function imLoaded(){

    var filterGroups;
    var checkboxes;
    var i, j;

    // set up callbacks for all of the checkboxes, only checkboxes in
    // "filterSet" DIVs are considered. This is probably too obsessive.
    filterGroups = document.querySelectorAll("div.filterSet");
    for(i = 0; i < filterGroups.length; i++){
        checkboxes = filterGroups[i].querySelectorAll("input[type='checkbox']");
        for(j = 0; j < checkboxes.length; j++){
            checkboxes[j].addEventListener("change", filterTable);
        }
    }

    var button_clear = document.getElementById("button_clear");
    button_clear.addEventListener("click", doUncheckAll);

    var button_default = document.getElementById("button_default");
    button_default.addEventListener("click", doDefaultChecked);

    var button_default = document.getElementById("button_linux");
    button_linux.addEventListener("click", doLinuxChecked);

    var button_windows = document.getElementById("button_windows");
    button_windows.addEventListener("click", doWindowsChecked);

    // do this to report the number of rows
    filterTable();
}

function doUncheckAll(){
    doCheckBoxes("uncheck");
    filterTable();
}

function doDefaultChecked(){
    doCheckBoxes("def_checked");
    filterTable();
}

function doLinuxChecked(){
    doCheckBoxes("linux");
    filterTable();
}

function doWindowsChecked(){
    doCheckBoxes("windows");
    filterTable();
}

function doCheckBoxes(x){
    var filterGroups;
    var checkboxes;
    var i, j;

    // set up callbacks for all of the checkboxes, only checkboxes in
    // "filterSet" DIVs are considered. This is probably too obsessive.
    filterGroups = document.querySelectorAll("div.filterSet");
    for(i = 0; i < filterGroups.length; i++){
        checkboxes = filterGroups[i].querySelectorAll("input[type='checkbox']");
        for(j = 0; j < checkboxes.length; j++){
            switch(x){
                case "uncheck":
                    checkboxes[j].checked=false;
                    break;
                case "def_checked":
                    if(checkboxes[j].hasAttribute("checked")){
                        checkboxes[j].checked = true;
                    } else {
                        checkboxes[j].checked = false;
                    }
                    break;
                case "linux":
                    if(
                        checkboxes[j].hasAttribute("data-checked-linux") ||
                        checkboxes[j].hasAttribute("data-newish") ||
                        checkboxes[j].hasAttribute("data-common-default")
                    ){
                        checkboxes[j].checked = true;
                    } else {
                        checkboxes[j].checked = false;
                    }
                    break;
                case "windows":
                    if(
                        checkboxes[j].hasAttribute("data-checked-windows") ||
                        checkboxes[j].hasAttribute("data-newish") ||
                        checkboxes[j].hasAttribute("data-common-default")
                    ){
                        checkboxes[j].checked = true;
                    } else {
                        checkboxes[j].checked = false;
                    }
                    break;
            }
        }
    }
}

// this function hides rows that should not be shown
function filterTable(){

    var filters = [];

    // boolean reported if any checkbox is checked
    var oneIsChecked = false;

    // the table listing qualified downloads
    var tt = document.getElementById("theTable");

    var filterGroups = document.querySelectorAll("div.filterSet");
    for(var i = 0; i < filterGroups.length; i++) {

        checkboxes = filterGroups[i].querySelectorAll("input[type='checkbox']");
        var checkedCheckboxes = filterGroups[i].querySelectorAll(":checked");
        if(checkedCheckboxes.length == 0){
            continue;
        }
        oneIsChecked = true;
        for( var j = 0; j < checkboxes.length; j++){
            if(! checkboxes[j].checked){
                filters.push(checkboxes[j].getAttribute("name"));
            }
        }
    }

    var e;
    var cssRule = "";
    var selector = "";
    if(oneIsChecked){
        e = document.createElement("style");
        e.setAttribute("id", "filterStyle");

        for(var i = 0; i < filters.length; i++){
            cssRule += "." + filters[i] + ", ";
        }
        cssRule = cssRule.slice(0, -2);
        selector = cssRule;
        cssRule += " { display: none; }\n";
    }

    var e_old = document.getElementById("filterStyle");
    if(e_old !== null){
        e_old.remove();
    }

    var rowCount = tt.rows.length;
    if(oneIsChecked){
        document.head.appendChild(e);
        e.sheet.insertRule(cssRule,0);
        rowCount -= tt.querySelectorAll(selector).length;
    }

    var rowCountSpan = document.getElementById("reportRowCount");
    rowCountSpan.textContent = "(found " + rowCount + " items)";
}

document.addEventListener("DOMContentLoaded", imLoaded);