/* 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）                                      */
/* ------------------------------------------------------------
 * 同一套解析同时服务「文件」（目录册，流式读不占内存）和「内存缓冲」
 * （档案册：page_cache 解压后直接探测，不必再落盘读文件）。
 * ============================================================ */
typedef struct probe_src {
    const unsigned char *mem;    /* 非 NULL = 内存源 */
    size_t len, pos;
    FILE *f;                     /* mem == NULL 时用 */
} probe_src;

static int ps_read(probe_src *s, void *buf, size_t n)
{
    if (s->mem) {
        if (n > s->len - s->pos) return 0;
        memcpy(buf, s->mem + s->pos, n);
        s->pos += n;
        return 1;
    }
    return fread(buf, 1, n, s->f) == n;
}

static int ps_getc(probe_src *s)
{
    if (s->mem) {
        if (s->pos >= s->len) return EOF;
        return s->mem[s->pos++];
    }
    return fgetc(s->f);
}

static int ps_skip(probe_src *s, long n)
{
    if (n < 0) return 0;
    if (s->mem) {
        if ((size_t)n > s->len - s->pos) return 0;
        s->pos += (size_t)n;
        return 1;
    }
    return fseek(s->f, n, SEEK_CUR) == 0;
}

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(probe_src *s, mr_img_info *in)
{
    unsigned char hdr[24];
    if (!ps_read(s, hdr, 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;
    /* IHDR 的位深/颜色类型（紧跟在宽高后）。截断头（stb 也读不下去）按 RGB 8bit 记。 */
    int depth = 8, ctype = 2;
    unsigned char ex[2];
    if (ps_read(s, ex, sizeof ex)) { depth = ex[0]; ctype = ex[1]; }
    int ch;
    switch (ctype) {
        case 0: ch = 1; break;                    /* 灰度 */
        case 2: ch = 3; break;                    /* RGB */
        case 3: ch = 3; break;                    /* 调色板：stb 展开成 RGB(A) */
        case 4: ch = 2; break;                    /* 灰度+alpha */
        case 6: ch = 4; break;                    /* RGBA */
        default: ch = 3; break;
    }
    if (ww > 0x7FFFFFu || hh > 0x7FFFFFu) return 0;   /* 防 int 溢出 */
    int bpc = (depth == 16) ? 2 : 1;
    in->w = (int)ww;
    in->h = (int)hh;
    in->codec = MR_IMG_CODEC_PNG;
    in->channels = ch;
    in->progressive = 0;
    /* ch==4：stb 直接解到目标 RGBA 缓冲（就是最终输出），中间面记 0。
     * 其余：stb 先解出 ch 通道源缓冲，再 convert_format 复制一张 RGBA。 */
    in->planes = (ch == 4) ? 0 : (long long)ww * hh * ch * bpc;
    return 1;
}

static int probe_jpeg(probe_src *s, mr_img_info *in)
{
    unsigned char b[2];
    if (!ps_read(s, b, 2) || b[0] != 0xFF || b[1] != 0xD8) return 0;
    for (;;) {
        int c = ps_getc(s);
        if (c == EOF) return 0;
        if (c != 0xFF) continue;
        int m = ps_getc(s);
        while (m == 0xFF) m = ps_getc(s);         /* 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 (!ps_read(s, lb, 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) {
            /* 5 字节就够拿宽高（精度 + 高 + 宽）；分量数与采样因子能读就读。
             * 只带最小 SOF 的合成头（宿主测试夹具）也必须能取到尺寸——尺寸探测是
             * M4 起的硬契约，不能因为预算模型要更多信息就退化。 */
            unsigned char so[5];
            if (len < 7 || !ps_read(s, so, sizeof so)) 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;
            int prog = (m == 0xC2 || m == 0xC6 || m == 0xCA || m == 0xCE);
            in->w = ww;
            in->h = hh;
            in->codec = MR_IMG_CODEC_JPEG;
            in->progressive = prog;
            in->channels = 3;
            /* 未知采样因子时按 4:4:4 估（3·W·H，偏保守）：宁可多算峰值，不要低估。 */
            in->planes = (long long)ww * hh * 3;
            unsigned char nc = 0;
            if (ps_read(s, &nc, 1) && nc >= 1 && nc <= 4 && len >= 8 + 3 * nc) {
                int hv[4] = { 0, 0, 0, 0 };
                int hmax = 1, vmax = 1, ok = 1;
                for (int i = 0; i < nc && ok; i++) {
                    unsigned char comp[3];        /* id / 采样因子 hv / 量化表 */
                    if (!ps_read(s, comp, sizeof comp)) { ok = 0; break; }
                    hv[i] = comp[1];
                    int ch = hv[i] >> 4, cv = hv[i] & 15;
                    if (ch < 1 || ch > 4 || cv < 1 || cv > 4) { ok = 0; break; }
                    if (ch > hmax) hmax = ch;
                    if (cv > vmax) vmax = cv;
                }
                for (int i = 0; ok && i < nc; i++) {
                    if (hmax % (hv[i] >> 4) != 0 || vmax % (hv[i] & 15) != 0) ok = 0;
                }
                if (ok) {
                    /* 分量面字节 = 与 stb 完全同式的 w2×h2（MCU 对齐 + 采样因子）；
                     * 渐进式每个分量还多一张 w2×h2×2 的 short 系数面（M20 实测 +23.5MB 的来源）。 */
                    long long mcu_x = (ww + 8 * hmax - 1) / (8 * hmax);
                    long long mcu_y = (hh + 8 * vmax - 1) / (8 * vmax);
                    long long planes = 0;
                    for (int i = 0; i < nc; i++) {
                        long long w2 = mcu_x * (hv[i] >> 4) * 8;
                        long long h2 = mcu_y * (hv[i] & 15) * 8;
                        planes += w2 * h2;
                        if (prog) planes += w2 * h2 * 2;
                    }
                    in->channels = nc;
                    in->planes = planes;
                }
            }
            return 1;
        }
        if (!ps_skip(s, len - 2)) return 0;
    }
}

