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Merge pull request #274 from ckeditor/t/269

Other: Optimized `diff()` function to use `fastDiff()` function internally for large data sets. Closes #269.
Piotrek Koszuliński 7 лет назад
Родитель
Сommit
18c29f342f

+ 20 - 1
packages/ckeditor5-utils/src/diff.js

@@ -7,6 +7,8 @@
  * @module utils/diff
  */
 
+import fastDiff from '../src/fastdiff';
+
 // The following code is based on the "O(NP) Sequence Comparison Algorithm"
 // by Sun Wu, Udi Manber, Gene Myers, Webb Miller.
 
@@ -16,6 +18,11 @@
  *
  *		diff( 'aba', 'acca' ); // [ 'equal', 'insert', 'insert', 'delete', 'equal' ]
  *
+ * This function is based on the "O(NP) Sequence Comparison Algorithm" by Sun Wu, Udi Manber, Gene Myers, Webb Miller.
+ * Unfortunately, while it gives the most precise results, its to complex for longer strings/arrow (above 200 items).
+ * Therefore, `diff()` automatically switches to {@link module:utils/fastdiff~fastDiff `fastDiff()`} when detecting
+ * such a scenario. The return formats of both functions are identical.
+ *
  * @param {Array|String} a Input array or string.
  * @param {Array|String} b Output array or string.
  * @param {Function} [cmp] Optional function used to compare array values, by default === is used.
@@ -27,11 +34,19 @@ export default function diff( a, b, cmp ) {
 		return a === b;
 	};
 
+	const aLength = a.length;
+	const bLength = b.length;
+
+	// Perform `fastDiff` for longer strings/arrays (see #269).
+	if ( aLength > 200 || bLength > 200 || aLength + bLength > 300 ) {
+		return diff.fastDiff( a, b, cmp, true );
+	}
+
 	// Temporary action type statics.
 	let _insert, _delete;
 
 	// Swapped the arrays to use the shorter one as the first one.
-	if ( b.length < a.length ) {
+	if ( bLength < aLength ) {
 		const tmp = a;
 
 		a = b;
@@ -117,3 +132,7 @@ export default function diff( a, b, cmp ) {
 	// We remove the first item that represents the action for the injected nulls.
 	return es[ delta ].slice( 1 );
 }
+
+// Store the API in static property to easily overwrite it in tests.
+// Too bad dependency injection does not work in Webpack + ES 6 (const) + Babel.
+diff.fastDiff = fastDiff;

+ 160 - 65
packages/ckeditor5-utils/src/fastdiff.js

@@ -8,8 +8,7 @@
  */
 
 /**
- * Finds position of the first and last change in the given strings and generates set of changes. Set of changes
- * can be applied to the input text in order to transform it into the output text, for example:
+ * Finds positions of the first and last change in the given string/array and generates a set of changes:
  *
  *		fastDiff( '12a', '12xyza' );
  *		// [ { index: 2, type: 'insert', values: [ 'x', 'y', 'z' ] } ]
@@ -20,17 +19,25 @@
  *		fastDiff( '12xyza', '12a' );
  *		// [ { index: 2, type: 'delete', howMany: 3 } ]
  *
- *		fastDiff( '12aa', '12a' );
+ *		fastDiff( [ '1', '2', 'a', 'a' ], [ '1', '2', 'a' ] );
  *		// [ { index: 3, type: 'delete', howMany: 1 } ]
  *
- *		fastDiff( '12abc3', '2ab' );
+ *		fastDiff( [ '1', '2', 'a', 'b', 'c', '3' ], [ '2', 'a', 'b' ] );
  *		// [ { index: 0, type: 'insert', values: [ '2', 'a', 'b' ] }, { index: 3, type: 'delete', howMany: 6 } ]
  *
- * Using returned results you can modify `oldText` to transform it into `newText`:
+ * Passed arrays can contain any type of data, however to compare them correctly custom comparator function
+ * should be passed as a third parameter:
  *
- * 		let input = '12abc3';
- * 		const output = '2ab';
- * 		const changes = fastDiff( input, output );
+ *		fastDiff( [ { value: 1 }, { value: 2 } ], [ { value: 1 }, { value: 3 } ], ( a, b ) => {
+ *			return a.value === b.value;
+ *		} );
+ *		// [ { index: 1, type: 'insert', values: [ { value: 3 } ] }, { index: 2, type: 'delete', howMany: 1 } ]
+ *
+ * The resulted set of changes can be applied to the input in order to transform it into the output, for example:
+ *
+ *		let input = '12abc3';
+ *		const output = '2ab';
+ *		const changes = fastDiff( input, output );
  *
  *		changes.forEach( change => {
  *			if ( change.type == 'insert' ) {
@@ -40,101 +47,156 @@
  *			}
  *		} );
  *
- *		input === output; // -> true
+ *		// input equals output now
+ *
+ * or in case of arrays:
+ *
+ *		let input = [ '1', '2', 'a', 'b', 'c', '3' ];
+ *		const output = [ '2', 'a', 'b' ];
+ *		const changes = fastDiff( input, output );
+ *
+ *		changes.forEach( change => {
+ *			if ( change.type == 'insert' ) {
+ *				input = input.slice( 0, change.index ).concat( change.values, input.slice( change.index ) );
+ *			} else if ( change.type == 'delete' ) {
+ *				input = input.slice( 0, change.index ).concat( input.slice( change.index + change.howMany ) );
+ *			}
+ *		} );
+ *
+ *		// input equals output now
  *
- * The output format of this function is compatible with {@link module:utils/difftochanges~diffToChanges} output format.
+ * By passing `true` as the fourth parameter (`atomicChanges`) the output of this function will become compatible with
+ * the {@link module:utils/diff~diff `diff()`} function:
  *
- * @param {String} oldText Input string.
- * @param {String} newText Input string.
+ *		fastDiff( '12a', '12xyza' );
+ *		// [ 'equal', 'equal', 'insert', 'insert', 'insert', 'equal' ]
+ *
+ * The default output format of this function is compatible with the output format of
+ * {@link module:utils/difftochanges~diffToChanges `diffToChanges()`}. The `diffToChanges()` input format is, in turn,
+ * compatible with the output of {@link module:utils/diff~diff `diff()`}:
+ *
+ *		const a = '1234';
+ *		const b = '12xyz34';
+ *
+ *		// Both calls will return the same results (grouped changes format).
+ *		fastDiff( a, b );
+ *		diffToChanges( diff( a, b ) );
+ *
+ *		// Again, both calls will return the same results (atomic changes format).
+ *		fastDiff( a, b, null, true );
+ *		diff( a, b );
+ *
+ *
+ * @param {Array|String} a Input array or string.
+ * @param {Array|String} b Input array or string.
+ * @param {Function} [cmp] Optional function used to compare array values, by default `===` (strict equal operator) is used.
+ * @param {Boolean} [atomicChanges=false] Whether an array of `inset|delete|equal` operations should
+ * be returned instead of changes set. This makes this function compatible with {@link module:utils/diff~diff `diff()`}.
  * @returns {Array} Array of changes.
  */
-export default function fastDiff( oldText, newText ) {
-	// Check if both texts are equal.
-	if ( oldText === newText ) {
-		return [];
+export default function fastDiff( a, b, cmp, atomicChanges = false ) {
+	// Set the comparator function.
+	cmp = cmp || function( a, b ) {
+		return a === b;
+	};
+
+	// Transform text or any iterable into arrays for easier, consistent processing.
+	if ( !Array.isArray( a ) ) {
+		a = Array.from( a );
+	}
+
+	if ( !Array.isArray( b ) ) {
+		b = Array.from( b );
 	}
 
