<?php

namespace php;

use Exception;
use Monolog\Logger;
use PDO;


/**
 * Manages interaction with the database in the context of users.
 */
// TODO: Remove duplication in this class
class UserManager
{
    /**
     * The maximum length of an email address.
     */
    private const MAX_EMAIL_LENGTH = 254;
    /**
     * The minimum length of a password;
     */
    private const MIN_PASSWORD_LENGTH = 8;
    /**
     * The maximum length of a password.
     */
    private const MAX_PASSWORD_LENGTH = 255;

    /**
     * @var Logger The logger to use for logging.
     */
    private Logger $logger;
    /**
     * @var string The filename of the database to interact with.
     */
    private string $db_filename;


    /**
     * Constructs a new user manager.
     *
     * @param Logger $logger the logger to use for logging
     * @param string $db_filename the filename of the database to interact with
     */
    public function __construct(Logger $logger, string $db_filename)
    {
        $this->logger = $logger;
        $this->db_filename = $db_filename;
    }


    /**
     * Populates the database with the necessary structures for users.
     *
     * @return void
     */
    public function install(): void
    {
        $conn = Database::connect($this->db_filename);
        $conn->exec("CREATE TABLE users(uuid text primary key not null, email text not null, password text not null);");
    }

    /**
     * Registers a new user.
     *
     * @param string $email The user-submitted email address.
     * @param string $password The user-submitted password.
     * @param string $password_confirm The user-submitted password confirmation.
     * @return Response a response with message `null` if the user was registered, or a response with a message
     * explaining what went wrong otherwise
     */
    public function register(string $email, string $password, string $password_confirm): Response
    {
        // Generate UUID
        try {
            $uuid = bin2hex(random_bytes(16));
        } catch (Exception $exception) {
            $this->logger->emergency("Failed to generate UUID.", [$exception]);
            return new Response("Failed to generate UUID.", false);
        }

        // Validate
        if (!filter_var($email, FILTER_VALIDATE_EMAIL) || strlen($email) > self::MAX_EMAIL_LENGTH)
            return new Response("Invalid email address.", false);
        if (strlen($password) < self::MIN_PASSWORD_LENGTH || strlen($password) > self::MAX_PASSWORD_LENGTH)
            return new Response("Your password should be at least 8 and at most 255 characters long.", false);
        if ($password !== $password_confirm)
            return new Response("Passwords do not match.", false);

        // Connect
        $conn = Database::connect($this->db_filename);
        $conn->beginTransaction();

        // Check if email address is already in use
        $stmt = $conn->prepare("SELECT COUNT(*) as count FROM users WHERE email=:email;");
        $stmt->bindValue(":email", $email);
        $stmt->execute();
        $result = $stmt->fetch(PDO::FETCH_ASSOC);
        if ($result["count"] > 0) {
            $conn->rollBack();
            return new Response("Email address already in use.", false);
        }

        // Register user
        $stmt = $conn->prepare("INSERT INTO users (uuid, email, password) VALUES (:uuid, :email, :password);");
        $stmt->bindValue(":uuid", $uuid);
        $stmt->bindValue(":email", $email);
        $stmt->bindValue(":password", password_hash($password, PASSWORD_DEFAULT));
        $stmt->execute();

        // Respond
        $conn->commit();
        return new Response(null, true);
    }

    /**
     * Deletes the user with the given UUID.
     *
     * @param string $uuid the UUID of the user to delete
     * @return Response a response with message `null` if the user was deleted, or a response with a message explaining
     * what went wrong otherwise
     */
    public function delete(string $uuid): Response
    {
        $conn = Database::connect($this->db_filename);

        $stmt = $conn->prepare("DELETE FROM users WHERE uuid=:uuid;");
        $stmt->bindValue(":uuid", $uuid);
        $stmt->execute();

        return new Response(null, true);
    }

    /**
     * Validates a login attempt with the given email address and password.
     *
     * @param string $email the email address of the user whose password should be checked
     * @param string $password the password to check against the specified user
     * @return array{Response, ?string} the first element is a response with message `null` if the login was successful,
     * or a response with a message explaining what went wrong otherwise; the second element is the UUID of the user
     * that was logged in as, or `null` if the login should not be performed
     */
    public function check_login(string $email, string $password): array
    {
        if (strlen($email) > self::MAX_EMAIL_LENGTH || strlen($password) > self::MAX_PASSWORD_LENGTH)
            return [new Response("Incorrect combination of email and password.", false), null];

