java-topology/defects/forgejo-0002/test/ForgejoLicenseSortTest.java

import java.util.*;

/**
 * Unit test simulating Forgejo forgejo-0002:
 * modules/repository/init.go LoadRepoConfig() license sort uses O(P*L) scans:
 *
 *   for _, name := range setting.Repository.PreferredLicenses {
 *       if util.SliceContainsString(Licenses, name, true) {  // O(L) scan
 *           sortedLicenses = append(sortedLicenses, name)
 *       }
 *   }
 *   for _, name := range Licenses {
 *       if !util.SliceContainsString(setting.Repository.PreferredLicenses, name, true) {  // O(P) scan
 *           sortedLicenses = append(sortedLicenses, name)
 *       }
 *   }
 *
 * Forgejo ships 776 licenses. Any preferred list of P entries costs O(P*776 + 776*P).
 * Fix: build sets for O(1) lookup before the loops.
 */
public class ForgejoLicenseSortTest {

    // Defective: O(P*L + L*P)
    static List<String> sortLicensesDefective(
            List<String> allLicenses, List<String> preferred) {
        List<String> sorted = new ArrayList<>(allLicenses.size());
        for (String name : preferred) {
            if (containsIgnoreCase(allLicenses, name)) {
                sorted.add(name);
            }
        }
        for (String name : allLicenses) {
            if (!containsIgnoreCase(preferred, name)) {
                sorted.add(name);
            }
        }
        return sorted;
    }

    static boolean containsIgnoreCase(List<String> list, String target) {
        String t = target.toLowerCase(Locale.ROOT);
        for (String s : list) {
            if (s.toLowerCase(Locale.ROOT).equals(t)) return true;
        }
        return false;
    }

    // Fixed: build sets first, then O(P + L)
    static List<String> sortLicensesFixed(
            List<String> allLicenses, List<String> preferred) {
        Set<String> licenseSet = new HashSet<>(allLicenses.size() * 2);
        for (String s : allLicenses) licenseSet.add(s.toLowerCase(Locale.ROOT));

        Set<String> preferredSet = new HashSet<>(preferred.size() * 2);
        for (String s : preferred) preferredSet.add(s.toLowerCase(Locale.ROOT));

        List<String> sorted = new ArrayList<>(allLicenses.size());
        for (String name : preferred) {
            if (licenseSet.contains(name.toLowerCase(Locale.ROOT))) {
                sorted.add(name);
            }
        }
        for (String name : allLicenses) {
            if (!preferredSet.contains(name.toLowerCase(Locale.ROOT))) {
                sorted.add(name);
            }
        }
        return sorted;
    }

    static long countDefectiveOps(List<String> allLicenses, List<String> preferred) {
        long ops = 0;
        // First loop: P * L
        for (String name : preferred) {
            ops += allLicenses.size();
        }
        // Second loop: L * P
        for (String name : allLicenses) {
            ops += preferred.size();
        }
        return ops;
    }

    static long countFixedOps(List<String> allLicenses, List<String> preferred) {
        // Build sets: O(L + P)
        long ops = allLicenses.size() + preferred.size();
        // Two loops: O(P + L)
        ops += preferred.size() + allLicenses.size();
        return ops;
    }

    // Build a realistic license list like Forgejo's 776 licenses
    static List<String> makeLicenses(int count) {
        List<String> licenses = new ArrayList<>(count);
        String[] templates = {
            "MIT", "Apache-2.0", "GPL-2.0", "GPL-3.0", "LGPL-2.1",
            "BSD-2-Clause", "BSD-3-Clause", "ISC", "MPL-2.0", "CDDL-1.0"
        };
        for (int i = 0; i < count; i++) {
            licenses.add(templates[i % templates.length] + "-variant-" + i);
        }
        return licenses;
    }

    public static void main(String[] args) {
        System.out.println("forgejo-0002: LoadRepoConfig license sort O(P*L) -> O(P+L)");
        System.out.println("=".repeat(60));

        // Correctness test with small data
        List<String> licenses = Arrays.asList(
            "MIT", "Apache-2.0", "GPL-2.0", "GPL-3.0", "BSD-2-Clause"
        );
        List<String> preferred = Arrays.asList("GPL-3.0", "MIT");

        List<String> defective = sortLicensesDefective(licenses, preferred);
        List<String> fixed = sortLicensesFixed(licenses, preferred);

        // Both should start with preferred items (in preferred order), rest follow
        if (!defective.get(0).equals("GPL-3.0") || !defective.get(1).equals("MIT")) {
            throw new AssertionError("Defective sort wrong ordering: " + defective);
        }
        if (!fixed.get(0).equals("GPL-3.0") || !fixed.get(1).equals("MIT")) {
            throw new AssertionError("Fixed sort wrong ordering: " + fixed);
        }
        if (defective.size() != fixed.size()) {
            throw new AssertionError("Size mismatch: " + defective.size() + " vs " + fixed.size());
        }
        System.out.println("PASS: correctness verified");

        // Benchmark: 776 licenses (realistic), various preferred counts
        System.out.printf("%n%-10s %15s %12s %10s%n",
            "licenses", "defective_ops", "fixed_ops", "ratio");
        System.out.println("-".repeat(48));

        int L = 776;
        List<String> allLicenses = makeLicenses(L);
        int[] prefCounts = {1, 5, 10, 20};
        for (int P : prefCounts) {
            List<String> pref = allLicenses.subList(0, P);
            long def = countDefectiveOps(allLicenses, pref);
            long fix = countFixedOps(allLicenses, pref);
            double ratio = (double) def / fix;
            System.out.printf("L=%-4d P=%-4d %15d %12d %9.1fx%n", L, P, def, fix, ratio);
        }

        long def776 = countDefectiveOps(allLicenses, allLicenses.subList(0, 5));
        long fix776 = countFixedOps(allLicenses, allLicenses.subList(0, 5));
        double ratio776 = (double) def776 / fix776;

        if (ratio776 < 4) {
            throw new AssertionError("Expected >4x ratio at L=776, P=5, got " + ratio776);
        }

        System.out.println("\nAll assertions PASS");
        System.out.println("Fix: build licensesSet and preferredSet before loops for O(1) lookup");
    }
}