/* logic/reader/page_source.c — 页源契约实现（纯 C）：目录册 + 图片头探测。
 *
 * 契约与两种消费方式的说明见 page_source.h。本文件不含 SDK 依赖：解码/释放由
 * UI 层注回回调，因此可在宿主测试里用假回调覆盖「空册/越界/重复 open-close/首末页」。
 */
#include "logic/reader/page_source.h"

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

/* ============================================================ */
/* 契约包装                                                      */
/* ============================================================ */
int mr_book_valid(const mr_book *b)
{
    return b && b->ops && b->ops->count && b->ops->open;
}

int mr_book_count(const mr_book *b)
{
    if (!mr_book_valid(b)) return 0;
    int n = b->ops->count(b->ctx);
    return n > 0 ? n : 0;
}

int mr_book_meta(const mr_book *b, int index, int *w, int *h)
{
    if (w) *w = 0;
    if (h) *h = 0;
    if (!mr_book_valid(b) || !b->ops->meta) return 0;
    if (index < 0 || index >= mr_book_count(b)) return 0;
    return b->ops->meta(b->ctx, index, w, h) ? 1 : 0;
}

meow_img *mr_book_open(mr_book *b, int index)
{
    if (!mr_book_valid(b)) return NULL;
    if (index < 0 || index >= mr_book_count(b)) return NULL;   /* 越界：契约边界 */
    return b->ops->open(b->ctx, index);
}

void mr_book_close(mr_book *b, meow_img *img)
{
    if (!img) return;
    if (!mr_book_valid(b) || !b->ops->close) return;
    b->ops->close(b->ctx, img);
}

void mr_book_destroy(mr_book *b)
{
    if (!b) return;
    if (b->ops && b->ops->destroy && b->ctx) b->ops->destroy(b->ctx);
    b->ops = NULL;
    b->ctx = NULL;
}

/* ============================================================ */
/* 目录册                                                        */
/* ============================================================ */
static int name_cmp_qsort(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);
}

void mr_dir_book_path(const mr_dir_book *db, int index, char *out, int outsz)
{
    if (!out || outsz <= 0) return;
    out[0] = '\0';
    if (!db || index < 0 || index >= db->count || !db->names[index]) return;
    size_t dl = strlen(db->dir);
    if (dl > 0 && db->dir[dl - 1] == '/')
        snprintf(out, (size_t)outsz, "%s%s", db->dir, db->names[index]);
    else
        snprintf(out, (size_t)outsz, "%s/%s", db->dir, db->names[index]);
}

void mr_dir_book_free(mr_dir_book *db)
{
    if (!db) return;
    for (int i = 0; i < db->count; i++) free(db->names[i]);
    free(db->names);
    db->names = NULL;
    db->count = 0;
}

int mr_dir_book_init(mr_dir_book *db, const char *dir, int maxdim,
                     mr_book_load_fn load, mr_book_unload_fn unload, void *ud)
{
    if (!db) return -1;
    memset(db, 0, sizeof *db);
    if (!dir || !dir[0] || !load || !unload) return -1;
    if (maxdim <= 0) maxdim = 720;
    if (strlen(dir) >= sizeof db->dir) return -1;

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

    snprintf(db->dir, sizeof db->dir, "%s", dir);
    db->maxdim = maxdim;
    db->load = load;
    db->unload = unload;
    db->ud = ud;

    int 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 (name[0] == '.') continue;                 /* 隐藏文件不参与成册 */
        if (!mr_path_is_image(name)) continue;

        char full[MR_PATH_MAX];
        size_t dl = strlen(db->dir);
        int n = (dl > 0 && db->dir[dl - 1] == '/')
                    ? snprintf(full, sizeof full, "%s%s", db->dir, name)
                    : snprintf(full, sizeof full, "%s/%s", db->dir, name);
        if (n <= 0 || n >= (int)sizeof full) continue;
        struct stat st;
        if (lstat(full, &st) != 0 || !S_ISREG(st.st_mode)) continue;   /* 跳过符号链接/目录 */

        if (db->count >= MR_BOOK_MAX_PAGES) break;
        if (db->count >= cap) {
            int nc = cap ? cap * 2 : 32;
            char **nn = (char **)realloc(db->names, (size_t)nc * sizeof *nn);
            if (!nn) { mr_dir_book_free(db); closedir(d); return -1; }
            db->names = nn;
            cap = nc;
        }
        size_t len = strlen(name);
        db->names[db->count] = (char *)malloc(len + 1);
        if (!db->names[db->count]) { mr_dir_book_free(db); closedir(d); return -1; }
        memcpy(db->names[db->count], name, len + 1);
        db->count++;
    }
    closedir(d);

    if (db->count > 1)
        qsort(db->names, (size_t)db->count, sizeof *db->names, name_cmp_qsort);
    return db->count;
}

