PHP/MYSQL Get data from the database for each specific user assigned - php

Question

I'm making project doctor appointment system and have 1 admin 3 normal users (doctors)assigned.
For each doctor, I want to only show to them the appointments specifically assigned to them to load on their dashboard. Appointment that was not assigned to them will not be listed on their dashboard.
Is it possible if I can insert a function when they log in? and get the data based from there ID? If so, how can I do it?
Below are my source code for admin and normal users.
<?php
session_start();
// connect to database
$db = mysqli_connect('localhost', 'root', '', 'appointments');
// variable declaration
$username = "";
$email = "";
$errors = array();
// call the register() function if register_btn is clicked
if (isset($_POST['register_btn'])) {
register();
}
// call the login() function if register_btn is clicked
if (isset($_POST['login_btn'])) {
login();
}
if (isset($_GET['logout'])) {
session_destroy();
unset($_SESSION['user']);
header("location: ../login.php");
}
// REGISTER USER
function register(){
global $db, $errors;
// receive all input values from the form
$username = e($_POST['username']);
$email = e($_POST['email']);
$password_1 = e($_POST['password_1']);
$password_2 = e($_POST['password_2']);
// form validation: ensure that the form is correctly filled
if (empty($username)) {
array_push($errors, "Username is required");
}
if (empty($email)) {
array_push($errors, "Email is required");
}
if (empty($password_1)) {
array_push($errors, "Password is required");
}
if ($password_1 != $password_2) {
array_push($errors, "The two passwords do not match");
}
// register user if there are no errors in the form
if (count($errors) == 0) {
$password = md5($password_1);//encrypt the password before saving in the database
if (isset($_POST['user_type'])) {
$user_type = e($_POST['user_type']);
$query = "INSERT INTO users (username, email, user_type, password)
VALUES('$username', '$email', '$user_type', '$password')";
mysqli_query($db, $query);
$_SESSION['success'] = "New user successfully created!!";
header('location: home.php');
}else{
$query = "INSERT INTO users (username, email, user_type, password)
VALUES('$username', '$email', 'user', '$password')";
mysqli_query($db, $query);
// get id of the created user
$logged_in_user_id = mysqli_insert_id($db);
$_SESSION['user'] = getUserById($logged_in_user_id); // put logged in user in session
$_SESSION['success'] = "You are now logged in";
header('location: index.php');
}
}
}
// return user array from their id
function getUserById($id){
global $db;
$query = "SELECT * FROM users WHERE id=" . $id;
$result = mysqli_query($db, $query);
$user = mysqli_fetch_assoc($result);
return $user;
}
// LOGIN USER
function login(){
global $db, $username, $errors;
// grap form values
$username = e($_POST['username']);
$password = e($_POST['password']);
// make sure form is filled properly
if (empty($username)) {
array_push($errors, "Username is required");
}
if (empty($password)) {
array_push($errors, "Password is required");
}
// attempt login if no errors on form
if (count($errors) == 0) {
$password = md5($password);
$query = "SELECT * FROM users WHERE username='$username' AND password='$password' LIMIT 1";
$results = mysqli_query($db, $query);
if (mysqli_num_rows($results) == 1) { // user found
// check if user is admin or user
$logged_in_user = mysqli_fetch_assoc($results);
if ($logged_in_user['user_type'] == 'admin') {
$_SESSION['user'] = $logged_in_user;
$_SESSION['success'] = "You are now logged in";
header('location: dashboard.php');
}else{
$_SESSION['user'] = $logged_in_user;
$_SESSION['success'] = "You are now logged in";
header('location: doctordashboard.php');
}
}else {
array_push($errors, "Invalid username or password");
}
}
}
function isLoggedIn()
{
if (isset($_SESSION['user'])) {
return true;
}else{
return false;
}
}
function isAdmin()
{
if (isset($_SESSION['user']) && $_SESSION['user']['user_type'] == 'admin' ) {
return true;
}else{
return false;
}
}
// escape string
function e($val){
global $db;
return mysqli_real_escape_string($db, trim($val));
}
function display_error() {
global $errors;
if (count($errors) > 0){
echo '<div class="error">';
foreach ($errors as $error){
echo $error .'<br>';
}
echo '</div>';
}
}
?>
Any help would be appreciated. Thanks