functions.php

<?php

function uidExists($conn, $username, $email) {
    $sql = "SELECT * FROM users WHERE username = ? OR email = ?;";
    $stmt = mysqli_stmt_init($conn);
    if (!mysqli_stmt_prepare($stmt, $sql)) {
        header("location: ../signup.php?error=stmtfailed");
        exit();
    }

    mysqli_stmt_bind_param($stmt, "ss", $username, $email);
    mysqli_stmt_execute($stmt);

    $resultData = mysqli_stmt_get_result($stmt);

    if ($row = mysqli_fetch_assoc($resultData)) {
        return $row;
    } else {
        $result = false;
        return $result;
    }

    mysqli_stmt_close($stmt);
}

function createUser($conn, $name, $email, $username, $password) {
    $sql = "INSERT INTO users (name, email, username, password) VALUES (?, ?, ?, ?);";
    $stmt = mysqli_stmt_init($conn);
    if (!mysqli_stmt_prepare($stmt, $sql)) { 
        header("location: ../signup.php?error=stmtfailed");
        exit();
    }

    $hashedpassword = password_hash($password, PASSWORD_DEFAULT);

    mysqli_stmt_bind_param($stmt, "ssss", $name, $email, $username, $hashedpassword);
    mysqli_stmt_execute($stmt);
    mysqli_stmt_close($stmt);
    header("location: ../signup.php?error=none");
    exit();
}

function loginUser($conn, $username, $password) {
    $uidExists = uidExists($conn, $username, $username);
    $admin = "admin";

    if ($uidExists === false) {
        header("location: ../login.php?error=wronglogin");
        exit();
    }

    $pwdHashed = $uidExists["password"];
    $checkPwd = password_verify($password, $pwdHashed);

    if ($checkPwd === false) {
        header("location: ../login.php?error=wronglogin");
        exit();
    } else if ($checkPwd === true) {
        session_start();
        $_SESSION["username"] = $uidExists["username"];
        header("location: ../index.php");
        exit();
    } else if ($username == $admin) {
        header("location: admin.php");
        exit();
    }
}