[WordPress] A simple, server-side based implementation of a protocol to be used in Ajax requests.

00-calling-the-protocol.php

<?php

$p = new Protocol();
$p->set_response( 'complete', 10 );
$p->get_response();

01-protocol.php

<?php

class Protocol {

    /**
     * Maintains the response that will be returned to the browser.
     * @var array
     */
    private $response;

    /**
     * A list of valid messages that the protocol can send to the caller.
     * @var array
     */
    private $valid_messages;

    /**
     * Maintains a boolean value of if the response is or isn't valid.
     * @var bool
     */
    private $valid_responses;

    /**
     * Instantiates the list of valid messages and the actual response (before
     * it has been formatted as JSON) for this protocol.
     *
     * This will be used throughout the class to use a message and file number
     * to return to the browser.
     */
    public function __construct() {

        $this->valid_messages = array(
            'INCOMPLETE',
            'COMPLETE',
            'NOT_FOUND',
        );

        $this->response = array(
            'MESSAGE'      => '',
            'FILE_NUMBER'  => -1,
        );
    }

    /**
     * Allows the user to define the message the protocol will use in its
     * response. If the message is not one of the predefined options, then
     * a default value, 'INVALID_MESSAGE_TYPE' will be used.
     *
     * @param string $message The message to place in the response.
     */
    public function set_message( $message ) {

        if ( ! $this->is_valid_message( $message ) ) {

            $this->response['MESSAGE'] = 'INVALID_MESSAGE_TYPE';
            return;
        }

        $message = strtoupper( $message );
        $this->response['MESSAGE'] = $message;
    }

    /**
     * Allows the user to explicitly set the file number they are working
     * with when preparing the response for the caller. If the number is
     * invalid, then a default value of "INVALID_FILE_NUMBER" will be used
     * as the response.
     *
     * @param int $number The file number being processed in this response.
     */
    public function set_file_number( $number ) {

        if ( ! $this->is_valid_number( $number ) ) {
            $this->response['FILE_NUMBER'] = 'INVALID_FILE_NUMBER';
            return;
        }

        $this->response['FILE_NUMBER'] = intval( $number );
    }

    /**
     * Allows the user to explicitly set the message and the file number with
     * which they are working to build a response for the protocol.
     *
     * @param string optional $message The message to place in the response.
     * @param int    optiona  $number The file number being processed in this response.
     */
    public function set_response( $message = '', $number = -1 ) {

        $this->set_message( $message );
        $this->set_file_number( $number );
    }

    /**
     * Retrieves the response from the protocol based on the defined message
     * and file number and returns the response in the form of JSON.
     *
     * @return string A JSON response of this protocol's response.
     */
    public function get_response() {

        $this->validate_response();
        return json_encode( $this->response );
    }

    /**
     * Determines if the specified message is valid. The message is considered
     * valid if it's part of the predefined set of messages and it's not
     * an empty string.
     *
     * @access private
     * @param  string  $message The message to evaluate.
     * @return bool             Whether or not the specified message is valid.
     */
    private function is_valid_message( $message ) {

        $is_valid =
            in_array( strtoupper( $message ), $this->valid_messages, true ) &&
            ! empty( $message );

        return $is_valid;
    }

    /**
     * Determines if the specified file number is valid. The number is
     * considered valid if greater than or equal to zero.
     *
     * @access private
     * @param  int  $int The message to evaluate.
     * @return bool      Whether or not the specified number is >= 0.
     */
    private function is_valid_number( $number ) {
        return ( $number >= 0 );
    }
}