nim-ffi/ffi/codegen/templates/cpp/cbor_helpers.hpp.tpl

// ── encode_cbor overloads (primitives + containers) ─────────────────────
// Per-struct encode_cbor / decode_cbor are emitted by cpp.nim next to each
// generated struct; these helpers cover the leaf types they defer into.
// Guarded so two nim-ffi headers can share a translation unit.
#ifndef NIM_FFI_CBOR_HELPERS_HPP_INCLUDED
#define NIM_FFI_CBOR_HELPERS_HPP_INCLUDED

inline CborError encode_cbor(CborEncoder& e, bool v) {
    return cbor_encode_boolean(&e, v);
}
inline CborError encode_cbor(CborEncoder& e, int64_t v) {
    return cbor_encode_int(&e, v);
}
inline CborError encode_cbor(CborEncoder& e, int32_t v) {
    return cbor_encode_int(&e, static_cast<int64_t>(v));
}
inline CborError encode_cbor(CborEncoder& e, uint64_t v) {
    return cbor_encode_uint(&e, v);
}
inline CborError encode_cbor(CborEncoder& e, double v) {
    return cbor_encode_double(&e, v);
}
inline CborError encode_cbor(CborEncoder& e, const std::string& v) {
    return cbor_encode_text_string(&e, v.data(), v.size());
}

template<typename T>
inline CborError encode_cbor(CborEncoder& e, const std::vector<T>& v) {
    CborEncoder arr;
    CborError err = cbor_encoder_create_array(&e, &arr, v.size());
    if (err) return err;
    for (const auto& item : v) {
        err = encode_cbor(arr, item);
        if (err) return err;
    }
    return cbor_encoder_close_container(&e, &arr);
}

template<typename T>
inline CborError encode_cbor(CborEncoder& e, const std::optional<T>& v) {
    if (!v) return cbor_encode_null(&e);
    return encode_cbor(e, *v);
}

// ── decode_cbor overloads ───────────────────────────────────────────────

inline CborError decode_cbor(CborValue& it, bool& out) {
    if (!cbor_value_is_boolean(&it)) return CborErrorImproperValue;
    CborError err = cbor_value_get_boolean(&it, &out);
    if (err) return err;
    return cbor_value_advance(&it);
}
inline CborError decode_cbor(CborValue& it, int64_t& out) {
    if (!cbor_value_is_integer(&it)) return CborErrorImproperValue;
    CborError err = cbor_value_get_int64_checked(&it, &out);
    if (err) return err;
    return cbor_value_advance(&it);
}
inline CborError decode_cbor(CborValue& it, int32_t& out) {
    int64_t tmp = 0;
    CborError err = decode_cbor(it, tmp);
    if (err) return err;
    out = static_cast<int32_t>(tmp);
    return CborNoError;
}
inline CborError decode_cbor(CborValue& it, uint64_t& out) {
    if (!cbor_value_is_unsigned_integer(&it)) return CborErrorImproperValue;
    CborError err = cbor_value_get_uint64(&it, &out);
    if (err) return err;
    return cbor_value_advance(&it);
}
inline CborError decode_cbor(CborValue& it, double& out) {
    if (cbor_value_is_double(&it)) {
        CborError err = cbor_value_get_double(&it, &out);
        if (err) return err;
        return cbor_value_advance(&it);
    }
    if (cbor_value_is_float(&it)) {
        float f = 0.0f;
        CborError err = cbor_value_get_float(&it, &f);
        if (err) return err;
        out = static_cast<double>(f);
        return cbor_value_advance(&it);
    }
    return CborErrorImproperValue;
}
inline CborError decode_cbor(CborValue& it, std::string& out) {
    if (!cbor_value_is_text_string(&it)) return CborErrorImproperValue;
    size_t len = 0;
    CborError err = cbor_value_get_string_length(&it, &len);
    if (err) return err;
    out.resize(len);
    err = cbor_value_copy_text_string(&it, out.empty() ? nullptr : &out[0], &len, nullptr);
    if (err) return err;
    return cbor_value_advance(&it);
}

template<typename T>
inline CborError decode_cbor(CborValue& it, std::vector<T>& out) {
    if (!cbor_value_is_array(&it)) return CborErrorImproperValue;
    size_t len = 0;
    CborError err = cbor_value_get_array_length(&it, &len);
    if (err) return err;
    out.clear();
    out.resize(len);
    CborValue inner;
    err = cbor_value_enter_container(&it, &inner);
    if (err) return err;
    for (size_t i = 0; i < len; ++i) {
        err = decode_cbor(inner, out[i]);
        if (err) return err;
    }
    return cbor_value_leave_container(&it, &inner);
}

template<typename T>
inline CborError decode_cbor(CborValue& it, std::optional<T>& out) {
    if (cbor_value_is_null(&it)) {
        out = std::nullopt;
        return cbor_value_advance(&it);
    }
    T tmp{};
    CborError err = decode_cbor(it, tmp);
    if (err) return err;
    out = std::move(tmp);
    return CborNoError;
}

// ── Public entry points ─────────────────────────────────────────────────

template<typename T>
inline Result<std::vector<std::uint8_t>> encodeCborFFI(const T& value) {
    // Start with a generous 4 KiB buffer; double on overflow until it fits.
    std::vector<std::uint8_t> buf(4096);
    while (true) {
        CborEncoder enc;
        cbor_encoder_init(&enc, buf.data(), buf.size(), 0);
        CborError err = encode_cbor(enc, value);
        if (err == CborNoError) {
            const size_t used = cbor_encoder_get_buffer_size(&enc, buf.data());
            buf.resize(used);
            return Result<std::vector<std::uint8_t>>::ok(std::move(buf));
        }
        if (err == CborErrorOutOfMemory) {
            const size_t extra = cbor_encoder_get_extra_bytes_needed(&enc);
            buf.resize(buf.size() + (extra > 0 ? extra : buf.size()));
            continue;
        }
        return Result<std::vector<std::uint8_t>>::err(
            std::string("FFI CBOR encode failed: ") + cbor_error_string(err));
    }
}

template<typename T>
inline Result<T> decodeCborFFI(const std::vector<std::uint8_t>& bytes) {
    CborParser parser;
    CborValue it;
    CborError err = cbor_parser_init(bytes.data(), bytes.size(), 0, &parser, &it);
    if (err != CborNoError) {
        return Result<T>::err(std::string("FFI CBOR parse init failed: ") +
                              cbor_error_string(err));
    }
    T out{};
    err = decode_cbor(it, out);
    if (err != CborNoError) {
        return Result<T>::err(std::string("FFI CBOR decode failed: ") +
                              cbor_error_string(err));
    }
    return Result<T>::ok(std::move(out));
}

#endif // NIM_FFI_CBOR_HELPERS_HPP_INCLUDED