-	const changeIndexes = findChangeBoundaryIndexes( oldText, newText );
+	// Find first and last change.
+	const changeIndexes = findChangeBoundaryIndexes( a, b, cmp );
 
-	return changeIndexesToChanges( newText, changeIndexes );
+	// Transform into changes array.
+	return atomicChanges ? changeIndexesToAtomicChanges( changeIndexes, b.length ) : changeIndexesToChanges( b, changeIndexes );
 }
 
-// Finds position of the first and last change in the given strings. For example:
+// Finds position of the first and last change in the given arrays. For example:
 //
-//		const indexes = findChangeBoundaryIndexes( '1234', '13424' );
+//		const indexes = findChangeBoundaryIndexes( [ '1', '2', '3', '4' ], [ '1', '3', '4', '2', '4' ] );
 //		console.log( indexes ); // { firstIndex: 1, lastIndexOld: 3, lastIndexNew: 4 }
 //
-// The above indexes means that in `oldText` modified part is `1[23]4` and in the `newText` it is `1[342]4`.
-// Based on such indexes, array with `insert`/`delete` operations which allows transforming
-// old text to the new one can be generated.
-//
-// It is expected that `oldText` and `newText` are different.
+// The above indexes means that in the first array the modified part is `1[23]4` and in the second array it is `1[342]4`.
+// Based on such indexes, array with `insert`/`delete` operations which allows transforming first value into the second one
+// can be generated.
 //
-// @param {String} oldText
-// @param {String} newText
+// @param {Array} arr1
+// @param {Array} arr2
+// @param {Function} cmp Comparator function.
 // @returns {Object}
-// @returns {Number} return.firstIndex Index of the first change in both strings (always the same for both).
-// @returns {Number} result.lastIndexOld Index of the last common character in `oldText` string.
-// @returns {Number} result.lastIndexNew Index of the last common character in `newText` string.
-function findChangeBoundaryIndexes( oldText, newText ) {
-	// Find the first difference between texts.
-	const firstIndex = findFirstDifferenceIndex( oldText, newText );
-
-	// Remove the common part of texts and reverse them to make it simpler to find the last difference between texts.
-	const oldTextReversed = cutAndReverse( oldText, firstIndex );
-	const newTextReversed = cutAndReverse( newText, firstIndex );
-
-	// Find the first difference between reversed texts.
-	// It should be treated as "how many characters from the end the last difference occurred".
+// @returns {Number} return.firstIndex Index of the first change in both values (always the same for both).
+// @returns {Number} result.lastIndexOld Index of the last common value in `arr1`.
+// @returns {Number} result.lastIndexNew Index of the last common value in `arr2`.
+function findChangeBoundaryIndexes( arr1, arr2, cmp ) {
+	// Find the first difference between passed values.
+	const firstIndex = findFirstDifferenceIndex( arr1, arr2, cmp );
+
+	// If arrays are equal return -1 indexes object.
+	if ( firstIndex === -1 ) {
+		return { firstIndex: -1, lastIndexOld: -1, lastIndexNew: -1 };
+	}
+
+	// Remove the common part of each value and reverse them to make it simpler to find the last difference between them.
+	const oldArrayReversed = cutAndReverse( arr1, firstIndex );
+	const newArrayReversed = cutAndReverse( arr2, firstIndex );
+
+	// Find the first difference between reversed values.
+	// It should be treated as "how many elements from the end the last difference occurred".
 	//
 	// For example:
 	//
-	// 			initial	->	after cut	-> reversed:
-	// oldText:	'321ba'	->	'21ba'		-> 'ab12'
-	// newText:	'31xba'	->	'1xba'		-> 'abx1'
-	// lastIndex:						->    2
+	// 				initial	->	after cut	-> reversed:
+	// oldValue:	'321ba'	->	'21ba'		-> 'ab12'
+	// newValue:	'31xba'	->	'1xba'		-> 'abx1'
+	// lastIndex:							-> 2
 	//
-	// So the last change occurred two characters from the end of the texts.
-	const lastIndex = findFirstDifferenceIndex( oldTextReversed, newTextReversed );
+	// So the last change occurred two characters from the end of the arrays.
+	const lastIndex = findFirstDifferenceIndex( oldArrayReversed, newArrayReversed, cmp );
 
 	// Use `lastIndex` to calculate proper offset, starting from the beginning (`lastIndex` kind of starts from the end).
-	const lastIndexOld = oldText.length - lastIndex;
-	const lastIndexNew = newText.length - lastIndex;
+	const lastIndexOld = arr1.length - lastIndex;
+	const lastIndexNew = arr2.length - lastIndex;
 
 	return { firstIndex, lastIndexOld, lastIndexNew };
 }
 
-// Returns a first index on which `oldText` and `newText` differ.
+// Returns a first index on which given arrays differ. If both arrays are the same, -1 is returned.
 //
-// @param {String} oldText
-// @param {String} newText
+// @param {Array} arr1
+// @param {Array} arr2
+// @param {Function} cmp Comparator function.
 // @returns {Number}
-function findFirstDifferenceIndex( oldText, newText ) {
-	for ( let i = 0; i < Math.max( oldText.length, newText.length ); i++ ) {
-		if ( oldText[ i ] !== newText[ i ] ) {
+function findFirstDifferenceIndex( arr1, arr2, cmp ) {
+	for ( let i = 0; i < Math.max( arr1.length, arr2.length ); i++ ) {
+		if ( arr1[ i ] === undefined || arr2[ i ] === undefined || !cmp( arr1[ i ], arr2[ i ] ) ) {
 			return i;
 		}
 	}
-	// No "backup" return cause we assume that `oldText` and `newText` differ. This means that they either have a
-	// difference or they have a different lengths. This means that the `if` condition will always be met eventually.
+
+	return -1; // Return -1 if arrays are equal.
 }
 
-// Removes `howMany` characters from the given `text` string starting from the beginning, then reverses and returns it.
+// Returns a copy of the given array with `howMany` elements removed starting from the beginning and in reversed order.
 //
-// @param {String} text Text to be processed.
-// @param {Number} howMany How many characters from text beginning to cut.
-// @returns {String} Shortened and reversed text.
-function cutAndReverse( text, howMany ) {
-	return text.substring( howMany ).split( '' ).reverse().join( '' );
+// @param {Array} arr Array to be processed.
+// @param {Number} howMany How many elements from array beginning to remove.
+// @returns {Array} Shortened and reversed array.
+function cutAndReverse( arr, howMany ) {
+	return arr.slice( howMany ).reverse();
 }
 
 // Generates changes array based on change indexes from `findChangeBoundaryIndexes` function. This function will
 // generate array with 0 (no changes), 1 (deletion or insertion) or 2 records (insertion and deletion).
 //
-// @param {String} newText New text for which change indexes were calculated.
+// @param {Array} newArray New array for which change indexes were calculated.
 // @param {Object} changeIndexes Change indexes object from `findChangeBoundaryIndexes` function.
 // @returns {Array.<Object>} Array of changes compatible with {@link module:utils/difftochanges~diffToChanges} format.
-function changeIndexesToChanges( newText, changeIndexes ) {
+function changeIndexesToChanges( newArray, changeIndexes ) {
 	const result = [];
 	const { firstIndex, lastIndexOld, lastIndexNew } = changeIndexes;
 
@@ -145,7 +207,7 @@ function changeIndexesToChanges( newText, changeIndexes ) {
 		result.push( {
 			index: firstIndex,
 			type: 'insert',
-			values: newText.substring( firstIndex, lastIndexNew ).split( '' )
+			values: newArray.slice( firstIndex, lastIndexNew )
 		} );
 	}
 
