/**
 * 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++ -*-

#ifndef FAISS_AUTO_TUNE_H
#define FAISS_AUTO_TUNE_H

#include <stdint.h>
#include <vector>

#include <faiss/Index.h>
#include <faiss/IndexBinary.h>

namespace faiss {

/**
 * Evaluation criterion. Returns a performance measure in [0,1],
 * higher is better.
 */
struct AutoTuneCriterion {
    idx_t nq;     ///< nb of queries this criterion is evaluated on
    idx_t nnn;    ///< nb of NNs that the query should request
    idx_t gt_nnn; ///< nb of GT NNs required to evaluate criterion

    std::vector<float> gt_D; ///< Ground-truth distances (size nq * gt_nnn)
    std::vector<idx_t> gt_I; ///< Ground-truth indexes (size nq * gt_nnn)

    AutoTuneCriterion(idx_t nq, idx_t nnn);

    /** Intitializes the gt_D and gt_I vectors. Must be called before evaluating
     *
     * @param gt_D_in  size nq * gt_nnn
     * @param gt_I_in  size nq * gt_nnn
     */
    void set_groundtruth(
            int gt_nnn,
            const float* gt_D_in,
            const idx_t* gt_I_in);

    /** Evaluate the criterion.
     *
     * @param D  size nq * nnn
     * @param I  size nq * nnn
     * @return the criterion, between 0 and 1. Larger is better.
     */
    virtual double evaluate(const float* D, const idx_t* I) const = 0;

    virtual ~AutoTuneCriterion() {}
};

struct OneRecallAtRCriterion : AutoTuneCriterion {
    idx_t R;

    OneRecallAtRCriterion(idx_t nq, idx_t R);

    double evaluate(const float* D, const idx_t* I) const override;

    ~OneRecallAtRCriterion() override {}
};

struct IntersectionCriterion : AutoTuneCriterion {
    idx_t R;

    IntersectionCriterion(idx_t nq, idx_t R);

    double evaluate(const float* D, const idx_t* I) const override;

    ~IntersectionCriterion() override {}
};

/**
 * Maintains a list of experimental results. Each operating point is a
 * (perf, t, key) triplet, where higher perf and lower t is
 * better. The key field is an arbitrary identifier for the operating point.
 *
 * Includes primitives to extract the Pareto-optimal operating points in the
 * (perf, t) space.
 */

struct OperatingPoint {
    double perf;     ///< performance measure (output of a Criterion)
    double t;        ///< corresponding execution time (ms)
    std::string key; ///< key that identifies this op pt
    int64_t cno;     ///< integer identifer
};

struct OperatingPoints {
    /// all operating points
    std::vector<OperatingPoint> all_pts;

    /// optimal operating points, sorted by perf
    std::vector<OperatingPoint> optimal_pts;

    // begins with a single operating point: t=0, perf=0
    OperatingPoints();

    /// add operating points from other to this, with a prefix to the keys
    int merge_with(
            const OperatingPoints& other,
            const std::string& prefix = "");

    void clear();

    /// add a performance measure. Return whether it is an optimal point
    bool add(double perf, double t, const std::string& key, size_t cno = 0);

    /// get time required to obtain a given performance measure
    double t_for_perf(double perf) const;

    /// easy-to-read output
    void display(bool only_optimal = true) const;

    /// output to a format easy to digest by gnuplot
    void all_to_gnuplot(const char* fname) const;
    void optimal_to_gnuplot(const char* fname) const;
};

/// possible values of a parameter, sorted from least to most expensive/accurate
struct ParameterRange {
    std::string name;
    std::vector<double> values;
};

/** Uses a-priori knowledge on the Faiss indexes to extract tunable parameters.
 */
struct ParameterSpace {
    /// all tunable parameters
    std::vector<ParameterRange> parameter_ranges;

    // exploration parameters

    /// verbosity during exploration
    int verbose;

    /// nb of experiments during optimization (0 = try all combinations)
    int n_experiments;

    /// maximum number of queries to submit at a time.
    size_t batchsize;

    /// use multithreading over batches (useful to benchmark
    /// independent single-searches)
    bool thread_over_batches;

    /// run tests several times until they reach at least this
    /// duration (to avoid jittering in MT mode)
    double min_test_duration;

    ParameterSpace();

    /// nb of combinations, = product of values sizes
    size_t n_combinations() const;

    /// returns whether combinations c1 >= c2 in the tuple sense
    bool combination_ge(size_t c1, size_t c2) const;

    /// get string representation of the combination
    std::string combination_name(size_t cno) const;

    /// print a description on stdout
    void display() const;

    /// add a new parameter (or return it if it exists)
    ParameterRange& add_range(const std::string& name);

    /// initialize with reasonable parameters for the index
    virtual void initialize(const Index* index);

    /// set a combination of parameters on an index
    void set_index_parameters(Index* index, size_t cno) const;

    /// set a combination of parameters described by a string
    void set_index_parameters(Index* index, const char* param_string) const;

    /// set one of the parameters, returns whether setting was successful
    virtual void set_index_parameter(
            Index* index,
            const std::string& name,
            double val) const;

    /** find an upper bound on the performance and a lower bound on t
     * for configuration cno given another operating point op */
    void update_bounds(
            size_t cno,
            const OperatingPoint& op,
            double* upper_bound_perf,
            double* lower_bound_t) const;

    /** explore operating points
     * @param index   index to run on
     * @param xq      query vectors (size nq * index.d)
     * @param crit    selection criterion
     * @param ops     resulting operating points
     */
    void explore(
            Index* index,
            size_t nq,
            const float* xq,
            const AutoTuneCriterion& crit,
            OperatingPoints* ops) const;

    virtual ~ParameterSpace() {}
};

} // namespace faiss

#endif
