QUnit.module( 'jquery.lengthLimit', () => {
	// Simple sample (20 chars, 20 bytes)
	const simpleSample = '12345678901234567890';

	// 3 bytes (euro-symbol)
	const U_20AC = '\u20AC';

	// Outside of the BMP (pile of poo emoji)
	const poop = '\uD83D\uDCA9'; // "💩"

	// Multi-byte sample (22 chars, 26 bytes)
	const mbSample = '1234567890' + U_20AC + '1234567890' + U_20AC;

	// Basic sendkey-implementation
	function addChars( $input, charstr ) {
		function x( $el, i ) {
			// Add character to the value
			return $el.val() + charstr.charAt( i );
		}

		for ( let c = 0; c < charstr.length; c++ ) {
			$input
				.val( x( $input, c ) )
				.trigger( 'change' );
		}
	}

	QUnit.test.each( 'byteLimit()', {

		'Plain text input': {
			$input: $( '<input>' ).attr( 'type', 'text' ),
			sample: simpleSample,
			expected: simpleSample
		},

		'Plain text input. Calling byteLimit with no parameters and no maxlength attribute (T38310)': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.byteLimit(),
			sample: simpleSample,
			expected: simpleSample
		},

		'Limit using the maxlength attribute': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.attr( 'maxlength', '10' )
				.byteLimit(),
			sample: simpleSample,
			expected: '1234567890'
		},

		'Limit using a custom value': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.byteLimit( 10 ),
			sample: simpleSample,
			expected: '1234567890'
		},

		'Limit using a custom value, overriding maxlength attribute': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.attr( 'maxlength', '10' )
				.byteLimit( 15 ),
			sample: simpleSample,
			expected: '123456789012345'
		},

		'Limit using a custom value (multibyte)': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.byteLimit( 14 ),
			sample: mbSample,
			expected: '1234567890' + U_20AC + '1'
		},

		'Limit using a custom value (multibyte, outside BMP)': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.byteLimit( 3 ),
			sample: poop,
			expected: ''
		},

		'Limit using a custom value (multibyte) overlapping a byte': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.byteLimit( 12 ),
			sample: mbSample,
			expected: '123456789012'
		},

		'Pass the limit and a callback as input filter': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.byteLimit( 6, ( val ) => {
					const title = mw.Title.newFromText( String( val ) );
					// Return without namespace prefix
					return title ? title.getMain() : '';
				} ),
			sample: 'User:Sample',
			expected: 'User:Sample'
		},

		'Limit using the maxlength attribute and pass a callback as input filter': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.attr( 'maxlength', '6' )
				.byteLimit( ( val ) => {
					const title = mw.Title.newFromText( String( val ) );
					// Return without namespace prefix
					return title ? title.getMain() : '';
				} ),
			sample: 'User:Sample',
			expected: 'User:Sample'
		},

		'Truncate with exceeded limit and filter callback': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.byteLimit( 6, ( val ) => {
					const title = mw.Title.newFromText( String( val ) );
					// Return without namespace prefix
					return title ? title.getMain() : '';
				} ),
			sample: 'User:Example',
			// The callback alters the value to be used to calculeate
			// the length. The altered value is "Exampl" which has
			// a length of 6, the "e" would exceed the limit.
			expected: 'User:Exampl'
		},

		'Input filter that increases the length': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.byteLimit( 10, ( text ) => 'prefix' + text ),
			sample: simpleSample,
			// Prefix adds 6 characters, limit is reached after 4
			expected: '1234'
		},

		// Regression tests for T43450
		'Input filter of which the base exceeds the limit': {
			$input: $( '<input>' ).attr( 'type', 'text' )
				.byteLimit( 3, ( text ) => 'prefix' + text ),
			sample: simpleSample,
			expected: ''
		},
		'Unpaired surrogates do not crash': {
			$input: $( '<input>' ).attr( 'type', 'text' ).byteLimit( 4 ),
			sample: '\uD800\uD800\uDFFF',
			expected: '\uD800'
		}
	}, ( assert, opt ) => {
		opt.$input.appendTo( '#qunit-fixture' );