@@ -159,3 +221,36 @@ function changeIndexesToChanges( newText, changeIndexes ) {
 
 	return result;
 }
+
+// Generates array with set `equal|insert|delete` operations based on change indexes from `findChangeBoundaryIndexes` function.
+//
+// @param {Object} changeIndexes Change indexes object from `findChangeBoundaryIndexes` function.
+// @param {Number} newLength Length of the new array on which `findChangeBoundaryIndexes` calculated change indexes.
+// @returns {Array.<String>} Array of changes compatible with {@link module:utils/diff~diff} format.
+function changeIndexesToAtomicChanges( changeIndexes, newLength ) {
+	const { firstIndex, lastIndexOld, lastIndexNew } = changeIndexes;
+
+	// No changes.
+	if ( firstIndex === -1 ) {
+		return Array( newLength ).fill( 'equal' );
+	}
+
+	let result = [];
+	if ( firstIndex > 0 ) {
+		result = result.concat( Array( firstIndex ).fill( 'equal' ) );
+	}
+
+	if ( lastIndexNew - firstIndex > 0 ) {
+		result = result.concat( Array( lastIndexNew - firstIndex ).fill( 'insert' ) );
+	}
+
+	if ( lastIndexOld - firstIndex > 0 ) {
+		result = result.concat( Array( lastIndexOld - firstIndex ).fill( 'delete' ) );
+	}
+
+	if ( lastIndexNew < newLength ) {
+		result = result.concat( Array( newLength - lastIndexNew ).fill( 'equal' ) );
+	}
+
+	return result;
+}

+ 46 - 0
packages/ckeditor5-utils/tests/_utils-tests/longtext.js

@@ -0,0 +1,46 @@
+/**
+ * @license Copyright (c) 2003-2019, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md.
+ */
+
+import getLongText from '../../tests/_utils/longtext';
+
+describe( 'utils', () => {
+	describe( 'getLongText', () => {
+		it( 'should return text with 0 length', () => {
+			expect( getLongText( 0 ).length ).to.equal( 0 );
+		} );
+
+		it( 'should return text with 553 length', () => {
+			expect( getLongText( 553 ).length ).to.equal( 553 );
+		} );
+
+		it( 'should return text with 1500 length', () => {
+			expect( getLongText( 1500 ).length ).to.equal( 1500 );
+		} );
+
+		it( 'should return text with 4000 length', () => {
+			expect( getLongText( 4000 ).length ).to.equal( 4000 );
+		} );
+
+		it( 'should return different text with fromStart=false', () => {
+			expect( getLongText( 100 ) ).to.not.equal( getLongText( 100, false ) );
+		} );
+
+		it( 'should return reversed text', () => {
+			const text1 = getLongText( 100 );
+			const text2 = getLongText( 100, true, true );
+
+			expect( text1 ).to.not.equal( text2 );
+			expect( text1 ).to.equal( text2.split( '' ).reverse().join( '' ) );
+		} );
+
+		it( 'should return reversed text (with fromStart=false)', () => {
+			const text1 = getLongText( 150, false );
+			const text2 = getLongText( 150, false, true );
+
+			expect( text1 ).to.not.equal( text2 );
+			expect( text1 ).to.equal( text2.split( '' ).reverse().join( '' ) );
+		} );
+	} );
+} );

+ 20 - 0
packages/ckeditor5-utils/tests/_utils/longtext.js

@@ -0,0 +1,20 @@
+/**
+ * @license Copyright (c) 2003-2019, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md.
+ */
+
+import longtext from './longtext.txt';
+
+/**
+ * Returns text of a given length.
+ *
+ * @param {Number} length Length of the resulting text.
+ * @param {Boolean} fromStart Whether text should be extracted from the start (or end) of the template string.
+ * @param {Boolean} reversed Whether given text should be reversed.
+ * @returns {String} Text of a given length.
+ */
+export default function getLongText( length, fromStart = true, reversed = false ) {
+	const baseText = longtext.repeat( Math.ceil( length / longtext.length ) );
+	const text = fromStart ? baseText.substring( 0, length ) : baseText.substring( longtext.length - length );
+	return reversed ? text.split( '' ).reverse().join( '' ) : text;
+}

+ 1 - 0
packages/ckeditor5-utils/tests/_utils/longtext.txt

@@ -0,0 +1 @@
+Ut at iaculis turpis, ut interdum erat. Proin quis erat eu odio posuere feugiat. Proin nec dui ac mauris facilisis condimentum et at mi. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Cras mi leo, tempor at ante eget, venenatis porttitor felis. Curabitur et velit mauris. Morbi blandit vestibulum leo. Donec sit amet nisi enim. Morbi viverra tortor arcu, et gravida orci venenatis et. Maecenas nec nulla ullamcorper, viverra ligula pulvinar, maximus dui. Nullam placerat vel tellus ac porttitor. Cras a mi risus. Nullam dictum sem leo, vel blandit magna pharetra et. Vestibulum scelerisque, ex vel vehicula pellentesque, lacus arcu mollis erat, a suscipit odio nulla et leo. Sed feugiat suscipit quam at rhoncus. Nulla luctus mi vitae bibendum venenatis. Suspendisse accumsan dui et consectetur maximus. Vivamus finibus tempus aliquam. Mauris enim est, tincidunt a eros nec, rhoncus mattis ipsum. Ut at eros pretium, aliquam lectus a, commodo augue. Aliquam ac diam id tellus dapibus egestas at at lorem. Nam elementum nisi non nisl condimentum, eu interdum nibh lobortis. Sed laoreet porttitor enim ut scelerisque. Fusce laoreet, massa at lobortis dictum, dolor felis bibendum ante, nec pulvinar est est iaculis nibh. Aenean a massa eros. Apulvinar, maximus dui. Nullam placerat vel tellus ac porttitor. Cras a mi risus. Nullam dictum sem leo, vel blandit magna pharetra et. Vestibulum scelerisque, ex vel vehicula pellentesque, lacus arcu mollis erat, a suscipit odio nulla et leo. Sed feugiat suscipit quam at rhoncus. Nulla luctus mi vitae bibendum venenati.

+ 37 - 0
packages/ckeditor5-utils/tests/diff.js

@@ -5,29 +5,66 @@
 
 import diff from '../src/diff';
 
+import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
+import getLongText from './_utils/longtext';
+
 describe( 'diff', () => {
+	let fastDiffSpy;
+
+	testUtils.createSinonSandbox();
+
+	beforeEach( () => {
+		fastDiffSpy = testUtils.sinon.spy( diff, 'fastDiff' );
+	} );
+
 	it( 'should diff strings', () => {
 		expect( diff( 'aba', 'acca' ) ).to.deep.equals( [ 'equal', 'insert', 'insert', 'delete', 'equal' ] );
+		testUtils.sinon.assert.notCalled( fastDiffSpy );
 	} );
 
 	it( 'should diff arrays', () => {
 		expect( diff( Array.from( 'aba' ), Array.from( 'acca' ) ) ).to.deep.equals( [ 'equal', 'insert', 'insert', 'delete', 'equal' ] );
+		testUtils.sinon.assert.notCalled( fastDiffSpy );
 	} );
 
 	it( 'should reverse result if the second string is shorter', () => {
 		expect( diff( 'acca', 'aba' ) ).to.deep.equals( [ 'equal', 'delete', 'delete', 'insert', 'equal' ] );
+		testUtils.sinon.assert.notCalled( fastDiffSpy );
 	} );
 
 	it( 'should diff if strings are same', () => {
 		expect( diff( 'abc', 'abc' ) ).to.deep.equals( [ 'equal', 'equal', 'equal' ] );
+		testUtils.sinon.assert.notCalled( fastDiffSpy );
 	} );
 
