/**
* Copyright 2009 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS-IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
undoModule = (function() {
var stack = (function() {
var stackElements = [];
// two types of stackElements:
// 1) { elementType: UNDOABLE_EVENT, eventType: "anything", [backset: <changeset>,]
// [selStart: <char number>, selEnd: <char number>, selFocusAtStart: <boolean>] }
// 2) { elementType: EXTERNAL_CHANGE, changeset: <changeset> }
// invariant: no two consecutive EXTERNAL_CHANGEs
var numUndoableEvents = 0;
var UNDOABLE_EVENT = "undoableEvent";
var EXTERNAL_CHANGE = "externalChange";
function clearStack() {
stackElements.length = 0;
stackElements.push({ elementType: UNDOABLE_EVENT, eventType: "bottom" });
numUndoableEvents = 1;
}
clearStack();
function pushEvent(event) {
var e = extend({}, event);
e.elementType = UNDOABLE_EVENT;
stackElements.push(e);
numUndoableEvents++;
//dmesg("pushEvent backset: "+event.backset);
}
function pushExternalChange(cs) {
var idx = stackElements.length-1;
if (stackElements[idx].elementType == EXTERNAL_CHANGE) {
stackElements[idx].changeset = Changeset.compose(stackElements[idx].changeset, cs, getAPool());
}
else {
stackElements.push({elementType: EXTERNAL_CHANGE, changeset: cs});
}
}
function _exposeEvent(nthFromTop) {
// precond: 0 <= nthFromTop < numUndoableEvents
var targetIndex = stackElements.length - 1 - nthFromTop;
var idx = stackElements.length - 1;
while (idx > targetIndex || stackElements[idx].elementType == EXTERNAL_CHANGE) {
if (stackElements[idx].elementType == EXTERNAL_CHANGE) {
var ex = stackElements[idx];
var un = stackElements[idx-1];
if (un.backset) {
var excs = ex.changeset;
var unbs = un.backset;
un.backset = Changeset.follow(excs, un.backset, false, getAPool());
ex.changeset = Changeset.follow(unbs, ex.changeset, true, getAPool());
if ((typeof un.selStart) == "number") {
var newSel = Changeset.characterRangeFollow(excs, un.selStart, un.selEnd);
un.selStart = newSel[0];
un.selEnd = newSel[1];
if (un.selStart == un.selEnd) {
un.selFocusAtStart = false;
}
}
}
stackElements[idx-1] = ex;
stackElements[idx] = un;
if (idx >= 2 && stackElements[idx-2].elementType == EXTERNAL_CHANGE) {
ex.changeset = Changeset.compose(stackElements[idx-2].changeset,
ex.changeset, getAPool());
stackElements.splice(idx-2, 1);
idx--;
}
}
else {
idx--;
}
}
}
function getNthFromTop(n) {
// precond: 0 <= n < numEvents()
_exposeEvent(n);
return stackElements[stackElements.length - 1 - n];
}
function numEvents() {
return numUndoableEvents;
}
function popEvent() {
// precond: numEvents() > 0
_exposeEvent(0);
numUndoableEvents--;
return stackElements.pop();
}
return {numEvents:numEvents, popEvent:popEvent, pushEvent: pushEvent,
pushExternalChange: pushExternalChange, clearStack: clearStack,
getNthFromTop:getNthFromTop};
})();
// invariant: stack always has at least one undoable event
var undoPtr = 0; // zero-index from top of stack, 0 == top
function clearHistory() {
stack.clearStack();
undoPtr = 0;
}
function _charOccurrences(str, c) {
var i = 0;
var count = 0;
while (i >= 0 && i < str.length) {
i = str.indexOf(c, i);
if (i >= 0) {
count++;
i++;
}
}
return count;
}
function _opcodeOccurrences(cs, opcode) {
return _charOccurrences(Changeset.unpack(cs).ops, opcode);
}
function _mergeChangesets(cs1, cs2) {
if (! cs1) return cs2;
if (! cs2) return cs1;
// Rough heuristic for whether changesets should be considered one action:
// each does exactly one insertion, no dels, and the composition does also; or
// each does exactly one deletion, no ins, and the composition does also.
