@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Monitored {
}

@Component
@Aspect
public class MonitorSlowCalls {
    private static final Logger LOG = LoggerFactory.getLogger(MonitorSlowCalls.class);

    private final MeterRegistry meterRegistry;
    private final long slowCallsLogThreshold;

    public MonitorSlowCalls(MeterRegistry meterRegistry, @Value("${slow-calls-log-threshold:500}") int slowCallsLogThreshold) {
        this.meterRegistry = meterRegistry;
        this.slowCallsLogThreshold = slowCallsLogThreshold;
    }

    @Pointcut("within(@se.plilja.Monitored *)")
    public void monitored() {
    }

    @Pointcut("execution(!private * *(..))")
    public void publicProtectedOrPackagePrivate() {
    }

    @Around("publicProtectedOrPackagePrivate() && monitored()")
    public Object monitorSlowCalls(ProceedingJoinPoint pjp) throws Throwable {
        long startTime = System.currentTimeMillis();
        try {
            Timer timer = meterRegistry.timer("method.timer", List.of(Tag.of("method", pjp.getSignature().getName())));
            Object result = timer.recordCallable(() -> proceed(pjp));
            long endTime = System.currentTimeMillis();
            logIfSlow(endTime - startTime, pjp);
            return result;
        } catch (Throwable throwable) {
            long endTime = System.currentTimeMillis();
            logIfSlow(endTime - startTime, pjp);
            throw throwable;
        }
    }

    // Don't want to catch the Throwable which the compiler will force us to to without this annotation
    @SneakyThrows
    private Object proceed(ProceedingJoinPoint pjp) {
        return pjp.proceed();
    }

    private void logIfSlow(long duration, ProceedingJoinPoint pjp) {
        String className = pjp.getTarget().getClass().getSimpleName();
        String methodName = pjp.getSignature().getName();
        if (duration >= slowCallsLogThreshold) {
            LOG.info("Call took [duration={}] [class={}] [method={}]", duration, className, methodName);
        } else {
            LOG.debug("Call took [duration={}] [class={}] [method={}]", duration, className, methodName);
        }
    }
}