 	it( 'should diff if one string is empty', () => {
 		expect( diff( '', 'abc' ) ).to.deep.equals( [ 'insert', 'insert', 'insert' ] );
+		testUtils.sinon.assert.notCalled( fastDiffSpy );
 	} );
 
 	it( 'should use custom comparator', () => {
 		expect( diff( 'aBc', 'abc' ) ).to.deep.equals( [ 'equal', 'insert', 'delete', 'equal' ] );
 		expect( diff( 'aBc', 'abc', ( a, b ) => a.toLowerCase() == b.toLowerCase() ) ).to.deep.equals( [ 'equal', 'equal', 'equal' ] );
+		testUtils.sinon.assert.notCalled( fastDiffSpy );
+	} );
+
+	it( 'should use fastDiff() internally for strings with 400+ length and length sum of 1400+', () => {
+		diff( getLongText( 400 ), getLongText( 1000 ) );
+		testUtils.sinon.assert.called( fastDiffSpy );
+	} );
+
+	it( 'should use fastDiff() internally for arrays with 400+ length and length sum of 1400+', () => {
+		diff( getLongText( 500 ).split( '' ), getLongText( 950 ).split( '' ) );
+		testUtils.sinon.assert.called( fastDiffSpy );
+	} );
+
+	it( 'should use fastDiff() internally for strings with length sum of 2000+', () => {
+		diff( getLongText( 100 ), getLongText( 2000 ) );
+		testUtils.sinon.assert.called( fastDiffSpy );
+	} );
+
+	it( 'should use fastDiff() internally for strings with length sum of 2000+', () => {
+		diff( getLongText( 10 ), getLongText( 1990 ) );
+		testUtils.sinon.assert.called( fastDiffSpy );
 	} );
 } );

+ 444 - 148
packages/ckeditor5-utils/tests/fastdiff.js

@@ -3,210 +3,506 @@
  * For licensing, see LICENSE.md.
  */
 
+/* global document */
+
 import fastDiff from '../src/fastdiff';
 import diff from '../src/diff';
 import diffToChanges from '../src/difftochanges';
 
 describe( 'fastDiff', () => {
-	it( 'should diff identical texts', () => {
-		expectDiff( '123', '123', [] );
-	} );
-
-	describe( 'insertion', () => {
-		it( 'should diff if old text is empty', () => {
-			expectDiff( '', '123', [ { index: 0, type: 'insert', values: [ '1', '2', '3' ] } ] );
+	describe( 'input types', () => {
+		it( 'should correctly handle strings', () => {
+			const changes = fastDiff( '123', 'abc123' );
+			expect( changes ).to.deep.equal( [ { index: 0, type: 'insert', values: [ 'a', 'b', 'c' ] } ] );
 		} );
 
-		it( 'should diff insertion on the beginning', () => {
-			expectDiff( '123', 'abc123', [ { index: 0, type: 'insert', values: [ 'a', 'b', 'c' ] } ] );
+		it( 'should correctly handle arrays', () => {
+			const changes = fastDiff( [ '1', '2', '3' ], [ 'a', 'b', 'c', '1', '2', '3' ] );
+			expect( changes ).to.deep.equal( [ { index: 0, type: 'insert', values: [ 'a', 'b', 'c' ] } ] );
 		} );
 
-		it( 'should diff insertion on the beginning (repetitive substring)', () => {
-			// Do not check compatibility with 'diffToChanges' as it generates:
-			// [ { index: 0, type: 'insert', values: [ 'a', 'b' ] }, { index: 5, type: 'insert', values: [ 'c', '1', '2', '3' ] } ]
-			expectDiff( '123', 'ab123c123', [ { index: 0, type: 'insert', values: [ 'a', 'b', '1', '2', '3', 'c' ] } ], false );
-		} );
+		it( 'should correctly handle node lists', () => {
+			const el1 = document.createElement( 'p' );
+			const el2 = document.createElement( 'h1' );
 
-		it( 'should diff insertion on the end', () => {
-			expectDiff( '123', '123abc', [ { index: 3, type: 'insert', values: [ 'a', 'b', 'c' ] } ] );
+			el1.appendChild( document.createElement( 'span' ) );
+			el1.appendChild( document.createElement( 'strong' ) );
+
+			el2.appendChild( document.createElement( 'div' ) );
+			el2.appendChild( document.createElement( 'strong' ) );
+
+			const changes = fastDiff( el1.childNodes, el2.childNodes );
+			expect( changes ).to.deep.equal( [
+				{ index: 0, type: 'insert', values: [ el2.childNodes[ 0 ], el2.childNodes[ 1 ] ] },
+				{ index: 2, type: 'delete', howMany: 2 }
+			] );
 		} );
+	} );
 
-		it( 'should diff insertion on the end (repetitive substring)', () => {
-			expectDiff( '123', '123ab123c', [ { index: 3, type: 'insert', values: [ 'a', 'b', '1', '2', '3', 'c' ] } ] );
+	describe( 'changes object', () => {
+		it( 'should diff identical texts', () => {
+			expectDiff( '123', '123', [] );
 		} );
 
-		it( 'should diff insertion in the middle', () => {
-			expectDiff( '123', '12abc3', [ { index: 2, type: 'insert', values: [ 'a', 'b', 'c' ] } ] );
+		it( 'should diff identical arrays', () => {
+			expectDiff( [ '1', '2', '3' ], [ '1', '2', '3' ], [] );
 		} );
 
-		it( 'should diff insertion in the middle (repetitive substring)', () => {
-			// Do not check compatibility with 'diffToChanges' as it generates:
-			// [ { index: 2, type: 'insert', values: [ 'a', 'b', '1', '2' ] }, { index: 7, type: 'insert', values: [ 'c', '3' ] } ]
-			expectDiff( '123', '12ab123c3', [ { index: 2, type: 'insert', values: [ 'a', 'b', '1', '2', '3', 'c' ] } ], false );
+		it( 'should diff arrays with custom comparator', () => {
+			expectDiff( [ 'a', 'b', 'c' ], [ 'A', 'B', 'C' ], [], true, ( a, b ) => a.toLowerCase() === b.toLowerCase() );
 		} );
 
