signup.php

<?php
if (isset($_POST['signup-submit'])) {

	require 'db.php';

	$username = $_POST['uid'];
	$email = $_POST['mail'];
	$password = $_POST['pwd'];
	$passwordRepeat = $_POST['pwd-repeat'];

	if (empty($username) || empty($email) || empty($password) || empty($passwordRepeat)) {
		header("Location: ../index.html?error=emptyfields&uid=".$username."&mail=".$email);
		exit();
	}
	else if (!filter_var($email, FILTER_VALIDDATA_EMAIL) && !preg_match("/[a-zA-Z0-9]*$/", $username)) {
		header("Location: ../index.html?error=invalidmailuid");
		exit();
	}
	else if (!filter_var($email, FILTER_VALIDDATA_EMAIL)) {
		header("Location: ../index.html?error=invalidmail&uid=".$username);
		exit();
	}
	else if (!preg_match("/[a-zA-Z0-9]*$/", $username)) {
		header("Location: ../index.html?error=invaliduid&mail=".$email);
		exit();
		}
	else if ($password !== $passwordRepeat) {
		header("Location: ../index.html?error=passwordcheck&uid=".$username."&mail=".$email);
		exit();
	}
	else {

		$sql = "SELECT * FROM users WHERE uidUsers=?;";
		$stmt = mysqli_stmt_init($conn);
		if (!mysqli_stmt_prepare($stmt, $sql)) {
			header("Location: ../index.html?error=sqlerror");
			exit();
		}
		else {
			mysqli_stmt_bind_param($stmt, "s", $mailuid);
			mysqli_stmt_execute($stmt);
			mysqli_stmt_store_result($stmt);
			$resultCheck = mysqli_stmt_num_rows($stmt);
			if ($resultCheck > 0) {
				header("Location: ../index.html?error=usertaken&mail=".$email);
				exit();
			}
			else {
				$sql = "INSERT INTO 'users' (uidUsers, emailUsers, pwdUsers) VALUES (?, ?, ?)";
				$stmt = mysqli_stmt_init($conn);
				if (!mysqli_stmt_prepare($stmt, $sql)) {
					header("Location: ../index.html?error=sqlerror");
				}
				else {
					$hashedPwd = password_hash($password, PASSWORD_DEFAULT);
					mysqli_stmt_bind_param($stmt, "sss", $username, $email, $hashedPwd);
					mysqli_stmt_execute($stmt);
					header("Location: ../index.html?signup=success");
					exit();
				}
			}
		}
	}
	mysqli_stmt_close($stmt);
	mysqli_close($conn);
 }
 else {
	header("Location: ../index.html");
	exit();
 }