// M0 T1 —— header + section table + fixup。见 docs/reference/steps/M0-gr2-reader.md
// 规格：MobileSource/Cross Platform/Granny-3D-SDK-main/source/granny_file_format.h + .cpp
//
// 本次实现范围：magic 识别 + grn_file_header + section 表解析（--sections 用）。
// section 解压（Oodle0/1）是 T2；类型树 / FileInfo 是 T3/T4 —— 仍是 stub。
#include "internal.h"
#include <cstdio>
#include <cstdlib>
#include <cstring>

namespace gr2 {
namespace {

// 小端读取 + 边界检查
inline bool rd32(const uint8_t* p, size_t len, size_t off, uint32_t& out) {
    if (off + 4 > len) return false;
    out = uint32_t(p[off]) | (uint32_t(p[off + 1]) << 8) |
          (uint32_t(p[off + 2]) << 16) | (uint32_t(p[off + 3]) << 24);
    return true;
}

// granny_file_format.cpp 里的 5 个已知 magic（LE u32 序列）
struct KnownMagic { uint32_t v[4]; Magic tag; const char* name; };
constexpr KnownMagic kMagics[] = {
    // GRNFileMV_Old —— Metin2 的 gr2（v6 era）用这个
    {{0xCAB067B8, 0x0FB16DF8, 0x7E8C7284, 0x1E00195E}, Magic::Bit32_LE, "Old(32LE)"},
    {{0xC06CDE29, 0x2B53A4BA, 0xA5B7F525, 0xEEE266F6}, Magic::Bit32_LE, "32Bit_LittleEndian"},
    {{0xB595110E, 0x4BB5A56A, 0x502828EB, 0x04B37825}, Magic::Bit32_BE, "32Bit_BigEndian"},
    {{0x5E499BE5, 0x141F636F, 0xA9EB131E, 0xC4EDBE90}, Magic::Bit64_LE, "64Bit_LittleEndian"},
    {{0xE3D49531, 0x624FDC20, 0x3AD036CC, 0x89FF82B1}, Magic::Bit64_BE, "64Bit_BigEndian"},
};

constexpr size_t kMagicStructSize = 32;   // grn_file_magic_value：4*u32 magic + HeaderSize + HeaderFormat + 2*u32 reserved
constexpr size_t kSectionSize     = 44;   // grn_section：11 * u32

} // namespace

const char* magic_name(Magic m) {
    switch (m) {
    case Magic::Bit32_LE: return "32-bit LE";
    case Magic::Bit32_BE: return "32-bit BE";
    case Magic::Bit64_LE: return "64-bit LE";
    case Magic::Bit64_BE: return "64-bit BE";
    default:              return "unknown";
    }
}
const char* compression_name(uint32_t f) {
    switch (f) {
    case 0: return "none";
    case 1: return "Oodle0";
    case 2: return "Oodle1";
    default: return "?";
    }
}

std::optional<File> File::load(const uint8_t* bytes, size_t len, LoadError* err) {
	if (err) *err = {};
    auto fail = [&](const char* stage, const char* msg) {
        if (err) *err = {stage, msg};
        return std::nullopt;
    };

    if (!bytes || len < kMagicStructSize + 32)
        return fail("header", "file too small");

    // ── magic ────────────────────────────────────────────────────────────
    uint32_t m[4];
    for (int i = 0; i < 4; ++i) rd32(bytes, len, size_t(i) * 4, m[i]);
    Magic magic = Magic::Unknown;
    for (const auto& k : kMagics) {
        if (m[0] == k.v[0] && m[1] == k.v[1] && m[2] == k.v[2] && m[3] == k.v[3]) {
            magic = k.tag;
            break;
        }
    }
    if (magic == Magic::Unknown)
        return fail("header", "not a Granny file (unknown magic)");
    if (magic != Magic::Bit32_LE)
        return fail("header", "only 32-bit little-endian supported (M0 range)");

    uint32_t header_size = 0, header_format = 0;
    rd32(bytes, len, 16, header_size);
    rd32(bytes, len, 20, header_format);   // 注意：这不是 section 压缩，section 压缩看每段 Format

    // ── grn_file_header（在 magic 结构之后）─────────────────────────────
    const size_t H = kMagicStructSize;   // header 起点
    // grn_file_header: Version(0) TotalSize(4) CRC(8) SectionArrayOffset(12)
    //   SectionArrayCount(16) RootObjectTypeDefinition{Section(20) Offset(24)}
    //   RootObject{Section(28) Offset(32)} TypeTag(36) ...
    uint32_t version = 0, total_size = 0, sec_off = 0, sec_count = 0;
    uint32_t rt_sec = 0, rt_off = 0, ro_sec = 0, ro_off = 0;
    if (!rd32(bytes, len, H + 0,  version)    ||
        !rd32(bytes, len, H + 4,  total_size) ||
        !rd32(bytes, len, H + 12, sec_off)    ||
        !rd32(bytes, len, H + 16, sec_count)  ||
        !rd32(bytes, len, H + 20, rt_sec)     ||
        !rd32(bytes, len, H + 24, rt_off)     ||
        !rd32(bytes, len, H + 28, ro_sec)     ||
        !rd32(bytes, len, H + 32, ro_off))
        return fail("header", "truncated grn_file_header");