static int probe_bmp(probe_src *s, mr_img_info *in)
{
    unsigned char hdr[26];
    if (!ps_read(s, hdr, 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;
    unsigned char ex[4];                          /* biPlanes(2) / biBitCount(2) */
    int bpp = 24;
    if (ps_read(s, ex, sizeof ex)) bpp = (int)((unsigned)ex[2] | ((unsigned)ex[3] << 8));
    in->w = ww;
    in->h = hh;
    in->codec = MR_IMG_CODEC_BMP;
    in->channels = bpp >= 8 ? bpp / 8 : 4;        /* stb 一律解到 RGBA 目标 */
    in->progressive = 0;
    in->planes = 0;                               /* stb 直接写 RGBA 目标，不另开源缓冲 */
    return 1;
}

static int probe_any(probe_src *s, mr_img_info *in)
{
    memset(in, 0, sizeof *in);
    for (int pass = 0; pass < 3; pass++) {
        s->pos = 0;
        if (s->f) rewind(s->f);
        int ok = (pass == 0) ? probe_png(s, in)
               : (pass == 1) ? probe_jpeg(s, in)
                             : probe_bmp(s, in);
        if (ok) return 1;
        memset(in, 0, sizeof *in);
    }
    return 0;
}

int mr_probe_info_mem(const void *buf, size_t len, mr_img_info *info)
{
    if (info) memset(info, 0, sizeof *info);
    if (!buf || len < 8 || !info) return 0;
    probe_src s = { (const unsigned char *)buf, len, 0, NULL };
    if (!probe_any(&s, info) || info->w <= 0 || info->h <= 0) {
        memset(info, 0, sizeof *info);
        return 0;
    }
    return 1;
}

int mr_probe_info(const char *path, mr_img_info *info)
{
    if (info) memset(info, 0, sizeof *info);
    if (!path || !path[0] || !info) return 0;
    FILE *f = fopen(path, "rb");
    if (!f) return 0;
    probe_src s = { NULL, 0, 0, f };
    int ok = probe_any(&s, info);
    fclose(f);
    if (!ok || info->w <= 0 || info->h <= 0) {
        memset(info, 0, sizeof *info);
        return 0;
    }
    return 1;
}

int mr_probe_size_mem(const void *buf, size_t len, int *w, int *h)
{
    mr_img_info in;
    if (w) *w = 0;
    if (h) *h = 0;
    if (!mr_probe_info_mem(buf, len, &in)) return 0;
    if (w) *w = in.w;
    if (h) *h = in.h;
    return 1;
}

int mr_probe_size(const char *path, int *w, int *h)
{
    mr_img_info in;
    if (w) *w = 0;
    if (h) *h = 0;
    if (!mr_probe_info(path, &in)) return 0;
    if (w) *w = in.w;
    if (h) *h = in.h;
    return 1;
}

/* ============================================================ */
/* 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;
}