java-topology/defects/ros2/unit/ListParametersAlgorithm.java

package unit;

import java.util.*;

/**
 * Unit test for ros2-0002: NodeParameters::list_parameters() O(P²) → O(P)
 *
 * Simulates prefix deduplication in NodeParameters::list_parameters():
 *   Defective: std::find on result.prefixes (grows to P) inside loop over P parameters
 *   Fixed:     unordered_set deduplication O(1) insert
 *
 * Compile: javac -d . ListParametersAlgorithm.java
 * Run:     java -ea unit.ListParametersAlgorithm
 */
public class ListParametersAlgorithm {

    static class Result {
        final List<String> names = new ArrayList<>();
        final List<String> prefixes = new ArrayList<>();
    }

    // ── defective implementation ──────────────────────────────────────────────

    static Result defectiveListParameters(List<String> parameterNames) {
        Result result = new Result();
        final char separator = '.';

        for (String name : parameterNames) {
            result.names.add(name);
            int lastSep = name.lastIndexOf(separator);
            if (lastSep != -1) {
                String prefix = name.substring(0, lastSep);
                // O(P) linear scan to deduplicate prefixes
                boolean found = false;
                for (String p : result.prefixes) {
                    if (p.equals(prefix)) { found = true; break; }
                }
                if (!found) result.prefixes.add(prefix);
            }
        }
        return result;
    }

    // ── fixed implementation ──────────────────────────────────────────────────

    static Result fixedListParameters(List<String> parameterNames) {
        Result result = new Result();
        final char separator = '.';
        Set<String> seenPrefixes = new HashSet<>();

        for (String name : parameterNames) {
            result.names.add(name);
            int lastSep = name.lastIndexOf(separator);
            if (lastSep != -1) {
                String prefix = name.substring(0, lastSep);
                if (seenPrefixes.add(prefix)) {   // O(1) insert + dedup
                    result.prefixes.add(prefix);
                }
            }
        }
        return result;
    }

    // ── tests ─────────────────────────────────────────────────────────────────

    static int pass = 0, total = 0;

    static void assertTrue(String name, boolean cond) {
        total++;
        if (cond) { pass++; System.out.println("PASS " + name); }
        else       System.out.println("FAIL " + name);
    }

    // Build nav2-style parameter names: namespace.group.param
    static List<String> buildNav2Params(int namespaces, int groups, int paramsPerGroup) {
        List<String> names = new ArrayList<>();
        for (int ns = 0; ns < namespaces; ns++) {
            for (int g = 0; g < groups; g++) {
                for (int p = 0; p < paramsPerGroup; p++) {
                    names.add("ns" + ns + ".group" + g + ".param" + p);
                }
            }
        }
        return names;
    }

    public static void main(String[] args) {
        // Test 1: empty parameters → empty result
        {
            Result d = defectiveListParameters(Collections.emptyList());
            Result f = fixedListParameters(Collections.emptyList());
            assertTrue("empty-defective", d.names.isEmpty() && d.prefixes.isEmpty());
            assertTrue("empty-fixed", f.names.isEmpty() && f.prefixes.isEmpty());
        }

        // Test 2: parameters with no separator → no prefixes
        {
            List<String> params = Arrays.asList("foo", "bar", "baz");
            Result d = defectiveListParameters(params);
            Result f = fixedListParameters(params);
            assertTrue("no-sep-defective", d.prefixes.isEmpty() && d.names.size() == 3);
            assertTrue("no-sep-fixed", f.prefixes.isEmpty() && f.names.size() == 3);
        }

        // Test 3: all same prefix → only one prefix entry
        {
            List<String> params = Arrays.asList("nav2.speed", "nav2.timeout", "nav2.max_vel");
            Result d = defectiveListParameters(params);
            Result f = fixedListParameters(params);
            assertTrue("same-prefix-dedup-defective", d.prefixes.size() == 1 && d.prefixes.get(0).equals("nav2"));
            assertTrue("same-prefix-dedup-fixed", f.prefixes.size() == 1 && f.prefixes.get(0).equals("nav2"));
        }

        // Test 4: multiple distinct prefixes
        {
            List<String> params = Arrays.asList(
                "nav2.speed", "nav2.timeout",
                "moveit.planning_time", "moveit.max_vel",
                "slam.resolution");
            Result d = defectiveListParameters(params);
            Result f = fixedListParameters(params);
            assertTrue("multi-prefix-defective", d.prefixes.size() == 3);
            assertTrue("multi-prefix-fixed", f.prefixes.size() == 3);
            assertTrue("multi-prefix-names-match", d.names.equals(f.names));
            // prefixes sets must be equal (order may differ)
            assertTrue("multi-prefix-sets-match",
                new HashSet<>(d.prefixes).equals(new HashSet<>(f.prefixes)));
        }

        // Test 5: nav2-style — 3 namespaces, 10 groups, 5 params each = 150 params, 30 unique prefixes
        {
            List<String> params = buildNav2Params(3, 10, 5);
            Result d = defectiveListParameters(params);
            Result f = fixedListParameters(params);
            assertTrue("nav2-names-count-defective", d.names.size() == 150);
            assertTrue("nav2-names-count-fixed", f.names.size() == 150);
            // Each ns.group is a unique "ns_X.group_Y" prefix → 3*10 = 30 unique prefixes
            assertTrue("nav2-prefix-count-defective", d.prefixes.size() == 30);
            assertTrue("nav2-prefix-count-fixed", f.prefixes.size() == 30);
            assertTrue("nav2-prefix-sets-match",
                new HashSet<>(d.prefixes).equals(new HashSet<>(f.prefixes)));
        }

        // Test 6: performance at P=500 (500 unique prefixes worst case)
        {
            List<String> params = new ArrayList<>();
            for (int i = 0; i < 500; i++) params.add("group" + i + ".param" + i);

            long t0 = System.nanoTime();
            for (int r = 0; r < 200; r++) defectiveListParameters(params);
            long tDef = System.nanoTime() - t0;

            t0 = System.nanoTime();
            for (int r = 0; r < 200; r++) fixedListParameters(params);
            long tFix = System.nanoTime() - t0;

            double ratio = (double) tDef / tFix;
            System.out.printf("  Perf P=500 unique: defective=%.1fms fixed=%.1fms ratio=%.1fx%n",
                tDef / 1e6, tFix / 1e6, ratio);
            assertTrue("perf-speedup", ratio > 3.0);
        }

        System.out.println(pass + "/" + total + " PASS");
        assert pass == total : pass + "/" + total + " passed";
    }
}