<?php
namespace YTKNS;

use Exception;

final class UserSessionNotFoundException extends Exception {};
final class UserSessionCreatedFailedException extends Exception {};

class UserSession {
    private const TOKEN_CHARS = 'abcdefghijklmnopqrstuvwxyz-0123456789_ABCDEFGHIJKLMNOPQRSTUVWXYZ';
    private static $instance = null;

    public static function instance(): ?self {
        return self::$instance;
    }
    public function setInstance(): void {
        self::$instance = $this;
    }
    public static function hasInstance(): bool {
        return !empty(self::$instance->session_token);
    }
    public static function unsetInstance(): void {
        self::$instance = null;
    }

    public function __construct() {
    }

    public function getUserId(): int {
        return $this->user_id ?? 0;
    }
    public function getUser(): User {
        return User::byId($this->getUserId());
    }

    public function getToken(): string {
        return $this->session_token;
    }
    public function getSmallToken(int $rounds = 5, int $length = 8, int $offset = 0): string {
        $token = $this->getToken();
        $tokenLength = strlen($token) - $length;

        for($i = 0; $i < $rounds; $i++)
            $offset = ord($token[$offset]) % $tokenLength;

        return str_rot13(substr($token, $offset, $length));
    }

    public function getCreated(): int {
        return $this->session_created ?? 0;
    }

    public function getExpires(): int {
        return $this->session_expires ?? 0;
    }

    public function getBump(): bool {
        return $this->session_bump ?? false;
    }

    public function getFirstIp(): string {
        return $this->session_ip_first ?? '';
    }
    
    public function getLastIp(): ?string {
        return $this->session_ip_last ?? null;
    }

    public function update(): void {
        $update = DB::prepare('
            UPDATE `ytkns_users_sessions`
            SET `session_expires` = IF(:bump, NOW() + INTERVAL 1 MONTH, `session_expires`),
                `session_ip_last` = INET6_ATON(:ip),
                `session_used` = NOW()
            WHERE `session_token` = :token
        ');
        $update->bindValue('bump', $this->getBump() ? 1 : 0);
        $update->bindValue('ip', $_SERVER['REMOTE_ADDR']);
        $update->bindValue('token', $this->getToken());
        $update->execute();
    }

    public function destroy(): void {
        $destroy = DB::prepare('
            DELETE FROM `ytkns_users_sessions`
            WHERE `session_token` = :token
        ');
        $destroy->bindValue('token', $this->getToken());
        $destroy->execute();
    }

    public static function generateToken(int $length = 64): string {
        $token = random_bytes($length);
        $chars = strlen(self::TOKEN_CHARS);

        for($i = 0; $i < $length; $i++)
            $token[$i] = self::TOKEN_CHARS[ord($token[$i]) % $chars];

        return $token;
    }

    public static function create(User $user, bool $bump = false): self {
        $token = self::generateToken();
        $create = DB::prepare('
            INSERT INTO `ytkns_users_sessions` (
                `user_id`, `session_token`, `session_ip_first`, `session_bump`
            ) VALUES (
                :user, :token, INET6_ATON(:ip), :bump
            )
        ');
        $create->bindValue('user', $user->getId());
        $create->bindValue('token', $token);
        $create->bindValue('ip', $_SERVER['REMOTE_ADDR']);
        $create->bindValue('bump', $bump ? 1 : 0);
        $create->execute();

        try {
            return self::byToken($token);
        } catch(UserSessionNotFoundException $ex) {
            throw new UserSessionCreatedFailedException;
        }
    }

    public static function byToken(string $token): self {
        $getSession = DB::prepare('
            SELECT `user_id`, `session_token`, `session_bump`, 
                UNIX_TIMESTAMP(`session_created`) AS `session_created`,
                UNIX_TIMESTAMP(`session_expires`) AS `session_expires`,
                INET6_NTOA(`session_ip_first`) AS `session_ip_first`, 
                INET6_NTOA(`session_ip_last`) AS `session_ip_last`
            FROM `ytkns_users_sessions`
            WHERE `session_token` = :token
        ');
        $getSession->bindValue('token', $token);
        $session = $getSession->execute() ? $getSession->fetchObject(self::class) : false;

        if(!$session)
            throw new UserSessionNotFoundException;

        return $session;
    }

    public static function purge(): void {
        DB::exec('
            DELETE FROM `ytkns_users_sessions`
            WHERE `session_expires` <= NOW()
        ');
    }
}