package defects.systemd_0004;

import org.junit.Test;
import static org.junit.Assert.*;

import java.util.*;

/**
 * Unit test demonstrating systemd-0004 CWE-407:
 * seccomp_load_syscall_filter_set() uses strv_contains (O(N) linear scan)
 * inside NULSTR_FOREACH over ~537 KNOWN syscalls, producing O(K*A) behavior.
 *
 * The sibling function already uses hashmap/set for O(1) lookup.
 * This test proves O(K*A) vs O(K+A) operation count at realistic scales.
 */
public class TestSeccompStrvToSet {

    /** Simulates strv_contains: linear scan of a list for a name. */
    static int strv_contains(List<String> added, String name) {
        for (String s : added) {
            if (s.equals(name)) return 1;  // found
        }
        return 0;  // not found
    }

    /** Simulates set_contains: O(1) hash lookup. */
    static int set_contains(Set<String> added_set, String name) {
        return added_set.contains(name) ? 1 : 0;
    }

    /**
     * Measures operation count for the O(K*A) defect vs O(K+A) fix.
     *
     * @param K  number of KNOWN syscalls (e.g. 537 on x86_64)
     * @param A  number of syscalls already added to filter (e.g. 300 for @default)
     */
    static long[] measureOps(int K, int A) {
        // Build KNOWN syscall list (K entries)
        List<String> known = new ArrayList<>();
        for (int i = 0; i < K; i++) {
            known.add("sys_" + i);
        }

        // Build added strv: first A syscalls already covered
        List<String> added_strv = new ArrayList<>();
        Set<String> added_set = new HashSet<>();
        for (int i = 0; i < A; i++) {
            added_strv.add("sys_" + i);
            added_set.add("sys_" + i);
        }

        // Defect: O(K*A) - strv_contains inside loop over KNOWN
        long ops_defect = 0;
        for (String name : known) {
            // strv_contains does up to A comparisons
            for (String s : added_strv) {
                ops_defect++;
                if (s.equals(name)) break;
            }
        }

        // Fix: O(K+A) - set_contains inside loop over KNOWN
        // Build set: A ops
        long ops_fix = A;  // set construction
        // Loop: K * O(1) lookups
        for (String name : known) {
            ops_fix++;  // one hash lookup per iteration
            if (added_set.contains(name)) continue;
        }

        return new long[]{ops_defect, ops_fix};
    }

    @Test
    public void testRealisticScale() {
        // K=537 (x86_64 KNOWN syscalls), A=300 (@default filter set size)
        int K = 537, A = 300;
        long[] ops = measureOps(K, A);
        long defect = ops[0], fix = ops[1];

        System.out.printf("K=%d, A=%d: defect=%,d ops, fix=%,d ops, speedup=%.1fx%n",
                K, A, defect, fix, (double) defect / fix);

        // The defect should be dramatically more expensive
        assertTrue("Defect should have > 10x more ops than fix at K=537, A=300",
                defect > fix * 10);

        // Compute expected speedup
        double speedup = (double) defect / fix;
        assertTrue("Speedup should be > 50x at K=537, A=300", speedup > 50.0);
    }

    @Test
    public void testSmallScale() {
        // Even at small scale (K=100, A=50) the defect shows clearly
        long[] ops = measureOps(100, 50);
        long defect = ops[0], fix = ops[1];
        System.out.printf("K=100, A=50: defect=%,d ops, fix=%,d ops, speedup=%.1fx%n",
                100, 50, defect, fix, (double) defect / fix);
        assertTrue("Defect always more expensive than fix", defect > fix);
    }

    @Test
    public void testMultipleArches() {
        // x86_64 runs 3 architectures (x86, x32, x86_64)
        int arches = 3, K = 537, A = 300;
        long total_defect = 0, total_fix = 0;
        for (int i = 0; i < arches; i++) {
            long[] ops = measureOps(K, A);
            total_defect += ops[0];
            total_fix += ops[1];
        }
        System.out.printf("3 arches: defect=%,d ops, fix=%,d ops, speedup=%.1fx%n",
                total_defect, total_fix, (double) total_defect / total_fix);
        assertTrue("3-arch total: defect > 100x fix", total_defect > total_fix * 100);
    }
}