MeowOS-SDK/tuku/logic/library.c

/* logic/library.c — 书库目录浏览：单层枚举 + 后台懒判定（纯 C）。
 *
 * 扫描（mr_library_scan / mr_library_scan_ex）与 os.meow.files 的 fsx_scan_dir 同构：
 *   - 一次 opendir/readdir，逐项 lstat（只认目录与档案文件；符号链接跳过防环）；
 *   - 隐藏项（"." 开头，含 . ..）跳过；系统目录/空目录/无图目录一律列出；
 *   - 目录名/档案文件名按 mr_natural_cmp 自然升序；条目到 MR_LIB_SCAN_MAX 后仍有条目 →
 *     截断标注。不再对子目录做任何递归/探测——首帧成本只与本层条目数线性相关。
 *
 * 懒判定（probe）：
 *   - mr_library_probe_dir 只读一层（图片项 lstat 校验普通文件），给出直接图片数与自然序首图；
 *   - mr_library_probe_path 按行类型探测：目录走上面的单层扫描；档案册调调用方注入的
 *     archive_pages（M11，logic 不依赖 zip）。两者共用 mtime(秒+纳秒)+size 失效的 256 项
 *     LRU 缓存 + 互斥锁，可被后台线程并发调用；探测期间目录/档案发生变化则不写缓存。
 *   - mr_library_apply_probe 把结果补回行；副标题由 mr_library_format_subtitle 统一生成，
 *     书行再拼 M7 的「· 续读 Pn」角标。
 *
 * M11 档案册：注入 archive_pages 时 .cbz/.zip 直接子文件也成行（懒探测页数）；
 * 未注入时只列目录（M7 书库语义）。册间衔接的兄弟表 = 含图目录 ∪ 含图片页的档案册。
 */
#include "library.h"
#include "logic/reader.h"   /* mr_cont_badge：书库行续读角标（M7） */

#include <ctype.h>
#include <dirent.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/stat.h>

#ifdef MR_LIBRARY_TEST_HOOKS
static mr_library_io_stats g_io;

void mr_library_test_io_reset(void)
{
    memset(&g_io, 0, sizeof g_io);
}

void mr_library_test_io_get(mr_library_io_stats *out)
{
    if (out) *out = g_io;
}

#define IO_OPEN()    (g_io.opendirs++)
#define IO_READDIR() (g_io.readdirs++)
#define IO_LSTAT()   (g_io.lstats++)
#else
#define IO_OPEN()    ((void)0)
#define IO_READDIR() ((void)0)
#define IO_LSTAT()   ((void)0)
#endif

/* 系统目录不参与**册间衔接**（M7 兄弟册表）；浏览本身已放开（不隐藏）。 */
static int ignored_dir_name(const char *name)
{
    static const char *const skip[] = { "MeowAPPs", "MeowData", "MeowOS", "lost+found" };
    if (!name || name[0] == '.') return 1;
    for (unsigned i = 0; i < sizeof skip / sizeof skip[0]; i++)
        if (strcmp(name, skip[i]) == 0) return 1;
    return 0;
}

static int copy_str(char *dst, int dstsz, const char *src)
{
    if (!dst || dstsz <= 0) return -1;
    if (!src) { dst[0] = '\0'; return 0; }
    int n = (int)strlen(src);
    if (n >= dstsz) return -1;
    memcpy(dst, src, (size_t)n + 1);
    return 0;
}

static int join_path(char *out, int outsz, const char *dir, const char *name)
{
    if (!out || outsz <= 0 || !dir || !name) return -1;
    int n;
    size_t dl = strlen(dir);
    if (dl > 0 && dir[dl - 1] == '/')
        n = snprintf(out, (size_t)outsz, "%s%s", dir, name);
    else
        n = snprintf(out, (size_t)outsz, "%s/%s", dir, name);
    return (n > 0 && n < outsz) ? 0 : -1;
}

int mr_path_is_image(const char *name)
{
    if (!name) return 0;
    const char *dot = strrchr(name, '.');
    if (!dot || dot == name) return 0;
    dot++;
    return strcasecmp(dot, "png") == 0 || strcasecmp(dot, "jpg") == 0 ||
           strcasecmp(dot, "jpeg") == 0 || strcasecmp(dot, "bmp") == 0;
}

