Contact Form 7 custom validation

cf7-custom-validation.php

<?php
// Add custom validation for CF7 form fields
function custom_text_validation_filter($result,$tag){
	$type = $tag['type'];
	$name = $tag['name'];
	$the_value = $_POST[$name];
	
	if($name == 'firstname'){
		if( empty($the_value) ) {
			$result['valid'] = false;
			$result['reason'][$name] = 'Please fill the required field.';
		} else {
			if( !preg_match( '/^([a-zA-Z \-.\'.\_]+)$/', stripslashes(str_replace( "'", "", $the_value))) ){
				$result['valid'] = false;
				$result['reason'][$name] = 'Please enter valid first name.';
			}
		}
	}
	if($name == 'lastname'){
		if( empty($the_value) ) {
			$result['valid'] = false;
			$result['reason'][$name] = 'Please fill the required field.';
		} else {
			if( !preg_match( '/^([a-zA-Z \-.\'.\_]+)$/', stripslashes(str_replace( "'", "", $the_value))) ){
				$result['valid'] = false;
				$result['reason'][$name] = 'Please enter valid last name.';
			}
		}
	}
	if($name == 'city'){
		if( !empty($the_value) ) {
			if( !preg_match( '/^([a-zA-Z \-.\'.\_]+)$/', stripslashes(str_replace( "'", "", $the_value))) ){
				$result['valid'] = false;
				$result['reason'][$name] = 'Please enter valid city name.';
			}
		}
	}
	if($name == 'phone'){
		if( !empty($the_value) ) {
			if( !preg_match( '/^(?:\([0-9]\d{2}\)\ ?|(?:[0-9]\d{2}\-))[0-9]\d{2}\-\d{4}$/', $the_value ) ){
				$result['valid'] = false;
				$result['reason'][$name] = 'Please enter valid phone no.';
			}
		}
	}
	return $result;
}
add_filter('wpcf7_validate_text','custom_text_validation_filter', 10, 2); // Normal field
add_filter('wpcf7_validate_text*', 'custom_text_validation_filter', 10, 2); // Req. field

?>