-		it( 'should diff insertion of duplicated content', () => {
-			expectDiff( '123', '123123', [ { index: 3, type: 'insert', values: [ '1', '2', '3' ] } ] );
+		describe( 'insertion', () => {
+			it( 'should diff if old text is empty', () => {
+				expectDiff( '', '123', [ { index: 0, type: 'insert', values: [ '1', '2', '3' ] } ] );
+			} );
+
+			it( 'should diff if old array is empty', () => {
+				expectDiff( [], [ '1', '2', '3' ], [ { index: 0, type: 'insert', values: [ '1', '2', '3' ] } ] );
+			} );
+
+			it( 'should diff insertion on the beginning', () => {
+				expectDiff( '123', 'abc123', [ { index: 0, type: 'insert', values: [ 'a', 'b', 'c' ] } ] );
+			} );
+
+			it( 'should diff insertion on the beginning (repetitive substring)', () => {
+				// Do not check compatibility with 'diffToChanges' as it generates:
+				// [ { index: 0, type: 'insert', values: [ 'a', 'b' ] }, { index: 5, type: 'insert', values: [ 'c', '1', '2', '3' ] } ]
+				expectDiff( '123', 'ab123c123', [ { index: 0, type: 'insert', values: [ 'a', 'b', '1', '2', '3', 'c' ] } ], false );
+			} );
+
+			it( 'should diff insertion on the end', () => {
+				expectDiff( '123', '123abc', [ { index: 3, type: 'insert', values: [ 'a', 'b', 'c' ] } ] );
+			} );
+
+			it( 'should diff insertion on the end (repetitive substring)', () => {
+				expectDiff( '123', '123ab123c', [ { index: 3, type: 'insert', values: [ 'a', 'b', '1', '2', '3', 'c' ] } ] );
+			} );
+
+			it( 'should diff insertion in the middle', () => {
+				expectDiff( '123', '12abc3', [ { index: 2, type: 'insert', values: [ 'a', 'b', 'c' ] } ] );
+			} );
+
+			it( 'should diff insertion in the middle (repetitive substring)', () => {
+				// Do not check compatibility with 'diffToChanges' as it generates:
+				// [ { index: 2, type: 'insert', values: [ 'a', 'b', '1', '2' ] }, { index: 7, type: 'insert', values: [ 'c', '3' ] } ]
+				expectDiff( '123', '12ab123c3', [ { index: 2, type: 'insert', values: [ 'a', 'b', '1', '2', '3', 'c' ] } ], false );
+			} );
+
+			it( 'should diff insertion of duplicated content', () => {
+				expectDiff( '123', '123123', [ { index: 3, type: 'insert', values: [ '1', '2', '3' ] } ] );
+			} );
+
+			it( 'should diff insertion of partially duplicated content', () => {
+				expectDiff( '123', '12323', [ { index: 3, type: 'insert', values: [ '2', '3' ] } ] );
+			} );
+
+			it( 'should diff insertion on both boundaries', () => {
+				// Do not check compatibility with 'diffToChanges' as it generates:
+				// [ { index: 2, type: 'insert', values: [ 'a', 'b' ] }, { index: 5, type: 'insert', values: [ 'c' ] } ]
+				expectDiff( '123', 'ab123c', [
+					{ index: 0, type: 'insert', values: [ 'a', 'b', '1', '2', '3', 'c' ] },
+					{ index: 6, type: 'delete', howMany: 3 }
+				], false );
+			} );
+
+			it( 'should diff insertion in array of objects', () => {
+				const o1 = { foo: 1 };
+				const o2 = { bar: 2 };
+
+				expectDiff( [ o1, o2 ], [ o1, o2, { baz: 3 } ], [
+					{ index: 2, type: 'insert', values: [ { baz: 3 } ] }
+				] );
+			} );
+
+			it( 'should diff insertion in array of objects with comparator', () => {
+				expectDiff( [ { text: 'foo' }, { text: 'bar' } ], [ { text: 'foo' }, { text: 'bar' }, { text: 'baz' } ], [
+					{ index: 2, type: 'insert', values: [ { text: 'baz' } ] }
+				], true, ( a, b ) => a.text === b.text );
+			} );
 		} );
 
-		it( 'should diff insertion of partially duplicated content', () => {
-			expectDiff( '123', '12323', [ { index: 3, type: 'insert', values: [ '2', '3' ] } ] );
+		describe( 'deletion', () => {
+			it( 'should diff if new text is empty', () => {
+				expectDiff( '123', '', [ { index: 0, type: 'delete', howMany: 3 } ] );
+			} );
+
+			it( 'should diff if new array is empty', () => {
+				expectDiff( [ '1', '2', '3' ], [], [ { index: 0, type: 'delete', howMany: 3 } ] );
+			} );
+
+			it( 'should diff deletion on the beginning', () => {
+				expectDiff( 'abc123', '123', [ { index: 0, type: 'delete', howMany: 3 } ] );
+			} );
+
+			it( 'should diff deletion on the beginning (repetitive substring)', () => {
+				// Do not check compatibility with 'diffToChanges' as it generates:
+				// [ { index: 0, type: 'delete', howMany: 2 }, { index: 3, type: 'delete', howMany: 4 } ]
+				expectDiff( 'ab123c123', '123', [ { index: 0, type: 'delete', howMany: 6 } ], false );
+			} );
+
+			it( 'should diff deletion on the end', () => {
+				expectDiff( '123abc', '123', [ { index: 3, type: 'delete', howMany: 3 } ] );
+			} );
+
+			it( 'should diff deletion on the end (repetitive substring)', () => {
+				expectDiff( '123ab123c', '123', [ { index: 3, type: 'delete', howMany: 6 } ] );
+			} );
+
+			it( 'should diff deletion in the middle', () => {
+				expectDiff( '12abc3', '123', [ { index: 2, type: 'delete', howMany: 3 } ] );
+			} );
+
+			it( 'should diff deletion in the middle (repetitive substring)', () => {
+				// Do not check compatibility with 'diffToChanges' as it generates:
+				// [ { index: 2, type: 'delete', howMany: 4 }, { index: 3, type: 'delete', howMany: 2 } ]
+				expectDiff( '12ab123c3', '123', [ { index: 2, type: 'delete', howMany: 6 } ], false );
+			} );
+
+			it( 'should diff deletion on both boundaries', () => {
+				// Do not check compatibility with 'diffToChanges' as it generates:
+				// [ { index: 0, type: 'delete', howMany: 1 }, { index: 3, type: 'delete', howMany: 2 } ]
+				expectDiff( '12abc3', '2ab', [
+					{ index: 0, type: 'insert', values: [ '2', 'a', 'b' ] },
+					{ index: 3, type: 'delete', howMany: 6 }
+				], false );
+			} );
+
+			it( 'should diff deletion of duplicated content', () => {
+				expectDiff( '123123', '123', [ { index: 3, type: 'delete', howMany: 3 } ] );
+			} );
+
+			it( 'should diff deletion of partially duplicated content', () => {
+				expectDiff( '12323', '123', [ { index: 3, type: 'delete', howMany: 2 } ] );
+			} );
+
+			it( 'should diff deletion of partially duplicated content 2', () => {
+				// Do not check compatibility with 'diffToChanges' as it generates:
+				// [ { index: 1, type: 'delete', howMany: 2 }, { index: 2, type: 'delete', howMany: 1 } ]
+				expectDiff( '11233', '13', [ { index: 1, type: 'delete', howMany: 3 } ], false );
+			} );
+
+			it( 'should diff deletion in array of objects', () => {
+				const o1 = { foo: 1 };
+				const o2 = { bar: 2 };
+
+				expectDiff( [ o1, o2 ], [ o2 ], [
+					{ index: 0, type: 'delete', howMany: 1 }
+				] );
+			} );
+
+			it( 'should diff insertion in array of objects with comparator', () => {
+				expectDiff( [ { text: 'foo' }, { text: 'bar' } ], [ { text: 'bar' } ], [
+					{ index: 0, type: 'delete', howMany: 1 }
+				], true, ( a, b ) => a.text === b.text );
+			} );
 		} );
 
