package support;

/**
 * MOAD-0003: A Leaked Context.
 *
 * Defect: request-scoped identity (user principal, tenant ID, transaction state)
 * stored in a ThreadLocal whose lifetime is the thread, not the unit of work.
 * When a thread-pool thread is reused for a second request, stale identity from
 * the first request bleeds into the second — even though the second request
 * never set any identity.
 *
 * Fix: always call ThreadLocal.remove() in a finally block after the request
 * completes.  Alternatively, pass context explicitly as a parameter (preferred).
 *
 * Scanner detects: ThreadLocal fields without a paired remove() call in a
 * finally block on the same code path that calls set().
 */
public class Moad0003Algorithm {

    /** The ambient carrier — shared across the simulated thread pool. */
    public static final ThreadLocal<String> REQUEST_IDENTITY = new ThreadLocal<>();

    // ── Defective: ThreadLocal set but never removed ───────────────────────

    /**
     * Simulates handling one HTTP request in the defective pattern.
     * Sets the ThreadLocal to 'identity' and processes the request.
     * DEFECT: never calls remove() — stale identity remains on the thread.
     *
     * @return the identity seen during this request
     */
    public static String handleDefective(String identity) {
        if (identity != null) {
            REQUEST_IDENTITY.set(identity);
        }
        // ... simulate request processing ...
        return REQUEST_IDENTITY.get();
        // DEFECT: no REQUEST_IDENTITY.remove() — next request sees this identity
    }

    /**
     * Simulates the next request on the same pooled thread.
     * The caller does NOT set an identity (anonymous request).
     * DEFECT: returns whatever the previous request left behind.
     *
     * @return the identity seen — should be null but is the previous caller's identity
     */
    public static String handleDefectiveAnonymous() {
        // Does not call REQUEST_IDENTITY.set() — anonymous request
        return REQUEST_IDENTITY.get(); // DEFECT: returns stale identity from previous request
    }

    // ── Fixed: ThreadLocal always removed in finally ───────────────────────

    /**
     * Simulates handling one HTTP request in the fixed pattern.
     * Sets the ThreadLocal, processes, then ALWAYS removes in finally.
     *
     * @return the identity seen during this request
     */
    public static String handleFixed(String identity) {
        if (identity != null) {
            REQUEST_IDENTITY.set(identity);
        }
        try {
            return REQUEST_IDENTITY.get();
        } finally {
            REQUEST_IDENTITY.remove(); // FIX: always clean up, even on exception
        }
    }

    /**
     * Simulates the next request on the same pooled thread (anonymous).
     * After the fixed handler ran, the ThreadLocal is null.
     *
     * @return the identity seen — null (clean)
     */
    public static String handleFixedAnonymous() {
        return REQUEST_IDENTITY.get(); // FIX: null — previous request cleaned up
    }

    /** Reset ThreadLocal between test cases. */
    public static void reset() {
        REQUEST_IDENTITY.remove();
    }
}