int mr_path_is_archive(const char *name)
{
    if (!name) return 0;
    const char *dot = strrchr(name, '.');
    if (!dot || dot == name) return 0;
    dot++;
    return strcasecmp(dot, "cbz") == 0 || strcasecmp(dot, "zip") == 0;
}

int mr_natural_cmp(const char *a, const char *b)
{
    const unsigned char *pa = (const unsigned char *)a;
    const unsigned char *pb = (const unsigned char *)b;
    if (!a || !b) return (a == b) ? 0 : (a ? 1 : -1);

    while (*pa && *pb) {
        if (isdigit(*pa) && isdigit(*pb)) {
            const unsigned char *za = pa, *zb = pb;
            while (*pa == '0') pa++;
            while (*pb == '0') pb++;
            const unsigned char *da = pa, *db = pb;
            while (isdigit(*pa)) pa++;
            while (isdigit(*pb)) pb++;

            size_t la = (size_t)(pa - da), lb = (size_t)(pb - db);
            if (la != lb) return la < lb ? -1 : 1;
            if (la > 0) {
                int c = memcmp(da, db, la);
                if (c != 0) return c < 0 ? -1 : 1;
            }
            size_t oa = (size_t)(da - za), ob = (size_t)(db - zb);
            if (oa != ob) return oa < ob ? -1 : 1;
            continue;
        }

        int ca = tolower(*pa), cb = tolower(*pb);
        if (ca != cb) return ca < cb ? -1 : 1;
        pa++;
        pb++;
    }
    if (*pa) return 1;
    if (*pb) return -1;
    return strcmp(a, b) < 0 ? -1 : (strcmp(a, b) > 0 ? 1 : 0);
}

/* 档案册探测（UI 注入；NULL=纯目录书库，档案文件不成行）。 */
static int archive_pages_at(mr_lib_archive_fn probe, void *ud, const char *path)
{
    if (!probe || !path || !path[0]) return 0;
    int n = probe(path, ud);
    return n > 0 ? n : 0;
}

/* ============================================================ */
/* 单层探测 + mtime/size 失效缓存                                */
/* ============================================================ */
int mr_library_probe_dir(const char *dir, mr_library_probe *out)
{
    if (!out) return -1;
    memset(out, 0, sizeof *out);
    if (!dir || !dir[0]) return -1;

    IO_OPEN();
    DIR *d = opendir(dir);
    if (!d) return -1;

    char best[MR_NAME_MAX];
    best[0] = '\0';
    out->empty = 1;
    struct dirent *de;
    while ((de = readdir(d)) != NULL) {
        IO_READDIR();
        const char *name = de->d_name;
        if (name[0] == '.') continue;      /* 隐藏项不算内容 */
        out->empty = 0;
        if (!mr_path_is_image(name)) continue;

        char full[MR_PATH_MAX];
        if (join_path(full, (int)sizeof full, dir, name) != 0) continue;
        IO_LSTAT();
        struct stat st;
        if (lstat(full, &st) != 0 || !S_ISREG(st.st_mode)) continue;

        out->pages++;
        if (best[0] == '\0' || mr_natural_cmp(name, best) < 0) {
            copy_str(best, (int)sizeof best, name);
            copy_str(out->cover, (int)sizeof out->cover, full);
        }
    }
    closedir(d);
    return 0;
}

#define MR_PROBE_CACHE_MAX 256

typedef struct probe_cache_entry {
    char               path[MR_PATH_MAX];
    long long          mtime_ns;
    long long          size;
    mr_library_probe   probe;
    unsigned long long last_use;
} probe_cache_entry;

static probe_cache_entry *g_cache[MR_PROBE_CACHE_MAX];
static unsigned long long g_cache_clock;
static pthread_mutex_t g_cache_lock = PTHREAD_MUTEX_INITIALIZER;

static long long stat_mtime_ns(const struct stat *st)
{
#if defined(__APPLE__)
    return (long long)st->st_mtimespec.tv_sec * 1000000000LL + st->st_mtimespec.tv_nsec;
#else
    return (long long)st->st_mtim.tv_sec * 1000000000LL + st->st_mtim.tv_nsec;
#endif
}

static probe_cache_entry *cache_find_locked(const char *path)
{
    for (int i = 0; i < MR_PROBE_CACHE_MAX; i++) {
        if (!g_cache[i]) continue;
        if (strcmp(g_cache[i]->path, path) == 0) return g_cache[i];
    }
    return NULL;
}

