CakePHP: File replacement doesn't work - php

Question

I'm very new on cakephp and I try to make an edit function with file replacement but it isn't working. If the file already exists I get an error message.
This is my admin_edit.ctp code:
<td>
<?php if (!empty($this->data['Stock']['filepath'])): ?>
<div class="input">
<label>Uploaded File</label>
<?php
echo $this->Form->input('filepath', array('type'=>'hidden', 'label' => false));
echo $this->Html->link(basename($this->data['Stock']['filepath']),
$this->data['Stock']['filepath']);
?>
</div>
<?php else: ?>
<?php echo $this->Form->input('filename',array('type' => 'file', 'label' => false)); ?>
<?php endif; ?>
</td>
here below stock.php validation code
public $validate = array(
'filename' => array(
// http://book.cakephp.org/2.0/en/models/data-validation.html#Validation::uploadError
'uploadError' => array(
'rule' => 'uploadError',
'message' => 'Something went wrong with the file upload - filename error',
'required' => FALSE,
'allowEmpty' => TRUE,
),
// http://book.cakephp.org/2.0/en/models/data-validation.html#Validation::mimeType
'mimeType' => array(
'rule' => array('mimeType', array('image/gif','image/png','image/jpg','image/jpeg')),
'message' => 'Invalid file, only images allowed',
'required' => FALSE,
'allowEmpty' => TRUE,
),
// custom callback to deal with the file upload
'processUpload' => array(
'rule' => 'processUpload',
'message' => 'Something went wrong processing your file - process error',
'required' => FALSE,
'allowEmpty' => TRUE,
'last' => TRUE,
)
processUpload :
public function processUpload($check=array()) {
// deal with uploaded file
if (!empty($check['filename']['tmp_name'])) {
// check file is uploaded
if (!is_uploaded_file($check['filename']['tmp_name'])) {
return FALSE;
}
// build full filename
$filename = WWW_ROOT . $this->uploadDir . DS . Inflector::slug(pathinfo($check['filename']['name'], PATHINFO_FILENAME)).'.'.pathinfo($check['filename']['name'], PATHINFO_EXTENSION);
// #todo check for duplicate filename
// try moving file
if (!move_uploaded_file($check['filename']['tmp_name'], $filename)) {
return FALSE;
// file successfully uploaded
} else {
// save the file path relative from WWW_ROOT e.g. uploads/example_filename.jpg
$this->data[$this->alias]['filepath'] = str_replace(DS, "/", str_replace(WWW_ROOT, "", $filename) );
}
}
return TRUE;
}
Error message :"Something went wrong with the file upload - filename error"
Before saving :
public function beforeSave($options = array()) {
// a file has been uploaded so grab the filepath
if (!empty($this->data[$this->alias]['filepath'])) {
$this->data[$this->alias]['filename'] = $this->data[$this->alias]['filepath'];
foreach (array_keys($this->hasAndBelongsToMany) as $model){
if(isset($this->data[$this->name][$model])){
$this->data[$model][$model] = $this->data[$this->name][$model];
unset($this->data[$this->name][$model]);
}
}
}
return parent::beforeSave($options);
Does anyone help me to find mistake ?
Thanks