ช่วยอธิบายโค้ด_php_หน่อยครับ_slim_framework

error_reporting(0);
session_start();

/* DATABASE CONFIGURATION */
define('DB_SERVER', 'localhost');
define('DB_USERNAME', 'root');
define('DB_PASSWORD', '');
define('DB_DATABASE', 'test');
define("BASE_URL", "http://localhost/test/");
define("SITE_KEY", 'yourSecretKey');


function getDB() 
{
	$dbhost=DB_SERVER;
	$dbuser=DB_USERNAME;
	$dbpass=DB_PASSWORD;
	$dbname=DB_DATABASE;
	$dbConnection = new PDO("mysql:host=$dbhost;dbname=$dbname", $dbuser, $dbpass);	
	$dbConnection->exec("set names utf8");
	$dbConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
	return $dbConnection;
}
/* DATABASE CONFIGURATION END */

/* API key encryption */
function apiToken($session_uid)
{
$key=md5(SITE_KEY.$session_uid);
return hash('sha256', $key);
}

<?php

require 'config.php';
require 'Slim/Slim.php';

\Slim\Slim::registerAutoloader();
$app = new \Slim\Slim();

$app->post('/login','login'); /* User login */
$app->post('/signup','signup'); /* User Signup  */
$app->post('/feed','feed'); /* User Feeds  */
$app->post('/feedUpdate','feedUpdate'); /* User Feeds  */
$app->post('/feedDelete','feedDelete'); /* User Feeds  */
//$app->post('/userDetails','userDetails'); /* User Details */
/*$app -> notFound(function() use ($app){
	$app->render('404.html');
});*/

$app->run();

/************************* USER LOGIN *************************************/
/* ### User login ### */
function login() {
    
    $request = \Slim\Slim::getInstance()->request();
    $data = json_decode($request->getBody());
    
    try {
        
        $db = getDB();
        $userData ='';
        $sql = "SELECT user_id, name, email, username FROM users WHERE (username=:username or email=:username) and password=:password ";
        $stmt = $db->prepare($sql);
        $stmt->bindParam("username", $data->username, PDO::PARAM_STR);
        $password=hash('sha256',$data->password);
        $stmt->bindParam("password", $password, PDO::PARAM_STR);
        $stmt->execute();
        $mainCount=$stmt->rowCount();
        $userData = $stmt->fetch(PDO::FETCH_OBJ);
        
        if(!empty($userData))
        {
            $user_id=$userData->user_id;
            $userData->token = apiToken($user_id);
        }
        
        $db = null;
         if($userData){
               $userData = json_encode($userData);
                echo '{"userData": ' .$userData . '}';
            } else {
               echo '{"error":{"text":"Bad request wrong username and password"}}';
            }

           
    }
    catch(PDOException $e) {
        echo '{"error":{"text":'. $e->getMessage() .'}}';
    }
}


/* ### User registration ### */
function signup() {
    $request = \Slim\Slim::getInstance()->request();
    $data = json_decode($request->getBody());
    $email=$data->email;
    $name=$data->name;
    $username=$data->username;
    $password=$data->password;
    
    try {
        
        $username_check = preg_match('~^[A-Za-z0-9_]{3,20}$~i', $username);
        $emain_check = preg_match('~^[a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.([a-zA-Z]{2,4})$~i', $email);
        $password_check = preg_match('~^[A-Za-z0-9!@#$%^&*()_]{6,20}$~i', $password);
        
        
        if (strlen(trim($username))>0 && strlen(trim($password))>0 && strlen(trim($email))>0 && $emain_check>0 && $username_check>0 && $password_check>0)
        {
            $db = getDB();
            $userData = '';
            $sql = "SELECT user_id FROM users WHERE username=:username or email=:email";
            $stmt = $db->prepare($sql);
            $stmt->bindParam("username", $username,PDO::PARAM_STR);
            $stmt->bindParam("email", $email,PDO::PARAM_STR);
            $stmt->execute();
            $mainCount=$stmt->rowCount();
            $created=time();
            if($mainCount==0)
            {
                
                /*Inserting user values*/
                $sql1="INSERT INTO users(username,password,email,name)VALUES(:username,:password,:email,:name)";
                $stmt1 = $db->prepare($sql1);
                $stmt1->bindParam("username", $username,PDO::PARAM_STR);
                $password=hash('sha256',$data->password);
                $stmt1->bindParam("password", $password,PDO::PARAM_STR);
                $stmt1->bindParam("email", $email,PDO::PARAM_STR);
                $stmt1->bindParam("name", $name,PDO::PARAM_STR);
                $stmt1->execute();
                
