#ifndef _CCRP_H_
#define _CCRP_H_

#include <cassert>
#include <cmath>
#include <list>
#include <iostream>
#include <vector>
#include <tr1/unordered_map>
#include <boost/functional/hash.hpp>
#include "sampler.h"

// Chinese restaurant process (Pitman-Yor parameters) with explicit table
// tracking.

template <typename Dish, typename DishHash = boost::hash<Dish> >
class CCRP {
 public:
  CCRP(double disc, double conc) : num_tables_(), num_customers_(), discount_(disc), concentration_(conc) {}

  void clear() {
    num_tables_ = 0;
    num_customers_ = 0;
    dish_locs_.clear();
  }

  unsigned num_tables(const Dish& dish) const {
    const typename std::tr1::unordered_map<Dish, DishLocations, DishHash>::const_iterator it = dish_locs_.find(dish);
    if (it == dish_locs_.end()) return 0;
    return it->second.table_counts_.size();
  }

  // returns +1 or 0 indicating whether a new table was opened
  int increment(const Dish& dish, const double& p0, MT19937* rng) {
    DishLocations& loc = dish_locs_[dish];
    bool share_table = false;
    if (loc.total_dish_count_) {
      const double p_empty = (concentration_ + num_tables_ * discount_) * p0;
      const double p_share = (loc.total_dish_count_ - loc.table_counts_.size() * discount_);
      share_table = rng->SelectSample(p_empty, p_share);
    }
    if (share_table) {
      double r = rng->next() * (loc.total_dish_count_ - loc.table_counts_.size() * discount_);
      for (typename std::list<unsigned>::iterator ti = loc.table_counts_.begin();
           ti != loc.table_counts_.end(); ++ti) {
        r -= (*ti - discount_);
        if (r <= 0.0) {
          ++(*ti);
          break;
        }
      }
      if (r > 0.0) {
        std::cerr << "Serious error: r=" << r << std::endl;
        Print(&std::cerr);
        assert(r <= 0.0);
      }
    } else {
      loc.table_counts_.push_back(1u);
      ++num_tables_;
    }
    ++loc.total_dish_count_;
    ++num_customers_;
    return (share_table ? 0 : 1);
  }

  // returns -1 or 0, indicating whether a table was closed
  int decrement(const Dish& dish, MT19937* rng) {
    DishLocations& loc = dish_locs_[dish];
    assert(loc.total_dish_count_);
    if (loc.total_dish_count_ == 1) {
      dish_locs_.erase(dish);
      --num_tables_;
      --num_customers_;
      return -1;
    } else {
      int delta = 0;
      // sample customer to remove UNIFORMLY. that is, do NOT use the discount
      // here. if you do, it will introduce (unwanted) bias!
      double r = rng->next() * loc.total_dish_count_;
      --loc.total_dish_count_;
      for (typename std::list<unsigned>::iterator ti = loc.table_counts_.begin();
           ti != loc.table_counts_.end(); ++ti) {
        r -= *ti;
        if (r <= 0.0) {
          if ((--(*ti)) == 0) {
            --num_tables_;
            delta = -1;
            loc.table_counts_.erase(ti);
          }
          break;
        }
      }
      if (r > 0.0) {
        std::cerr << "Serious error: r=" << r << std::endl;
        Print(&std::cerr);
        assert(r <= 0.0);
      }
      --num_customers_;
      return delta;
    }
  }

  double prob(const Dish& dish, const double& p0) const {
    const typename std::tr1::unordered_map<Dish, DishLocations, DishHash>::const_iterator it = dish_locs_.find(dish);
    const double r = num_tables_ * discount_ + concentration_;
    if (it == dish_locs_.end()) {
      return r * p0 / (num_customers_ + concentration_);
    } else {
      return (it->second.total_dish_count_ - discount_ * it->second.table_counts_.size() + r * p0) /
               (num_customers_ + concentration_);
    }
  }

  // taken from http://en.wikipedia.org/wiki/Chinese_restaurant_process
  // does not include P_0's
  double log_crp_prob() const {
    double lp = 0.0;
    if (num_customers_) {
      const double r = lgamma(1.0 - discount_);
      lp = lgamma(concentration_) - lgamma(concentration_ + num_customers_)
           + num_tables_ * discount_ + lgamma(concentration_ / discount_ + num_tables_)
           - lgamma(concentration_ / discount_);
      for (typename std::tr1::unordered_map<Dish, DishLocations, DishHash>::const_iterator it = dish_locs_.begin();
           it != dish_locs_.end(); ++it) {
        const DishLocations& cur = it->second;
        lp += lgamma(cur.total_dish_count_ - discount_) - r;
      }
    }
    return lp;
  }

  struct DishLocations {
    DishLocations() : total_dish_count_() {}
    unsigned total_dish_count_;        // customers at all tables with this dish
    std::list<unsigned> table_counts_; // list<> gives O(1) deletion and insertion, which we want
                                       // .size() is the number of tables for this dish
  };

  void Print(std::ostream* out) const {
    for (typename std::tr1::unordered_map<Dish, DishLocations, DishHash>::const_iterator it = dish_locs_.begin();
         it != dish_locs_.end(); ++it) {
      (*out) << it->first << " (" << it->second.total_dish_count_ << " on " << it->second.table_counts_.size() << " tables): ";
      for (typename std::list<unsigned>::const_iterator i = it->second.table_counts_.begin();
           i != it->second.table_counts_.end(); ++i) {
        (*out) << " " << *i;
      }
      (*out) << std::endl;
    }
  }

  typedef typename std::tr1::unordered_map<Dish, DishLocations, DishHash>::const_iterator const_iterator;
  const_iterator begin() const {
    return dish_locs_.begin();
  }
  const_iterator end() const {
    return dish_locs_.end();
  }

  unsigned num_tables_;
  unsigned num_customers_;
  std::tr1::unordered_map<Dish, DishLocations, DishHash> dish_locs_;

  double discount_;
  double concentration_;
};

template <typename T,typename H>
std::ostream& operator<<(std::ostream& o, const CCRP<T,H>& c) {
  c.Print(&o);
  return o;
}

#endif