/**
 * Create a table of contents for this document, and insert the TOC into
 * the document by replacing the node specified by the replace argument.
 **/
function maketoc(replace) {
    // Create a <div> element that is the root of the TOC tree
    var toc = document.createElement("div");
    toc.setAttribute("align", "left");
    toc.setAttribute("class", "div_toc");

    // Set a background color and font for the TOC.  We'll learn about
    // the style property in the next chapter
    toc.style.backgroundColor = "white";
    toc.style.fontFamily = "sans-serif";

    // Start the TOC with an anchor so we can link back to it.
    var anchor = document.createElement("a");  // Create an <a> node
    anchor.setAttribute("name", "Obsah");        // Give it a name
    toc.appendChild(anchor);                   // And insert it

    // Make the body of the anchor the title of the TOC
    anchor.appendChild(document.createTextNode("Obsah"));

    // Create a <table> element that will hold the TOC and add it 
    var table = document.createElement("table");
    toc.appendChild(table);

    // Create a <tbody> element that holds the rows of the TOC
    var tbody = document.createElement("tbody");
    table.appendChild(tbody);

    // Initialize an array that keeps track of section numbers
    var sectionNumbers = [0,0,0,0,0,0];

    // Recursively traverse the body of the document, looking for sections
    // marked with <h1>, <h2>, ... tags, and use them to create the TOC
    // by adding rows to the table.
    addSections(document.getElementById('blog_content'), tbody, sectionNumbers);

    // Finally, insert the TOC into the document by replacing the node
    // specified by the replace argument with the TOC sub-tree
    replace.parentNode.replaceChild(toc, replace);

    // This method recursively traverses the tree rooted at node n, looking
    // for <h1> through <h6> tags and uses the content of these tags to build
    // the table of contents by adding rows to the HTML table specified by the
    // toc argument.  It uses the sectionNumbers array to keep track of the
    // current section number.
    // This function is defined inside of maketoc() so that it is not
    // visible from the outside.  maketoc() is the only function
    // exported by this JavaScript module.
    function addSections(n, toc, sectionNumbers) {
        // Loop through all the children of n
        for(var m = n.firstChild; m != null; m = m.nextSibling) {
	    // Check whether m is a heading element.  It would be nice if we
            // could just use (m instanceof HTMLHeadingElement), but this is
            // not required by the specification and it does not work in IE.
            // Therefore we've got to check the tagname to see if it is H1-H6.
            if ((m.nodeType == 1) &&  /* Node.ELEMENT_NODE */ 
                (m.tagName.length == 2) && (m.tagName.charAt(0) == "H")) {
		// Figure out what level heading it is
                var level = parseInt(m.tagName.charAt(1));
                if (!isNaN(level) && (level >= 2) && (level <= 6)) {
		    // Increment the section number for this heading level
		    sectionNumbers[level-1]++;
		    // And reset all lower heading level numbers to zero
		    for(var i = level; i < 6; i++) sectionNumbers[i] = 0;
		    // Now combine section numbers for all heading levels
		    // to produce a section number like 2.3.1

        var sectionNumber = "";
		    for(var i = 1; i < level; i++) {
			sectionNumber += sectionNumbers[i];
			if (i < level-1) sectionNumber += ".";
		    }

		    // Create an anchor to mark the beginning of this section.
		    // This will be the target of a link we add to the TOC.
		    var anchor = document.createElement("a");
		    anchor.setAttribute("name", "Nadpis_"+sectionNumber);

		    // Create a link back to the TOC and make it a
		    // child of the anchor
		    var backlink_div = document.createElement("div");
		    backlink_div.setAttribute("align", "right");
		    var backlink = document.createElement("a");
		    backlink.setAttribute("href", "#Obsah");
		    backlink.appendChild(document.createTextNode("Obsah"));
		    backlink_div.appendChild(backlink);
		    anchor.appendChild(backlink_div);

		    // Insert the anchor into the document right before the
		    // section header
		    n.insertBefore(anchor, m);

		    // Now create a link to this section.  It will be added
		    // to the TOC below.
		    var link = document.createElement("a");
		    link.setAttribute("href", "#Nadpis_" + sectionNumber);
		    // Get the heading text using a function defined below
		    var sectionTitle = getTextContent(m);
		    // Use the heading text as the content of the link.
		    link.appendChild(document.createTextNode(sectionTitle));

		    // Create a new row for the TOC
		    var row = document.createElement("tr");
		    // Create two columns for the row
		    var col1 = document.createElement("td");
		    var col2 = document.createElement("td");
		    var bold_id = document.createElement("b");
		    // Make the first column right-aligned and put the section
		    // number in it
		    bold_id.appendChild(document.createTextNode(sectionNumber));
		    bold_id.innerHTML += "&nbsp;-";
		    col1.setAttribute("align", "right");
		    col1.appendChild(bold_id);
		    // Put a link to the section in the second column
		    col2.appendChild(link);
		    // Add the columns to the row, and the row to the table
		    row.appendChild(col1);
		    row.appendChild(col2);
		    toc.appendChild(row);

		    // Modify the section header element itself to add
		    // the section number as part of the section title
		    /*m.insertBefore(document.createTextNode(sectionNumber+": "),
				   m.firstChild);*/
                }
            }
	    else { // Otherwise, this is not a heading element, so recurse
		addSections(m, toc, sectionNumbers);
	    }
        }
    }

    // This utility function traverses the node n, returning the content of
    // all text nodes found, and discarding any HTML tags.  This is also
    // defined as a nested function so that it is private to this module.
    function getTextContent(n) {
        var s = '';
        var children = n.childNodes;
        for(var i = 0; i < children.length; i++) {
            var child = children[i];
            if (child.nodeType == 3 /*Node.TEXT_NODE*/) s += child.data;
            else s += getTextContent(child);
        }
        return s;
    }
}