mirror of https://github.com/status-im/codimd.git
530 lines
17 KiB
JavaScript
530 lines
17 KiB
JavaScript
if (typeof ot === 'undefined') {
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// Export for browsers
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var ot = {};
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}
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ot.TextOperation = (function () {
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'use strict';
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// Constructor for new operations.
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function TextOperation () {
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if (!this || this.constructor !== TextOperation) {
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// => function was called without 'new'
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return new TextOperation();
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}
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// When an operation is applied to an input string, you can think of this as
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// if an imaginary cursor runs over the entire string and skips over some
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// parts, deletes some parts and inserts characters at some positions. These
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// actions (skip/delete/insert) are stored as an array in the "ops" property.
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this.ops = [];
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// An operation's baseLength is the length of every string the operation
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// can be applied to.
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this.baseLength = 0;
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// The targetLength is the length of every string that results from applying
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// the operation on a valid input string.
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this.targetLength = 0;
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}
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TextOperation.prototype.equals = function (other) {
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if (this.baseLength !== other.baseLength) { return false; }
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if (this.targetLength !== other.targetLength) { return false; }
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if (this.ops.length !== other.ops.length) { return false; }
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for (var i = 0; i < this.ops.length; i++) {
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if (this.ops[i] !== other.ops[i]) { return false; }
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}
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return true;
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};
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// Operation are essentially lists of ops. There are three types of ops:
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//
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// * Retain ops: Advance the cursor position by a given number of characters.
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// Represented by positive ints.
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// * Insert ops: Insert a given string at the current cursor position.
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// Represented by strings.
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// * Delete ops: Delete the next n characters. Represented by negative ints.
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var isRetain = TextOperation.isRetain = function (op) {
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return typeof op === 'number' && op > 0;
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};
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var isInsert = TextOperation.isInsert = function (op) {
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return typeof op === 'string';
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};
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var isDelete = TextOperation.isDelete = function (op) {
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return typeof op === 'number' && op < 0;
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};
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// After an operation is constructed, the user of the library can specify the
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// actions of an operation (skip/insert/delete) with these three builder
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// methods. They all return the operation for convenient chaining.
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// Skip over a given number of characters.
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TextOperation.prototype.retain = function (n) {
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if (typeof n !== 'number') {
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throw new Error("retain expects an integer");
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}
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if (n === 0) { return this; }
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this.baseLength += n;
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this.targetLength += n;
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if (isRetain(this.ops[this.ops.length-1])) {
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// The last op is a retain op => we can merge them into one op.
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this.ops[this.ops.length-1] += n;
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} else {
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// Create a new op.
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this.ops.push(n);
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}
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return this;
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};
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// Insert a string at the current position.
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TextOperation.prototype.insert = function (str) {
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if (typeof str !== 'string') {
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throw new Error("insert expects a string");
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}
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if (str === '') { return this; }
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this.targetLength += str.length;
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var ops = this.ops;
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if (isInsert(ops[ops.length-1])) {
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// Merge insert op.
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ops[ops.length-1] += str;
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} else if (isDelete(ops[ops.length-1])) {
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// It doesn't matter when an operation is applied whether the operation
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// is delete(3), insert("something") or insert("something"), delete(3).
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// Here we enforce that in this case, the insert op always comes first.
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// This makes all operations that have the same effect when applied to
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// a document of the right length equal in respect to the `equals` method.
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if (isInsert(ops[ops.length-2])) {
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ops[ops.length-2] += str;
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} else {
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ops[ops.length] = ops[ops.length-1];
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ops[ops.length-2] = str;
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}
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} else {
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ops.push(str);
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}
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return this;
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};
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// Delete a string at the current position.
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TextOperation.prototype['delete'] = function (n) {
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if (typeof n === 'string') { n = n.length; }
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if (typeof n !== 'number') {
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throw new Error("delete expects an integer or a string");
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}
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if (n === 0) { return this; }
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if (n > 0) { n = -n; }
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this.baseLength -= n;
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if (isDelete(this.ops[this.ops.length-1])) {
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this.ops[this.ops.length-1] += n;
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} else {
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this.ops.push(n);
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}
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return this;
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};
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// Tests whether this operation has no effect.
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TextOperation.prototype.isNoop = function () {
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return this.ops.length === 0 || (this.ops.length === 1 && isRetain(this.ops[0]));
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};
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// Pretty printing.
