action/action.php

<?php

require_once __DIR__ . "/../config/conn.php";
if ($_SERVER["REQUEST_METHOD"] == "POST" && isset($_POST['submit'])) {
    print_r($_POST);
    //backend_validation_file
    require __DIR__."/../backend_validation/code.php";


    $username = $_POST['user_name'];
    $firstname = validate_firstName($_POST['first_name']) ;
    $lastname = validate_lastName($_POST['last_name']);
    $email = validate_email($_POST['email']);
    $phone = validate_phone($_POST['phone']);
    $age = validate_Age($_POST['age']);
    $password = compare_passwords($_POST['password'],$_POST['no-password']);
    $hashedPassword = password_hash($password, PASSWORD_DEFAULT);
    $target_file =  file_validation($_FILES["fileToUpload"]);


    $checkQuery = "SELECT * FROM `user` WHERE username = ?";
    $checkStmt = mysqli_prepare($conn, $checkQuery);
    mysqli_stmt_bind_param($checkStmt, 's', $username);
    mysqli_stmt_execute($checkStmt);
    $result = mysqli_stmt_get_result($checkStmt);

    if (mysqli_num_rows($result) > 0) {

        // In the script on the initial page:
        echo '<script>';
        echo '  window.location.href = "/../ajax_insert/index.php?alert=Username exists";';
        echo '</script>';
    } else {
        if(($firstname!="false")&&($lastname!="false")&&($email!="false")&&($phone!="false")&&($age!="false")&&($password!="false")){


            // "<-------Preparing data insertion--------->"

            $query = 'INSERT INTO user(username,first_name,last_name,email,phone,age,password,fileLocation) VALUES (?, ?, ?, ?, ?, ?, ?, ?)';

            $stmt = mysqli_prepare($conn, $query);
            mysqli_stmt_bind_param($stmt, 'ssssiiss', $username, $firstname, $lastname, $email, $phone, $age, $hashedPassword, $target_file);

            if (mysqli_stmt_execute($stmt)){
                // echo "Sent!";
                echo '<script>';
                echo '  window.location.href = "/../ajax_insert/index.php?alert=Data Sent!;';
                echo '</script>';

                // // No output before header!
                // mysqli_stmt_close($stmt);
                // header("Location: login.php");
                // exit;

            } else {

                echo "Error: " . mysqli_connect_error($conn);
            }

            mysqli_stmt_close($stmt);
        }else{
            echo "Fix all of the inputs";
        }
    }
    mysqli_stmt_close($checkStmt);
}

mysqli_close($conn);
?>