java-topology/tests/support/Moad0002Algorithm.java

package support;

/**
 * MOAD-0002: An Intertangled Defect.
 *
 * Defect: independent subsystems (Audio, Display) share a single mutable static
 * state object.  Any write by one subsystem is immediately visible to all others.
 * Two independent execution contexts cannot coexist — they trample each other's
 * configuration silently, with no exception thrown.
 *
 * Fix: each subsystem receives an immutable Context snapshot at construction.
 * No shared state.  N contexts exist independently, and subsystem writes
 * affect only the context they own.
 *
 * Scanner detects: static mutable fields accessed from multiple subsystem classes
 * without synchronization or phase isolation.
 */
public class Moad0002Algorithm {

    // ── Defective: shared mutable global state ────────────────────────────────

    /**
     * God object holding all subsystem configuration.
     * The intertangle point: audio, display, and locale all live here.
     */
    public static final class SharedState {
        public int    volume     = 50;
        public int    brightness = 100;
        public String locale     = "en";
    }

    /** Singleton — all defective subsystems reference this one object. */
    public static final SharedState GLOBAL = new SharedState();

    public static final class DefectiveAudioSystem {
        public void   setVolume(int v)    { GLOBAL.volume = v; }
        public int    getVolume()         { return GLOBAL.volume; }
        public void   setLocale(String l) { GLOBAL.locale = l; }
        public String getLocale()         { return GLOBAL.locale; }
    }

    public static final class DefectiveDisplaySystem {
        public void   setBrightness(int b) { GLOBAL.brightness = b; }
        public int    getBrightness()      { return GLOBAL.brightness; }
        public void   setLocale(String l)  { GLOBAL.locale = l; }
        public String getLocale()          { return GLOBAL.locale; }
    }

    // ── Fixed: each subsystem owns an isolated immutable context ──────────────

    /** Immutable per-context snapshot.  Passed to subsystems at construction. */
    public static final class Context {
        public final int    volume;
        public final int    brightness;
        public final String locale;

        public Context(int volume, int brightness, String locale) {
            this.volume     = volume;
            this.brightness = brightness;
            this.locale     = locale;
        }
    }

    public static final class FixedAudioSystem {
        private final Context ctx;
        public FixedAudioSystem(Context ctx) { this.ctx = ctx; }
        public int    getVolume() { return ctx.volume; }
        public String getLocale() { return ctx.locale; }
    }

    public static final class FixedDisplaySystem {
        private final Context ctx;
        public FixedDisplaySystem(Context ctx) { this.ctx = ctx; }
        public int    getBrightness() { return ctx.brightness; }
        public String getLocale()     { return ctx.locale; }
    }

    /** Reset GLOBAL between test cases so tests do not bleed into each other. */
    public static void resetGlobal() {
        GLOBAL.volume     = 50;
        GLOBAL.brightness = 100;
        GLOBAL.locale     = "en";
    }
}