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TextOperation.prototype.toString = function () {
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// map: build a new array by applying a function to every element in an old
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// array.
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var map = Array.prototype.map || function (fn) {
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var arr = this;
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var newArr = [];
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for (var i = 0, l = arr.length; i < l; i++) {
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newArr[i] = fn(arr[i]);
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}
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return newArr;
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};
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return map.call(this.ops, function (op) {
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if (isRetain(op)) {
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return "retain " + op;
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} else if (isInsert(op)) {
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return "insert '" + op + "'";
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} else {
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return "delete " + (-op);
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}
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}).join(', ');
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};
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// Converts operation into a JSON value.
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TextOperation.prototype.toJSON = function () {
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return this.ops;
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};
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// Converts a plain JS object into an operation and validates it.
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TextOperation.fromJSON = function (ops) {
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var o = new TextOperation();
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for (var i = 0, l = ops.length; i < l; i++) {
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var op = ops[i];
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if (isRetain(op)) {
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o.retain(op);
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} else if (isInsert(op)) {
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o.insert(op);
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} else if (isDelete(op)) {
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o['delete'](op);
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} else {
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throw new Error("unknown operation: " + JSON.stringify(op));
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}
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}
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return o;
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};
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// Apply an operation to a string, returning a new string. Throws an error if
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// there's a mismatch between the input string and the operation.
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TextOperation.prototype.apply = function (str) {
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var operation = this;
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if (str.length !== operation.baseLength) {
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throw new Error("The operation's base length must be equal to the string's length.");
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}
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var newStr = [], j = 0;
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var strIndex = 0;
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var ops = this.ops;
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for (var i = 0, l = ops.length; i < l; i++) {
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var op = ops[i];
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if (isRetain(op)) {
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if (strIndex + op > str.length) {
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throw new Error("Operation can't retain more characters than are left in the string.");
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}
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// Copy skipped part of the old string.
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newStr[j++] = str.slice(strIndex, strIndex + op);
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strIndex += op;
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} else if (isInsert(op)) {
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// Insert string.
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newStr[j++] = op;
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} else { // delete op
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strIndex -= op;
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}
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}
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if (strIndex !== str.length) {
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throw new Error("The operation didn't operate on the whole string.");
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}
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return newStr.join('');
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};
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// Computes the inverse of an operation. The inverse of an operation is the
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// operation that reverts the effects of the operation, e.g. when you have an
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// operation 'insert("hello "); skip(6);' then the inverse is 'delete("hello ");
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// skip(6);'. The inverse should be used for implementing undo.
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TextOperation.prototype.invert = function (str) {
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var strIndex = 0;
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var inverse = new TextOperation();
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var ops = this.ops;
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for (var i = 0, l = ops.length; i < l; i++) {
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var op = ops[i];
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if (isRetain(op)) {
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inverse.retain(op);
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strIndex += op;
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} else if (isInsert(op)) {
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inverse['delete'](op.length);
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} else { // delete op
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inverse.insert(str.slice(strIndex, strIndex - op));
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strIndex -= op;
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}
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}
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return inverse;
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};
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// Compose merges two consecutive operations into one operation, that
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// preserves the changes of both. Or, in other words, for each input string S
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// and a pair of consecutive operations A and B,
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// apply(apply(S, A), B) = apply(S, compose(A, B)) must hold.
