/*
Copyright (c) by respective owners including Yahoo!, Microsoft, and
individual contributors. All rights reserved.  Released under a BSD
license as described in the file LICENSE.
*/
#pragma once

#include <stdint.h>
#include "constant.h"
#include "feature_group.h"
#include <vector>
#include <string>

namespace INTERACTIONS
{
/*
 * By default include interactions of feature with itself.
 * This approach produces slightly more interactions but it's safier
 * for some cases, as discussed in issues/698
 * Previous behaviour was: include interactions of feature with itself only if its value != value^2.
 *
 */
constexpr bool feature_self_interactions = true;
// must return logical expression
/*old: ft_value != 1.0 && feature_self_interactions_for_value_other_than_1*/
#define PROCESS_SELF_INTERACTIONS(ft_value) feature_self_interactions

// 3 template functions to pass T() proper argument (feature idx in regressor, or its coefficient)

template <class R, void (*T)(R&, const float, float&), class W>
inline void call_T(R& dat, W& weights, const float ft_value, const uint64_t ft_idx)
{
  T(dat, ft_value, weights[ft_idx]);
}

template <class R, void (*T)(R&, const float, const float&), class W>
inline void call_T(R& dat, const W& weights, const float ft_value, const uint64_t ft_idx)
{
  T(dat, ft_value, weights[ft_idx]);
}

template <class R, void (*T)(R&, float, uint64_t), class W>
inline void call_T(R& dat, W& /*weights*/, const float ft_value, const uint64_t ft_idx)
{
  T(dat, ft_value, ft_idx);
}

// state data used in non-recursive feature generation algorithm
// contains N feature_gen_data records (where N is length of interaction)
struct feature_gen_data
{
  size_t loop_idx;  // current feature id in namespace
  uint64_t hash;    // hash of feature interactions of previous namespaces in the list
  float x;          // value of feature interactions of previous namespaces in the list
  size_t loop_end;  // last feature id. May be less than number of features if namespace involved in interaction more
                    // than once calculated at preprocessing together with same_ns
  size_t self_interaction;  // namespace interacting with itself
  features* ft_arr;
  //    feature_gen_data(): loop_idx(0), x(1.), loop_end(0), self_interaction(false) {}
};

// The inline function below may be adjusted to change the way
// synthetic (interaction) features' values are calculated, e.g.,
// fabs(value1-value2) or even value1>value2?1.0:-1.0
// Beware - its result must be non-zero.
inline float INTERACTION_VALUE(float value1, float value2) { return value1 * value2; }

// uncomment line below to disable usage of inner 'for' loops for pair and triple interactions
// end switch to usage of non-recursive feature generation algorithm for interactions of any length

// #define GEN_INTER_LOOP

template <class R, class S, void (*T)(R&, float, S), bool audit, void (*audit_func)(R&, const audit_strings*), class W>
inline void inner_kernel(R& dat, features::iterator_all& begin, features::iterator_all& end, const uint64_t offset,
    W& weights, feature_value ft_value, feature_index halfhash)
{
  if (audit)
  {
    for (; begin != end; ++begin)
    {
      audit_func(dat, begin.audit().get());
      call_T<R, T>(dat, weights, INTERACTION_VALUE(ft_value, begin.value()), (begin.index() ^ halfhash) + offset);
      audit_func(dat, nullptr);
    }
  }
  else
  {
    for (; begin != end; ++begin)
      call_T<R, T>(dat, weights, INTERACTION_VALUE(ft_value, begin.value()), (begin.index() ^ halfhash) + offset);
  }
}

// this templated function generates new features for given example and set of interactions
// and passes each of them to given function T()
// it must be in header file to avoid compilation problems
template <class R, class S, void (*T)(R&, float, S), bool audit, void (*audit_func)(R&, const audit_strings*),
    class W>  // nullptr func can't be used as template param in old compilers
inline void generate_interactions(std::vector<std::string>& interactions, bool permutations, example_predict& ec,
    R& dat,
    W& weights)  // default value removed to eliminate ambiguity in old complers
{
  features* features_data = ec.feature_space.data();

  // often used values
  const uint64_t offset = ec.ft_offset;
  //    const uint64_t stride_shift = all.stride_shift; // it seems we don't need stride shift in FTRL-like hash

  // statedata for generic non-recursive iteration
  v_array<feature_gen_data> state_data = v_init<feature_gen_data>();

  feature_gen_data empty_ns_data;  // micro-optimization. don't want to call its constructor each time in loop.
  empty_ns_data.loop_idx = 0;
  empty_ns_data.x = 1.;
  empty_ns_data.loop_end = 0;
  empty_ns_data.self_interaction = false;

  // loop throw the set of possible interactions
  for (auto& ns : interactions)
  {  // current list of namespaces to interact.

