java-topology/defects/thunderbird-0007/test/ThunderbirdInitServerTest.java

import java.util.*;

/**
 * Unit test for thunderbird-0007: about3Pane.js SmartServerPane.initServer()
 * existingURIs Array.includes() O(N²) in do-while loop.
 *
 * Models the JavaScript pattern:
 *   let existingURIs = Array.from(existingRows, li => li.uri);   // re-built each iteration
 *   do {
 *     const folderURI = remainingFolderURIs.shift();
 *     if (existingURIs.includes(folderURI)) continue;            // O(F) per check
 *     this.addFolder(...);
 *     existingURIs = Array.from(existingRows, li => li.uri);     // full rebuild!
 *   } while (remainingFolderURIs.length);
 *
 * Fix: replace Array with Set so membership checks are O(1).
 */
public class ThunderbirdInitServerTest {

    // --- Defective implementation (Array + linear includes + full rebuild) ---

    static int initServerDefective(List<String> remainingFolderURIs,
                                    List<String> initialExistingURIs) {
        List<String> existingRows = new ArrayList<>(initialExistingURIs);
        int ops = 0;

        List<String> remaining = new ArrayList<>(remainingFolderURIs);
        List<String> existingURIs = new ArrayList<>(existingRows);

        while (!remaining.isEmpty()) {
            String folderURI = remaining.remove(0);
            // O(F) scan — the defect
            ops++;
            boolean found = existingURIs.contains(folderURI);
            if (found) continue;

            // addFolder: mutates existingRows
            existingRows.add(folderURI);

            // Full rebuild — another O(F) scan hidden here
            existingURIs = new ArrayList<>(existingRows);
            ops += existingRows.size(); // cost of rebuild
        }
        return ops;
    }

    // --- Fixed implementation (Set + O(1) has()) ---

    static int initServerFixed(List<String> remainingFolderURIs,
                                List<String> initialExistingURIs) {
        List<String> existingRows = new ArrayList<>(initialExistingURIs);
        int ops = 0;

        List<String> remaining = new ArrayList<>(remainingFolderURIs);
        Set<String> existingURIs = new HashSet<>(existingRows);

        while (!remaining.isEmpty()) {
            String folderURI = remaining.remove(0);
            ops++;
            if (existingURIs.contains(folderURI)) continue;

            // addFolder: just add to Set, no rebuild
            existingRows.add(folderURI);
            existingURIs.add(folderURI);
        }
        return ops;
    }

    // --- Helper ---

    static List<String> makeFolderURIs(int count, String prefix) {
        List<String> uris = new ArrayList<>();
        for (int i = 0; i < count; i++) {
            uris.add("imap://user@server/mailbox/" + prefix + i);
        }
        return uris;
    }

    public static void main(String[] args) {
        System.out.println("=== thunderbird-0007: initServer existingURIs O(N²) ===\n");

        // Test 1: correctness - no duplicates processed
        {
            List<String> existing = makeFolderURIs(3, "existing-");
            List<String> remaining = makeFolderURIs(5, "new-");
            // Add overlap: one of the new folders is already in existing
            remaining.add(existing.get(0));  // duplicate

            // Both implementations should accept the same non-duplicate count
            // (just verify they run without error and give non-negative ops)
            int opsD = initServerDefective(new ArrayList<>(remaining), new ArrayList<>(existing));
            int opsF = initServerFixed(new ArrayList<>(remaining), new ArrayList<>(existing));
            assert opsD > 0 : "FAIL: defective returned 0 ops";
            assert opsF > 0 : "FAIL: fixed returned 0 ops";
            System.out.println("PASS correctness: defective=" + opsD + " ops, fixed=" + opsF + " ops");
        }

        // Test 2: small N — verify both give same logical result
        {
            for (int n : new int[]{10, 50, 100}) {
                List<String> existing = makeFolderURIs(2, "e-");
                List<String> remaining = makeFolderURIs(n, "r-");
                int opsD = initServerDefective(new ArrayList<>(remaining), new ArrayList<>(existing));
                int opsF = initServerFixed(new ArrayList<>(remaining), new ArrayList<>(existing));
                // Fixed should always use fewer ops than defective for N > small constant
                System.out.printf("N=%-4d  defective=%6d ops  fixed=%4d ops  ratio=%.1fx%n",
                    n, opsD, opsF, (double) opsD / opsF);
            }
        }

        // Test 3: ratio benchmark at F=500 (large IMAP account)
        {
            int F = 500;
            List<String> existing = makeFolderURIs(10, "existing-");
            List<String> remaining = makeFolderURIs(F, "folder-");

            long t0 = System.nanoTime();
            int opsD = initServerDefective(new ArrayList<>(remaining), new ArrayList<>(existing));
            long t1 = System.nanoTime();
            int opsF = initServerFixed(new ArrayList<>(remaining), new ArrayList<>(existing));
            long t2 = System.nanoTime();

            double ratio = (double) opsD / opsF;
            System.out.printf("%nF=%-4d  defective=%8d ops  fixed=%6d ops  op-ratio=%.1fx%n",
                F, opsD, opsF, ratio);
            System.out.printf("       defective=%6d µs   fixed=%5d µs%n",
                (t1 - t0) / 1000, (t2 - t1) / 1000);

            assert ratio > 5.0 : "FAIL: expected ratio > 5x at F=500, got " + ratio;
            System.out.println("PASS: ratio > 5x confirmed");
        }

        // Test 4: all-duplicate case (everything already in tree)
        {
            List<String> existing = makeFolderURIs(100, "folder-");
            List<String> remaining = new ArrayList<>(existing);  // 100% overlap
            int opsD = initServerDefective(new ArrayList<>(remaining), new ArrayList<>(existing));
            int opsF = initServerFixed(new ArrayList<>(remaining), new ArrayList<>(existing));
            // Both should still handle this correctly (skip all)
            assert opsD > 0 : "FAIL: defective should still do ops on duplicate check";
            System.out.println("PASS all-duplicate: defective=" + opsD + " fixed=" + opsF);
        }

        System.out.println("\nAll tests PASS");
    }
}