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TextOperation.prototype.compose = function (operation2) {
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var operation1 = this;
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if (operation1.targetLength !== operation2.baseLength) {
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throw new Error("The base length of the second operation has to be the target length of the first operation");
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}
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var operation = new TextOperation(); // the combined operation
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var ops1 = operation1.ops, ops2 = operation2.ops; // for fast access
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var i1 = 0, i2 = 0; // current index into ops1 respectively ops2
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var op1 = ops1[i1++], op2 = ops2[i2++]; // current ops
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while (true) {
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// Dispatch on the type of op1 and op2
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if (typeof op1 === 'undefined' && typeof op2 === 'undefined') {
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// end condition: both ops1 and ops2 have been processed
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break;
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}
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if (isDelete(op1)) {
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operation['delete'](op1);
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op1 = ops1[i1++];
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continue;
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}
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if (isInsert(op2)) {
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operation.insert(op2);
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op2 = ops2[i2++];
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continue;
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}
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if (typeof op1 === 'undefined') {
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throw new Error("Cannot compose operations: first operation is too short.");
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}
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if (typeof op2 === 'undefined') {
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throw new Error("Cannot compose operations: first operation is too long.");
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}
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if (isRetain(op1) && isRetain(op2)) {
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if (op1 > op2) {
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operation.retain(op2);
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op1 = op1 - op2;
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op2 = ops2[i2++];
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} else if (op1 === op2) {
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operation.retain(op1);
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op1 = ops1[i1++];
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op2 = ops2[i2++];
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} else {
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operation.retain(op1);
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op2 = op2 - op1;
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op1 = ops1[i1++];
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}
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} else if (isInsert(op1) && isDelete(op2)) {
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if (op1.length > -op2) {
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op1 = op1.slice(-op2);
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op2 = ops2[i2++];
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} else if (op1.length === -op2) {
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op1 = ops1[i1++];
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op2 = ops2[i2++];
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} else {
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op2 = op2 + op1.length;
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op1 = ops1[i1++];
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}
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} else if (isInsert(op1) && isRetain(op2)) {
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if (op1.length > op2) {
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operation.insert(op1.slice(0, op2));
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op1 = op1.slice(op2);
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op2 = ops2[i2++];
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} else if (op1.length === op2) {
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operation.insert(op1);
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op1 = ops1[i1++];
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op2 = ops2[i2++];
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} else {
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operation.insert(op1);
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op2 = op2 - op1.length;
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op1 = ops1[i1++];
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}
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} else if (isRetain(op1) && isDelete(op2)) {
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if (op1 > -op2) {
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operation['delete'](op2);
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op1 = op1 + op2;
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op2 = ops2[i2++];
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} else if (op1 === -op2) {
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operation['delete'](op2);
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op1 = ops1[i1++];
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op2 = ops2[i2++];
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} else {
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operation['delete'](op1);
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op2 = op2 + op1;
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op1 = ops1[i1++];
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}
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} else {
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throw new Error(
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"This shouldn't happen: op1: " +
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JSON.stringify(op1) + ", op2: " +
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JSON.stringify(op2)
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);
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}
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}
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return operation;
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};
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function getSimpleOp (operation, fn) {
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var ops = operation.ops;
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var isRetain = TextOperation.isRetain;
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switch (ops.length) {
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case 1:
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return ops[0];
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case 2:
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return isRetain(ops[0]) ? ops[1] : (isRetain(ops[1]) ? ops[0] : null);
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case 3:
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if (isRetain(ops[0]) && isRetain(ops[2])) { return ops[1]; }
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}
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return null;
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}
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function getStartIndex (operation) {
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if (isRetain(operation.ops[0])) { return operation.ops[0]; }
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return 0;
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}
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// When you use ctrl-z to undo your latest changes, you expect the program not
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// to undo every single keystroke but to undo your last sentence you wrote at
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// a stretch or the deletion you did by holding the backspace key down. This
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// This can be implemented by composing operations on the undo stack. This
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// method can help decide whether two operations should be composed. It
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// returns true if the operations are consecutive insert operations or both
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// operations delete text at the same position. You may want to include other
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// factors like the time since the last change in your decision.
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TextOperation.prototype.shouldBeComposedWith = function (other) {
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if (this.isNoop() || other.isNoop()) { return true; }
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var startA = getStartIndex(this), startB = getStartIndex(other);
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var simpleA = getSimpleOp(this), simpleB = getSimpleOp(other);
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if (!simpleA || !simpleB) { return false; }
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if (isInsert(simpleA) && isInsert(simpleB)) {
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return startA + simpleA.length === startB;
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}
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if (isDelete(simpleA) && isDelete(simpleB)) {
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// there are two possibilities to delete: with backspace and with the
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// delete key.
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return (startB - simpleB === startA) || startA === startB;
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}
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return false;
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};
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// Decides whether two operations should be composed with each other
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// if they were inverted, that is
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// `shouldBeComposedWith(a, b) = shouldBeComposedWithInverted(b^{-1}, a^{-1})`.
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TextOperation.prototype.shouldBeComposedWithInverted = function (other) {
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if (this.isNoop() || other.isNoop()) { return true; }
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var startA = getStartIndex(this), startB = getStartIndex(other);
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var simpleA = getSimpleOp(this), simpleB = getSimpleOp(other);
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if (!simpleA || !simpleB) { return false; }
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if (isInsert(simpleA) && isInsert(simpleB)) {
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return startA + simpleA.length === startB || startA === startB;
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}
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if (isDelete(simpleA) && isDelete(simpleB)) {
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return startB - simpleB === startA;
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}
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return false;
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};
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// Transform takes two operations A and B that happened concurrently and
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// produces two operations A' and B' (in an array) such that
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// `apply(apply(S, A), B') = apply(apply(S, B), A')`. This function is the
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// heart of OT.
