quagga/src/reader/code_39_reader.js

An advanced barcode-scanner written in JavaScript

import BarcodeReader from './barcode_reader';
import ArrayHelper from '../common/array_helper';

function Code39Reader() {
    BarcodeReader.call(this);
}

var properties = {
    ALPHABETH_STRING: {value: "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. *$/+%"},
    ALPHABET: {value: [48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78,
        79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 45, 46, 32, 42, 36, 47, 43, 37]},
    CHARACTER_ENCODINGS: {value: [0x034, 0x121, 0x061, 0x160, 0x031, 0x130, 0x070, 0x025, 0x124, 0x064, 0x109, 0x049,
        0x148, 0x019, 0x118, 0x058, 0x00D, 0x10C, 0x04C, 0x01C, 0x103, 0x043, 0x142, 0x013, 0x112, 0x052, 0x007, 0x106,
        0x046, 0x016, 0x181, 0x0C1, 0x1C0, 0x091, 0x190, 0x0D0, 0x085, 0x184, 0x0C4, 0x094, 0x0A8, 0x0A2, 0x08A, 0x02A
    ]},
    ASTERISK: {value: 0x094},
    FORMAT: {value: "code_39", writeable: false}
};

Code39Reader.prototype = Object.create(BarcodeReader.prototype, properties);
Code39Reader.prototype.constructor = Code39Reader;

Code39Reader.prototype._decode = function() {
    var self = this,
        counters = [0, 0, 0, 0, 0, 0, 0, 0, 0],
        result = [],
        start = self._findStart(),
        decodedChar,
        lastStart,
        pattern,
        nextStart;

    if (!start) {
        return null;
    }
    nextStart = self._nextSet(self._row, start.end);

    do {
        counters = self._toCounters(nextStart, counters);
        pattern = self._toPattern(counters);
        if (pattern < 0) {
            return null;
        }
        decodedChar = self._patternToChar(pattern);
        if (decodedChar < 0){
            return null;
        }
        result.push(decodedChar);
        lastStart = nextStart;
        nextStart += ArrayHelper.sum(counters);
        nextStart = self._nextSet(self._row, nextStart);
    } while (decodedChar !== '*');
    result.pop();

    if (!result.length) {
        return null;
    }

    if (!self._verifyTrailingWhitespace(lastStart, nextStart, counters)) {
        return null;
    }

    return {
        code: result.join(""),
        start: start.start,
        end: nextStart,
        startInfo: start,
        decodedCodes: result
    };
};

Code39Reader.prototype._verifyTrailingWhitespace = function(lastStart, nextStart, counters) {
    var trailingWhitespaceEnd,
        patternSize = ArrayHelper.sum(counters);

    trailingWhitespaceEnd = nextStart - lastStart - patternSize;
    if ((trailingWhitespaceEnd * 3) >= patternSize) {
        return true;
    }
    return false;
};

Code39Reader.prototype._patternToChar = function(pattern) {
    var i,
        self = this;

    for (i = 0; i < self.CHARACTER_ENCODINGS.length; i++) {
        if (self.CHARACTER_ENCODINGS[i] === pattern) {
            return String.fromCharCode(self.ALPHABET[i]);
        }
    }
    return -1;
};

Code39Reader.prototype._findNextWidth = function(counters, current) {
    var i,
        minWidth = Number.MAX_VALUE;

    for (i = 0; i < counters.length; i++) {
        if (counters[i] < minWidth && counters[i] > current) {
            minWidth = counters[i];
        }
    }

    return minWidth;
};

Code39Reader.prototype._toPattern = function(counters) {
    var numCounters = counters.length,
        maxNarrowWidth = 0,
        numWideBars = numCounters,
        wideBarWidth = 0,
        self = this,
        pattern,
        i;

    while (numWideBars > 3) {
        maxNarrowWidth = self._findNextWidth(counters, maxNarrowWidth);
        numWideBars = 0;
        pattern = 0;
        for (i = 0; i < numCounters; i++) {
            if (counters[i] > maxNarrowWidth) {
                pattern |= 1 << (numCounters - 1 - i);
                numWideBars++;
                wideBarWidth += counters[i];
            }
        }

        if (numWideBars === 3) {
            for (i = 0; i < numCounters && numWideBars > 0; i++) {
                if (counters[i] > maxNarrowWidth) {
                    numWideBars--;
                    if ((counters[i] * 2) >= wideBarWidth) {
                        return -1;
                    }
                }
            }
            return pattern;
        }
    }
    return -1;
};

Code39Reader.prototype._findStart = function() {
    var self = this,
        offset = self._nextSet(self._row),
        patternStart = offset,
        counter = [0, 0, 0, 0, 0, 0, 0, 0, 0],
        counterPos = 0,
        isWhite = false,
        i,
        j,
        whiteSpaceMustStart;

    for ( i = offset; i < self._row.length; i++) {
        if (self._row[i] ^ isWhite) {
            counter[counterPos]++;
        } else {
            if (counterPos === counter.length - 1) {
                // find start pattern
                if (self._toPattern(counter) === self.ASTERISK) {
                    whiteSpaceMustStart = Math.floor(Math.max(0, patternStart - ((i - patternStart) / 4)));
                    if (self._matchRange(whiteSpaceMustStart, patternStart, 0)) {
                        return {
                            start: patternStart,
                            end: i
                        };
                    }
                }

                patternStart += counter[0] + counter[1];
                for ( j = 0; j < 7; j++) {
                    counter[j] = counter[j + 2];
                }
                counter[7] = 0;
                counter[8] = 0;
                counterPos--;
            } else {
                counterPos++;
            }
            counter[counterPos] = 1;
            isWhite = !isWhite;
        }
    }
    return null;
};

export default Code39Reader;