classmate-photos.js

(function () {
    var calculateNUSMatricNumber = function (id) {
        var matches = id.toUpperCase().match(/^A\d{7}|U\d{6,7}/);
        if (matches) {
            var match = matches[0];
     
            // Discard 3rd digit from U-prefixed NUSNET ID
            if (match[0] === 'U' && match.length === 8) {
                match = match.slice(0, 3) + match.slice(4);
            }
     
            var weights = {
                U: [0, 1, 3, 1, 2, 7],
                A: [1, 1, 1, 1, 1, 1]
            }[match[0]];
     
            for (var i = 0, sum = 0, digits = match.slice(-6); i < 6; i++) {
                sum += weights[i] * digits[i];
            }
     
            return match + 'YXWURNMLJHEAB'[sum % 13];
        }
    };

    var PHOTO_URL = 'https://mysoc.nus.edu.sg/mysoc/images/stdphoto.php?matric=';
    var NOPHOTO_URL = 'https://ivle.nus.edu.sg/images/nophoto.jpg';
    var TYPES = ['U', 'P', 'X'];
    
    var imgs = document.getElementsByTagName('img');
    for (var i = 0; i < imgs.length; i++) {
        var img = imgs[i];
        if (img.id && img.src === NOPHOTO_URL) {
            var matricNumber = calculateNUSMatricNumber(img.id);
            if (matricNumber) {
                (function () {
                    var typeIndex = 0;
                    img.onerror = function () {
                        this.src = typeIndex < TYPES.length ? PHOTO_URL + matricNumber + '&type=' + TYPES[typeIndex++] : NOPHOTO_URL;
                    }
                    img.onerror.call(img);
                })();
            }
        }
    }
})();