-		it( 'should diff insertion on both boundaries', () => {
-			// Do not check compatibility with 'diffToChanges' as it generates:
-			// [ { index: 2, type: 'insert', values: [ 'a', 'b' ] }, { index: 5, type: 'insert', values: [ 'c' ] } ]
-			expectDiff( '123', 'ab123c', [
-				{ index: 0, type: 'insert', values: [ 'a', 'b', '1', '2', '3', 'c' ] },
-				{ index: 6, type: 'delete', howMany: 3 }
-			], false );
+		describe( 'replacement', () => {
+			it( 'should diff replacement of entire text', () => {
+				// Do not check compatibility with 'diffToChanges' as it has changes in reveres order ('delete', 'insert') here.
+				expectDiff( '12345', 'abcd', [
+					{ index: 0, type: 'insert', values: [ 'a', 'b', 'c', 'd' ] },
+					{ index: 4, type: 'delete', howMany: 5 }
+				], false );
+			} );
+
+			it( 'should diff replacement on the beginning', () => {
+				expectDiff( '12345', 'abcd345', [
+					{ index: 0, type: 'insert', values: [ 'a', 'b', 'c', 'd' ] },
+					{ index: 4, type: 'delete', howMany: 2 }
+				] );
+			} );
+
+			it( 'should diff replacement on the beginning (repetitive substring)', () => {
+				// Do not check compatibility with 'diffToChanges' as it has changes in reveres order ('delete', 'insert') here.
+				expectDiff( '12345', '345345', [
+					{ index: 0, type: 'insert', values: [ '3', '4', '5' ] },
+					{ index: 3, type: 'delete', howMany: 2 }
+				], false );
+			} );
+
+			it( 'should diff replacement on the end', () => {
+				// Do not check compatibility with 'diffToChanges' as it has changes in reveres order ('delete', 'insert') here.
+				expectDiff( '12345', '12ab', [
+					{ index: 2, type: 'insert', values: [ 'a', 'b' ] },
+					{ index: 4, type: 'delete', howMany: 3 }
+				], false );
+			} );
+
+			it( 'should diff replacement on the end (repetitive substring)', () => {
+				// Do not check compatibility with 'diffToChanges' as it generates:
+				// [ { index: 3, type: 'insert', values: [ '1', '2', '3' ] }, { index: 7, type: 'delete', howMany: 1 } ]
+				expectDiff( '12345', '1231234', [
+					{ index: 3, type: 'insert', values: [ '1', '2', '3', '4' ] },
+					{ index: 7, type: 'delete', howMany: 2 }
+				], false );
+			} );
+
+			it( 'should diff insertion of duplicated content', () => {
+				expectDiff( '1234', '123123', [
+					{ index: 3, type: 'insert', values: [ '1', '2', '3' ] },
+					{ index: 6, type: 'delete', howMany: 1 }
+				], false );
+			} );
+
+			it( 'should diff insertion of duplicated content', () => {
+				expectDiff( '1234', '13424', [
+					{ index: 1, type: 'insert', values: [ '3', '4', '2' ] },
+					{ index: 4, type: 'delete', howMany: 2 }
+				], false );
+			} );
+
+			it( 'should diff replacement in the middle', () => {
+				expectDiff( '12345', '12ab5', [
+					{ index: 2, type: 'insert', values: [ 'a', 'b' ] },
+					{ index: 4, type: 'delete', howMany: 2 }
+				] );
+			} );
+
+			it( 'should diff replacement in the middle (repetitive substring)', () => {
+				// Do not check compatibility with 'diffToChanges' as it generates:
+				// [ { index: 2, type: 'insert', values: [ '1', '2' ] }, { index: 7, type: 'insert', values: [ '5' ] } ]
+				expectDiff( '12345', '12123455', [
+					{ index: 2, type: 'insert', values: [ '1', '2', '3', '4', '5' ] },
+					{ index: 7, type: 'delete', howMany: 2 }
+				], false );
+			} );
+
+			it( 'should diff replacement of duplicated content', () => {
+				// Do not check compatibility with 'diffToChanges' as it has changes in reveres order ('delete', 'insert') here.
+				expectDiff( '123123', '123333', [
+					{ index: 3, type: 'insert', values: '33'.split( '' ) },
+					{ index: 5, type: 'delete', howMany: 2 }
+				], false );
+			} );
+
+			it( 'should diff replacement in array of objects', () => {
+				const o1 = { foo: 1 };
+				const o2 = { bar: 2 };
+
+				expectDiff( [ o1, o2 ], [ o1, { baz: 3 } ], [
+					{ index: 1, type: 'insert', values: [ { baz: 3 } ] },
+					{ index: 2, type: 'delete', howMany: 1 }
+				] );
+			} );
+
+			it( 'should diff insertion in array of objects with comparator', () => {
+				expectDiff( [ { text: 'foo' }, { text: 'bar' } ], [ { text: 'foo' }, { text: 'baz' } ], [
+					{ index: 1, type: 'insert', values: [ { text: 'baz' } ] },
+					{ index: 2, type: 'delete', howMany: 1 }
+				], true, ( a, b ) => a.text === b.text );
+			} );
 		} );
 	} );
 
-	describe( 'deletion', () => {
-		it( 'should diff if new text is empty', () => {
-			expectDiff( '123', '', [ { index: 0, type: 'delete', howMany: 3 } ] );
+	describe( 'changes linear', () => {
+		it( 'should diff identical texts', () => {
+			expectDiffLinear( '123', '123', 'eee' );
 		} );
 
-		it( 'should diff deletion on the beginning', () => {
-			expectDiff( 'abc123', '123', [ { index: 0, type: 'delete', howMany: 3 } ] );
+		it( 'should diff identical arrays', () => {
+			expectDiffLinear( [ '1', '2', '3' ], [ '1', '2', '3' ], 'eee' );
 		} );
 
-		it( 'should diff deletion on the beginning (repetitive substring)', () => {
-			// Do not check compatibility with 'diffToChanges' as it generates:
-			// [ { index: 0, type: 'delete', howMany: 2 }, { index: 3, type: 'delete', howMany: 4 } ]
-			expectDiff( 'ab123c123', '123', [ { index: 0, type: 'delete', howMany: 6 } ], false );
+		it( 'should diff arrays with custom comparator', () => {
+			expectDiffLinear( [ 'a', 'b', 'c' ], [ 'A', 'B', 'C' ], 'eee', true, ( a, b ) => a.toLowerCase() === b.toLowerCase() );
 		} );
 
-		it( 'should diff deletion on the end', () => {
-			expectDiff( '123abc', '123', [ { index: 3, type: 'delete', howMany: 3 } ] );
-		} );
+		describe( 'insertion', () => {
+			it( 'should diff if old text is empty', () => {
+				expectDiffLinear( '', '123', 'iii' );
+			} );
 
-		it( 'should diff deletion on the end (repetitive substring)', () => {
-			expectDiff( '123ab123c', '123', [ { index: 3, type: 'delete', howMany: 6 } ] );
-		} );
+			it( 'should diff if old array is empty', () => {
+				expectDiffLinear( [], [ '1', '2', '3' ], 'iii' );
+			} );
 
-		it( 'should diff deletion in the middle', () => {
-			expectDiff( '12abc3', '123', [ { index: 2, type: 'delete', howMany: 3 } ] );
-		} );
+			it( 'should diff insertion on the beginning', () => {
+				expectDiffLinear( '123', 'abc123', 'iiieee' );
+			} );
 
-		it( 'should diff deletion in the middle (repetitive substring)', () => {
-			// Do not check compatibility with 'diffToChanges' as it generates:
-			// [ { index: 2, type: 'delete', howMany: 4 }, { index: 3, type: 'delete', howMany: 2 } ]
-			expectDiff( '12ab123c3', '123', [ { index: 2, type: 'delete', howMany: 6 } ], false );
-		} );
+			it( 'should diff insertion on the beginning (repetitive substring)', () => {
+				expectDiffLinear( '123', 'ab123c123', 'iiiiiieee', false );
+			} );
 
-		it( 'should diff deletion on both boundaries', () => {
-			// Do not check compatibility with 'diffToChanges' as it generates:
-			// [ { index: 0, type: 'delete', howMany: 1 }, { index: 3, type: 'delete', howMany: 2 } ]
-			expectDiff( '12abc3', '2ab', [
-				{ index: 0, type: 'insert', values: [ '2', 'a', 'b' ] },
-				{ index: 3, type: 'delete', howMany: 6 }
-			], false );
-		} );
+			it( 'should diff insertion on the end', () => {
+				expectDiffLinear( '123', '123abc', 'eeeiii' );
+			} );
 
