function searchPage(topics) {
    highlightAllWords(topics);
}

var highlightAllWords = function(topics) {
    Object.keys(topics.topics).forEach(function(topic) {
        highlightTopic(topic);
    })
}

function highlightTopic(topic) {
    let found = 0;
    if (topic == null || topic.length === 0) return;
    var topicRegex = new RegExp(topic, 'gi');
    var treeWalker = document.createTreeWalker(
        document.body,
        NodeFilter.SHOW_TEXT,
        {
            acceptNode: function(node) {
                var result = NodeFilter.FILTER_SKIP;
                if (topicRegex.test(node.nodeValue)) {
                    found += 1
                    console.log('found', found);
                    if (found <= 6) {
                        console.log('foound less than 6', found)
                        result = NodeFilter.FILTER_ACCEPT
                        return result;
                    }
                };
            }
        }, false
    )

    var skipTagName = {
        "NOSCRIPT": true,
        "SCRIPT": true,
        "STYLE": true
    }

    var nodeList = [];
    while (treeWalker.nextNode()) {
        if (!skipTagName[treeWalker.currentNode.parentNode.tagName]) {
            nodeList.push(treeWalker.currentNode);
        }
    }

    nodeList.forEach(function (n) {
        var rangeList = [];
        // find sub-string ranges
        var startingIndex = 0;
        do {
            // console.log(word, startingIndex, n.parentNode, n.textContent);
            startingIndex = n.textContent.indexOf(topic, startingIndex + 1);
            if (startingIndex !== -1) {
                var topicRange = document.createRange();
                topicRange.setStart(n, startingIndex);
                topicRange.setEnd(n, startingIndex + topic.length);
                rangeList.push(topicRange);
            }
        } while (startingIndex !== -1);

        // highlight all ranges
        rangeList.forEach(function (r) {
            highlightRange(r);
        });
    });
}


// highlight the keyword by surround it by `i`
var highlightRange = function (range) {
    const bgColorCode = '#000000';
    var anchor = document.createElement("A");
    var selectorName = anchor.className = "highlighted_text";
    anchor.classList.add("highlighted_text");

    // range.surroundContents(iNode) will throw exception if word across multi tag
    if (!ruleExistenceDict[bgColorCode]) {
        sheet.insertRule([".", selectorName, " { background: #", bgColorCode, " !important; }"].join(""), 0);
        ruleExistenceDict[bgColorCode] = true;
        console.log(sheet);
    }
    anchor.appendChild(range.extractContents());
    anchor.href = `https://google.com/?search=${
                        range.extractContents()
                    }`;
    range.insertNode(anchor);
};