static void cache_put_locked(const char *path, long long mtime_ns, long long size,
                             const mr_library_probe *p)
{
    probe_cache_entry *e = cache_find_locked(path);
    if (!e) {
        int slot = -1;
        for (int i = 0; i < MR_PROBE_CACHE_MAX; i++)
            if (!g_cache[i]) { slot = i; break; }
        if (slot < 0) {                        /* 满：淘汰最久未用项 */
            int lru = 0;
            unsigned long long oldest = g_cache[0]->last_use;
            for (int i = 1; i < MR_PROBE_CACHE_MAX; i++) {
                if (g_cache[i]->last_use < oldest) {
                    oldest = g_cache[i]->last_use;
                    lru = i;
                }
            }
            free(g_cache[lru]);
            g_cache[lru] = NULL;
            slot = lru;
        }
        e = (probe_cache_entry *)malloc(sizeof *e);
        if (!e) return;                        /* 缓存只是加速：失败就每次现算 */
        if (copy_str(e->path, (int)sizeof e->path, path) != 0) {
            free(e);
            return;
        }
        g_cache[slot] = e;
    }
    e->mtime_ns = mtime_ns;
    e->size = size;
    e->probe = *p;
    e->last_use = ++g_cache_clock;
}

void mr_library_probe_cache_clear(void)
{
    pthread_mutex_lock(&g_cache_lock);
    for (int i = 0; i < MR_PROBE_CACHE_MAX; i++) {
        free(g_cache[i]);
        g_cache[i] = NULL;
    }
    g_cache_clock = 0;
    pthread_mutex_unlock(&g_cache_lock);
}

/* 无缓存探测：目录=单层目录扫描；档案册=注入回调取页数。 */
static int probe_path_uncached(const char *path, int is_archive,
                               mr_lib_archive_fn archive_pages, void *ud,
                               mr_library_probe *out)
{
    struct stat st;
    if (stat(path, &st) != 0) return -1;
    if (is_archive) {
        if (!archive_pages || !S_ISREG(st.st_mode)) return -1;
        out->pages = archive_pages_at(archive_pages, ud, path);
        out->empty = 0;
        out->cover[0] = '\0';
        return 0;
    }
    if (!S_ISDIR(st.st_mode)) return -1;
    return mr_library_probe_dir(path, out);
}

int mr_library_probe_path(const char *path, int is_archive,
                          mr_lib_archive_fn archive_pages, void *ud,
                          mr_library_probe *out)
{
    if (!out) return -1;
    memset(out, 0, sizeof *out);
    if (!path || !path[0]) return -1;

    struct stat st;
    if (stat(path, &st) != 0) return -1;
    if (is_archive ? !S_ISREG(st.st_mode) : !S_ISDIR(st.st_mode)) return -1;

    long long mtime_ns = stat_mtime_ns(&st);
    long long size = (long long)st.st_size;

    pthread_mutex_lock(&g_cache_lock);
    probe_cache_entry *hit = cache_find_locked(path);
    if (hit && hit->mtime_ns == mtime_ns && hit->size == size) {
        *out = hit->probe;
        hit->last_use = ++g_cache_clock;
        pthread_mutex_unlock(&g_cache_lock);
        return 0;
    }
    pthread_mutex_unlock(&g_cache_lock);

    mr_library_probe p;
    memset(&p, 0, sizeof p);
    if (probe_path_uncached(path, is_archive, archive_pages, ud, &p) != 0) return -1;

    /* 评审 P2：只把「探测前后完全一致」的结果写入缓存。
     * 探测期间目录/档案的 mtime 或 size 变了（新增/替换文件），说明结果可能不完整，
     * 不能绑定到新 mtime 上当「新鲜」——本次直接返回，下次调用重新探测。 */
    struct stat st2;
    if (stat(path, &st2) == 0 && stat_mtime_ns(&st2) == mtime_ns &&
        (long long)st2.st_size == size) {
        pthread_mutex_lock(&g_cache_lock);
        cache_put_locked(path, mtime_ns, size, &p);
        pthread_mutex_unlock(&g_cache_lock);
    }

    *out = p;
    return 0;
}

int mr_library_probe_cached(const char *dir, mr_library_probe *out)
{
    return mr_library_probe_path(dir, 0, NULL, NULL, out);
}

