336 lines
9.0 KiB
JavaScript
336 lines
9.0 KiB
JavaScript
/**
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* This code is mostly from the old Etherpad. Please help us to comment this code.
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* This helps other people to understand this code better and helps them to improve it.
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* TL;DR COMMENTS ON THIS FILE ARE HIGHLY APPRECIATED
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*/
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/**
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* Copyright 2009 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS-IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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var Changeset = require('/easysync2').Changeset;
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var extend = require('/ace2_common').extend;
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var undoModule = (function()
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{
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var stack = (function()
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{
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var stackElements = [];
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// two types of stackElements:
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// 1) { elementType: UNDOABLE_EVENT, eventType: "anything", [backset: <changeset>,]
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// [selStart: <char number>, selEnd: <char number>, selFocusAtStart: <boolean>] }
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// 2) { elementType: EXTERNAL_CHANGE, changeset: <changeset> }
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// invariant: no two consecutive EXTERNAL_CHANGEs
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var numUndoableEvents = 0;
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var UNDOABLE_EVENT = "undoableEvent";
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var EXTERNAL_CHANGE = "externalChange";
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function clearStack()
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{
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stackElements.length = 0;
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stackElements.push(
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{
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elementType: UNDOABLE_EVENT,
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eventType: "bottom"
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});
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numUndoableEvents = 1;
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}
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clearStack();
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function pushEvent(event)
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{
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var e = extend(
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{}, event);
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e.elementType = UNDOABLE_EVENT;
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stackElements.push(e);
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numUndoableEvents++;
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//dmesg("pushEvent backset: "+event.backset);
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}
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function pushExternalChange(cs)
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{
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var idx = stackElements.length - 1;
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if (stackElements[idx].elementType == EXTERNAL_CHANGE)
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{
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stackElements[idx].changeset = Changeset.compose(stackElements[idx].changeset, cs, getAPool());
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}
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else
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{
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stackElements.push(
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{
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elementType: EXTERNAL_CHANGE,
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changeset: cs
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});
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}
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}
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function _exposeEvent(nthFromTop)
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{
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// precond: 0 <= nthFromTop < numUndoableEvents
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var targetIndex = stackElements.length - 1 - nthFromTop;
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var idx = stackElements.length - 1;
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while (idx > targetIndex || stackElements[idx].elementType == EXTERNAL_CHANGE)
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{
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if (stackElements[idx].elementType == EXTERNAL_CHANGE)
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{
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var ex = stackElements[idx];
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var un = stackElements[idx - 1];
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if (un.backset)
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{
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var excs = ex.changeset;
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var unbs = un.backset;
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un.backset = Changeset.follow(excs, un.backset, false, getAPool());
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ex.changeset = Changeset.follow(unbs, ex.changeset, true, getAPool());
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if ((typeof un.selStart) == "number")
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{
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var newSel = Changeset.characterRangeFollow(excs, un.selStart, un.selEnd);
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un.selStart = newSel[0];
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un.selEnd = newSel[1];
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if (un.selStart == un.selEnd)
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{
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un.selFocusAtStart = false;
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}
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}
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}
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stackElements[idx - 1] = ex;
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stackElements[idx] = un;
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if (idx >= 2 && stackElements[idx - 2].elementType == EXTERNAL_CHANGE)
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{
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ex.changeset = Changeset.compose(stackElements[idx - 2].changeset, ex.changeset, getAPool());
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stackElements.splice(idx - 2, 1);
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idx--;
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}
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}
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else
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{
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idx--;
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}
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}
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}
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function getNthFromTop(n)
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{
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// precond: 0 <= n < numEvents()
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_exposeEvent(n);
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return stackElements[stackElements.length - 1 - n];
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}
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function numEvents()
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{
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return numUndoableEvents;
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}
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function popEvent()
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{
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// precond: numEvents() > 0
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_exposeEvent(0);
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numUndoableEvents--;
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return stackElements.pop();
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}
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return {
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numEvents: numEvents,
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popEvent: popEvent,
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pushEvent: pushEvent,
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pushExternalChange: pushExternalChange,
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clearStack: clearStack,
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getNthFromTop: getNthFromTop
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};
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})();
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// invariant: stack always has at least one undoable event
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var undoPtr = 0; // zero-index from top of stack, 0 == top
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function clearHistory()
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{
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stack.clearStack();
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undoPtr = 0;
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}
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function _charOccurrences(str, c)
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{
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var i = 0;
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var count = 0;
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while (i >= 0 && i < str.length)
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{
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i = str.indexOf(c, i);
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if (i >= 0)
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{
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count++;
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i++;
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}
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}
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return count;
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}
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function _opcodeOccurrences(cs, opcode)
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{
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return _charOccurrences(Changeset.unpack(cs).ops, opcode);
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}
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function _mergeChangesets(cs1, cs2)
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{
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if (!cs1) return cs2;
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if (!cs2) return cs1;
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// Rough heuristic for whether changesets should be considered one action:
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// each does exactly one insertion, no dels, and the composition does also; or
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// each does exactly one deletion, no ins, and the composition does also.