                $userData=internalUserDetails($email);
                
            }
            
            $db = null;
         

            if($userData){
               $userData = json_encode($userData);
                echo '{"userData": ' .$userData . '}';
            } else {
               echo '{"error":{"text":"Enter valid data"}}';
            }

           
        }
        else{
            echo '{"error":{"text":"Enter valid data"}}';
        }
    }
    catch(PDOException $e) {
        echo '{"error":{"text":'. $e->getMessage() .'}}';
    }
}


/* ### internal Username Details ### */
function internalUserDetails($input) {
    
    try {
        $db = getDB();
        $sql = "SELECT user_id, name, email, username FROM users WHERE username=:input or email=:input";
        $stmt = $db->prepare($sql);
        $stmt->bindParam("input", $input,PDO::PARAM_STR);
        $stmt->execute();
        $usernameDetails = $stmt->fetch(PDO::FETCH_OBJ);
        $usernameDetails->token = apiToken($usernameDetails->user_id);
        $db = null;
        return $usernameDetails;
        
    } catch(PDOException $e) {
        echo '{"error":{"text":'. $e->getMessage() .'}}';
    }
    
}

function feed(){
    $request = \Slim\Slim::getInstance()->request();
    $data = json_decode($request->getBody());
    $user_id=$data->user_id;
    $token=$data->token;
    
    $systemToken=apiToken($user_id);
   
    try {
         
        if($systemToken == $token){
            $feedData = '';
            $db = getDB();
            $sql = "SELECT * FROM feed WHERE user_id_fk=:user_id ORDER BY feed_id DESC";
            $stmt = $db->prepare($sql);
            $stmt->bindParam("user_id", $user_id, PDO::PARAM_INT);
            $stmt->execute();
            $feedData = $stmt->fetchAll(PDO::FETCH_OBJ);
           
            $db = null;
            echo '{"feedData": ' . json_encode($feedData) . '}';
        } else{
            echo '{"error":{"text":"No access"}}';
        }
       
    } catch(PDOException $e) {
        echo '{"error":{"text":'. $e->getMessage() .'}}';
    }
    
    
    
}

function feedUpdate(){

    $request = \Slim\Slim::getInstance()->request();
    $data = json_decode($request->getBody());
    $user_id=$data->user_id;
    $token=$data->token;
    $feed=$data->feed;
    
    $systemToken=apiToken($user_id);
   
    try {
         
        if($systemToken == $token){
         
            
            $feedData = '';
            $db = getDB();
            $sql = "INSERT INTO feed ( feed, created, user_id_fk) VALUES (:feed,:created,:user_id)";
            $stmt = $db->prepare($sql);
            $stmt->bindParam("feed", $feed, PDO::PARAM_STR);
            $stmt->bindParam("user_id", $user_id, PDO::PARAM_INT);
            $created = time();
            $stmt->bindParam("created", $created, PDO::PARAM_INT);
            $stmt->execute();
            


            $sql1 = "SELECT * FROM feed WHERE user_id_fk=:user_id ORDER BY feed_id DESC LIMIT 1";
            $stmt1 = $db->prepare($sql1);
            $stmt1->bindParam("user_id", $user_id, PDO::PARAM_INT);
            $stmt1->execute();
            $feedData = $stmt1->fetch(PDO::FETCH_OBJ);


            $db = null;
            echo '{"feedData": ' . json_encode($feedData) . '}';
        } else{
            echo '{"error":{"text":"No access"}}';
        }
       
    } catch(PDOException $e) {
        echo '{"error":{"text":'. $e->getMessage() .'}}';
    }

}

function feedDelete(){
    $request = \Slim\Slim::getInstance()->request();
    $data = json_decode($request->getBody());
    $user_id=$data->user_id;
    $token=$data->token;
    $feed_id=$data->feed_id;
    
    $systemToken=apiToken($user_id);
   
    try {
         
        if($systemToken == $token){
            $feedData = '';
            $db = getDB();
            $sql = "Delete * FROM feed WHERE user_id_fk=:user_id AND feed_id=:feed_id";
            $stmt = $db->prepare($sql);
            $stmt->bindParam("user_id", $user_id, PDO::PARAM_INT);
            $stmt->bindParam("feed_id", $feed_id, PDO::PARAM_INT);
            $stmt->execute();
            
           
            $db = null;
            echo '{"success":{"text":"Feed deleted"}}';
        } else{
            echo '{"error":{"text":"No access"}}';
        }
       
    } catch(PDOException $e) {
        echo '{"error":{"text":'. $e->getMessage() .'}}';
    }
    
    
    
}






?>