-		it( 'should diff deletion of duplicated content', () => {
-			expectDiff( '123123', '123', [ { index: 3, type: 'delete', howMany: 3 } ] );
-		} );
+			it( 'should diff insertion on the end (repetitive substring)', () => {
+				expectDiffLinear( '123', '123ab123c', 'eeeiiiiii' );
+			} );
 
-		it( 'should diff deletion of partially duplicated content', () => {
-			expectDiff( '12323', '123', [ { index: 3, type: 'delete', howMany: 2 } ] );
-		} );
+			it( 'should diff insertion in the middle', () => {
+				expectDiffLinear( '123', '12abc3', 'eeiiie' );
+			} );
 
-		it( 'should diff deletion of partially duplicated content 2', () => {
-			// Do not check compatibility with 'diffToChanges' as it generates:
-			// [ { index: 1, type: 'delete', howMany: 2 }, { index: 2, type: 'delete', howMany: 1 } ]
-			expectDiff( '11233', '13', [ { index: 1, type: 'delete', howMany: 3 } ], false );
-		} );
-	} );
+			it( 'should diff insertion in the middle (repetitive substring)', () => {
+				expectDiffLinear( '123', '12ab123c3', 'eeiiiiiie', false );
+			} );
 
-	describe( 'replacement', () => {
-		it( 'should diff replacement of entire text', () => {
-			// Do not check compatibility with 'diffToChanges' as it has changes in reveres order ('delete', 'insert') here.
-			expectDiff( '12345', 'abcd', [
-				{ index: 0, type: 'insert', values: [ 'a', 'b', 'c', 'd' ] },
-				{ index: 4, type: 'delete', howMany: 5 }
-			], false );
-		} );
+			it( 'should diff insertion of duplicated content', () => {
+				expectDiffLinear( '123', '123123', 'eeeiii' );
+			} );
 
-		it( 'should diff replacement on the beginning', () => {
-			expectDiff( '12345', 'abcd345', [
-				{ index: 0, type: 'insert', values: [ 'a', 'b', 'c', 'd' ] },
-				{ index: 4, type: 'delete', howMany: 2 }
-			] );
-		} );
+			it( 'should diff insertion of partially duplicated content', () => {
+				expectDiffLinear( '123', '12323', 'eeeii' );
+			} );
 
-		it( 'should diff replacement on the beginning (repetitive substring)', () => {
-			// Do not check compatibility with 'diffToChanges' as it has changes in reveres order ('delete', 'insert') here.
-			expectDiff( '12345', '345345', [
-				{ index: 0, type: 'insert', values: [ '3', '4', '5' ] },
-				{ index: 3, type: 'delete', howMany: 2 }
-			], false );
-		} );
+			it( 'should diff insertion on both boundaries', () => {
+				expectDiffLinear( '123', 'ab123c', 'iiiiiiddd', false );
+			} );
 
-		it( 'should diff replacement on the end', () => {
-			// Do not check compatibility with 'diffToChanges' as it has changes in reveres order ('delete', 'insert') here.
-			expectDiff( '12345', '12ab', [
-				{ index: 2, type: 'insert', values: [ 'a', 'b' ] },
-				{ index: 4, type: 'delete', howMany: 3 }
-			], false );
-		} );
+			it( 'should diff insertion in array of objects', () => {
+				const o1 = { foo: 1 };
+				const o2 = { bar: 2 };
 
-		it( 'should diff replacement on the end (repetitive substring)', () => {
-			// Do not check compatibility with 'diffToChanges' as it generates:
-			// [ { index: 3, type: 'insert', values: [ '1', '2', '3' ] }, { index: 7, type: 'delete', howMany: 1 } ]
-			expectDiff( '12345', '1231234', [
-				{ index: 3, type: 'insert', values: [ '1', '2', '3', '4' ] },
-				{ index: 7, type: 'delete', howMany: 2 }
-			], false );
-		} );
+				expectDiffLinear( [ o1, o2 ], [ o1, o2, { baz: 3 } ], 'eei' );
+			} );
 
-		it( 'should diff insertion of duplicated content', () => {
-			expectDiff( '1234', '123123', [
-				{ index: 3, type: 'insert', values: [ '1', '2', '3' ] },
-				{ index: 6, type: 'delete', howMany: 1 }
-			], false );
+			it( 'should diff insertion in array of objects with comparator', () => {
+				expectDiffLinear( [ { text: 'foo' }, { text: 'bar' } ], [ { text: 'foo' }, { text: 'bar' }, { text: 'baz' } ],
+					'eei', true, ( a, b ) => a.text === b.text );
+			} );
 		} );
 
-		it( 'should diff insertion of duplicated content', () => {
-			expectDiff( '1234', '13424', [
-				{ index: 1, type: 'insert', values: [ '3', '4', '2' ] },
-				{ index: 4, type: 'delete', howMany: 2 }
-			], false );
-		} );
+		describe( 'deletion', () => {
+			it( 'should diff if new text is empty', () => {
+				expectDiffLinear( '123', '', 'ddd' );
+			} );
 
-		it( 'should diff replacement in the middle', () => {
-			expectDiff( '12345', '12ab5', [
-				{ index: 2, type: 'insert', values: [ 'a', 'b' ] },
-				{ index: 4, type: 'delete', howMany: 2 }
-			] );
-		} );
+			it( 'should diff if new array is empty', () => {
+				expectDiffLinear( [ '1', '2', '3' ], [], 'ddd' );
+			} );
+
+			it( 'should diff deletion on the beginning', () => {
+				expectDiffLinear( 'abc123', '123', 'dddeee' );
+			} );
+
+			it( 'should diff deletion on the beginning (repetitive substring)', () => {
+				expectDiffLinear( 'ab123c123', '123', 'ddddddeee', false );
+			} );
 
-		it( 'should diff replacement in the middle (repetitive substring)', () => {
-			// Do not check compatibility with 'diffToChanges' as it generates:
-			// [ { index: 2, type: 'insert', values: [ '1', '2' ] }, { index: 7, type: 'insert', values: [ '5' ] } ]
-			expectDiff( '12345', '12123455', [
-				{ index: 2, type: 'insert', values: [ '1', '2', '3', '4', '5' ] },
-				{ index: 7, type: 'delete', howMany: 2 }
-			], false );
+			it( 'should diff deletion on the end', () => {
+				expectDiffLinear( '123abc', '123', 'eeeddd' );
+			} );
+
+			it( 'should diff deletion on the end (repetitive substring)', () => {
+				expectDiffLinear( '123ab123c', '123', 'eeedddddd' );
+			} );
+
+			it( 'should diff deletion in the middle', () => {
+				expectDiffLinear( '12abc3', '123', 'eeddde' );
+			} );
+
+			it( 'should diff deletion in the middle (repetitive substring)', () => {
+				expectDiffLinear( '12ab123c3', '123', 'eedddddde', false );
+			} );
+
+			it( 'should diff deletion on both boundaries', () => {
+				expectDiffLinear( '12abc3', '2ab', 'iiidddddd', false );
+			} );
+
+			it( 'should diff deletion of duplicated content', () => {
+				expectDiffLinear( '123123', '123', 'eeeddd' );
+			} );
+
+			it( 'should diff deletion of partially duplicated content', () => {
+				expectDiffLinear( '12323', '123', 'eeedd' );
+			} );
+
+			it( 'should diff deletion of partially duplicated content 2', () => {
+				expectDiffLinear( '11233', '13', 'eddde', false );
+			} );
+
+			it( 'should diff deletion in array of objects', () => {
+				const o1 = { foo: 1 };
+				const o2 = { bar: 2 };
+
+				expectDiffLinear( [ o1, o2 ], [ o2 ], 'de' );
+			} );
+
+			it( 'should diff insertion in array of objects with comparator', () => {
+				expectDiffLinear( [ { text: 'foo' }, { text: 'bar' } ], [ { text: 'bar' } ], 'de', true, ( a, b ) => a.text === b.text );
+			} );
 		} );
 
