/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

// -*- c++ -*-

#pragma once

#include <vector>

#include <faiss/IndexFlatCodes.h>
#include <faiss/IndexIVF.h>
#include <faiss/IndexPQ.h>

namespace faiss {

struct IndexIVFPQ;

/** Same as an IndexIVFPQ without the inverted lists: codes are stored
 * sequentially
 *
 * The class is mainly inteded to store encoded vectors that can be
 * accessed randomly, the search function is not implemented.
 */
struct Index2Layer : IndexFlatCodes {
    /// first level quantizer
    Level1Quantizer q1;

    /// second level quantizer is always a PQ
    ProductQuantizer pq;

    /// size of the code for the first level (ceil(log8(q1.nlist)))
    size_t code_size_1;

    /// size of the code for the second level
    size_t code_size_2;

    Index2Layer(
            Index* quantizer,
            size_t nlist,
            int M,
            int nbit = 8,
            MetricType metric = METRIC_L2);

    Index2Layer();
    ~Index2Layer();

    void train(idx_t n, const float* x) override;

    /// not implemented
    void search(
            idx_t n,
            const float* x,
            idx_t k,
            float* distances,
            idx_t* labels) const override;

    DistanceComputer* get_distance_computer() const override;

    /// transfer the flat codes to an IVFPQ index
    void transfer_to_IVFPQ(IndexIVFPQ& other) const;

    /* The standalone codec interface */
    void sa_encode(idx_t n, const float* x, uint8_t* bytes) const override;
    void sa_decode(idx_t n, const uint8_t* bytes, float* x) const override;
};

} // namespace faiss
