package unit;

import java.util.*;

/**
 * zeek-0001 — CWE-407: O(n²) rule deduplication in per-packet signature matching
 *
 * Models Zeek src/RuleMatcher.cc is_member_of():
 *   Slow: std::ranges::find(matched_rules, idx)  — O(R) per call, 6 calls per packet
 *   Fast: unordered_set<intptr_t>::count(idx)    — O(1) per call
 *
 * As a connection accumulates matched rules over P packets,
 * each packet costs O(R_matched) per check. Over P packets with R total rules:
 *   Slow: O(P * R_matched_avg * 6) = O(P * R) with fully loaded state
 *   Fast: O(P * 1 * 6) = O(P)
 */
public class ZeekRuleMatcherTest {

    // --- SLOW: vector-based matched_rules (defective) ---
    static boolean isMemberOfSlow(List<Long> matched, long ruleIdx) {
        for (long r : matched) {
            if (r == ruleIdx) return true;
        }
        return false;
    }

    /**
     * Simulate P packets across a connection, each triggering up to batchSize rules.
     * Per packet: 6 is_member_of checks per candidate rule.
     * Returns total operations (inner loop iterations).
     */
    static long simulateSlowConnection(int totalRules, int packetsPerConn, int rulesMatchedPerPacket) {
        List<Long> matchedRules = new ArrayList<>();
        long ops = 0;
        Random rng = new Random(7);

        for (int pkt = 0; pkt < packetsPerConn; pkt++) {
            // Select rulesMatchedPerPacket candidates to check
            for (int i = 0; i < rulesMatchedPerPacket; i++) {
                long ruleIdx = rng.nextInt(totalRules);

                // 6 is_member_of calls model the 6 call sites in RuleMatcher.cc
                for (int call = 0; call < 6; call++) {
                    for (long r : matchedRules) {  // O(R) scan
                        ops++;
                        if (r == ruleIdx) break;
                    }
                }

                // Add to matched_rules if not already present (ExecRuleActions)
                if (!isMemberOfSlow(matchedRules, ruleIdx)) {
                    matchedRules.add(ruleIdx);
                }
            }
        }
        return ops;
    }

    // --- FAST: hash set matched_rules (fixed) ---
    static long simulateFastConnection(int totalRules, int packetsPerConn, int rulesMatchedPerPacket) {
        Set<Long> matchedRules = new HashSet<>();
        long ops = 0;
        Random rng = new Random(7);

        for (int pkt = 0; pkt < packetsPerConn; pkt++) {
            for (int i = 0; i < rulesMatchedPerPacket; i++) {
                long ruleIdx = rng.nextInt(totalRules);

                // 6 O(1) hash lookups
                for (int call = 0; call < 6; call++) {
                    ops++;  // single hash lookup
                    matchedRules.contains(ruleIdx);
                }

                matchedRules.add(ruleIdx);
            }
        }
        return ops;
    }

    public static void main(String[] args) {
        // R = total rules in IDS ruleset (large enterprise deployment)
        // P = packets per connection
        // B = rules fired per packet (typically low, but state accumulates)
        final int R = 500;
        final int P = 1000;
        final int B = 5;  // rules that trigger per packet (accumulates in matched_rules)

        // Correctness: same rule indices should be found/not-found by both
        List<Long> slowList = new ArrayList<>(Arrays.asList(10L, 20L, 30L, 50L, 99L));
        Set<Long> fastSet   = new HashSet<>(Arrays.asList(10L, 20L, 30L, 50L, 99L));

        assert isMemberOfSlow(slowList, 30L)  : "slow: should find 30";
        assert !isMemberOfSlow(slowList, 40L) : "slow: should miss 40";
        assert fastSet.contains(30L)          : "fast: should find 30";
        assert !fastSet.contains(40L)         : "fast: should miss 40";

        long slowOps = simulateSlowConnection(R, P, B);
        long fastOps = simulateFastConnection(R, P, B);

        assert slowOps > fastOps : "slow should cost more ops, got slow=" + slowOps + " fast=" + fastOps;

        double speedup = (double) slowOps / fastOps;

        System.out.println("zeek-0001 CWE-407: is_member_of O(R) vector scan vs O(1) hash set");
        System.out.println("  R (rules) = " + R + ", P (packets/conn) = " + P + ", B (rules/pkt) = " + B);
        System.out.println("  Slow ops (vector linear scan, 6x per pkt): " + slowOps);
        System.out.println("  Fast ops (hash set, 6x per pkt):           " + fastOps);
        System.out.printf ("  Speedup: %.0fx%n", speedup);
        System.out.println();

        // Verify the quadratic growth: at 2× rules the slow cost should ~4× (quadratic)
        long slowOpsHalfR  = simulateSlowConnection(R/2, P, B);
        long slowOpsDoubleR= simulateSlowConnection(R*2, P, B);
        double ratio = (double) slowOpsDoubleR / slowOpsHalfR;
        // For a truly quadratic structure ratio approaches 4.0; assert it's super-linear
        assert ratio > 2.0 : "expected super-linear growth, got ratio=" + ratio;

        long fastOpsHalfR   = simulateFastConnection(R/2, P, B);
        long fastOpsDoubleR = simulateFastConnection(R*2, P, B);
        double fastRatio = (double) fastOpsDoubleR / fastOpsHalfR;
        // Fast should be roughly linear (ratio ~2) or even flat (constant O(1) per call)
        assert fastRatio < ratio : "fast should scale better than slow";

        System.out.println("Quadratic growth check (R/2 → 2R):");
        System.out.println("  Slow ops ratio: " + String.format("%.2f", ratio) + "x  (>2 confirms super-linear)");
        System.out.println("  Fast ops ratio: " + String.format("%.2f", fastRatio) + "x  (near-linear)");
        System.out.println();

        System.out.println("2/2 PASS");
    }
}