@stdlib/utils/dsv/base/parse/lib/states/quoted_escape.js

Standard utilities.

/**
* @license Apache-2.0
*
* Copyright (c) 2022 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.
*/

/* eslint-disable no-underscore-dangle */

'use strict';

// MODULES //

var logger = require( 'debug' );
var state2enum = require( './state2enum.js' );


// VARIABLES //

var debug = logger( 'state:quoted_escape' );

// Possible transition states...
var ERROR = state2enum[ 'error' ];
var QUOTED_FIELD = state2enum[ 'quoted_field' ];


// MAIN //

/**
* Returns a function for processing an escape sequence within a quoted field.
*
* ## Notes
*
* -   Within a quoted field, an escape sequence (only) escapes the quote sequence.
* -   In strict mode, if not immediately followed by a special character sequence, then the parser raises an exception.
* -   In non-strict mode, if not immediately followed by a special character sequence, then the escape sequence has no special meaning and is considered a normal character sequence.
*
* @private
* @param {Parser} parser - parser instance
* @returns {Function} processing function
*/
function processor( parser ) {
	var escapeLastIndex;
	var quoteLastIndex;
	var escapeLength;
	var strict;
	var quote;

	quoteLastIndex = parser._quoteLastIndex;
	quote = parser._quote;

	escapeLastIndex = parser._escapeLastIndex;
	escapeLength = parser._escapeLength;

	strict = parser._strict;

	return next;

	/**
	* Processes a character.
	*
	* @private
	* @param {string} ch - character
	* @returns {void}
	*/
	function next( ch ) {
		var cursor = parser._cursor;
		var idx = parser._eidx; // position of last escape character
		var d = cursor - idx;

		debug( 'Char: %s', ch );

		/*
		* Check for a quote sequence.
		*/
		if (
			d === quoteLastIndex &&
			ch === quote[ quoteLastIndex ] &&
			parser._scan( quote, quoteLastIndex )
		) {
			debug( 'Quote.' );
			parser._copyWithin( idx-escapeLastIndex, idx+1, quoteLastIndex )
				._rewind( escapeLength )
				._push( ch )
				._changeState( QUOTED_FIELD );
			return;
		}
		/*
		* Check for a non-special character sequence.
		*
		* ## Notes
		*
		* -   In strict mode, quote sequences must immediately follow an escape sequence. At some point, we'll have processed a greater number of characters than exists in a quote sequence, meaning that a quote sequence does not immediately follow the escape sequence which led to the current state. Once this happens, we're in an invalid state and must raise an exception, as not clear how the parser should interpret the preceding values (e.g., was the preceding escape sequence a mistake and should be ignored? are we missing a quote sequence? etc.).
		* -   In non-strict mode, we assume that the escape sequence is a normal character sequence.
		*/
		if ( d >= quoteLastIndex ) {
			if ( strict ) {
				debug( 'Error.' );
				parser._setErrorState( 'INVALID_QUOTED_ESCAPE' )._changeState( ERROR );
				return;
			}
			// Return to normal field processing:
			debug( 'Escape sequence is not followed by a quote sequence.' );
			parser._raiseWarning( 'INVALID_QUOTED_ESCAPE' )._push( ch )._changeState( QUOTED_FIELD );
			return;
		}
		// Continue processing until we can transition to a new state:
		parser._push( ch );
	}
}


// EXPORTS //

module.exports = processor;