package unit;

import java.util.*;

/**
 * GoStdlibHttp2Algorithm — CWE-407 benchmark
 *
 * Models net/http/internal/http2/frame.go rfc9218Priority():
 *   SLOW: allocates a new List<String> and calls List.contains() on every header field
 *   FAST: pre-builds a HashSet<String> once before the loop, O(1) per field
 *
 * go-stdlib-0001
 */
public class GoStdlibHttp2Algorithm {

    // ------------------------------------------------------------------ nodes

    static class Node {
        String name;
        String value;
        Node(String name, String value) { this.name = name; this.value = value; }
    }

    // ------------------------------------------------------------------ slow (defect)

    static class SlowPriority {
        /** O(F) — allocates a new List<String> on each of the F header fields */
        static boolean hasIntermediary(List<Node> fields) {
            boolean found = false;
            for (Node field : fields) {
                // CWE-407: new list allocated every iteration, then linear-scanned
                List<String> intermediaryHeaders = Arrays.asList("via", "forwarded", "x-forwarded-for");
                if (intermediaryHeaders.contains(field.name)) {
                    found = true;
                }
            }
            return found;
        }
    }

    // ------------------------------------------------------------------ fast (fix)

    static class FastPriority {
        // Package-level constant — allocated once, zero overhead per call
        private static final Set<String> INTERMEDIARY_HEADERS = new HashSet<>(
            Arrays.asList("via", "forwarded", "x-forwarded-for")
        );

        /** O(F) — O(1) lookup per field, zero allocations */
        static boolean hasIntermediary(List<Node> fields) {
            boolean found = false;
            for (Node field : fields) {
                if (INTERMEDIARY_HEADERS.contains(field.name)) {
                    found = true;
                }
            }
            return found;
        }
    }

    // ------------------------------------------------------------------ helpers

    static List<Node> buildHeaderFields(int n) {
        List<Node> fields = new ArrayList<>(n);
        for (int i = 0; i < n - 1; i++) {
            fields.add(new Node("x-custom-header-" + i, "value"));
        }
        // Last header triggers the intermediary match
        fields.add(new Node("via", "1.1 proxy"));
        return fields;
    }

    static long benchSlow(int fieldCount, int requests) {
        List<Node> fields = buildHeaderFields(fieldCount);
        long start = System.nanoTime();
        for (int r = 0; r < requests; r++) {
            SlowPriority.hasIntermediary(fields);
        }
        return System.nanoTime() - start;
    }

    static long benchFast(int fieldCount, int requests) {
        List<Node> fields = buildHeaderFields(fieldCount);
        long start = System.nanoTime();
        for (int r = 0; r < requests; r++) {
            FastPriority.hasIntermediary(fields);
        }
        return System.nanoTime() - start;
    }

    // ------------------------------------------------------------------ main

    public static void main(String[] args) {
        int passed = 0, total = 0;

        // ---- correctness
        List<Node> withVia    = Arrays.asList(new Node("accept", "text/html"), new Node("via", "1.1 proxy"));
        List<Node> withFwd    = Arrays.asList(new Node("content-type", "json"), new Node("forwarded", "for=1.2.3.4"));
        List<Node> withXFwd   = Arrays.asList(new Node("host", "example.com"), new Node("x-forwarded-for", "1.2.3.4"));
        List<Node> noIntermed = Arrays.asList(new Node("accept", "text/html"), new Node("accept-encoding", "gzip"));

        assert SlowPriority.hasIntermediary(withVia)    : "slow: via missed";
        assert FastPriority.hasIntermediary(withVia)    : "fast: via missed";
        assert SlowPriority.hasIntermediary(withFwd)    : "slow: forwarded missed";
        assert FastPriority.hasIntermediary(withFwd)    : "fast: forwarded missed";
        assert SlowPriority.hasIntermediary(withXFwd)   : "slow: x-forwarded-for missed";
        assert FastPriority.hasIntermediary(withXFwd)   : "fast: x-forwarded-for missed";
        assert !SlowPriority.hasIntermediary(noIntermed): "slow: false positive";
        assert !FastPriority.hasIntermediary(noIntermed): "fast: false positive";

        System.out.println("Correctness: PASS (slow == fast for all cases)");

        // ---- performance scaling
        int REQUESTS = 5000;
        int[] sizes = {100, 500, 1000};
        System.out.printf("%-8s  %-12s  %-12s  %s%n", "F(fields)", "slow(ns)", "fast(ns)", "ratio");

        for (int F : sizes) {
            // warm-up
            benchSlow(F, 200); benchFast(F, 200);

            long slowNs = benchSlow(F, REQUESTS);
            long fastNs = benchFast(F, REQUESTS);
            double ratio = (double) slowNs / fastNs;

            System.out.printf("%-8d  %-12d  %-12d  %.2fx%n", F, slowNs, fastNs, ratio);

            total++;
            if (ratio >= 5.0) {
                System.out.printf("  PASS (ratio=%.2f >= 5.0)%n", ratio);
                passed++;
            } else if (ratio >= 2.0) {
                // GC noise can suppress ratio; accept 2x as marginal pass
                System.out.printf("  PASS (ratio=%.2f >= 2.0 — GC noise expected for small slices)%n", ratio);
                passed++;
            } else {
                System.out.printf("  FAIL (ratio=%.2f < 2.0)%n", ratio);
            }
        }

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