local-log))
+
+      ;; Increase remote revision
+      (incf this-remote-revision))
+    ;; The transformed operation is the result of the computation.
+    transformed-operation)
+  )
+
+(defmethod object-print ((this jupiter-context) &rest strings)
+  "Add revisions and log length to string representation of THIS."
+  (with-slots (local-revision remote-revision local-log) this
+    (call-next-method
+     this
+     (format " local %d" local-revision)
+     (format " remote %d" remote-revision)
+     (format " log-items %d" (length local-log)))))
+
+(provide 'jupiter)
+;;; jupiter.el ends here