package unit;
import java.util.*;

/**
 * LinuxTest — CWE-407 benchmark for linux-0002, linux-0003, linux-0004
 *
 * linux-0002 (AUDIT_FILTER_INODES_QUADRATIC):
 *   Models audit_filter_inodes() + audit_filter_rules():
 *   SLOW: for each name [O(F)]: for each rule [O(R)]: for each inode-field: scan names [O(F)]
 *         Total O(F * R * F) = O(F²R)
 *   FAST: for each name [O(F)]: hash-lookup rule by inode [O(1)]: O(1) field check
 *         Total O(F)
 *
 * linux-0003 (DEV_ALLOC_NAME_NESTED_ALTNAME):
 *   Models __dev_alloc_name():
 *   SLOW: for each netdev [O(D)]: for each altname [O(A)]: sscanf+snprintf+strcmp [O(1)]
 *         Total O(D * A)
 *   FAST: maintain prefix bitmap; populate on registration; find_first_zero in O(D+A) once
 *         Lookup: O(1) — single bitmap load
 *
 * linux-0004 (NEIGH_PARMS_IFINDEX_LINEAR_SCAN):
 *   Models lookup_neigh_parms():
 *   SLOW: list_for_each_entry(p, &tbl->parms_list) — O(P) per command
 *   FAST: xarray / HashMap keyed by ifindex — O(1) per command
 */
public class LinuxTest {

    // =========================================================================
    // linux-0002: audit_filter_inodes quadratic names_list re-scan
    // =========================================================================

    /** One audit_names entry — inode + dev pair (like struct audit_names). */
    static class AuditName {
        final long ino;
        final int  devMajor;
        AuditName(long ino, int devMajor) { this.ino = ino; this.devMajor = devMajor; }
    }

    /** One audit rule field (type + value). */
    static class AuditField {
        static final int TYPE_INODE    = 1;
        static final int TYPE_DEVMAJOR = 2;
        final int type;
        final long val;
        AuditField(int type, long val) { this.type = type; this.val = val; }
    }

    /** One audit rule with multiple fields. */
    static class AuditRule {
        final List<AuditField> fields;
        AuditRule(List<AuditField> fields) { this.fields = fields; }
    }

    /**
     * SLOW: audit_filter_inodes as currently implemented.
     *
     * Outer loop: for each name N in namesList [O(F)]
     *   Middle:   for each rule E in rulesBucket [O(R/B)]
     *     Inner:  for each field of type AUDIT_INODE/DEVMAJOR:
     *               scan namesList again [O(F)]
     *
     * Returns total comparison count (proxy for CPU work).
     */
    static long auditFilterInodes_slow(List<AuditName> namesList,
                                       List<AuditRule> rulesBucket) {
        long ops = 0;
        for (AuditName name : namesList) {                    // O(F) outer
            for (AuditRule rule : rulesBucket) {              // O(R/B) middle
                for (AuditField f : rule.fields) {            // O(fields)
                    ops++;
                    if (f.type == AuditField.TYPE_INODE) {
                        // name is non-null here (per-name path) — use it directly
                        boolean match = (name.ino == f.val);
                        if (!match) {
                            // Simulate the bug: when called with name=null from
                            // audit_filter_syscall, the inner scan fires:
                            for (AuditName n : namesList) {   // O(F) inner re-scan
                                ops++;
                                if (n.ino == f.val) break;
                            }
                        }
                    } else if (f.type == AuditField.TYPE_DEVMAJOR) {
                        boolean match = (name.devMajor == f.val);
                        if (!match) {
                            for (AuditName n : namesList) {   // O(F) inner re-scan
                                ops++;
                                if (n.devMajor == f.val) break;
                            }
                        }
                    }
                }
            }
        }
        return ops;
    }

    /**
     * FAST: pass 'name' to audit_filter_rules so inner re-scan is skipped.
     *
     * When name != null, each field check is O(1) — compare against the
     * specific name, no re-scan of namesList.  Total: O(F * R/B * fields).
     */
    static long auditFilterInodes_fast(List<AuditName> namesList,
                                       List<AuditRule> rulesBucket) {
        long ops = 0;
        for (AuditName name : namesList) {                    // O(F)
            for (AuditRule rule : rulesBucket) {              // O(R/B)
                for (AuditField f : rule.fields) {            // O(fields)
                    ops++;
                    if (f.type == AuditField.TYPE_INODE) {
                        // name is always non-null in this path — O(1) check
                        @SuppressWarnings("unused")
                        boolean match = (name.ino == f.val);
                    } else if (f.type == AuditField.TYPE_DEVMAJOR) {
                        @SuppressWarnings("unused")
                        boolean match = (name.devMajor == f.val);
                    }
                }
            }
        }
        return ops;
    }

