/**
  * 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));
     $fieldparam = strtolower(required_param('field', PARAM_PATH));
     $name = substr(trim(strtolower(optional_param('name', $fieldparam, PARAM_PATH))), 0, 30);
     $comment = required_param('comment', PARAM_CLEAN);
     $comment = trim($comment);
     $type = required_param('type', PARAM_INT);
     $length = strtolower(optional_param('length', NULL, PARAM_ALPHANUM));
     $decimals = optional_param('decimals', NULL, PARAM_INT);
     $unsigned = optional_param('unsigned', false, PARAM_BOOL);
     $notnull = optional_param('notnull', false, PARAM_BOOL);
     $sequence = optional_param('sequence', false, PARAM_BOOL);
     $default = optional_param('default', NULL, PARAM_PATH);
     $default = trim($default);
     $editeddir =& $XMLDB->editeddirs[$dirpath];
     $structure =& $editeddir->xml_file->getStructure();
     $table =& $structure->getTable($tableparam);
     $field =& $table->getField($fieldparam);
     $oldhash = $field->getHash();
     $errors = array();
     /// To store all the errors found
     /// Perform some automatic asumptions
     if ($sequence) {
         $unsigned = true;
         $notnull = true;
         $default = NULL;
     }
     if ($type != XMLDB_TYPE_NUMBER && $type != XMLDB_TYPE_FLOAT) {
         $decimals = NULL;
     }
     if ($type == XMLDB_TYPE_BINARY) {
         $default = NULL;
     }
     if ($default === '') {
         $default = NULL;
     }
     /// Perform some checks
     /// Check empty name
     if (empty($name)) {
         $errors[] = $this->str['fieldnameempty'];
     }
     /// Check incorrect name
     if ($name == 'changeme') {
         $errors[] = $this->str['incorrectfieldname'];
     }
     /// Check duplicate name
     if ($fieldparam != $name && $table->getField($name)) {
         $errors[] = $this->str['duplicatefieldname'];
     }
     /// Integer checks
     if ($type == XMLDB_TYPE_INTEGER) {
         if (!(is_numeric($length) && !empty($length) && intval($length) == floatval($length) && $length > 0 && $length <= 20)) {
             $errors[] = $this->str['integerincorrectlength'];
         }
         if (!(empty($default) || is_numeric($default) && !empty($default) && intval($default) == floatval($default))) {
             $errors[] = $this->str['defaultincorrect'];
         }
     }
     /// Number checks
     if ($type == XMLDB_TYPE_NUMBER) {
         if (!(is_numeric($length) && !empty($length) && intval($length) == floatval($length) && $length > 0 && $length <= 20)) {
             $errors[] = $this->str['numberincorrectlength'];
         }
         if (!(empty($decimals) || is_numeric($decimals) && !empty($decimals) && intval($decimals) == floatval($decimals) && $decimals >= 0 && $decimals < $length)) {
             $errors[] = $this->str['numberincorrectdecimals'];
         }
         if (!(empty($default) || is_numeric($default) && !empty($default))) {
             $errors[] = $this->str['defaultincorrect'];
         }
     }
     /// Float checks
     if ($type == XMLDB_TYPE_FLOAT) {
         if (!(empty($length) || is_numeric($length) && !empty($length) && intval($length) == floatval($length) && $length > 0 && $length <= 20)) {
             $errors[] = $this->str['floatincorrectlength'];
         }
         if (!(empty($decimals) || is_numeric($decimals) && !empty($decimals) && intval($decimals) == floatval($decimals) && $decimals >= 0 && $decimals < $length)) {
             $errors[] = $this->str['floatincorrectdecimals'];
         }
         if (!(empty($default) || is_numeric($default) && !empty($default))) {
             $errors[] = $this->str['defaultincorrect'];
         }
     }
     /// Char checks
     if ($type == XMLDB_TYPE_CHAR) {
         if (!(is_numeric($length) && !empty($length) && intval($length) == floatval($length) && $length > 0 && $length <= 255)) {
             $errors[] = $this->str['charincorrectlength'];
         }
         if ($default !== NULL && $default !== '') {
             if (substr($default, 0, 1) == "'" || substr($default, -1, 1) == "'") {
                 $errors[] = $this->str['defaultincorrect'];
             }
         }
     }
     /// Text checks
     if ($type == XMLDB_TYPE_TEXT) {
         if ($length != 'small' && $length != 'medium' && $length != 'big') {
             $errors[] = $this->str['textincorrectlength'];
         }
         if ($default !== NULL && $default !== '') {
             if (substr($default, 0, 1) == "'" || substr($default, -1, 1) == "'") {
                 $errors[] = $this->str['defaultincorrect'];
             }
         }
     }
     /// Binary checks
     if ($type == XMLDB_TYPE_BINARY) {
         if ($length != 'small' && $length != 'medium' && $length != 'big') {
             $errors[] = $this->str['binaryincorrectlength'];
         }
     }
     if (!empty($errors)) {
         $tempfield = new xmldb_field($name);
         $tempfield->setType($type);
         $tempfield->setLength($length);
         $tempfield->setDecimals($decimals);
         $tempfield->setUnsigned($unsigned);
         $tempfield->setNotNull($notnull);
         $tempfield->setSequence($sequence);
         $tempfield->setDefault($default);
         /// 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>' . $tempfield->readableInfo() . '</p>', 'index.php?action=edit_field&amp;field=' . $field->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 ($fieldparam != $name) {
             $field->setName($name);
             if ($field->getPrevious()) {
                 $prev =& $table->getField($field->getPrevious());
                 $prev->setNext($name);
                 $prev->setChanged(true);
             }
             if ($field->getNext()) {
                 $next =& $table->getField($field->getNext());
                 $next->setPrevious($name);
                 $next->setChanged(true);
             }
         }
         /// Set comment
         $field->setComment($comment);
         /// Set the rest of fields
         $field->setType($type);
         $field->setLength($length);
         $field->setDecimals($decimals);
         $field->setUnsigned($unsigned);
         $field->setNotNull($notnull);
         $field->setSequence($sequence);
         $field->setDefault($default);
         /// If the hash has changed from the old one, change the version
         /// and mark the structure as changed
         $field->calculateHash(true);
         if ($oldhash != $field->getHash()) {
             $field->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;
 }