#ifndef GEN_INTER_LOOP

    // unless GEN_INTER_LOOP is defined we use nested 'for' loops for interactions length 2 (pairs) and 3 (triples)
    // and generic non-recursive algorythm for all other cases.
    // nested 'for' loops approach is faster, but can't be used for interation of any length.

    const size_t len = ns.size();

    if (len == 2)  // special case of pairs
    {
      features& first = features_data[(uint8_t)ns[0]];
      if (first.nonempty())
      {
        features& second = features_data[(uint8_t)ns[1]];
        if (second.nonempty())
        {
          const bool same_namespace = (!permutations && (ns[0] == ns[1]));

          for (size_t i = 0; i < first.indicies.size(); ++i)
          {
            feature_index halfhash = FNV_prime * (uint64_t)first.indicies[i];
            if (audit)
              audit_func(dat, first.space_names[i].get());
            // next index differs for permutations and simple combinations
            feature_value ft_value = first.values[i];
            features::features_value_index_audit_range range = second.values_indices_audit();
            features::iterator_all begin = range.begin();
            if (same_namespace)
              begin += (PROCESS_SELF_INTERACTIONS(ft_value)) ? i : i + 1;

            features::iterator_all end = range.end();
            inner_kernel<R, S, T, audit, audit_func>(dat, begin, end, offset, weights, ft_value, halfhash);

            if (audit)
              audit_func(dat, nullptr);
          }  // end for(fst)
        }    // end if (data[snd] size > 0)
      }      // end if (data[fst] size > 0)
    }
    else if (len == 3)  // special case for triples
    {
      features& first = features_data[(uint8_t)ns[0]];
      if (first.nonempty())
      {
        features& second = features_data[(uint8_t)ns[1]];
        if (second.nonempty())
        {
          features& third = features_data[(uint8_t)ns[2]];
          if (third.nonempty())
          {  // don't compare 1 and 3 as interaction is sorted
            const bool same_namespace1 = (!permutations && (ns[0] == ns[1]));
            const bool same_namespace2 = (!permutations && (ns[1] == ns[2]));

            for (size_t i = 0; i < first.indicies.size(); ++i)
            {
              if (audit)
                audit_func(dat, first.space_names[i].get());
              const uint64_t halfhash1 = FNV_prime * (uint64_t)first.indicies[i];
              const float& first_ft_value = first.values[i];
              size_t j = 0;
              if (same_namespace1)  // next index differs for permutations and simple combinations
                j = (PROCESS_SELF_INTERACTIONS(first_ft_value)) ? i : i + 1;

              for (; j < second.indicies.size(); ++j)
              {  // f3 x k*(f2 x k*f1)
                if (audit)
                  audit_func(dat, second.space_names[j].get());
                feature_index halfhash = FNV_prime * (halfhash1 ^ (uint64_t)second.indicies[j]);
                feature_value ft_value = INTERACTION_VALUE(first_ft_value, second.values[j]);

                features::features_value_index_audit_range range = third.values_indices_audit();
                features::iterator_all begin = range.begin();
                if (same_namespace2)  // next index differs for permutations and simple combinations
                  begin += (PROCESS_SELF_INTERACTIONS(ft_value)) ? j : j + 1;

                features::iterator_all end = range.end();
                inner_kernel<R, S, T, audit, audit_func>(dat, begin, end, offset, weights, ft_value, halfhash);
                if (audit)
                  audit_func(dat, nullptr);
              }  // end for (snd)
              if (audit)
                audit_func(dat, nullptr);
            }  // end for (fst)

          }  // end if (data[thr] size > 0)
        }    // end if (data[snd] size > 0)
      }      // end if (data[fst] size > 0)
    }
    else  // generic case: quatriples, etc.

#endif
    {
      bool must_skip_interaction = false;
      // preparing state data
      feature_gen_data* fgd = state_data.begin();
      feature_gen_data* fgd2;  // for further use
      for (namespace_index n : ns)
      {
        features& ft = features_data[(int32_t)n];
        const size_t ft_cnt = ft.indicies.size();

        if (ft_cnt == 0)
        {
          must_skip_interaction = true;
          break;
        }

        if (fgd == state_data.end())
        {
          state_data.push_back(empty_ns_data);
          fgd = state_data.end() - 1;  // reassign as memory could be realloced
        }

        fgd->loop_end = ft_cnt - 1;  // saving number of features for each namespace
        fgd->ft_arr = &ft;
        ++fgd;
      }