    // =========================================================================
    // linux-0003: __dev_alloc_name nested O(D * A) altname sscanf
    // =========================================================================

    /** One net_device with primary name and alt names. */
    static class NetDev {
        final String name;
        final List<String> altNames;
        NetDev(String name, List<String> altNames) {
            this.name = name; this.altNames = altNames;
        }
    }

    /**
     * SLOW: models __dev_alloc_name.
     *
     * for_each_netdev [O(D)]:
     *   netdev_for_each_altname [O(A)]:
     *     sscanf-equivalent (indexOf + parseInt) + snprintf + strcmp
     * Returns total string operations performed.
     */
    static long devAllocName_slow(List<NetDev> devices, String prefix) {
        long ops = 0;
        Set<Integer> inuse = new HashSet<>();

        for (NetDev d : devices) {                            // O(D)
            // check alt names
            for (String altName : d.altNames) {               // O(A)
                ops++;
                if (altName.startsWith(prefix)) {
                    try {
                        int idx = Integer.parseInt(altName.substring(prefix.length()));
                        if (idx >= 0) inuse.add(idx);
                    } catch (NumberFormatException ignored) {}
                }
            }
            // check primary name
            ops++;
            if (d.name.startsWith(prefix)) {
                try {
                    int idx = Integer.parseInt(d.name.substring(prefix.length()));
                    if (idx >= 0) inuse.add(idx);
                } catch (NumberFormatException ignored) {}
            }
        }

        // find first free slot
        int i = 0;
        while (inuse.contains(i)) i++;
        return ops;
    }

    /**
     * FAST: maintain a pre-built inuse bitmap updated at registration time.
     *
     * Registration: O(1) per device/altname.
     * Allocation: O(1) — single bitmap.nextClearBit().
     * Returns ops = 1 (the single bitmap query).
     */
    static long devAllocName_fast(BitSet inuseBitmap) {
        @SuppressWarnings("unused")
        int slot = inuseBitmap.nextClearBit(0);
        return 1;
    }

    /** Build the pre-indexed bitmap that the fast path uses. */
    static BitSet buildInuseBitmap(List<NetDev> devices, String prefix) {
        BitSet bm = new BitSet();
        for (NetDev d : devices) {
            for (String altName : d.altNames) {
                if (altName.startsWith(prefix)) {
                    try {
                        int idx = Integer.parseInt(altName.substring(prefix.length()));
                        if (idx >= 0) bm.set(idx);
                    } catch (NumberFormatException ignored) {}
                }
            }
            if (d.name.startsWith(prefix)) {
                try {
                    int idx = Integer.parseInt(d.name.substring(prefix.length()));
                    if (idx >= 0) bm.set(idx);
                } catch (NumberFormatException ignored) {}
            }
        }
        return bm;
    }

    // =========================================================================
    // linux-0004: lookup_neigh_parms O(P) list scan vs O(1) map lookup
    // =========================================================================

    /** Simulates struct neigh_parms — one per registered netdev. */
    static class NeighParms {
        final int ifindex;
        int baseReachableTime;
        NeighParms(int ifindex) { this.ifindex = ifindex; this.baseReachableTime = 30000; }
    }

    /**
     * SLOW: list_for_each_entry(p, &tbl->parms_list) — O(P).
     * Returns number of comparisons (list nodes visited).
     */
    static long lookupNeighParms_slow(List<NeighParms> paramsList, int ifindex) {
        long ops = 0;
        for (NeighParms p : paramsList) {
            ops++;
            if (p.ifindex == ifindex) return ops;
        }
        return ops; // not found
    }

    /**
     * FAST: HashMap (xarray equivalent) keyed by ifindex — O(1).
     * Returns 1 (single map probe).
     */
    static long lookupNeighParms_fast(Map<Integer, NeighParms> paramsMap, int ifindex) {
        paramsMap.get(ifindex);
        return 1;
    }

    // =========================================================================
    // Benchmark harness
    // =========================================================================

    static void bench(String label, Runnable slow, Runnable fast,
                      long sOps, long fOps) {
        long t0 = System.nanoTime();
        slow.run();
        long tSlow = System.nanoTime() - t0;
        t0 = System.nanoTime();
        fast.run();
        long tFast = System.nanoTime() - t0;

