/*

 * 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.

 */

#pragma once

#include <faiss/impl/io.h>

#include <faiss/invlists/InvertedLists.h>

#include <string>

namespace faiss {

/** Callbacks to handle other types of InvertedList objects.

 *

 * The callbacks should be registered with add_callback before calling

 * read_index or read_InvertedLists. The callbacks for

 * OnDiskInvertedLists are registrered by default. The invlist type is

 * identified by:

 *

 * - the key (a fourcc) at read time

 * - the class name (as given by typeid.name) at write time

 */

struct InvertedListsIOHook {

    const std::string key;       ///< string version of the fourcc

    const std::string classname; ///< typeid.name

    InvertedListsIOHook(const std::string& key, const std::string& classname);

    /// write the index to the IOWriter (including the fourcc)

    virtual void write(const InvertedLists* ils, IOWriter* f) const = 0;

    /// called when the fourcc matches this class's fourcc

    virtual InvertedLists* read(IOReader* f, int io_flags) const = 0;

    /** read from a ArrayInvertedLists into this invertedlist type.

     * For this to work, the callback has to be enabled and the io_flag has to

     * be set to IO_FLAG_SKIP_IVF_DATA | (16 upper bits of the fourcc)

     *

     * (default implementation fails)

     */

    virtual InvertedLists* read_ArrayInvertedLists(

            IOReader* f,

            int io_flags,

            size_t nlist,

            size_t code_size,

            const std::vector<size_t>& sizes) const;

    virtual ~InvertedListsIOHook() {}

    /**************************** Manage the set of callbacks ******/

    // transfers ownership

    static void add_callback(InvertedListsIOHook*);

    static void print_callbacks();

    static InvertedListsIOHook* lookup(int h);

    static InvertedListsIOHook* lookup_classname(const std::string& classname);

};

} // namespace faiss