/* ============================================================ */
/* 行状态：副标题 / 补位 / 行合成                                */
/* ============================================================ */
/* 基础副标题（不含 M7 续读角标）。 */
static void entry_subtitle(mr_library_entry *e)
{
    switch (e->probe_state) {
    case MR_LIB_READY:
        if (e->pages > 0)
            snprintf(e->subtitle, sizeof e->subtitle, "%d page%s", e->pages,
                     e->pages == 1 ? "" : "s");
        else if (!e->is_archive && e->empty)
            snprintf(e->subtitle, sizeof e->subtitle, "空目录");
        else
            snprintf(e->subtitle, sizeof e->subtitle, "无图片");
        break;
    case MR_LIB_FAILED:
        snprintf(e->subtitle, sizeof e->subtitle, "无法读取");
        break;
    default:
        snprintf(e->subtitle, sizeof e->subtitle, "…");
        break;
    }
}

/* 续读角标（M7）：有 last page 记录的书行，在副标题后缀「· 续读 Pn」。
 * 档案册以档案路径为册标识，同一套逻辑复用。
 * config 读失败/无记录时 mr_cont_badge 返回 0，副标题保持原样。 */
static void entry_badge(mr_library_entry *e)
{
    if (e->has_images != 1) return;
    char badge[24];
    if (!mr_cont_badge(e->path, badge, (int)sizeof badge)) return;
    int used = (int)strlen(e->subtitle);
    if (used < (int)sizeof e->subtitle - 2)
        snprintf(e->subtitle + used, sizeof e->subtitle - (size_t)used, " · %s", badge);
}

void mr_library_format_subtitle(mr_library_entry *e)
{
    if (!e) return;
    entry_subtitle(e);
    entry_badge(e);
}

void mr_library_free(mr_library *lib)
{
    if (!lib) return;
    free(lib->items);
    lib->items = NULL;
    lib->count = 0;
    lib->cap = 0;
    lib->truncated = 0;
}

static int lib_add(mr_library *lib, const mr_library_entry *e)
{
    if (lib->count >= lib->cap) {
        int cap = lib->cap ? lib->cap * 2 : 16;
        mr_library_entry *ni = (mr_library_entry *)realloc(lib->items,
                                                           (size_t)cap * sizeof *ni);
        if (!ni) return -1;
        lib->items = ni;
        lib->cap = cap;
    }
    lib->items[lib->count++] = *e;
    return 0;
}

static int entry_cmp(const void *pa, const void *pb)
{
    const mr_library_entry *a = (const mr_library_entry *)pa;
    const mr_library_entry *b = (const mr_library_entry *)pb;
    return mr_natural_cmp(a->name, b->name);
}

/* 文件夹册行（M13）：一律列出、初始待探测；是否「书」由后台 probe 决定。 */
static int add_dir_entry(mr_library *lib, const char *name, const char *full)
{
    mr_library_entry e;
    memset(&e, 0, sizeof e);
    if (copy_str(e.name, (int)sizeof e.name, name) != 0) return 0;
    if (copy_str(e.path, (int)sizeof e.path, full) != 0) return 0;
    e.pages = -1;
    e.has_images = -1;
    e.probe_state = MR_LIB_PENDING;
    mr_library_format_subtitle(&e);
    return lib_add(lib, &e);
}

/* 档案册（.cbz/.zip）行：文件即一本书，点入直接阅读。
 * pages<0=待后台探测（M13 懒算）；>=0=已知页数（扫描期注入的旧路径/测试用）。
 * cover 留空——缩略图由 UI 解压档内首图（mr_zip_cover_path）生成。 */
static int add_archive_entry(mr_library *lib, const char *name, const char *full,
                             int pages)
{
    mr_library_entry e;
    memset(&e, 0, sizeof e);
    if (copy_str(e.name, (int)sizeof e.name, name) != 0) return 0;
    if (copy_str(e.path, (int)sizeof e.path, full) != 0) return 0;
    e.is_archive = 1;
    if (pages < 0) {
        e.pages = -1;
        e.has_images = -1;
        e.probe_state = MR_LIB_PENDING;
    } else {
        e.pages = pages;
        e.has_images = (pages > 0) ? 1 : 0;
        e.probe_state = MR_LIB_READY;
    }
    mr_library_format_subtitle(&e);
    return lib_add(lib, &e);
}