        System.out.printf("  %-52s  slow=%,d  fast=%,d  ops-ratio=%.1fx  time-ratio=%.1fx%n",
                label, sOps, fOps,
                fOps == 0 ? Double.MAX_VALUE : (double) sOps / fOps,
                tFast == 0 ? Double.MAX_VALUE : (double) tSlow / tFast);
    }

    // =========================================================================
    // main
    // =========================================================================

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

        System.out.println("LinuxTest — CWE-407 benchmark (linux-0002 / 0003 / 0004)");
        System.out.println("=".repeat(80));

        // ------------------------------------------------------------------
        // linux-0002: audit_filter_inodes quadratic re-scan
        // ------------------------------------------------------------------
        System.out.println("\nlinux-0002: audit_filter_inodes O(F²R) vs O(FR)");
        {
            // F=50 files (e.g. compiler opening many headers)
            // R=20 rules, 2 AUDIT_INODE fields each
            int F = 50, R = 20;
            List<AuditName> names = new ArrayList<>(F);
            for (int i = 0; i < F; i++) names.add(new AuditName(1000L + i, 8));

            List<AuditField> fields = Arrays.asList(
                new AuditField(AuditField.TYPE_INODE,    999L),   // no match — triggers inner scan
                new AuditField(AuditField.TYPE_DEVMAJOR, 99)
            );
            List<AuditRule> rules = new ArrayList<>(R);
            for (int i = 0; i < R; i++) rules.add(new AuditRule(fields));

            int OPS = 10_000;
            long[] sOps = {0}, fOps = {0};
            Runnable slow = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++) ops += auditFilterInodes_slow(names, rules);
                sOps[0] = ops;
            };
            Runnable fast = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++) ops += auditFilterInodes_fast(names, rules);
                fOps[0] = ops;
            };
            slow.run(); fast.run();
            bench("audit filter F=50 R=20 (10k syscalls)", slow, fast, sOps[0], fOps[0]);
            total++;
            // slow does F * R * fields * F inner = 50*20*2*50 = 100000 per call
            // fast does F * R * fields = 50*20*2 = 2000 per call
            // ratio should be ~F = 50x
            assert sOps[0] > fOps[0] * 10
                : "FAIL linux-0002 F=50 R=20: slow=" + sOps[0] + " fast=" + fOps[0];
            passed++;
        }
        {
            // F=200 files (large recursive compile), R=50 rules
            int F = 200, R = 50;
            List<AuditName> names = new ArrayList<>(F);
            for (int i = 0; i < F; i++) names.add(new AuditName(2000L + i, 8));

            List<AuditField> fields = Arrays.asList(
                new AuditField(AuditField.TYPE_INODE, 9999L),     // never matches — full inner scan
                new AuditField(AuditField.TYPE_DEVMAJOR, 99)
            );
            List<AuditRule> rules = new ArrayList<>(R);
            for (int i = 0; i < R; i++) rules.add(new AuditRule(fields));

            int OPS = 2_000;
            long[] sOps = {0}, fOps = {0};
            Runnable slow = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++) ops += auditFilterInodes_slow(names, rules);
                sOps[0] = ops;
            };
            Runnable fast = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++) ops += auditFilterInodes_fast(names, rules);
                fOps[0] = ops;
            };
            slow.run(); fast.run();
            bench("audit filter F=200 R=50 (2k syscalls)", slow, fast, sOps[0], fOps[0]);
            total++;
            assert sOps[0] > fOps[0] * 50
                : "FAIL linux-0002 F=200 R=50: slow=" + sOps[0] + " fast=" + fOps[0];
            passed++;
        }

        // ------------------------------------------------------------------
        // linux-0003: __dev_alloc_name nested altname scan
        // ------------------------------------------------------------------
        System.out.println("\nlinux-0003: __dev_alloc_name O(D*A) vs O(1)");
        {
            // D=300 devices, A=2 alt names each (typical container node)
            int D = 300, A = 2;
            String prefix = "veth";
            List<NetDev> devices = new ArrayList<>(D);
            for (int i = 0; i < D; i++) {
                List<String> alts = new ArrayList<>(A);
                for (int j = 0; j < A; j++) alts.add("wan" + i + "-" + j);
                devices.add(new NetDev(prefix + i, alts));
            }
            BitSet bitmap = buildInuseBitmap(devices, prefix);

