JwtService.java

package com.crimeLink.analyzer.service;

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

import java.nio.charset.StandardCharsets;
import java.security.Key;
import java.security.MessageDigest;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;

@Service
public class JwtService {

    @Value("${jwt.secret}")
    private String secretKey;

    @Value("${jwt.expiration}")
    private long jwtExpiration;

    public String extractUsername(String token) {
        return extractClaim(token, Claims::getSubject);
    }

    public <T> T extractClaim(String token, Function<Claims, T> claimsResolver) {
        final Claims claims = extractAllClaims(token);
        return claimsResolver.apply(claims);
    }

    public String generateToken(UserDetails userDetails) {
        return generateToken(new HashMap<>(), userDetails);
    }

    public String generateToken(Map<String, Object> extraClaims, UserDetails userDetails) {
        return buildToken(extraClaims, userDetails, jwtExpiration);
    }

    private String buildToken(
            Map<String, Object> extraClaims,
            UserDetails userDetails,
            long expiration
    ) {
        // Add authorities (roles) to JWT claims
        extraClaims.put("authorities", userDetails.getAuthorities().stream()
                .map(authority -> authority.getAuthority())
                .toList());
        
        return Jwts
                .builder()
                .claims(extraClaims)
                .subject(userDetails.getUsername())
                .issuedAt(new Date(System.currentTimeMillis()))
                .expiration(new Date(System.currentTimeMillis() + expiration))
                .signWith(getSignInKey())
                .compact();
    }

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

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

    private Date extractExpiration(String token) {
        return extractClaim(token, Claims::getExpiration);
    }

    private Claims extractAllClaims(String token) {
        return Jwts
                .parser()
                .verifyWith(Keys.hmacShaKeyFor(Decoders.BASE64.decode(secretKey)))
                .build()
                .parseSignedClaims(token)
                .getPayload();
    }

    private Key getSignInKey() {
        byte[] keyBytes;
        try {
            keyBytes = Decoders.BASE64.decode(secretKey);
        } catch (IllegalArgumentException ex) {
            // Fallback for non-base64 secrets: derive a stable 32-byte key
            byte[] raw = secretKey.getBytes(StandardCharsets.UTF_8);
            if (raw.length < 32) {
                try {
                    keyBytes = MessageDigest.getInstance("SHA-256").digest(raw);
                } catch (Exception e) {
                    keyBytes = raw;
                }
            } else {
                keyBytes = raw;
            }
        }
        return Keys.hmacShaKeyFor(keyBytes);
    }
}