Press n or j to go to the next uncovered block, b, p or k for the previous block.
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* @license Apache-2.0
*
* Copyright (c) 2021 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// cspell:ignore अनुच्छेद
// MODULES //
var isString = require( '@stdlib/assert/is-string' ).isPrimitive;
var isInteger = require( '@stdlib/assert/is-integer' );
var codePointAt = require( '@stdlib/string/code-point-at' );
var hasUTF16SurrogatePairAt = require( '@stdlib/assert/has-utf16-surrogate-pair-at' );
var grapheme = require( '@stdlib/string/tools/grapheme-cluster-break' );
var format = require( '@stdlib/string/format' );
// VARIABLES //
var breakType = grapheme.breakType;
var breakProperty = grapheme.breakProperty;
var emojiProperty = grapheme.emojiProperty;
// MAIN //
/**
* Returns the previous extended grapheme cluster break in a string before a specified position.
*
* @param {string} str - input string
* @param {integer} [fromIndex=str.length-1] - position
* @throws {TypeError} first argument must be a string
* @throws {TypeError} second argument must be an integer
* @returns {NonNegativeInteger} previous grapheme break position
*
* @example
* var out = prevGraphemeClusterBreak( 'last man standing', 4 );
* // returns 3
*
* @example
* var out = prevGraphemeClusterBreak( 'presidential election', 8 );
* // returns 7
*
* @example
* var out = prevGraphemeClusterBreak( 'अनुच्छेद', 2 );
* // returns 0
*
* @example
* var out = prevGraphemeClusterBreak( '🌷', 1 );
* // returns -1
*/
function prevGraphemeClusterBreak( str, fromIndex ) {
var breaks;
var emoji;
var ans;
var len;
var idx;
var cp;
var i;
if ( !isString( str ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a string. Value: `%s`.', str ) );
}
len = str.length;
if ( arguments.length > 1 ) {
if ( !isInteger( fromIndex ) ) {
throw new TypeError( format( 'invalid argument. Second argument must be an integer. Value: `%s`.', fromIndex ) );
}
idx = fromIndex;
} else {
idx = len - 1;
}
if ( len === 0 || idx <= 0 ) {
return -1;
}
if ( idx >= len ) {
idx = len - 1;
}
// Initialize caches for storing grapheme break and emoji properties:
breaks = [];
emoji = [];
// Get the code point for the starting index:
cp = codePointAt( str, 0 );
// Get the corresponding grapheme break and emoji properties:
breaks.push( breakProperty( cp ) );
emoji.push( emojiProperty( cp ) );
ans = -1;
for ( i = 1; i <= idx; i++ ) {
// If the current character is part of a surrogate pair, move along...
if ( hasUTF16SurrogatePairAt( str, i-1 ) ) {
ans = i-2;
breaks.length = 0;
emoji.length = 0;
continue;
}
cp = codePointAt( str, i );
// Get the corresponding grapheme break and emoji properties:
breaks.push( breakProperty( cp ) );
emoji.push( emojiProperty( cp ) );
// Determine if we've encountered a grapheme cluster break...
if ( breakType( breaks, emoji ) > 0 ) {
ans = i-1;
breaks.length = 0;
emoji.length = 0;
continue;
}
}
return ans;
}
// EXPORTS //
module.exports = prevGraphemeClusterBreak;
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