source: backend/src/main/java/com/finki/icare/service/JwtService.java

package com.finki.icare.service;

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.security.Keys;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;

import javax.crypto.SecretKey;
import java.nio.charset.StandardCharsets;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

@Service
public class JwtService {

    @Value("${JWT_SECRET}")
    private String secretKey;

    @Value("${JWT_EXPIRATION}")
    private long jwtExpiration;

    private SecretKey getSigningKey() {
        return Keys.hmacShaKeyFor(secretKey.getBytes(StandardCharsets.UTF_8));
    }

    public String generateToken(String username, Integer userId, String userType) {
        Map<String, Object> claims = new HashMap<>();
        claims.put("userId", userId);
        claims.put("userType", userType);

        return Jwts.builder()
                .claims(claims)
                .subject(username)
                .issuedAt(new Date(System.currentTimeMillis()))
                .expiration(new Date(System.currentTimeMillis() + jwtExpiration))
                .signWith(getSigningKey())
                .compact();
    }

    public String extractUsername(String token) {
        return extractClaims(token).getSubject();
    }

    public Integer extractUserId(String token) {
        return extractClaims(token).get("userId", Integer.class);
    }

    public String extractUserType(String token) {
        return extractClaims(token).get("userType", String.class);
    }

    public boolean isTokenValid(String token, String username) {
        final String extractedUsername = extractUsername(token);
        return (extractedUsername.equals(username) && !isTokenExpired(token));
    }

    private boolean isTokenExpired(String token) {
        return extractClaims(token).getExpiration().before(new Date());
    }

    private Claims extractClaims(String token) {
        return Jwts.parser()
                .verifyWith(getSigningKey())
                .build()
                .parseSignedClaims(token)
                .getPayload();
    }
}