// A little weird in that it won't merge "make bold" with "insert char"
// but will merge "make bold and insert char" with "insert char",
// though that isn't expected to come up.
var plusCount1 = _opcodeOccurrences(cs1, '+');
var plusCount2 = _opcodeOccurrences(cs2, '+');
var minusCount1 = _opcodeOccurrences(cs1, '-');
var minusCount2 = _opcodeOccurrences(cs2, '-');
if (plusCount1 == 1 && plusCount2 == 1 && minusCount1 == 0 && minusCount2 == 0) {
var merge = Changeset.compose(cs1, cs2, getAPool());
var plusCount3 = _opcodeOccurrences(merge, '+');
var minusCount3 = _opcodeOccurrences(merge, '-');
if (plusCount3 == 1 && minusCount3 == 0) {
return merge;
}
}
else if (plusCount1 == 0 && plusCount2 == 0 && minusCount1 == 1 && minusCount2 == 1) {
var merge = Changeset.compose(cs1, cs2, getAPool());
var plusCount3 = _opcodeOccurrences(merge, '+');
var minusCount3 = _opcodeOccurrences(merge, '-');
if (plusCount3 == 0 && minusCount3 == 1) {
return merge;
}
}
return null;
}
function reportEvent(event) {
var topEvent = stack.getNthFromTop(0);
function applySelectionToTop() {
if ((typeof event.selStart) == "number") {
topEvent.selStart = event.selStart;
topEvent.selEnd = event.selEnd;
topEvent.selFocusAtStart = event.selFocusAtStart;
}
}
if ((! event.backset) || Changeset.isIdentity(event.backset)) {
applySelectionToTop();
}
else {
var merged = false;
if (topEvent.eventType == event.eventType) {
var merge = _mergeChangesets(event.backset, topEvent.backset);
if (merge) {
topEvent.backset = merge;
//dmesg("reportEvent merge: "+merge);
applySelectionToTop();
merged = true;
}
}
if (! merged) {
stack.pushEvent(event);
}
undoPtr = 0;
}
}
function reportExternalChange(changeset) {
if (changeset && ! Changeset.isIdentity(changeset)) {
stack.pushExternalChange(changeset);
}
}
function _getSelectionInfo(event) {
if ((typeof event.selStart) != "number") {
return null;
}
else {
return {selStart: event.selStart, selEnd: event.selEnd,
selFocusAtStart: event.selFocusAtStart};
}
}
// For "undo" and "redo", the change event must be returned
// by eventFunc and NOT reported through the normal mechanism.
// "eventFunc" should take a changeset and an optional selection info object,
// or can be called with no arguments to mean that no undo is possible.
// "eventFunc" will be called exactly once.
function performUndo(eventFunc) {
if (undoPtr < stack.numEvents()-1) {
var backsetEvent = stack.getNthFromTop(undoPtr);
var selectionEvent = stack.getNthFromTop(undoPtr+1);
var undoEvent = eventFunc(backsetEvent.backset, _getSelectionInfo(selectionEvent));
stack.pushEvent(undoEvent);
undoPtr += 2;
}
else eventFunc();
}
function performRedo(eventFunc) {
if (undoPtr >= 2) {
var backsetEvent = stack.getNthFromTop(0);
var selectionEvent = stack.getNthFromTop(1);
eventFunc(backsetEvent.backset, _getSelectionInfo(selectionEvent));
stack.popEvent();
undoPtr -= 2;
}
else eventFunc();
}
function getAPool() {
return undoModule.apool;
}
return {clearHistory:clearHistory, reportEvent:reportEvent, reportExternalChange:reportExternalChange,
performUndo:performUndo, performRedo:performRedo, enabled: true,
apool: null}; // apool is filled in by caller
})();