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TextOperation.transform = function (operation1, operation2) {
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if (operation1.baseLength !== operation2.baseLength) {
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throw new Error("Both operations have to have the same base length");
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}
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var operation1prime = new TextOperation();
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var operation2prime = new TextOperation();
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var ops1 = operation1.ops, ops2 = operation2.ops;
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var i1 = 0, i2 = 0;
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var op1 = ops1[i1++], op2 = ops2[i2++];
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while (true) {
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// At every iteration of the loop, the imaginary cursor that both
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// operation1 and operation2 have that operates on the input string must
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// have the same position in the input string.
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if (typeof op1 === 'undefined' && typeof op2 === 'undefined') {
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// end condition: both ops1 and ops2 have been processed
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break;
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}
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// next two cases: one or both ops are insert ops
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// => insert the string in the corresponding prime operation, skip it in
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// the other one. If both op1 and op2 are insert ops, prefer op1.
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if (isInsert(op1)) {
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operation1prime.insert(op1);
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operation2prime.retain(op1.length);
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op1 = ops1[i1++];
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continue;
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}
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if (isInsert(op2)) {
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operation1prime.retain(op2.length);
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operation2prime.insert(op2);
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op2 = ops2[i2++];
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continue;
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}
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if (typeof op1 === 'undefined') {
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throw new Error("Cannot compose operations: first operation is too short.");
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}
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if (typeof op2 === 'undefined') {
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throw new Error("Cannot compose operations: first operation is too long.");
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}
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var minl;
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if (isRetain(op1) && isRetain(op2)) {
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// Simple case: retain/retain
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if (op1 > op2) {
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minl = op2;
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op1 = op1 - op2;
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op2 = ops2[i2++];
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} else if (op1 === op2) {
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minl = op2;
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op1 = ops1[i1++];
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op2 = ops2[i2++];
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} else {
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minl = op1;
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op2 = op2 - op1;
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op1 = ops1[i1++];
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}
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operation1prime.retain(minl);
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operation2prime.retain(minl);
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} else if (isDelete(op1) && isDelete(op2)) {
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// Both operations delete the same string at the same position. We don't
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// need to produce any operations, we just skip over the delete ops and
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// handle the case that one operation deletes more than the other.
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if (-op1 > -op2) {
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op1 = op1 - op2;
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op2 = ops2[i2++];
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} else if (op1 === op2) {
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op1 = ops1[i1++];
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op2 = ops2[i2++];
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} else {
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op2 = op2 - op1;
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op1 = ops1[i1++];
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}
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// next two cases: delete/retain and retain/delete
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} else if (isDelete(op1) && isRetain(op2)) {
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if (-op1 > op2) {
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minl = op2;
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op1 = op1 + op2;
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op2 = ops2[i2++];
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} else if (-op1 === op2) {
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minl = op2;
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op1 = ops1[i1++];
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op2 = ops2[i2++];
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} else {
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||
minl = -op1;
|
||
op2 = op2 + op1;
|
||
op1 = ops1[i1++];
|
||
}
|
||
operation1prime['delete'](minl);
|
||
} else if (isRetain(op1) && isDelete(op2)) {
|
||
if (op1 > -op2) {
|
||
minl = -op2;
|
||
op1 = op1 + op2;
|
||
op2 = ops2[i2++];
|
||
} else if (op1 === -op2) {
|
||
minl = op1;
|
||
op1 = ops1[i1++];
|
||
op2 = ops2[i2++];
|
||
} else {
|
||
minl = op1;
|
||
op2 = op2 + op1;
|
||
op1 = ops1[i1++];
|
||
}
|
||
operation2prime['delete'](minl);
|
||
} else {
|
||
throw new Error("The two operations aren't compatible");
|
||
}
|
||
}
|
||
|
||
return [operation1prime, operation2prime];
|
||
};
|
||
|
||
return TextOperation;
|
||
|
||
}());
|
||
|
||
// Export for CommonJS
|
||
if (typeof module === 'object') {
|
||
module.exports = ot.TextOperation;
|
||
} |