            int OPS = 5_000;
            long[] sOps = {0}, fOps = {0};
            Runnable slow = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++) ops += devAllocName_slow(devices, prefix);
                sOps[0] = ops;
            };
            Runnable fast = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++) ops += devAllocName_fast(bitmap);
                fOps[0] = ops;
            };
            slow.run(); fast.run();
            bench("dev_alloc_name D=300 A=2 (5k renames)", slow, fast, sOps[0], fOps[0]);
            total++;
            // slow: D + D*A = 300 + 600 = 900 ops per call -> 4.5M total
            // fast: 1 op per call -> 5k total
            // ratio: ~900x
            assert sOps[0] > fOps[0] * 50
                : "FAIL linux-0003 D=300 A=2: slow=" + sOps[0] + " fast=" + fOps[0];
            passed++;
        }
        {
            // D=800 devices, A=3 alt names — Kubernetes node at scale
            int D = 800, A = 3;
            String prefix = "veth";
            List<NetDev> devices = new ArrayList<>(D);
            for (int i = 0; i < D; i++) {
                List<String> alts = new ArrayList<>(A);
                for (int j = 0; j < A; j++) alts.add("altname" + i + "_" + j);
                devices.add(new NetDev(prefix + i, alts));
            }
            BitSet bitmap = buildInuseBitmap(devices, prefix);

            int OPS = 1_000;
            long[] sOps = {0}, fOps = {0};
            Runnable slow = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++) ops += devAllocName_slow(devices, prefix);
                sOps[0] = ops;
            };
            Runnable fast = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++) ops += devAllocName_fast(bitmap);
                fOps[0] = ops;
            };
            slow.run(); fast.run();
            bench("dev_alloc_name D=800 A=3 (1k renames)", slow, fast, sOps[0], fOps[0]);
            total++;
            assert sOps[0] > fOps[0] * 100
                : "FAIL linux-0003 D=800 A=3: slow=" + sOps[0] + " fast=" + fOps[0];
            passed++;
        }

        // ------------------------------------------------------------------
        // linux-0004: lookup_neigh_parms linear scan vs HashMap
        // ------------------------------------------------------------------
        System.out.println("\nlinux-0004: lookup_neigh_parms O(P) vs O(1)");
        {
            // P=400 parms (VxLAN gateway with 400 VTEPs + bridge ports)
            int P = 400;
            List<NeighParms> paramsList = new ArrayList<>(P);
            Map<Integer, NeighParms> paramsMap = new HashMap<>(P * 2);
            for (int i = 1; i <= P; i++) {
                NeighParms p = new NeighParms(i);
                paramsList.add(p);
                paramsMap.put(i, p);
            }
            int targetIfindex = P; // worst case: last entry in list

            int OPS = 100_000;
            long[] sOps = {0}, fOps = {0};
            Runnable slow = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++)
                    ops += lookupNeighParms_slow(paramsList, targetIfindex);
                sOps[0] = ops;
            };
            Runnable fast = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++)
                    ops += lookupNeighParms_fast(paramsMap, targetIfindex);
                fOps[0] = ops;
            };
            slow.run(); fast.run();
            bench("neigh_parms lookup P=400 worst-case (100k)", slow, fast, sOps[0], fOps[0]);
            total++;
            // slow: P ops per lookup -> 400 * 100k = 40M
            // fast: 1 op per lookup -> 100k
            // ratio: ~400x
            assert sOps[0] > fOps[0] * 100
                : "FAIL linux-0004 P=400: slow=" + sOps[0] + " fast=" + fOps[0];
            passed++;
        }
        {
            // P=1000 parms, ifindex not found (no entry for this dev) — full walk
            int P = 1000;
            List<NeighParms> paramsList = new ArrayList<>(P);
            Map<Integer, NeighParms> paramsMap = new HashMap<>(P * 2);
            for (int i = 1; i <= P; i++) {
                NeighParms p = new NeighParms(i);
                paramsList.add(p);
                paramsMap.put(i, p);
            }
            int missingIfindex = 9999; // not in list

            int OPS = 50_000;
            long[] sOps = {0}, fOps = {0};
            Runnable slow = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++)
                    ops += lookupNeighParms_slow(paramsList, missingIfindex);
                sOps[0] = ops;
            };
            Runnable fast = () -> {
                long ops = 0;
                for (int i = 0; i < OPS; i++)
                    ops += lookupNeighParms_fast(paramsMap, missingIfindex);
                fOps[0] = ops;
            };
            slow.run(); fast.run();
            bench("neigh_parms lookup P=1000 not-found (50k)", slow, fast, sOps[0], fOps[0]);
            total++;
            assert sOps[0] > fOps[0] * 500
                : "FAIL linux-0004 P=1000 not-found: slow=" + sOps[0] + " fast=" + fOps[0];
            passed++;
        }

        System.out.println("\n" + passed + "/" + total + " PASS");
        if (passed < total) System.exit(1);
    }
}