/*
 * include/shard/Alias.h
 *
 * Copyright (C) 2023 Douglas B. Rumbaugh <drumbaugh@psu.edu>
 *                    Dong Xie <dongx@psu.edu>
 *
 * Distributed under the Modified BSD License.
 *
 * A shard shim around the psudb::Alias Walker's Alias
 * structure. Designed to be used along side the WSS
 * query in include/query/wss.h
 *
 * TODO: The code in this file is very poorly commented.
 */
#pragma once

#include <vector>

#include "framework/ShardRequirements.h"

#include "psu-ds/Alias.h"
#include "psu-ds/BloomFilter.h"
#include "util/SortedMerge.h"
#include "util/bf_config.h"

using psudb::BloomFilter;
using psudb::byte;
using psudb::CACHELINE_SIZE;

namespace de {

template <WeightedRecordInterface R> class Alias {
public:
  typedef R RECORD;

private:
  typedef decltype(R::key) K;
  typedef decltype(R::value) V;
  typedef decltype(R::weight) W;

public:
  Alias(BufferView<R> buffer)
      : m_data(nullptr), m_alias(nullptr), m_total_weight(0), m_reccnt(0),
        m_tombstone_cnt(0), m_alloc_size(0),
        m_bf(new BloomFilter<R>(BF_FPR, buffer.get_tombstone_count(),
                                BF_HASH_FUNCS)) {

    m_alloc_size = psudb::sf_aligned_alloc(
        CACHELINE_SIZE, buffer.get_record_count() * sizeof(Wrapped<R>),
        (byte **)&m_data);

    auto res = sorted_array_from_bufferview<R>(std::move(buffer), m_data, m_bf);
    m_reccnt = res.record_count;
    m_tombstone_cnt = res.tombstone_count;

    if (m_reccnt > 0) {
      std::vector<W> weights;
      for (size_t i = 0; i < m_reccnt; i++) {
        weights.emplace_back(m_data[i].rec.weight);
        m_total_weight += m_data[i].rec.weight;
      }

      build_alias_structure(weights);
    }
  }

  Alias(std::vector<const Alias *> const &shards)
      : m_data(nullptr), m_alias(nullptr), m_total_weight(0), m_reccnt(0),
        m_tombstone_cnt(0), m_alloc_size(0), m_bf(nullptr) {

    size_t attemp_reccnt = 0;
    size_t tombstone_count = 0;
    auto cursors =
        build_cursor_vec<R, Alias>(shards, &attemp_reccnt, &tombstone_count);

    m_bf = new BloomFilter<R>(BF_FPR, tombstone_count, BF_HASH_FUNCS);
    m_alloc_size = psudb::sf_aligned_alloc(
        CACHELINE_SIZE, attemp_reccnt * sizeof(Wrapped<R>), (byte **)&m_data);

    auto res = sorted_array_merge<R>(cursors, m_data, m_bf);
    m_reccnt = res.record_count;
    m_tombstone_cnt = res.tombstone_count;

    if (m_reccnt > 0) {
      std::vector<W> weights;
      for (size_t i = 0; i < m_reccnt; i++) {
        weights.emplace_back(m_data[i].rec.weight);
        m_total_weight += m_data[i].rec.weight;
      }

      build_alias_structure(weights);
    }
  }

  ~Alias() {
    free(m_data);
    delete m_alias;
    delete m_bf;
  }

  Wrapped<R> *point_lookup(const R &rec, bool filter = false) {
    if (filter && !m_bf->lookup(rec)) {
      return nullptr;
    }

    size_t idx = get_lower_bound(rec.key);
    if (idx >= m_reccnt) {
      return nullptr;
    }

    while (idx < (m_reccnt - 1) && m_data[idx].rec < rec)
      ++idx;

    if (m_data[idx].rec == rec) {
      return m_data + idx;
    }

    return nullptr;
  }

  Wrapped<R> *get_data() const { return m_data; }

  size_t get_record_count() const { return m_reccnt; }

  size_t get_tombstone_count() const { return m_tombstone_cnt; }

  const Wrapped<R> *get_record_at(size_t idx) const {
    if (idx >= m_reccnt)
      return nullptr;
    return m_data + idx;
  }

  size_t get_memory_usage() const { return 0; }

  size_t get_aux_memory_usage() const {
    return (m_bf) ? m_bf->memory_usage() : 0;
  }

  W get_total_weight() const { return m_total_weight; }

  size_t get_weighted_sample(gsl_rng *rng) const { return m_alias->get(rng); }

  size_t get_lower_bound(const K &key) const {
    size_t min = 0;
    size_t max = m_reccnt - 1;

    while (min < max) {
      size_t mid = (min + max) / 2;

      if (key > m_data[mid].rec.key) {
        min = mid + 1;
      } else {
        max = mid;
      }
    }

    return min;
  }

private:
  void build_alias_structure(std::vector<W> &weights) {

    // normalize the weights vector
    std::vector<double> norm_weights(weights.size());

    for (size_t i = 0; i < weights.size(); i++) {
      norm_weights[i] = (double)weights[i] / (double)m_total_weight;
    }

    // build the alias structure
    m_alias = new psudb::Alias(norm_weights);
  }

  Wrapped<R> *m_data;
  psudb::Alias *m_alias;
  W m_total_weight;
  size_t m_reccnt;
  size_t m_tombstone_cnt;
  size_t m_alloc_size;
  BloomFilter<R> *m_bf;
};
} // namespace de