java-topology/defects/ansible/unit/AnsibleRoleGetVarsAlgorithm.java

package unit;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * ansible-0001: Role.get_vars() seen-list O(D²) deduplication
 *
 * Slow: uses List for seen-set — dep not in seen is O(D) per iteration → O(D²) total
 * Fast: uses HashSet for seen-set — dep not in seen is O(1) per iteration → O(D) total
 *
 * Verifies: slow_ops >= D*(D-1)/2, fast_ops == D, ratio >= 10x at D=200
 */
public class AnsibleRoleGetVarsAlgorithm {

    static long slowOps = 0;
    static long fastOps = 0;

    /** Simulated Role dependency — identity-based equality (no custom equals/hashCode) */
    static class MockDep {
        final int id;
        MockDep(int id) { this.id = id; }
    }

    /**
     * Slow version: seen is an ArrayList — contains() is O(D)
     * Mirrors: seen = []; if dep not in seen: seen.append(dep)
     */
    static int slowGetVars(List<MockDep> allDependencies) {
        slowOps = 0;
        List<MockDep> seen = new ArrayList<>();
        int combinedCount = 0;
        for (MockDep dep : allDependencies) {
            // Each call to contains() scans the entire seen list — O(seen.size())
            for (MockDep s : seen) {
                slowOps++;
                if (s == dep) break; // found
            }
            // Equivalent of: if dep not in seen
            boolean inSeen = false;
            for (MockDep s : seen) {
                if (s == dep) { inSeen = true; break; }
            }
            if (!inSeen) {
                // combine_vars equivalent
                combinedCount++;
                seen.add(dep);
            }
        }
        return combinedCount;
    }

    /**
     * Fast version: seen is a HashSet — contains() is O(1)
     * Mirrors: seen = set(); if dep not in seen: seen.add(dep)
     */
    static int fastGetVars(List<MockDep> allDependencies) {
        fastOps = 0;
        Set<MockDep> seen = new HashSet<>();
        int combinedCount = 0;
        for (MockDep dep : allDependencies) {
            fastOps++;
            if (!seen.contains(dep)) {
                combinedCount++;
                seen.add(dep);
            }
        }
        return combinedCount;
    }

    /**
     * Build a dependency list with D unique deps, no duplicates (worst case for seen growth).
     */
    static List<MockDep> buildDeps(int D) {
        List<MockDep> deps = new ArrayList<>();
        for (int i = 0; i < D; i++) {
            deps.add(new MockDep(i));
        }
        return deps;
    }

    public static void main(String[] args) {
        int passed = 0;
        int total = 0;

        // Test 1: basic correctness — both produce same combined count
        {
            total++;
            int D = 10;
            List<MockDep> deps = buildDeps(D);
            int slowResult = slowGetVars(deps);
            int fastResult = fastGetVars(deps);
            boolean ok = (slowResult == D && fastResult == D);
            System.out.println((ok ? "PASS" : "FAIL") + " [correctness D=" + D + "]: slow=" + slowResult + " fast=" + fastResult);
            if (ok) passed++;
        }

        // Test 2: with duplicates — both should deduplicate identically
        {
            total++;
            int D = 5;
            List<MockDep> unique = buildDeps(D);
            List<MockDep> depsWithDups = new ArrayList<>();
            for (MockDep dep : unique) { depsWithDups.add(dep); depsWithDups.add(dep); } // each dep appears twice
            int slowResult = slowGetVars(depsWithDups);
            int fastResult = fastGetVars(depsWithDups);
            boolean ok = (slowResult == D && fastResult == D);
            System.out.println((ok ? "PASS" : "FAIL") + " [dedup D=" + D + " with dupes]: slow=" + slowResult + " fast=" + fastResult);
            if (ok) passed++;
        }

        // Test 3: slow op count is O(D²) — at least D*(D-1)/2 comparisons
        {
            total++;
            int D = 200;
            List<MockDep> deps = buildDeps(D);
            slowGetVars(deps);
            long minExpectedSlowOps = (long) D * (D - 1) / 2;
            boolean ok = slowOps >= minExpectedSlowOps;
            System.out.println((ok ? "PASS" : "FAIL") + " [slow O(D²) D=" + D + "]: ops=" + slowOps + " >= " + minExpectedSlowOps);
            if (ok) passed++;
        }

        // Test 4: fast op count is exactly O(D) — one check per dep
        {
            total++;
            int D = 200;
            List<MockDep> deps = buildDeps(D);
            fastGetVars(deps);
            boolean ok = (fastOps == D);
            System.out.println((ok ? "PASS" : "FAIL") + " [fast O(D) D=" + D + "]: ops=" + fastOps + " == " + D);
            if (ok) passed++;
        }

        // Test 5: ratio >= 10x at D=200
        {
            total++;
            int D = 200;
            List<MockDep> deps = buildDeps(D);
            slowGetVars(deps);
            long slowCount = slowOps;
            fastGetVars(deps);
            long fastCount = fastOps;
            double ratio = (double) slowCount / fastCount;
            boolean ok = ratio >= 10.0;
            System.out.printf((ok ? "PASS" : "FAIL") + " [ratio D=%d]: slowOps=%d fastOps=%d ratio=%.1fx%n", D, slowCount, fastCount, ratio);
            if (ok) passed++;
        }

        System.out.println(passed + "/" + total + " PASS");
        if (passed != total) System.exit(1);
    }
}