function addMarkToMsg(start, end) {
    var textarea = document.getElementById('id_text');
    if(!textarea) return;
    if( document.selection ) {
        textarea.focus();
        sel = document.selection.createRange();
        sel.text = start + sel.text + end;
    } else if(textarea.selectionStart || textarea.selectionStart == '0') {
        textarea.focus();
        var startPos = textarea.selectionStart;
        var endPos = textarea.selectionEnd;
        textarea.value = textarea.value.substring(0, startPos) + start + textarea.value.substring(startPos, endPos) + end + textarea.value.substring( endPos, textarea.value.length );
    } else {
        textarea.value += start + end;
    }
    return false;
}

function addMarkPanel() {
    $('.mark_btn').on('click', function() {
        switch($(this).attr('id')) {
            case "italic":
                return addMarkToMsg('_', '_');
            case "bold":
                return addMarkToMsg('__', '__');
            case "spoiler":
                return addMarkToMsg('%%', '%%');
            case "comment":
                return addMarkToMsg('//', '');
            case "quote":
                return addMarkToMsg('>', '');
        }
    });
}