/* ============================================================ */
/* 单层扫描                                                      */
/* ============================================================ */
int mr_library_scan_ex(mr_library *lib, const char *dir, int max_depth,
                       mr_lib_archive_fn archive_pages, void *ud)
{
    (void)max_depth;   /* 兼容旧签名：扫描不再递归 */
    (void)ud;
    if (!lib) return -1;
    mr_library_free(lib);
    if (!dir || !dir[0]) return -1;

    IO_OPEN();
    DIR *d = opendir(dir);
    if (!d) return -1;

    struct dirent *de;
    while ((de = readdir(d)) != NULL) {
        IO_READDIR();
        const char *name = de->d_name;
        if (name[0] == '.') continue;      /* . .. 与隐藏项 */

        char full[MR_PATH_MAX];
        if (join_path(full, (int)sizeof full, dir, name) != 0) continue;

        IO_LSTAT();
        struct stat st;
        if (lstat(full, &st) != 0) continue;
        if (S_ISLNK(st.st_mode)) continue;

        int is_dir = S_ISDIR(st.st_mode);
        int is_arch = (!is_dir && archive_pages && S_ISREG(st.st_mode) &&
                       mr_path_is_archive(name));
        if (!is_dir && !is_arch) continue;
        if (lib->count >= MR_LIB_SCAN_MAX) { lib->truncated = 1; break; }

        int rc = is_dir ? add_dir_entry(lib, name, full)
                        : add_archive_entry(lib, name, full, -1);
        if (rc != 0) {
            closedir(d);
            mr_library_free(lib);
            return -1;
        }
    }
    closedir(d);

    if (lib->count > 1)
        qsort(lib->items, (size_t)lib->count, sizeof *lib->items, entry_cmp);
    return lib->count;
}

int mr_library_scan(mr_library *lib, const char *dir, int max_depth)
{
    return mr_library_scan_ex(lib, dir, max_depth, NULL, NULL);
}

int mr_library_apply_probe(mr_library *lib, int idx, const mr_library_probe *p)
{
    if (!lib || !p || idx < 0 || idx >= lib->count) return 0;
    mr_library_entry *e = &lib->items[idx];
    e->pages = p->pages;
    e->empty = p->empty;
    e->has_images = (p->pages > 0) ? 1 : 0;
    e->probe_state = MR_LIB_READY;
    copy_str(e->cover, (int)sizeof e->cover, p->cover);
    mr_library_format_subtitle(e);
    return 1;
}

int mr_library_mark_error(mr_library *lib, int idx)
{
    if (!lib || idx < 0 || idx >= lib->count) return 0;
    mr_library_entry *e = &lib->items[idx];
    e->pages = -1;
    e->empty = 0;
    e->has_images = 0;
    e->probe_state = MR_LIB_FAILED;
    e->cover[0] = '\0';
    mr_library_format_subtitle(e);
    return 1;
}

int mr_library_row_at(const mr_library *lib, int idx, mr_library_row *out)
{
    static char trunc_sub[48];
    static int  trunc_ready;

    if (!lib || !out) return 0;
    if (idx == lib->count && lib->truncated) {
        if (!trunc_ready) {
            snprintf(trunc_sub, sizeof trunc_sub, "仅显示前 %d 项", MR_LIB_SCAN_MAX);
            trunc_ready = 1;
        }
        memset(out, 0, sizeof *out);
        out->title = "已截断";
        out->subtitle = trunc_sub;
        out->disabled = 1;
        out->index = -1;
        return 1;
    }
    if (idx < 0 || idx >= lib->count) return 0;

    const mr_library_entry *e = &lib->items[idx];
    memset(out, 0, sizeof *out);
    out->title = e->name;
    out->subtitle = e->subtitle;
    out->is_book = (e->has_images == 1);
    out->is_archive = e->is_archive;
    out->index = idx;
    return 1;
}

int mr_path_parent(const char *path, char *out, int outsz)
{
    if (!path || !out || outsz <= 0) return -1;
    size_t n = strlen(path);
    while (n > 1 && path[n - 1] == '/') n--;
    if (n <= 1) {
        if (outsz < 2) return -1;
        out[0] = '/';
        out[1] = '\0';
        return 0;
    }
    while (n > 0 && path[n - 1] != '/') n--;
    while (n > 1 && path[n - 1] == '/') n--;
    if (n >= (size_t)outsz) return -1;
    memcpy(out, path, n);
    out[n] = '\0';
    return 0;
}

