codimd/public/vendor/ot/text-operation.js

530 lines
17 KiB
JavaScript
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

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