/* meow_sig.h — .mpk 签名块格式（MPK_SIGNATURE_DESIGN §3.1）+ 被签消息构造（§3.1）。
 *
 * .mpk = [ tar.gz bytes ......................... ] [ meow_sig_block（定长 LE）]
 *
 * meow_sig_block（packed，总长 MEOW_SIG_BLOCK_LEN）：
 *   char     magic[8];          "MEOWSIG1"
 *   uint8_t  alg;               1 = ed25519
 *   uint8_t  flags;             0
 *   uint16_t pad;               (0)
 *   char     package[64];       权威包名（== app.json.package == 文件名茎）
 *   uint8_t  payload_sha256[32];sha256(整个 .mpk 去掉尾部 footer 的其余字节)
 *   uint8_t  sig[64];           Ed25519(pk, msg)
 *   uint32_t msg_len;           实际签名的 msg 字节数（LE）
 *   uint32_t block_len;         本块总长（LE；= MEOW_SIG_BLOCK_LEN）
 *
 * 被签消息 msg = "MEOWSIG1" || alg(1B) || package_len(4B,LE) || package || payload_sha256(32B)。
 * 本文件由 meow_verify 与 meow_sign 共用（meow_sign 用相对路径 include）。 */
#ifndef MEOW_SIG_H
#define MEOW_SIG_H

#include <stdint.h>
#include <string.h>

#define MEOW_SIG_MAGIC        "MEOWSIG1"
#define MEOW_SIG_MAGIC_LEN    8
#define MEOW_SIG_ALG_ED25519  1
#define MEOW_SIG_PKG_MAX      64
#define MEOW_SIG_SHA256_LEN   32
#define MEOW_SIG_SIG_LEN      64

typedef struct __attribute__((packed)) {
    uint8_t  magic[MEOW_SIG_MAGIC_LEN];
    uint8_t  alg;
    uint8_t  flags;
    uint16_t pad;
    char     package[MEOW_SIG_PKG_MAX];
    uint8_t  payload_sha256[MEOW_SIG_SHA256_LEN];
    uint8_t  sig[MEOW_SIG_SIG_LEN];
    uint32_t msg_len;
    uint32_t block_len;
} meow_sig_block_t;

#define MEOW_SIG_BLOCK_LEN  (sizeof(meow_sig_block_t))   /* 定长 180 */

/* 按字节读取 LE 的 uint32（避免 packed 解引用对齐告警） */
static inline uint32_t meow_le32(const uint8_t *p)
{
    return (uint32_t)p[0] | ((uint32_t)p[1] << 8) |
           ((uint32_t)p[2] << 16) | ((uint32_t)p[3] << 24);
}
static inline void meow_le32_put(uint8_t *p, uint32_t v)
{
    p[0] = (uint8_t)(v & 0xff);
    p[1] = (uint8_t)((v >> 8) & 0xff);
    p[2] = (uint8_t)((v >> 16) & 0xff);
    p[3] = (uint8_t)((v >> 24) & 0xff);
}

#define MEOW_SIG_MSG_MAX (MEOW_SIG_MAGIC_LEN + 1 + 4 + MEOW_SIG_PKG_MAX + MEOW_SIG_SHA256_LEN)

/* 按设计构造被签消息 msg = "MEOWSIG1" || alg(1B) || package_len(4B,LE) || package || payload_sha256(32B)。
 * 返回 msg 字节数。签名端与验签端必须用同一构造（meow_sign / meow_verify 共用）。 */
static inline unsigned meow_sig_msg_build(char *out, const char *package,
                                          const uint8_t payload_sha256[MEOW_SIG_SHA256_LEN])
{
    unsigned pkg_len = (unsigned)strlen(package);
    if (pkg_len > MEOW_SIG_PKG_MAX) pkg_len = MEOW_SIG_PKG_MAX;
    unsigned o = 0;
    memcpy(out + o, MEOW_SIG_MAGIC, MEOW_SIG_MAGIC_LEN); o += MEOW_SIG_MAGIC_LEN;
    out[o++] = MEOW_SIG_ALG_ED25519;
    meow_le32_put((uint8_t *)out + o, (uint32_t)pkg_len); o += 4;
    memcpy(out + o, package, pkg_len); o += pkg_len;
    memcpy(out + o, payload_sha256, MEOW_SIG_SHA256_LEN); o += MEOW_SIG_SHA256_LEN;
    return o;
}

#endif /* MEOW_SIG_H */