-		it( 'should diff replacement of duplicated content', () => {
-			// Do not check compatibility with 'diffToChanges' as it has changes in reveres order ('delete', 'insert') here.
-			expectDiff( '123123', '123333', [
-				{ index: 3, type: 'insert', values: '33'.split( '' ) },
-				{ index: 5, type: 'delete', howMany: 2 }
-			], false );
+		describe( 'replacement', () => {
+			it( 'should diff replacement of entire text', () => {
+				expectDiffLinear( '12345', 'abcd', 'iiiiddddd', false );
+			} );
+
+			it( 'should diff replacement on the beginning', () => {
+				expectDiffLinear( '12345', 'abcd345', 'iiiiddeee' );
+			} );
+
+			it( 'should diff replacement on the beginning (repetitive substring)', () => {
+				expectDiffLinear( '12345', '345345', 'iiiddeee', false );
+			} );
+
+			it( 'should diff replacement on the end', () => {
+				expectDiffLinear( '12345', '12ab', 'eeiiddd', false );
+			} );
+
+			it( 'should diff replacement on the end (repetitive substring)', () => {
+				expectDiffLinear( '12345', '1231234', 'eeeiiiidd', false );
+			} );
+
+			it( 'should diff insertion of duplicated content', () => {
+				expectDiffLinear( '1234', '123123', 'eeeiiid' );
+			} );
+
+			it( 'should diff insertion of duplicated content', () => {
+				expectDiffLinear( '1234', '13424', 'eiiidde', false );
+			} );
+
+			it( 'should diff replacement in the middle', () => {
+				expectDiffLinear( '12345', '12ab5', 'eeiidde' );
+			} );
+
+			it( 'should diff replacement in the middle (repetitive substring)', () => {
+				expectDiffLinear( '12345', '12123455', 'eeiiiiidde', false );
+			} );
+
+			it( 'should diff replacement of duplicated content', () => {
+				expectDiffLinear( '123123', '123333', 'eeeiidde', false );
+			} );
+
+			it( 'should diff replacement in array of objects', () => {
+				const o1 = { foo: 1 };
+				const o2 = { bar: 2 };
+
+				expectDiffLinear( [ o1, o2 ], [ o1, { baz: 3 } ], 'eid' );
+			} );
+
+			it( 'should diff insertion in array of objects with comparator', () => {
+				expectDiffLinear( [ { text: 'foo' }, { text: 'bar' } ], [ { text: 'foo' }, { text: 'baz' } ], 'eid',
+					true, ( a, b ) => a.text === b.text );
+			} );
 		} );
 	} );
 } );
 
-function expectDiff( oldText, newText, expected, checkDiffToChangesCompatibility = true ) {
-	const result = fastDiff( oldText, newText );
+function expectDiff( oldText, newText, expected, checkDiffToChangesCompatibility = true, comparator = null ) {
+	const result = fastDiff( oldText, newText, comparator );
 
-	expect( result ).to.deep.equals( expected );
+	expect( result ).to.deep.equals( expected, 'fastDiff changes failed' );
 
 	if ( checkDiffToChangesCompatibility ) {
-		expect( result ).to.deep.equals( diffToChanges( diff( oldText, newText ), newText ), 'diffToChanges compatibility' );
+		expect( result ).to.deep.equals(
+			diffToChanges( diff( oldText, newText, comparator ), newText ), 'diffToChanges compatibility failed' );
+	}
+}
+
+function expectDiffLinear( oldText, newText, expected, checkDiffCompatibility = true, comparator = null ) {
+	const actions = { d: 'delete', e: 'equal', i: 'insert' };
+	const expectedArray = expected.split( '' ).map( item => actions[ item ] );
+	const result = fastDiff( oldText, newText, comparator, true );
+
+	expect( result ).to.deep.equals( expectedArray, 'fastDiff linear result failed' );
+
+	if ( checkDiffCompatibility ) {
+		expect( result ).to.deep.equals( diff( oldText, newText, comparator ), 'diff compatibility failed' );
 	}
 }

+ 1 - 0
packages/ckeditor5-utils/tests/manual/diff/diff.html

@@ -0,0 +1 @@
+See browser dev console output.

+ 60 - 0
packages/ckeditor5-utils/tests/manual/diff/diff.js

@@ -0,0 +1,60 @@
+/**
+ * @license Copyright (c) 2003-2019, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md.
+ */
+
+/* global console, setTimeout */
+
+import diff from '../../../src/diff';
+import getLongText from '../../_utils/longtext';
+
+// Tests
+setTimeout( () => {
+	console.log( 'Testing... (t1 length - t2 length - avg time - times)' );
+
+	execTime( getLongText( 300 ), getLongText( 700, false, true ) );
+	execTime( getLongText( 350 ), getLongText( 700, false, true ) );
+	execTime( getLongText( 400 ), getLongText( 700, false, true ) );
+	execTime( getLongText( 450 ), getLongText( 700, false, true ) );
+
+	execTime( getLongText( 300 ), getLongText( 800, false, true ) );
+	execTime( getLongText( 350 ), getLongText( 800, false, true ) );
+	execTime( getLongText( 400 ), getLongText( 800, false, true ) );
+	execTime( getLongText( 450 ), getLongText( 800, false, true ) );
+
+	execTime( getLongText( 300 ), getLongText( 900, false, true ) );
+	execTime( getLongText( 350 ), getLongText( 900, false, true ) );
+	execTime( getLongText( 400 ), getLongText( 900, false, true ) );
+	execTime( getLongText( 450 ), getLongText( 900, false, true ) );
+
+	execTime( getLongText( 300 ), getLongText( 1000, false, true ) );
+	execTime( getLongText( 350 ), getLongText( 1000, false, true ) );
+	execTime( getLongText( 400 ), getLongText( 1000, false, true ) );
+	execTime( getLongText( 450 ), getLongText( 1000, false, true ) );
+
+	execTime( getLongText( 300 ), getLongText( 1200, false, true ) );
+	execTime( getLongText( 350 ), getLongText( 1200, false, true ) );
+	execTime( getLongText( 400 ), getLongText( 1200, false, true ) );
+	execTime( getLongText( 450 ), getLongText( 1200, false, true ) );
+
+	execTime( getLongText( 300 ), getLongText( 1500, false, true ) );
+	execTime( getLongText( 350 ), getLongText( 1500, false, true ) );
+	execTime( getLongText( 400 ), getLongText( 1500, false, true ) );
+	execTime( getLongText( 450 ), getLongText( 1500, false, true ) );
+}, 500 );
+
+// Helpers
+function execTime( text1, text2 ) {
+	const times = [];
+
+	for ( let i = 0; i < 15; i++ ) {
+		const start = Number( new Date() );
+
+		diff( text1, text2 );
+
+		times.push( Number( new Date() ) - start );
+	}
+
+	console.log( 'l1: ' + text1.length, 'l2: ' + text2.length,
+		'avg: ' + Math.round( times.reduce( ( a, b ) => a + b, 0 ) / times.length ) + 'ms', times );
+}

+ 3 - 0
packages/ckeditor5-utils/tests/manual/diff/diff.md

@@ -0,0 +1,3 @@
+## `diff()`
+
+Checks `diff()` performance.