function check_login() {
  if (element("login_username").value == "" || element("login_password").value == "") {
    return false;
  }
  return true;
}

function check_quick_contact() {
  if (element("qc_email").value == "" || element("qc_email").value == "E-mail:") {
    alert("Musíte zadat e-mailovou adresu.");
    element("qc_email").className = "inactive";
    return false;
  }

  if (element("qc_jmeno").value == "" || element("qc_jmeno").value == "Jméno:") {
    alert("Musíte zadat jméno.");
    element("qc_jmeno").className = "inactive";
    return false;
  }

  if (element("qc_zprava").value == "" || element("qc_zprava").value == "Dotaz:") {
    alert("Musíte zadat obsah vzkazu.");
    element("qc_zprava").className = "inactive";
    return false;
  }

  return true;
}

function typing(obj) {
  if (obj.value == "E-mail:" || obj.value == "Jméno:" || obj.value == "Dotaz:") {
    obj.value = "";
  }
  
  obj.className = "";
} 

function untyping(obj) {
  if (obj.value == "") {
    if (obj.id == "qc_email") {
      obj.value = "E-mail:";
    }
    if (obj.id == "qc_jmeno") {
      obj.value = "Jméno:";
    }
    if (obj.id == "qc_zprava") {
      obj.value = "Dotaz:";
    }        
  
    obj.className = "inactive";
  }
}


function check_quick_contact_en() {
  if (element("qc_email").value == "" || element("qc_email").value == "E-mail:") {
    alert("You have to fill in your e-mail address.");
    element("qc_email").className = "inactive";
    return false;
  }

  if (element("qc_jmeno").value == "" || element("qc_jmeno").value == "Name:") {
    alert("You have to fill in your name.");
    element("qc_jmeno").className = "inactive";
    return false;
  }

  if (element("qc_zprava").value == "" || element("qc_zprava").value == "Request:") {
    alert("You have to fill in the text of message.");
    element("qc_zprava").className = "inactive";
    return false;
  }

  return true;
}

function typing_en(obj) {
  if (obj.value == "E-mail:" || obj.value == "Name:" || obj.value == "Request:") {
    obj.value = "";
  }
  
  obj.className = "";
} 

function untyping_en(obj) {
  if (obj.value == "") {
    if (obj.id == "qc_email") {
      obj.value = "E-mail:";
    }
    if (obj.id == "qc_jmeno") {
      obj.value = "Name:";
    }
    if (obj.id == "qc_zprava") {
      obj.value = "Request:";
    }        
  
    obj.className = "inactive";
  }
}

/*
 * HTML object manipulation functions / START
 */
 
/**
 * get HTML element defined by id
 *
 * @return obj    HTML element
 */
function element(id) {
  var obj = document.getElementById(id);
  
  return obj;
}
 
/**
 * hide HTML element
 *    
 * @param mixed obj    object or object's id
 * @return void
 */
function elementHide(obj) {
  if (element(obj)) {    // object identified by its id
    obj = element(obj);
  }
  
  obj.style.display = "none";
}

/**
 * show HTML element
 *    
 * @param mixed obj            object or object's id
 * @param boolean is_inline    [optional] if element is inline, pass true as second parameter
 * @return void
 */
function elementShow(obj, is_inline) {
  if (element(obj)) {    // object identified by its id
    obj = element(obj);
  }

  obj.style.display = (is_inline ? "inline" : "block");
}

/**
 * switch element class name - if element has className class_1, replace it with class_2 and vice versa
 *    
 * @param mixed obj         object or object's id
 * @param string class_1    name of class 1
 * @param string class_2    name of class 2
 * @return void
 */
function switchClass(obj, class_1, class_2) {
  if (element(obj)) {    // object identified by its id
    obj = element(obj);
  }
  
  if (obj.className == "") {    // class name empty -> set class name from class_1
    obj.className = class_1;
  } else {
    if (obj.className.indexOf(class_1) != -1) {    // class_1 exists -> replace with class_2
      obj.className = obj.className.replace(class_1, class_2);
    } else {
      if ((obj.className.indexOf(class_2) != -1) && (class_2 != "")) {    // class_2 exists -> replace with class_1
        obj.className = obj.className.replace(class_2, class_1);
      } else {    // if not found, add class_1 to existing
        obj.className = obj.className + " " + class_1;
      }
    }
  }
}

/*
 * HTML object manipulation functions / END
 */
 
/**
 * display message dialog. If confirmed, redirect to address stored in link's 'href' attribute
 *    
 * @param string msg    message to be displayed
 * @param object obj    link object to use href from
 * @return boolean      true if message has been confirmed, false otherwise
 */
function dialogConfirmRedirect(msg, obj) {
  var status = confirm(msg);
  if (status) {
    obj.href;
  }
  
  return status;
}