/**
  * Invoke method, every class will have its own
  * returns true/false on completion, setting both
  * errormsg and output as necessary
  */
 function invoke()
 {
     parent::invoke();
     $result = true;
     /// Set own core attributes
     $this->does_generate = ACTION_NONE;
     //$this->does_generate = ACTION_GENERATE_HTML;
     /// These are always here
     global $CFG, $XMLDB;
     /// Do the job, setting result as needed
     if (!data_submitted()) {
         ///Basic prevention
         print_error('wrongcall', 'error');
     }
     /// Get parameters
     $dirpath = required_param('dir', PARAM_PATH);
     $dirpath = $CFG->dirroot . $dirpath;
     $tableparam = strtolower(required_param('table', PARAM_PATH));
     $indexparam = strtolower(required_param('index', PARAM_PATH));
     $name = trim(strtolower(optional_param('name', $indexparam, PARAM_PATH)));
     $comment = required_param('comment', PARAM_CLEAN);
     $comment = trim($comment);
     $unique = required_param('unique', PARAM_INT);
     $fields = required_param('fields', PARAM_CLEAN);
     $fields = str_replace(' ', '', trim(strtolower($fields)));
     $editeddir =& $XMLDB->editeddirs[$dirpath];
     $structure =& $editeddir->xml_file->getStructure();
     $table =& $structure->getTable($tableparam);
     $index =& $table->getIndex($indexparam);
     $oldhash = $index->getHash();
     $errors = array();
     /// To store all the errors found
     /// Perform some checks
     /// Check empty name
     if (empty($name)) {
         $errors[] = $this->str['indexnameempty'];
     }
     /// Check incorrect name
     if ($name == 'changeme') {
         $errors[] = $this->str['incorrectindexname'];
     }
     /// Check duplicate name
     if ($indexparam != $name && $table->getIndex($name)) {
         $errors[] = $this->str['duplicateindexname'];
     }
     $fieldsarr = explode(',', $fields);
     /// Check the fields isn't empty
     if (empty($fieldsarr[0])) {
         $errors[] = $this->str['nofieldsspecified'];
     } else {
         /// Check that there aren't duplicate column names
         $uniquearr = array_unique($fieldsarr);
         if (count($fieldsarr) != count($uniquearr)) {
             $errors[] = $this->str['duplicatefieldsused'];
         }
         /// Check that all the fields in belong to the table
         foreach ($fieldsarr as $field) {
             if (!$table->getField($field)) {
                 $errors[] = $this->str['fieldsnotintable'];
                 break;
             }
         }
         /// Check that there isn't any key using exactly the same fields
         $tablekeys = $table->getKeys();
         if ($tablekeys) {
             foreach ($tablekeys as $tablekey) {
                 $keyfieldsarr = $tablekey->getFields();
                 /// Compare both arrays, looking for diferences
                 $diferences = array_merge(array_diff($fieldsarr, $keyfieldsarr), array_diff($keyfieldsarr, $fieldsarr));
                 if (empty($diferences)) {
                     $errors[] = $this->str['fieldsusedinkey'];
                     break;
                 }
             }
         }
         /// Check that there isn't any index using exactlt the same fields
         $tableindexes = $table->getIndexes();
         if ($tableindexes) {
             foreach ($tableindexes as $tableindex) {
                 /// Skip checking against itself
                 if ($indexparam == $tableindex->getName()) {
                     continue;
                 }
                 $indexfieldsarr = $tableindex->getFields();
                 /// Compare both arrays, looking for diferences
                 $diferences = array_merge(array_diff($fieldsarr, $indexfieldsarr), array_diff($indexfieldsarr, $fieldsarr));
                 if (empty($diferences)) {
                     $errors[] = $this->str['fieldsusedinindex'];
                     break;
                 }
             }
         }
     }
     if (!empty($errors)) {
         $tempindex = new xmldb_index($name);
         $tempindex->setUnique($unique);
         $tempindex->setFields($fieldsarr);
         /// Prepare the output
         $site = get_site();
         $navlinks = array();
         $navlinks[] = array('name' => $this->str['administration'], 'link' => '../index.php', 'type' => 'misc');
         $navlinks[] = array('name' => 'XMLDB', 'link' => 'index.php', 'type' => 'misc');
         $navigation = build_navigation($navlinks);
         print_header("{$site->shortname}: XMLDB", "{$site->fullname}", $navigation);
         notice('<p>' . implode(', ', $errors) . '</p>
                  <p>' . $tempindex->readableInfo() . '</p>', 'index.php?action=edit_index&amp;index=' . $index->getName() . '&amp;table=' . $table->getName() . '&amp;dir=' . urlencode(str_replace($CFG->dirroot, '', $dirpath)));
         die;
         /// re-die :-P
     }
     /// Continue if we aren't under errors
     if (empty($errors)) {
         /// If there is one name change, do it, changing the prev and next
         /// atributes of the adjacent fields
         if ($indexparam != $name) {
             $index->setName($name);
             if ($index->getPrevious()) {
                 $prev =& $table->getIndex($index->getPrevious());
                 $prev->setNext($name);
                 $prev->setChanged(true);
             }
             if ($index->getNext()) {
                 $next =& $table->getIndex($index->getNext());
                 $next->setPrevious($name);
                 $next->setChanged(true);
             }
         }
         /// Set comment
         $index->setComment($comment);
         /// Set the rest of fields
         $index->setUnique($unique);
         $index->setFields($fieldsarr);
         /// If the hash has changed from the old one, change the version
         /// and mark the structure as changed
         $index->calculateHash(true);
         if ($oldhash != $index->getHash()) {
             $index->setChanged(true);
             $table->setChanged(true);
             /// Recalculate the structure hash
             $structure->calculateHash(true);
             $structure->setVersion(userdate(time(), '%Y%m%d', 99, false));
             /// Mark as changed
             $structure->setChanged(true);
         }
         /// Launch postaction if exists (leave this here!)
         if ($this->getPostAction() && $result) {
             return $this->launch($this->getPostAction());
         }
     }
     /// Return ok if arrived here
     return $result;
 }