/*
 * test_index_stress.c — correctness of the persistent treap index
 * (Section 9.1's sort order; see CLAUDE.md's "Known performance
 * characteristics" and BENCH.md for why it replaced a flat array) under
 * heavy, randomized structural churn, cross-checked against an
 * independent reference model rather than just "did it not crash."
 *
 * This exercises exactly the code path BENCH.md's O(n^2) finding and its
 * fix live in: upper.c's snapshot_upsert/snapshot_remove and the treap
 * (split3/merge, node refcounting) beneath them, at a scale (thousands
 * of entries, non-sequential insertion/deletion order, nested
 * directories, renames) the other test files don't reach.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "packfs.h"
#include "test_harness.h"

#define N 8000

static int g_alive[N];

static void name_for(int id, char *buf, size_t cap) {
    /* deliberately nested, to exercise readdir's prefix-range logic at
     * more than one level, not just a flat root directory */
    snprintf(buf, cap, "/d%03d/f%06d.dat", id % 50, id);
}

static void shuffle(int *order, int n) {
    for (int i = n - 1; i > 0; i--) {
        int j = rand() % (i + 1);
        int t = order[i]; order[i] = order[j]; order[j] = t;
    }
}

static void create_one(Vfs *v, int id) {
    char path[64], parent[16];
    name_for(id, path, sizeof(path));
    snprintf(parent, sizeof(parent), "/d%03d", id % 50);
    int err = 0;
    if (vfs_stat(v, parent, &(VfsStat){0}) != VFS_OK) vfs_mkdir(v, parent);
    VfsFile *f = vfs_open(v, path, VFS_O_WRONLY | VFS_O_CREAT | VFS_O_TRUNC, &err);
    CHECK(f != NULL);
    if (!f) return;
    char payload[32];
    int n = snprintf(payload, sizeof(payload), "id=%d", id);
    CHECK_EQ_INT(vfs_write(f, payload, (pfs_usize)n), n);
    vfs_close(f);
    g_alive[id] = 1;
}

static void delete_one(Vfs *v, int id) {
    char path[64];
    name_for(id, path, sizeof(path));
    CHECK_EQ_INT(vfs_unlink(v, path), VFS_OK);
    g_alive[id] = 0;
}

/* Cross-checks the live tree against g_alive[]: every alive id must
 * stat successfully with the right content; every dead id must NOENT;
 * and the total count reachable via nested readdir must match the
 * reference model's count exactly (not just "at least"). */
static void verify_consistency(Vfs *v) {
    int expected_total = 0;
    for (int id = 0; id < N; id++) {
        char path[64];
        name_for(id, path, sizeof(path));
        VfsStat st;
        int rc = vfs_stat(v, path, &st);
        if (g_alive[id]) {
            expected_total++;
            CHECK_EQ_INT(rc, VFS_OK);
            if (rc == VFS_OK) {
                CHECK_EQ_INT(st.kind, VFS_KIND_FILE);
                int err = 0;
                VfsFile *f = vfs_open(v, path, VFS_O_RDONLY, &err);
                CHECK(f != NULL);
                if (f) {
                    char buf[32] = {0}, expect[32];
                    vfs_read(f, buf, sizeof(buf) - 1);
                    snprintf(expect, sizeof(expect), "id=%d", id);
                    CHECK_STR_EQ(buf, expect);
                    vfs_close(f);
                }
            }
        } else {
            CHECK_EQ_INT(rc, VFS_ERR_NOENT);
        }
    }

    /* Full nested readdir sweep: sum of children across every /dNNN that
     * still has any live file must equal the reference model's count.
     * This exercises upper_visit_range's prefix pruning at every
     * directory, not just the root. */
    int counted = 0;
    for (int d = 0; d < 50; d++) {
        char dirpath[16];
        snprintf(dirpath, sizeof(dirpath), "/d%03d", d);
        VfsDir dir;
        if (vfs_readdir(v, dirpath, &dir) == VFS_OK) {
            counted += (int)dir.count;
            vfs_dir_free(&dir);
        }
    }
    CHECK_EQ_INT(counted, expected_total);
}

int main(void) {
    srand(20260914);
    Vfs *v = vfs_new();
    Backend *mem = backend_mem_new();
    CHECK_EQ_INT(vfs_mount(v, "/", mem), VFS_OK);

    int order[N];
    for (int i = 0; i < N; i++) order[i] = i;

    /* round 1: create everything, in randomized (non-sequential) order —
     * the exact pattern that made the flat array O(n^2); the treap must
     * both stay correct and (implicitly, via this test completing in
     * reasonable time under sanitizers) stay fast. */
    shuffle(order, N);
    for (int i = 0; i < N; i++) create_one(v, order[i]);
    verify_consistency(v);

    /* round 2: delete a random 40%, in a different random order */
    shuffle(order, N);
    for (int i = 0; i < N * 2 / 5; i++) delete_one(v, order[i]);
    verify_consistency(v);

    /* round 3: recreate half of what was just deleted, delete a
     * different random slice of what's still alive, interleaved by
     * iterating one combined shuffled order over "toggle this id" */
    shuffle(order, N);
    for (int i = 0; i < N; i++) {
        int id = order[i];
        if (id % 3 == 0) {
            if (g_alive[id]) delete_one(v, id); else create_one(v, id);
        }
    }
    verify_consistency(v);

    /* renames: move a sample of live files to a fresh, previously-unused
     * path, verify old path gone / new path present with right content */
    for (int id = 0; id < N; id += 37) {
        if (!g_alive[id]) continue;
        char from[64], to[80];
        name_for(id, from, sizeof(from));
        snprintf(to, sizeof(to), "%s.moved", from);
        CHECK_EQ_INT(vfs_rename(v, from, to), VFS_OK);
        VfsStat st;
        CHECK_EQ_INT(vfs_stat(v, from, &st), VFS_ERR_NOENT);
        CHECK_EQ_INT(vfs_stat(v, to, &st), VFS_OK);
        CHECK_EQ_INT(vfs_rename(v, to, from), VFS_OK); /* move it back so verify_consistency's model still holds */
    }
    verify_consistency(v);

    /* final: delete everything still alive, in yet another random order;
     * the tree must end up empty and every readdir empty. */
    shuffle(order, N);
    for (int i = 0; i < N; i++) if (g_alive[order[i]]) delete_one(v, order[i]);
    verify_consistency(v);
    for (int d = 0; d < 50; d++) {
        char dirpath[16];
        snprintf(dirpath, sizeof(dirpath), "/d%03d", d);
        VfsDir dir;
        if (vfs_readdir(v, dirpath, &dir) == VFS_OK) {
            CHECK_EQ_INT(dir.count, 0);
            vfs_dir_free(&dir);
        }
    }

    vfs_unmount(v, "/");
    backend_free(mem);
    vfs_free(v);
    TEST_MAIN_END();
}