import java.util.*;

/**
 * Unit test simulating Istio CWE-407 defect:
 * istio-0001: reportGatewayStatus addressesToReport dedup
 *
 * In pilot/pkg/config/kube/gateway/conversion.go (and agentgateway/gateway_status.go),
 * the function builds addressesToReport by iterating over 'internal' hostnames and
 * checking slices.Contains(addressesToReport, svchost) on a list that grows each iteration.
 *
 * Complexity: O(I^2) where I = number of internal gateway hostnames.
 * Fix: use a map[string]struct{} seen-set for O(1) membership checks.
 */
public class IstioTest {

    /** Defect version: O(I^2) - slices.Contains on growing list */
    static List<String> reportAddressesDefect(List<String> internal, List<String> pending) {
        List<String> addressesToReport = new ArrayList<>();
        for (String hostport : internal) {
            String svchost = splitHost(hostport);
            // O(P) scan on pending + O(A) scan on growing addressesToReport
            if (!pending.contains(svchost) && !addressesToReport.contains(svchost)) {
                addressesToReport.add(svchost);
            }
        }
        return addressesToReport;
    }

    /** Fixed version: O(I) - map-based seen set for O(1) lookups */
    static List<String> reportAddressesFixed(List<String> internal, List<String> pending) {
        Set<String> pendingSet = new HashSet<>(pending);
        Set<String> seenHosts = new HashSet<>();
        List<String> addressesToReport = new ArrayList<>();
        for (String hostport : internal) {
            String svchost = splitHost(hostport);
            if (!pendingSet.contains(svchost) && seenHosts.add(svchost)) {
                addressesToReport.add(svchost);
            }
        }
        return addressesToReport;
    }

    static String splitHost(String hostport) {
        int colon = hostport.lastIndexOf(':');
        if (colon > 0) return hostport.substring(0, colon);
        return hostport;
    }

    static long benchmarkDefect(int n) {
        List<String> internal = new ArrayList<>();
        List<String> pending = new ArrayList<>();
        // Simulate n internal gateway hostnames (e.g. istio-ingressgateway.istio-system.svc.cluster.local:80)
        for (int i = 0; i < n; i++) {
            internal.add("gw-svc-" + i + ".istio-system.svc.cluster.local:80");
        }
        long start = System.nanoTime();
        for (int iter = 0; iter < 200; iter++) {
            reportAddressesDefect(internal, pending);
        }
        return System.nanoTime() - start;
    }

    static long benchmarkFixed(int n) {
        List<String> internal = new ArrayList<>();
        List<String> pending = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            internal.add("gw-svc-" + i + ".istio-system.svc.cluster.local:80");
        }
        long start = System.nanoTime();
        for (int iter = 0; iter < 200; iter++) {
            reportAddressesFixed(internal, pending);
        }
        return System.nanoTime() - start;
    }

    public static void main(String[] args) {
        // Correctness: both versions must return same result
        List<String> internal = Arrays.asList(
            "gw-a.istio-system.svc.cluster.local:80",
            "gw-b.istio-system.svc.cluster.local:80",
            "gw-a.istio-system.svc.cluster.local:443",  // duplicate host, different port
            "gw-c.istio-system.svc.cluster.local:80"
        );
        List<String> pending = Arrays.asList("gw-c.istio-system.svc.cluster.local");

        List<String> defectResult = reportAddressesDefect(internal, pending);
        List<String> fixedResult = reportAddressesFixed(internal, pending);

        System.out.println("Defect result: " + defectResult);
        System.out.println("Fixed  result: " + fixedResult);
        assert defectResult.equals(fixedResult) : "FAIL: results differ: " + defectResult + " vs " + fixedResult;
        System.out.println("Correctness: PASS");

        // Both should contain gw-a and gw-b, but NOT gw-c (pending)
        assert defectResult.contains("gw-a.istio-system.svc.cluster.local") : "FAIL: missing gw-a";
        assert defectResult.contains("gw-b.istio-system.svc.cluster.local") : "FAIL: missing gw-b";
        assert !defectResult.contains("gw-c.istio-system.svc.cluster.local") : "FAIL: gw-c should be excluded (pending)";
        assert defectResult.size() == 2 : "FAIL: expected 2 unique non-pending hosts, got " + defectResult.size();
        System.out.println("Exclusion of pending and dedup: PASS");

        // Benchmark at I=500 (many gateway replicas/ports across multiple gateway services)
        int n = 500;
        // Warmup
        benchmarkDefect(n); benchmarkFixed(n);

        long defectNs = benchmarkDefect(n);
        long fixedNs  = benchmarkFixed(n);
        // Ensure fixed is not too short to measure
        if (fixedNs < 1_000_000) fixedNs = 1_000_000;

        double ratio = (double) defectNs / fixedNs;
        System.out.printf("Benchmark n=%d x200: defect=%dms fixed=%dms ratio=%.1fx%n",
            n, defectNs / 1_000_000, fixedNs / 1_000_000, ratio);

        assert ratio > 1.5 : "FAIL: expected defect to be measurably slower (got " + ratio + "x)";
        System.out.println("Performance regression: PASS (ratio=" + String.format("%.1f", ratio) + "x)");

        System.out.println("ALL PASS");
    }
}