java-topology/defects/ruby/unit/RubyGemsDependentGemsAlgorithm.java

package unit;

import java.util.*;

/**
 * RubyGemsDependentGemsAlgorithm — CWE-407 test for ruby-0003
 *
 * Models Gem::Specification#dependent_gems + #find_all_satisfiers:
 *   slow: for each spec, for each dep: Gem::Specification.each — O(N² × D)
 *   fast: build name_index once, then name_index[dep.name].select — O(N × D)
 *
 * Test: for N gems with D deps each, slow does N*D*N ops; fast does N*D + N_matches.
 * Ratio must be >= 10x at N=200.
 */
public class RubyGemsDependentGemsAlgorithm {

    static final class GemSpec {
        final String name;
        final String version;
        final List<String> depNames; // simplified: just dep gem names

        GemSpec(String name, String version, List<String> depNames) {
            this.name = name;
            this.version = version;
            this.depNames = depNames;
        }

        boolean satisfiesRequirement(String depName) {
            return this.name.equals(depName);
        }
    }

    // --- SLOW: O(N² × D) ---
    // Gem::Specification.each inside find_all_satisfiers inside dependent_gems
    static class SlowDependentGems {
        long comparisons = 0;

        // find_all_satisfiers(dep): scans all N specs
        List<GemSpec> findAllSatisfiers(List<GemSpec> allSpecs, String depName) {
            List<GemSpec> result = new ArrayList<>();
            for (GemSpec spec : allSpecs) {
                comparisons++;
                if (spec.satisfiesRequirement(depName)) {
                    result.add(spec);
                }
            }
            return result;
        }

        // dependent_gems(self, allSpecs): find specs that depend on self
        List<Object[]> dependentGems(GemSpec self, List<GemSpec> allSpecs) {
            List<Object[]> out = new ArrayList<>();
            for (GemSpec spec : allSpecs) {          // O(N) outer
                for (String depName : spec.depNames) { // O(D) deps
                    comparisons++;
                    if (self.satisfiesRequirement(depName)) {
                        // find_all_satisfiers: O(N) inner
                        List<GemSpec> sats = findAllSatisfiers(allSpecs, depName);
                        out.add(new Object[]{spec, depName, sats});
                    }
                }
            }
            return out;
        }
    }

    // --- FAST: O(N × D) ---
    // Build name_index once, then O(matches) lookup
    static class FastDependentGems {
        long ops = 0;

        List<Object[]> dependentGems(GemSpec self, List<GemSpec> allSpecs) {
            // Build reverse index: name -> [specs]
            Map<String, List<GemSpec>> nameIndex = new HashMap<>();
            for (GemSpec s : allSpecs) {
                nameIndex.computeIfAbsent(s.name, k -> new ArrayList<>()).add(s);
                ops++;
            }

            List<Object[]> out = new ArrayList<>();
            for (GemSpec spec : allSpecs) {          // O(N) outer
                for (String depName : spec.depNames) { // O(D) deps
                    ops++;
                    if (self.satisfiesRequirement(depName)) {
                        // O(matches) lookup, not O(N)
                        List<GemSpec> sats = nameIndex.getOrDefault(depName, Collections.emptyList());
                        out.add(new Object[]{spec, depName, sats});
                    }
                }
            }
            return out;
        }
    }

    static List<GemSpec> makeSpecs(int n, int depsPerSpec) {
        List<String> names = new ArrayList<>();
        for (int i = 0; i < n; i++) names.add("gem_" + i);

        List<GemSpec> specs = new ArrayList<>();
        Random rng = new Random(42);
        for (int i = 0; i < n; i++) {
            List<String> deps = new ArrayList<>();
            for (int d = 0; d < depsPerSpec; d++) {
                deps.add(names.get(rng.nextInt(n)));
            }
            specs.add(new GemSpec("gem_" + i, "1.0." + i, deps));
        }
        return specs;
    }

    public static void main(String[] args) {
        int[] sizes = {50, 100, 200, 300};
        int depsPerSpec = 5;
        System.out.println("RubyGemsDependentGemsAlgorithm — ruby-0003");
        System.out.println("  Pattern: find_all_satisfiers O(N) scan inside O(N×D) loop vs reverse index");
        System.out.println("  Simulation: D=" + depsPerSpec + " deps per gem");
        System.out.println();

        int passed = 0;
        int total = 0;

        for (int n : sizes) {
            List<GemSpec> allSpecs = makeSpecs(n, depsPerSpec);
            GemSpec target = allSpecs.get(0); // gem_0 is the gem being uninstalled

            SlowDependentGems slow = new SlowDependentGems();
            FastDependentGems fast = new FastDependentGems();

            List<Object[]> slowResult = slow.dependentGems(target, allSpecs);
            List<Object[]> fastResult = fast.dependentGems(target, allSpecs);

            // Both should find the same number of dependent specs
            boolean sameCount = slowResult.size() == fastResult.size();

            double ratio = (double) slow.comparisons / fast.ops;
            boolean correctRatio = n >= 100 ? ratio >= 10.0 : ratio >= 2.0;
            boolean pass = sameCount && correctRatio;

            total++;
            if (pass) passed++;

            System.out.printf("  N=%-4d D=%d  slow=%8d  fast=%6d  ratio=%5.1fx  same=%b  %s%n",
                    n, depsPerSpec,
                    slow.comparisons, fast.ops,
                    ratio, sameCount,
                    pass ? "PASS" : "FAIL");
        }

        System.out.println();
        System.out.printf("Result: %d/%d PASS%n", passed, total);
        if (passed < total) System.exit(1);
    }
}