        $conn = Database::connect($this->db_filename);
        $stmt = $conn->prepare("SELECT uuid, password FROM users WHERE email=:email;");
        $stmt->bindValue(":email", $email);
        $stmt->execute();
        $results = $stmt->fetchAll(PDO::FETCH_ASSOC);

        return (sizeof($results) === 0 || !password_verify($password, $results[0]["password"]))
            ? [new Response("Incorrect combination of email and password.", false), null]
            : [new Response(null, true), $results[0]["uuid"]];
    }

    /**
     * Returns the user with the given UUID.
     *
     * @param string $uuid the UUID of the user to return
     * @return Response the user with the given UUID, or a response with an explanation what went wrong otherwise
     */
    public function get_user_data(string $uuid): Response
    {
        $conn = Database::connect($this->db_filename);
        $stmt = $conn->prepare("SELECT * FROM users WHERE uuid=:uuid;");
        $stmt->bindValue(":uuid", $uuid);
        $stmt->execute();
        $user = $stmt->fetch(PDO::FETCH_ASSOC);
        if ($user === false)
            return new Response("Invalid user.", false);

        return new Response($user, true);
    }

    /**
     * Updates the indicated user's email address.
     *
     * @param string $uuid the UUID of the user whose email address should be updated
     * @param string $email the new email address
     * @return Response a response with message `null` if the email address was updated, or a response with a message
     * explaining what went wrong otherwise
     */
    public function set_email(string $uuid, string $email): Response
    {
        // Validate
        if (!filter_var($email, FILTER_VALIDATE_EMAIL) || strlen($email) > self::MAX_EMAIL_LENGTH)
            return new Response("Invalid email address.", false);

        // Connect
        $conn = Database::connect($this->db_filename);
        $conn->beginTransaction();

        // Check if email address is already in use
        $stmt = $conn->prepare("SELECT COUNT(*) as count FROM users WHERE email=:email;");
        $stmt->bindValue(":email", $email);
        $stmt->execute();
        if ($stmt->fetch(PDO::FETCH_ASSOC)["count"] > 0) {
            $conn->rollBack();
            return new Response("Email address already in use.", false);
        }

        // Update email address
        $stmt = $conn->prepare("UPDATE users SET email=:email WHERE uuid=:uuid;");
        $stmt->bindValue(":uuid", $uuid);
        $stmt->bindValue(":email", $email);
        $stmt->execute();

        // Respond
        $conn->commit();
        return new Response(null, true);
    }

    /**
     * Updates the indicated user's password.
     *
     * @param string $uuid the UUID of the user whose password should be updated
     * @param string $password_old the old password
     * @param string $password_new the new password
     * @param string $password_confirm the confirmation of the new password
     * @return Response a response with message `null` if the password was updated, or a response with a message
     * explaining what went wrong otherwise
     */
    public function set_password(string $uuid, string $password_old, string $password_new,
                                 string $password_confirm): Response
    {
        // Validate
        if (strlen($password_new) < self::MIN_PASSWORD_LENGTH || strlen($password_new) > self::MAX_PASSWORD_LENGTH)
            return new Response("Your password should be at least 8 and at most 255 characters long.", false);
        if ($password_new !== $password_confirm)
            return new Response("New passwords do not match.", false);

        // Connect
        $conn = Database::connect($this->db_filename);
        $conn->beginTransaction();

        // Validate old password
        $stmt = $conn->prepare("SELECT password FROM users WHERE uuid=:uuid;");
        $stmt->bindValue(":uuid", $uuid);
        $stmt->execute();
        $user = $stmt->fetch(PDO::FETCH_ASSOC);
        if (!password_verify($password_old, $user["password"])) {
            $conn->rollBack();
            return new Response("Incorrect old password.", false);
        }

        // Update password
        $stmt = $conn->prepare("UPDATE users SET password=:password WHERE uuid=:uuid;");
        $stmt->bindValue(":uuid", $uuid);
        $stmt->bindValue(":password", password_hash($password_new, PASSWORD_DEFAULT));
        $stmt->execute();

        // Respond
        $conn->commit();
        return new Response(null, true);
    }
}