/*

 * Copyright (c) Meta Platforms, Inc. and affiliates.

 *

 * This source code is licensed under the MIT license found in the

 * LICENSE file in the root directory of this source tree.

 */

#include <faiss/impl/random_access_reader.h>

#include <cerrno>

#include <cstring>

#include <faiss/impl/FaissAssert.h>

#ifndef _WIN32

#include <fcntl.h>

#include <unistd.h>

#endif

namespace faiss {

/*******************************************************

 * ReadRef — default borrow() implementation

 *******************************************************/

namespace {

/// ReadRef that owns a heap-allocated buffer.

struct OwnedReadRef : ReadRef {

    std::unique_ptr<uint8_t[]> buf_;

    OwnedReadRef(std::unique_ptr<uint8_t[]> buf, size_t len)

            : buf_(std::move(buf)) {

        data_ = buf_.get();

        size_ = len;

    }

};

} // namespace

std::unique_ptr<ReadRef> RandomAccessReader::borrow(

        size_t offset,

        size_t nbytes) const {

    auto buf = std::make_unique<uint8_t[]>(nbytes);

    read_at(offset, buf.get(), nbytes);

    return std::make_unique<OwnedReadRef>(std::move(buf), nbytes);

}

/*******************************************************

 * FileRandomAccessReader — default POSIX pread backend

 *******************************************************/

FileRandomAccessReader::FileRandomAccessReader(const std::string& filename) {

#ifndef _WIN32

    fd_ = ::open(filename.c_str(), O_RDONLY);

    FAISS_THROW_IF_NOT_FMT(

            fd_ >= 0,

            "FileRandomAccessReader: cannot open %s: %s",

            filename.c_str(),

            strerror(errno));

#else

    FAISS_THROW_MSG("FileRandomAccessReader is not supported on Windows");

#endif

}

FileRandomAccessReader::~FileRandomAccessReader() {

#ifndef _WIN32

    if (fd_ >= 0) {

        ::close(fd_);

    }

#endif

}

void FileRandomAccessReader::read_at(

        size_t offset,

        void* ptr,

        size_t nbytes) const {

#ifndef _WIN32

    size_t done = 0;

    auto* out = static_cast<uint8_t*>(ptr);

    while (done < nbytes) {

        ssize_t nr = ::pread(fd_, out + done, nbytes - done, offset + done);

        FAISS_THROW_IF_NOT_MSG(

                nr >= 0, "pread failed in FileRandomAccessReader");

        FAISS_THROW_IF_NOT_MSG(

                nr > 0, "unexpected EOF in FileRandomAccessReader");

        done += static_cast<size_t>(nr);

    }

#else

    (void)offset;

    (void)ptr;

    (void)nbytes;

    FAISS_THROW_MSG("FileRandomAccessReader is not supported on Windows");

#endif

}

} // namespace faiss