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// A little weird in that it won't merge "make bold" with "insert char"
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// but will merge "make bold and insert char" with "insert char",
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// though that isn't expected to come up.
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var plusCount1 = _opcodeOccurrences(cs1, '+');
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var plusCount2 = _opcodeOccurrences(cs2, '+');
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var minusCount1 = _opcodeOccurrences(cs1, '-');
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var minusCount2 = _opcodeOccurrences(cs2, '-');
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if (plusCount1 == 1 && plusCount2 == 1 && minusCount1 == 0 && minusCount2 == 0)
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{
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var merge = Changeset.compose(cs1, cs2, getAPool());
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var plusCount3 = _opcodeOccurrences(merge, '+');
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var minusCount3 = _opcodeOccurrences(merge, '-');
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if (plusCount3 == 1 && minusCount3 == 0)
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{
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return merge;
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}
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}
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else if (plusCount1 == 0 && plusCount2 == 0 && minusCount1 == 1 && minusCount2 == 1)
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{
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var merge = Changeset.compose(cs1, cs2, getAPool());
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var plusCount3 = _opcodeOccurrences(merge, '+');
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var minusCount3 = _opcodeOccurrences(merge, '-');
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if (plusCount3 == 0 && minusCount3 == 1)
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{
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return merge;
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}
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}
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return null;
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}
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function reportEvent(event)
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{
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var topEvent = stack.getNthFromTop(0);
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function applySelectionToTop()
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{
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if ((typeof event.selStart) == "number")
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{
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topEvent.selStart = event.selStart;
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topEvent.selEnd = event.selEnd;
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topEvent.selFocusAtStart = event.selFocusAtStart;
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}
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}
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if ((!event.backset) || Changeset.isIdentity(event.backset))
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{
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applySelectionToTop();
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}
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else
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{
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var merged = false;
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if (topEvent.eventType == event.eventType)
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{
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var merge = _mergeChangesets(event.backset, topEvent.backset);
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if (merge)
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{
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topEvent.backset = merge;
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//dmesg("reportEvent merge: "+merge);
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applySelectionToTop();
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merged = true;
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}
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}
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if (!merged)
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{
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stack.pushEvent(event);
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}
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undoPtr = 0;
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}
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}
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function reportExternalChange(changeset)
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{
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if (changeset && !Changeset.isIdentity(changeset))
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{
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stack.pushExternalChange(changeset);
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}
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}
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function _getSelectionInfo(event)
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{
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if ((typeof event.selStart) != "number")
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{
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return null;
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}
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else
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{
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return {
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selStart: event.selStart,
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selEnd: event.selEnd,
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selFocusAtStart: event.selFocusAtStart
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};
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}
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}
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// For "undo" and "redo", the change event must be returned
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// by eventFunc and NOT reported through the normal mechanism.
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// "eventFunc" should take a changeset and an optional selection info object,
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// or can be called with no arguments to mean that no undo is possible.
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// "eventFunc" will be called exactly once.
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function performUndo(eventFunc)
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{
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if (undoPtr < stack.numEvents() - 1)
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{
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var backsetEvent = stack.getNthFromTop(undoPtr);
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var selectionEvent = stack.getNthFromTop(undoPtr + 1);
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var undoEvent = eventFunc(backsetEvent.backset, _getSelectionInfo(selectionEvent));
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stack.pushEvent(undoEvent);
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undoPtr += 2;
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}
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else eventFunc();
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}
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function performRedo(eventFunc)
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{
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if (undoPtr >= 2)
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{
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var backsetEvent = stack.getNthFromTop(0);
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var selectionEvent = stack.getNthFromTop(1);
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eventFunc(backsetEvent.backset, _getSelectionInfo(selectionEvent));
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stack.popEvent();
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undoPtr -= 2;
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}
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else eventFunc();
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}
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function getAPool()
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{
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return undoModule.apool;
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}
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return {
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clearHistory: clearHistory,
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reportEvent: reportEvent,
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reportExternalChange: reportExternalChange,
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performUndo: performUndo,
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performRedo: performRedo,
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enabled: true,
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apool: null
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}; // apool is filled in by caller
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})();
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exports.undoModule = undoModule;
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