		// Simulate pressing keys for each of the sample characters
		addChars( opt.$input, opt.sample );

		assert.strictEqual(
			opt.$input.val(),
			opt.expected,
			'New value matches the expected string'
		);
	} );

	QUnit.test( 'Confirm properties and attributes set', ( assert ) => {
		let $el;

		$el = $( '<input>' ).attr( 'type', 'text' )
			.attr( 'maxlength', '7' )
			.appendTo( '#qunit-fixture' )
			.byteLimit();

		assert.strictEqual( $el.attr( 'maxlength' ), '7', 'maxlength attribute unchanged for simple limit' );

		$el = $( '<input>' ).attr( 'type', 'text' )
			.attr( 'maxlength', '7' )
			.appendTo( '#qunit-fixture' )
			.byteLimit( 12 );

		assert.strictEqual( $el.attr( 'maxlength' ), '12', 'maxlength attribute updated for custom limit' );

		$el = $( '<input>' ).attr( 'type', 'text' )
			.attr( 'maxlength', '7' )
			.appendTo( '#qunit-fixture' )
			.byteLimit( 12, ( val ) => val );

		assert.strictEqual( $el.attr( 'maxlength' ), undefined, 'maxlength attribute removed for limit with callback' );

		$( '<input>' ).attr( 'type', 'text' )
			.addClass( 'mw-test-byteLimit-foo' )
			.attr( 'maxlength', '7' )
			.appendTo( '#qunit-fixture' );

		$( '<input>' ).attr( 'type', 'text' )
			.addClass( 'mw-test-byteLimit-foo' )
			.attr( 'maxlength', '12' )
			.appendTo( '#qunit-fixture' );

		$el = $( '.mw-test-byteLimit-foo' );

		assert.strictEqual( $el.length, 2, 'Verify that there are no other elements clashing with this test suite' );

		$el.byteLimit();
	} );

	QUnit.test( 'Trim from insertion when limit exceeded', ( assert ) => {
		let $el;

		// Use a new <input> because the bug only occurs on the first time
		// the limit it reached (T42850)
		$el = $( '<input>' ).attr( 'type', 'text' )
			.appendTo( '#qunit-fixture' )
			.byteLimit( 3 )
			.val( 'abc' ).trigger( 'change' )
			.val( 'zabc' ).trigger( 'change' );

		assert.strictEqual( $el.val(), 'abc', 'Trim from the insertion point (at 0), not the end' );

		$el = $( '<input>' ).attr( 'type', 'text' )
			.appendTo( '#qunit-fixture' )
			.byteLimit( 3 )
			.val( 'abc' ).trigger( 'change' )
			.val( 'azbc' ).trigger( 'change' );

		assert.strictEqual( $el.val(), 'abc', 'Trim from the insertion point (at 1), not the end' );
	} );

	QUnit.test( 'Do not cut up false matching substrings in emoji insertions', ( assert ) => {
		const oldVal = '\uD83D\uDCA9\uD83D\uDCA9', // "💩💩"
			newVal = '\uD83D\uDCA9\uD83D\uDCB9\uD83E\uDCA9\uD83D\uDCA9', // "💩💹🢩💩"
			expected = '\uD83D\uDCA9\uD83D\uDCB9\uD83D\uDCA9'; // "💩💹💩"

		// Possible bad results:
		// * With no surrogate support:
		//   '\uD83D\uDCA9\uD83D\uDCB9\uD83E\uDCA9' "💩💹🢩"
		// * With correct trimming but bad detection of inserted text:
		//   '\uD83D\uDCA9\uD83D\uDCB9\uDCA9' "💩💹�"

		const $el = $( '<input>' ).attr( 'type', 'text' )
			.appendTo( '#qunit-fixture' )
			.byteLimit( 12 )
			.val( oldVal ).trigger( 'change' )
			.val( newVal ).trigger( 'change' );

		assert.strictEqual( $el.val(), expected, 'Pasted emoji correctly trimmed at the end' );
	} );
} );