/* ============================================================ */
/* 册间衔接（M7 / M11）                                          */
/* ============================================================ */
int mr_library_dir_has_images(const char *dir)
{
    if (!dir || !dir[0]) return 0;
    DIR *d = opendir(dir);
    if (!d) return 0;

    int found = 0;
    struct dirent *de;
    while ((de = readdir(d)) != NULL) {
        const char *name = de->d_name;
        if (name[0] == '.' || !mr_path_is_image(name)) continue;
        char full[MR_PATH_MAX];
        if (join_path(full, (int)sizeof full, dir, name) != 0) continue;
        struct stat st;
        if (lstat(full, &st) != 0 || !S_ISREG(st.st_mode)) continue;
        found = 1;
        break;
    }
    closedir(d);
    return found;
}

static int name_ptr_cmp(const void *pa, const void *pb)
{
    const char *a = *(const char *const *)pa;
    const char *b = *(const char *const *)pb;
    return mr_natural_cmp(a, b);
}

/* 兄弟册判据（M11）：目录=直接含图；普通文件=档案册且有图片页。
 * 两者同列，交给 name_ptr_cmp 自然序混排。 */
static int sibling_is_book(const char *full, const struct stat *st,
                           mr_lib_archive_fn probe, void *ud)
{
    if (S_ISDIR(st->st_mode)) return mr_library_dir_has_images(full);
    if (S_ISREG(st->st_mode)) {
        const char *slash = strrchr(full, '/');
        const char *name = slash ? slash + 1 : full;
        if (!mr_path_is_archive(name)) return 0;
        return archive_pages_at(probe, ud, full) > 0;
    }
    return 0;
}

int mr_book_adjacent_ex(const char *dir, int delta, char *out, int outsz,
                        mr_lib_archive_fn archive_pages, void *ud)
{
    if (!out || outsz <= 0) return -1;
    out[0] = '\0';
    if (!dir || !dir[0] || (delta != 1 && delta != -1)) return -1;

    char norm[MR_PATH_MAX];
    size_t dl = strlen(dir);
    while (dl > 1 && dir[dl - 1] == '/') dl--;
    if (dl >= sizeof norm) return -1;
    memcpy(norm, dir, dl);
    norm[dl] = '\0';

    const char *slash = strrchr(norm, '/');
    if (!slash || !slash[1]) return -1;
    const char *cur = slash + 1;

    char parent[MR_PATH_MAX];
    if (mr_path_parent(norm, parent, (int)sizeof parent) != 0) return -1;

    DIR *d = opendir(parent);
    if (!d) return 0;

    char **names = NULL;
    int n = 0, cap = 0;
    struct dirent *de;
    while ((de = readdir(d)) != NULL) {
        const char *name = de->d_name;
        if (strcmp(name, ".") == 0 || strcmp(name, "..") == 0) continue;
        if (ignored_dir_name(name)) continue;

        char full[MR_PATH_MAX];
        if (join_path(full, (int)sizeof full, parent, name) != 0) continue;
        struct stat st;
        if (lstat(full, &st) != 0) continue;
        if (S_ISLNK(st.st_mode)) continue;
        if (!sibling_is_book(full, &st, archive_pages, ud)) continue;

        if (n >= cap) {
            int nc = cap ? cap * 2 : 16;
            char **nn = (char **)realloc(names, (size_t)nc * sizeof *nn);
            if (!nn) break;
            names = nn;
            cap = nc;
        }
        size_t len = strlen(name);
        names[n] = (char *)malloc(len + 1);
        if (!names[n]) break;
        memcpy(names[n], name, len + 1);
        n++;
    }
    closedir(d);

    int rc = 0;
    if (n > 1) qsort(names, (size_t)n, sizeof *names, name_ptr_cmp);
    int idx = -1;
    for (int i = 0; i < n; i++)
        if (strcmp(names[i], cur) == 0) { idx = i; break; }
    int target = idx + delta;
    if (idx >= 0 && target >= 0 && target < n) {
        if (join_path(out, outsz, parent, names[target]) == 0) rc = 1;
    }
    for (int i = 0; i < n; i++) free(names[i]);
    free(names);
    return rc;
}

int mr_book_adjacent(const char *dir, int delta, char *out, int outsz)
{
    return mr_book_adjacent_ex(dir, delta, out, outsz, NULL, NULL);
}