      // if any of interacting namespace has 0 features - whole interaction is skipped
      if (must_skip_interaction)
        continue;  // no_data_to_interact

      if (!permutations)  // adjust state_data for simple combinations
      {                   // if permutations mode is disabeled then namespaces in ns are already sorted and thus grouped
        // (in fact, currently they are sorted even for enabled permutations mode)
        // let's go throw the list and calculate number of features to skip in namespaces which
        // repeated more than once to generate only simple combinations of features

        size_t margin = 0;  // number of features to ignore if namespace has been seen before

        // iterate list backward as margin grows in this order

        for (fgd = state_data.end() - 1; fgd > state_data.begin(); --fgd)
        {
          fgd2 = fgd - 1;
          fgd->self_interaction = (fgd->ft_arr == fgd2->ft_arr);  // state_data.begin().self_interaction is always false
          if (fgd->self_interaction)
          {
            size_t& loop_end = fgd2->loop_end;

            if (!PROCESS_SELF_INTERACTIONS((*fgd2->ft_arr).values[loop_end - margin]))
            {
              ++margin;  // otherwise margin can't be increased
              must_skip_interaction = loop_end < margin;
              if (must_skip_interaction)
                break;
            }

            if (margin != 0)
              loop_end -= margin;  // skip some features and increase margin
          }
          else if (margin != 0)
            margin = 0;
        }

        // if impossible_without_permutations == true then we faced with case like interaction 'aaaa'
        // where namespace 'a' contains less than 4 unique features. It's impossible to make simple
        // combination of length 4 without repetitions from 3 or less elements.
        if (must_skip_interaction)
          continue;  // impossible_without_permutations
      }              // end of state_data adjustment

      fgd = state_data.begin();     // always equal to first ns
      fgd2 = state_data.end() - 1;  // always equal to last ns
      fgd->loop_idx = 0;            // loop_idx contains current feature id for curently processed namespace.

      // beware: micro-optimization.
      /* start & end are always point to features in last namespace of interaction.
      for 'all.permutations == true' they are constant.*/
      size_t start_i = 0;

      feature_gen_data* cur_data = fgd;
      // end of micro-optimization block

      // generic feature generation cycle for interactions of any length
      bool do_it = true;
      while (do_it)
      {
        if (cur_data < fgd2)  // can go further threw the list of namespaces in interaction
        {
          feature_gen_data* next_data = cur_data + 1;
          size_t feature = cur_data->loop_idx;
          features& fs = *(cur_data->ft_arr);

          if (next_data->self_interaction)
          {  // if next namespace is same, we should start with loop_idx + 1 to avoid feature interaction with itself
            // unless feature has value x and x != x*x. E.g. x != 0 and x != 1. Features with x == 0 are already
            // filtered out in parce_args.cc::maybeFeature().

            next_data->loop_idx =
                (PROCESS_SELF_INTERACTIONS(fs.values[feature])) ? cur_data->loop_idx : cur_data->loop_idx + 1;
          }
          else
            next_data->loop_idx = 0;

          if (audit)
            audit_func(dat, fs.space_names[feature].get());

          if (cur_data == fgd)  // first namespace
          {
            next_data->hash = FNV_prime * (uint64_t)fs.indicies[feature];
            next_data->x = fs.values[feature];  // data->x == 1.
          }
          else
          {  // feature2 xor (16777619*feature1)
            next_data->hash = FNV_prime * (cur_data->hash ^ (uint64_t)fs.indicies[feature]);
            next_data->x = INTERACTION_VALUE(fs.values[feature], cur_data->x);
          }

          ++cur_data;
        }
        else
        {                     // last namespace - iterate its features and go back
          if (!permutations)  // start value is not a constant in this case
            start_i = fgd2->loop_idx;

          features& fs = *(fgd2->ft_arr);

          feature_value ft_value = fgd2->x;
          feature_index halfhash = fgd2->hash;

          features::features_value_index_audit_range range = fs.values_indices_audit();
          features::iterator_all begin = range.begin();
          begin += start_i;
          features::iterator_all end = range.begin();
          end += fgd2->loop_end + 1;
          inner_kernel<R, S, T, audit, audit_func, W>(dat, begin, end, offset, weights, ft_value, halfhash);

          // trying to go back increasing loop_idx of each namespace by the way

          bool go_further = true;

          do
          {
            --cur_data;
            go_further = (++cur_data->loop_idx > cur_data->loop_end);  // increment loop_idx
            if (audit)
              audit_func(dat, nullptr);
          } while (go_further && cur_data != fgd);

          do_it = !(cur_data == fgd && go_further);
          // if do_it==false - we've reached 0 namespace but its 'cur_data.loop_idx > cur_data.loop_end' -> exit the
          // while loop
        }  // if last namespace
      }    // while do_it
    }
  }  // foreach interaction in all.interactions

  state_data.delete_v();
}
}  // namespace INTERACTIONS