QRCode-decode/src/lib/Decoder.js

var GF256 = require('./GF256')
var BitMatrixParser = require('./BitMatrixParser')
var DataBlock = require('./DataBlock')
var QRCodeDataBlockReader = require('./QRCodeDataBlockReader')
var ReedSolomonDecoder = require('./ReedSolomonDecoder')

var Decoder = {};
Decoder.rsDecoder = new ReedSolomonDecoder(GF256.QR_CODE_FIELD);

Decoder.correctErrors = function (codewordBytes, numDataCodewords) {
	var numCodewords = codewordBytes.length;
	// First read into an array of ints
	var codewordsInts = new Array(numCodewords);
	for (var i = 0; i < numCodewords; i++) {
		codewordsInts[i] = codewordBytes[i] & 0xFF;
	}
	var numECCodewords = codewordBytes.length - numDataCodewords;
	try {
		Decoder.rsDecoder.decode(codewordsInts, numECCodewords);
		//var corrector = new ReedSolomon(codewordsInts, numECCodewords);
		//corrector.correct();
	}
	catch (rse) {
		throw rse;
	}
	// Copy back into array of bytes -- only need to worry about the bytes that were data
	// We don't care about errors in the error-correction codewords
	for (var i = 0; i < numDataCodewords; i++) {
		codewordBytes[i] = codewordsInts[i];
	}
}

Decoder.decode = function (bits) {
	var parser = new BitMatrixParser(bits);
	var version = parser.readVersion();
	var ecLevel = parser.readFormatInformation().ErrorCorrectionLevel;

	// Read codewords
	var codewords = parser.readCodewords();

	// Separate into data blocks
	var dataBlocks = DataBlock.getDataBlocks(codewords, version, ecLevel);

	// Count total number of data bytes
	var totalBytes = 0;
	for (var i = 0; i < dataBlocks.length; i++) {
		totalBytes += dataBlocks[i].NumDataCodewords;
	}
	var resultBytes = new Array(totalBytes);
	var resultOffset = 0;

	// Error-correct and copy data blocks together into a stream of bytes
	for (var j = 0; j < dataBlocks.length; j++) {
		var dataBlock = dataBlocks[j];
		var codewordBytes = dataBlock.Codewords;
		var numDataCodewords = dataBlock.NumDataCodewords;
		Decoder.correctErrors(codewordBytes, numDataCodewords);
		for (var i = 0; i < numDataCodewords; i++) {
			resultBytes[resultOffset++] = codewordBytes[i];
		}
	}

	// Decode the contents of that stream of bytes
	var reader = new QRCodeDataBlockReader(resultBytes, version.VersionNumber, ecLevel.Bits);
	return reader;
	//return DecodedBitStreamParser.decode(resultBytes, version, ecLevel);
}

module.exports = Decoder;