source: node_modules/autolinker/dist/es2015/truncate/truncate-smart.js@ d24f17c

/**
 * Date: 2015-10-05
 * Author: Kasper Søfren <soefritz@gmail.com> (https://github.com/kafoso)
 *
 * A truncation feature, where the ellipsis will be placed at a section within
 * the URL making it still somewhat human readable.
 *
 * @param {String} url                                           A URL.
 * @param {Number} truncateLen           The maximum length of the truncated output URL string.
 * @param {String} ellipsisChars         The characters to place within the url, e.g. "...".
 * @return {String} The truncated URL.
 */
export function truncateSmart(url, truncateLen, ellipsisChars) {
    var ellipsisLengthBeforeParsing;
    var ellipsisLength;
    if (ellipsisChars == null) {
        ellipsisChars = '&hellip;';
        ellipsisLength = 3;
        ellipsisLengthBeforeParsing = 8;
    }
    else {
        ellipsisLength = ellipsisChars.length;
        ellipsisLengthBeforeParsing = ellipsisChars.length;
    }
    var parse_url = function (url) {
        // Functionality inspired by PHP function of same name
        var urlObj = {};
        var urlSub = url;
        var match = urlSub.match(/^([a-z]+):\/\//i);
        if (match) {
            urlObj.scheme = match[1];
            urlSub = urlSub.substr(match[0].length);
        }
        match = urlSub.match(/^(.*?)(?=(\?|#|\/|$))/i);
        if (match) {
            urlObj.host = match[1];
            urlSub = urlSub.substr(match[0].length);
        }
        match = urlSub.match(/^\/(.*?)(?=(\?|#|$))/i);
        if (match) {
            urlObj.path = match[1];
            urlSub = urlSub.substr(match[0].length);
        }
        match = urlSub.match(/^\?(.*?)(?=(#|$))/i);
        if (match) {
            urlObj.query = match[1];
            urlSub = urlSub.substr(match[0].length);
        }
        match = urlSub.match(/^#(.*?)$/i);
        if (match) {
            urlObj.fragment = match[1];
            //urlSub = urlSub.substr(match[0].length);  -- not used. Uncomment if adding another block.
        }
        return urlObj;
    };
    var buildUrl = function (urlObj) {
        var url = '';
        if (urlObj.scheme && urlObj.host) {
            url += urlObj.scheme + '://';
        }
        if (urlObj.host) {
            url += urlObj.host;
        }
        if (urlObj.path) {
            url += '/' + urlObj.path;
        }
        if (urlObj.query) {
            url += '?' + urlObj.query;
        }
        if (urlObj.fragment) {
            url += '#' + urlObj.fragment;
        }
        return url;
    };
    var buildSegment = function (segment, remainingAvailableLength) {
        var remainingAvailableLengthHalf = remainingAvailableLength / 2, startOffset = Math.ceil(remainingAvailableLengthHalf), endOffset = -1 * Math.floor(remainingAvailableLengthHalf), end = '';
        if (endOffset < 0) {
            end = segment.substr(endOffset);
        }
        return segment.substr(0, startOffset) + ellipsisChars + end;
    };
    if (url.length <= truncateLen) {
        return url;
    }
    var availableLength = truncateLen - ellipsisLength;
    var urlObj = parse_url(url);
    // Clean up the URL
    if (urlObj.query) {
        var matchQuery = urlObj.query.match(/^(.*?)(?=(\?|\#))(.*?)$/i);
        if (matchQuery) {
            // Malformed URL; two or more "?". Removed any content behind the 2nd.
            urlObj.query = urlObj.query.substr(0, matchQuery[1].length);
            url = buildUrl(urlObj);
        }
    }
    if (url.length <= truncateLen) {
        return url;
    }
    if (urlObj.host) {
        urlObj.host = urlObj.host.replace(/^www\./, '');
        url = buildUrl(urlObj);
    }
    if (url.length <= truncateLen) {
        return url;
    }
    // Process and build the URL
    var str = '';
    if (urlObj.host) {
        str += urlObj.host;
    }
    if (str.length >= availableLength) {
        if (urlObj.host.length == truncateLen) {
            return (urlObj.host.substr(0, truncateLen - ellipsisLength) + ellipsisChars).substr(0, availableLength + ellipsisLengthBeforeParsing);
        }
        return buildSegment(str, availableLength).substr(0, availableLength + ellipsisLengthBeforeParsing);
    }
    var pathAndQuery = '';
    if (urlObj.path) {
        pathAndQuery += '/' + urlObj.path;
    }
    if (urlObj.query) {
        pathAndQuery += '?' + urlObj.query;
    }
    if (pathAndQuery) {
        if ((str + pathAndQuery).length >= availableLength) {
            if ((str + pathAndQuery).length == truncateLen) {
                return (str + pathAndQuery).substr(0, truncateLen);
            }
            var remainingAvailableLength = availableLength - str.length;
            return (str + buildSegment(pathAndQuery, remainingAvailableLength)).substr(0, availableLength + ellipsisLengthBeforeParsing);
        }
        else {
            str += pathAndQuery;
        }
    }
    if (urlObj.fragment) {
        var fragment = '#' + urlObj.fragment;
        if ((str + fragment).length >= availableLength) {
            if ((str + fragment).length == truncateLen) {
                return (str + fragment).substr(0, truncateLen);
            }
            var remainingAvailableLength2 = availableLength - str.length;
            return (str + buildSegment(fragment, remainingAvailableLength2)).substr(0, availableLength + ellipsisLengthBeforeParsing);
        }
        else {
            str += fragment;
        }
    }
    if (urlObj.scheme && urlObj.host) {
        var scheme = urlObj.scheme + '://';
        if ((str + scheme).length < availableLength) {
            return (scheme + str).substr(0, truncateLen);
        }
    }
    if (str.length <= truncateLen) {
        return str;
    }
    var end = '';
    if (availableLength > 0) {
        end = str.substr(-1 * Math.floor(availableLength / 2));
    }
    return (str.substr(0, Math.ceil(availableLength / 2)) + ellipsisChars + end).substr(0, availableLength + ellipsisLengthBeforeParsing);
}
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