create mvc files for register feature

controllers/register.inc.php

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+<?php
+//Controllers handle the logic of the application
+
+declare(strict_types=1);
+
+function is_input_empty(string $fullname, string $email, string $username, string $password){
+   if(empty ($fullname) || empty ($email) || empty ($username) || empty ($password)){
+      return true;
+   }
+   return false;
+}
+
+function is_email_invalid(string $email){
+    if(!filter_var($email, FILTER_VALIDATE_EMAIL)){
+        return true;
+    }
+    return false;
+}
+
+function is_username_taken(object $pdo, string $username){
+    if(get_username($pdo, $username)){
+        return true;
+    }
+    return false;
+}
+
+function is_email_registered(object $pdo, string $email){
+     if(get_email($pdo, $email)){
+        return true;
+    }
+    return false;
+}

models/register.inc.php

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+<?php
+// Models actually interact with the database
+
+declare(strict_types=1);
+
+
+function get_username(object $pdo, string $username){
+    $query = "SELECT username FROM users WHERE username = :username"; // :username is a named placeholder
+    $stmt = $pdo->prepare($query); // prepare the query
+    $stmt->bindParam(":username", $username, PDO::PARAM_STR); // bind the $username variable to the :username placeholder
+    $stmt->execute(); // execute the query
+
+    $result = $stmt->fetch(PDO::FETCH_ASSOC); //fetch the result from the query
+    return $result;
+}
+
+function get_email(object $pdo, string $email){
+    $query = "SELECT email FROM users WHERE email = :email"; // :email is a named placeholder
+    $stmt = $pdo->prepare($query); // prepare the query
+    $stmt->bindParam(":email", $email, PDO::PARAM_STR); // bind the $email variable to the :email placeholder
+    $stmt->execute(); // execute the query
+
+    $result = $stmt->fetch(PDO::FETCH_ASSOC); //fetch the result from the query
+    return $result;
+}

views/register.inc.php

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+<?php
+//Views are responsible for displaying the data to the user
+
+declare(strict_types=1);
+
+function check_and_print_register_errors(){
+    if(isset($_SESSION["errors_register"])){
+        $errors = $_SESSION["errors_register"];
+        if(count($errors) > 0){
+            echo "<section class='error'>";
+            echo "<h1 class='error__title'>Errors occurred while registering: </h1>";
+            foreach($errors as $error){
+                echo "<p class='error__item'>$error</p>";
+            }
+            echo "</section>";
+            unset($_SESSION["errors_register"]);
+        }
+
+    }
+}