    // ── section 表 ──────────────────────────────────────────────────────
    // SectionArrayOffset 相对 grn_file_header 起点（H）
    const size_t sec_base = H + sec_off;
    if (sec_count > 64)
        return fail("section", "implausible section count");
    if (sec_base + size_t(sec_count) * kSectionSize > len)
        return fail("section", "section array out of range");

    // ── AC 自检（不致命，仅 GR2_DEBUG 打日志）──────────────────────────
    if (std::getenv("GR2_DEBUG")) {
        if (version != 6 && version != 7)
            std::fprintf(stderr, "gr2: warn: format_version=%u (期望 6/7)\n", version);
        if (total_size != len)
            std::fprintf(stderr, "gr2: warn: total_size=%u != file size %zu\n", total_size, len);
    }

    File out;
    out.magic_      = magic;
    out.version_    = version;
    out.total_size_ = total_size;
    out.impl_       = std::make_shared<Impl>();
    out.impl_->sections.resize(sec_count);
    out.impl_->raw.resize(sec_count);
    out.sections_.reserve(sec_count);

    // ── 逐 section：读头 + T2 展开 ─────────────────────────────────────
    for (uint32_t i = 0; i < sec_count; ++i) {
        const size_t s = sec_base + size_t(i) * kSectionSize;
        uint32_t f[11];
        for (int j = 0; j < 11; ++j) rd32(bytes, len, s + size_t(j) * 4, f[j]);
        // f: Format DataOffset DataSize ExpandedDataSize InternalAlignment
        //    First16Bit First8Bit PtrFixupOff PtrFixupCount MixedFixupOff MixedFixupCount
        detail::GrnSection gs{};
        gs.compression        = f[0];
        gs.data_offset        = f[1];
        gs.data_size          = f[2];
        gs.expanded_data_size = f[3];
        gs.internal_alignment = f[4];
        gs.first16bit         = f[5];
        gs.first8bit          = f[6];
        gs.pointer_fixup_off  = f[7];
        gs.pointer_fixup_count= f[8];
        gs.mixed_fixup_off    = f[9];
        gs.mixed_fixup_count  = f[10];

        if (size_t(gs.data_offset) > len || size_t(gs.data_size) > len - size_t(gs.data_offset))
            return fail("section", "section data out of range");

        out.impl_->raw[i] = gs;
        LoadError sec_err;
        if (!out.impl_->decompress_section(gs, bytes + gs.data_offset,
                                           out.impl_->sections[i], &sec_err)) {
            if (err) {
                *err = sec_err;
                err->message += " (section " + std::to_string(i) + ")";
            }
            return std::nullopt;
        }
        out.sections_.push_back(out.impl_->sections[i].info);
    }

    // ── T1：fixup 索引（需要展开后的 section 数据 + 原始 section 头）──────
    out.impl_->build_fixups(bytes, len);
    out.impl_->root_type = { int32_t(rt_sec), rt_off };
    out.impl_->root_obj  = { int32_t(ro_sec), ro_off };

    // ── T3/T4：类型树 + FileInfo 汇总。失败必须传播；返回一个看似成功但
    // FileInfo 为空的对象会让上层把损坏文件误判成合法的空模型。
    LoadError fi_err;
    if (!out.impl_->build_fileinfo(out.info_, &fi_err)) {
        if (err) *err = fi_err;
        return std::nullopt;
    }

    (void)header_size; (void)header_format;
    return out;
}

std::optional<File> File::load_path(const std::string& path, LoadError* err) {
    FILE* f = std::fopen(path.c_str(), "rb");
    if (!f) { if (err) *err = {"open", "cannot open " + path}; return std::nullopt; }
    std::fseek(f, 0, SEEK_END);
    long n = std::ftell(f);
    std::fseek(f, 0, SEEK_SET);
    std::vector<uint8_t> buf(n > 0 ? size_t(n) : 0);
    if (!buf.empty()) {
        size_t rd = std::fread(buf.data(), 1, buf.size(), f);
        if (rd != buf.size()) { std::fclose(f); if (err) *err = {"open", "short read"}; return std::nullopt; }
    }
    std::fclose(f);
    return load(buf.data(), buf.size(), err);
}

double File::bind_pose_self_check(int skeleton) const {
    return impl_ ? impl_->skeleton_self_check(skeleton) : 1e9;
}

std::span<const uint8_t> File::section_bytes(size_t i) const {
    if (!impl_ || i >= impl_->sections.size()) return {};
    const auto& d = impl_->sections[i].data;
    return {d.data(), d.size()};
}

} // namespace gr2