/* ============================================================ */
/* 图片头探测（不解码像素）                                      */
/* ============================================================ */
static unsigned probe_be32(const unsigned char *p)
{
    return ((unsigned)p[0] << 24) | ((unsigned)p[1] << 16) | ((unsigned)p[2] << 8) | p[3];
}

static int probe_png(FILE *f, int *w, int *h)
{
    unsigned char hdr[24];
    if (fread(hdr, 1, sizeof hdr, f) != sizeof hdr) return 0;
    static const unsigned char sig[8] = { 0x89, 'P', 'N', 'G', 0x0D, 0x0A, 0x1A, 0x0A };
    if (memcmp(hdr, sig, 8) != 0 || memcmp(hdr + 12, "IHDR", 4) != 0) return 0;
    unsigned ww = probe_be32(hdr + 16), hh = probe_be32(hdr + 20);
    if (ww == 0 || hh == 0) return 0;
    *w = (int)ww;
    *h = (int)hh;
    return 1;
}

static int probe_jpeg(FILE *f, int *w, int *h)
{
    unsigned char b[2];
    if (fread(b, 1, 2, f) != 2 || b[0] != 0xFF || b[1] != 0xD8) return 0;
    for (;;) {
        int c = fgetc(f);
        if (c == EOF) return 0;
        if (c != 0xFF) continue;
        int m = fgetc(f);
        while (m == 0xFF) m = fgetc(f);           /* 填充字节 */
        if (m == EOF) return 0;
        if (m == 0xD8 || m == 0x01 || (m >= 0xD0 && m <= 0xD7)) continue;   /* 无长度段 */
        if (m == 0xD9 || m == 0xDA) return 0;     /* EOI/SOS 前没等到 SOF */
        unsigned char lb[2];
        if (fread(lb, 1, 2, f) != 2) return 0;
        int len = ((int)lb[0] << 8) | lb[1];
        if (len < 2) return 0;
        int is_sof = (m >= 0xC0 && m <= 0xCF) && m != 0xC4 && m != 0xC8 && m != 0xCC;
        if (is_sof) {
            unsigned char so[5];
            if (len < 7 || fread(so, 1, 5, f) != 5) return 0;
            int hh = ((int)so[1] << 8) | so[2];
            int ww = ((int)so[3] << 8) | so[4];
            if (ww <= 0 || hh <= 0) return 0;
            *w = ww;
            *h = hh;
            return 1;
        }
        if (fseek(f, len - 2, SEEK_CUR) != 0) return 0;
    }
}

static int probe_bmp(FILE *f, int *w, int *h)
{
    unsigned char hdr[26];
    if (fread(hdr, 1, sizeof hdr, f) != sizeof hdr) return 0;
    if (hdr[0] != 'B' || hdr[1] != 'M') return 0;
    int ww = (int)((unsigned)hdr[18] | ((unsigned)hdr[19] << 8) |
                   ((unsigned)hdr[20] << 16) | ((unsigned)hdr[21] << 24));
    int hh = (int)((unsigned)hdr[22] | ((unsigned)hdr[23] << 8) |
                   ((unsigned)hdr[24] << 16) | ((unsigned)hdr[25] << 24));
    if (hh < 0) hh = -hh;                         /* 自底向上 BMP */
    if (ww <= 0 || hh <= 0) return 0;
    *w = ww;
    *h = hh;
    return 1;
}

int mr_probe_size(const char *path, int *w, int *h)
{
    if (w) *w = 0;
    if (h) *h = 0;
    if (!path || !path[0] || !w || !h) return 0;
    FILE *f = fopen(path, "rb");
    if (!f) return 0;
    int ok = probe_png(f, w, h);
    if (!ok) { rewind(f); ok = probe_jpeg(f, w, h); }
    if (!ok) { rewind(f); ok = probe_bmp(f, w, h); }
    fclose(f);
    if (ok && (*w <= 0 || *h <= 0)) { *w = *h = 0; return 0; }
    return ok;
}

/* ============================================================ */
/* mr_book_ops 适配器（目录册）                                  */
/* ============================================================ */
static int dir_ops_count(void *ctx)
{
    mr_dir_book *db = (mr_dir_book *)ctx;
    return db ? db->count : 0;
}

static int dir_ops_meta(void *ctx, int index, int *w, int *h)
{
    mr_dir_book *db = (mr_dir_book *)ctx;
    if (w) *w = 0;
    if (h) *h = 0;
    if (!db || index < 0 || index >= db->count) return 0;
    char path[MR_PATH_MAX];
    mr_dir_book_path(db, index, path, (int)sizeof path);
    return mr_probe_size(path, w, h);
}

static meow_img *dir_ops_open(void *ctx, int index)
{
    mr_dir_book *db = (mr_dir_book *)ctx;
    if (!db || index < 0 || index >= db->count) return NULL;
    char path[MR_PATH_MAX];
    mr_dir_book_path(db, index, path, (int)sizeof path);
    if (!path[0]) return NULL;
    return db->load(path, db->ud, db->maxdim);
}

static void dir_ops_close(void *ctx, meow_img *img)
{
    mr_dir_book *db = (mr_dir_book *)ctx;
    if (db && db->unload && img) db->unload(img);
}

static void dir_ops_destroy(void *ctx)
{
    mr_dir_book *db = (mr_dir_book *)ctx;
    if (db) mr_dir_book_free(db);
}

static const mr_book_ops g_dir_ops = {
    dir_ops_count, dir_ops_meta, dir_ops_open, dir_ops_close, dir_ops_destroy,
};

void mr_dir_book_bind(mr_book *b, mr_dir_book *db)
{
    if (!b) return;
    b->ops = db ? &g_dir_ops : NULL;
    b->ctx = db;
}