//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___RANDOM_DISCRETE_DISTRIBUTION_H
#define _LIBCPP___RANDOM_DISCRETE_DISTRIBUTION_H

#include <__algorithm/upper_bound.h>
#include <__config>
#include <__random/is_valid.h>
#include <__random/uniform_real_distribution.h>
#include <cstddef>
#include <iosfwd>
#include <numeric>
#include <vector>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

template<class _IntType = int>
class _LIBCPP_TEMPLATE_VIS discrete_distribution
{
    static_assert(__libcpp_random_is_valid_inttype<_IntType>::value, "IntType must be a supported integer type");
public:
    // types
    typedef _IntType result_type;

    class _LIBCPP_TEMPLATE_VIS param_type
    {
        vector<double> __p_;
    public:
        typedef discrete_distribution distribution_type;

        _LIBCPP_INLINE_VISIBILITY
        param_type() {}
        template<class _InputIterator>
            _LIBCPP_INLINE_VISIBILITY
            param_type(_InputIterator __f, _InputIterator __l)
            : __p_(__f, __l) {__init();}
#ifndef _LIBCPP_CXX03_LANG
        _LIBCPP_INLINE_VISIBILITY
        param_type(initializer_list<double> __wl)
            : __p_(__wl.begin(), __wl.end()) {__init();}
#endif // _LIBCPP_CXX03_LANG
        template<class _UnaryOperation>
            param_type(size_t __nw, double __xmin, double __xmax,
                       _UnaryOperation __fw);

        vector<double> probabilities() const;

        friend _LIBCPP_INLINE_VISIBILITY
            bool operator==(const param_type& __x, const param_type& __y)
            {return __x.__p_ == __y.__p_;}
        friend _LIBCPP_INLINE_VISIBILITY
            bool operator!=(const param_type& __x, const param_type& __y)
            {return !(__x == __y);}

    private:
        void __init();

        friend class discrete_distribution;

        template <class _CharT, class _Traits, class _IT>
        friend
        basic_ostream<_CharT, _Traits>&
        operator<<(basic_ostream<_CharT, _Traits>& __os,
                   const discrete_distribution<_IT>& __x);

        template <class _CharT, class _Traits, class _IT>
        friend
        basic_istream<_CharT, _Traits>&
        operator>>(basic_istream<_CharT, _Traits>& __is,
                   discrete_distribution<_IT>& __x);
    };

private:
    param_type __p_;

public:
    // constructor and reset functions
    _LIBCPP_INLINE_VISIBILITY
    discrete_distribution() {}
    template<class _InputIterator>
        _LIBCPP_INLINE_VISIBILITY
        discrete_distribution(_InputIterator __f, _InputIterator __l)
            : __p_(__f, __l) {}
#ifndef _LIBCPP_CXX03_LANG
    _LIBCPP_INLINE_VISIBILITY
    discrete_distribution(initializer_list<double> __wl)
        : __p_(__wl) {}
#endif // _LIBCPP_CXX03_LANG
    template<class _UnaryOperation>
        _LIBCPP_INLINE_VISIBILITY
        discrete_distribution(size_t __nw, double __xmin, double __xmax,
                              _UnaryOperation __fw)
        : __p_(__nw, __xmin, __xmax, __fw) {}
    _LIBCPP_INLINE_VISIBILITY
    explicit discrete_distribution(const param_type& __p)
        : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY
    void reset() {}

    // generating functions
    template<class _URNG>
        _LIBCPP_INLINE_VISIBILITY
        result_type operator()(_URNG& __g)
        {return (*this)(__g, __p_);}
    template<class _URNG> result_type operator()(_URNG& __g, const param_type& __p);

    // property functions
    _LIBCPP_INLINE_VISIBILITY
    vector<double> probabilities() const {return __p_.probabilities();}

    _LIBCPP_INLINE_VISIBILITY
    param_type param() const {return __p_;}
    _LIBCPP_INLINE_VISIBILITY
    void param(const param_type& __p) {__p_ = __p;}

    _LIBCPP_INLINE_VISIBILITY
    result_type min() const {return 0;}
    _LIBCPP_INLINE_VISIBILITY
    result_type max() const {return __p_.__p_.size();}

    friend _LIBCPP_INLINE_VISIBILITY
        bool operator==(const discrete_distribution& __x,
                        const discrete_distribution& __y)
        {return __x.__p_ == __y.__p_;}
    friend _LIBCPP_INLINE_VISIBILITY
        bool operator!=(const discrete_distribution& __x,
                        const discrete_distribution& __y)
        {return !(__x == __y);}

    template <class _CharT, class _Traits, class _IT>
    friend
    basic_ostream<_CharT, _Traits>&
    operator<<(basic_ostream<_CharT, _Traits>& __os,
               const discrete_distribution<_IT>& __x);

    template <class _CharT, class _Traits, class _IT>
    friend
    basic_istream<_CharT, _Traits>&
    operator>>(basic_istream<_CharT, _Traits>& __is,
               discrete_distribution<_IT>& __x);
};

template<class _IntType>
template<class _UnaryOperation>
discrete_distribution<_IntType>::param_type::param_type(size_t __nw,
                                                        double __xmin,
                                                        double __xmax,
                                                        _UnaryOperation __fw)
{
    if (__nw > 1)
    {
        __p_.reserve(__nw - 1);
        double __d = (__xmax - __xmin) / __nw;
        double __d2 = __d / 2;
        for (size_t __k = 0; __k < __nw; ++__k)
            __p_.push_back(__fw(__xmin + __k * __d + __d2));
        __init();
    }
}

template<class _IntType>
void
discrete_distribution<_IntType>::param_type::__init()
{
    if (!__p_.empty())
    {
        if (__p_.size() > 1)
        {
            double __s = _VSTD::accumulate(__p_.begin(), __p_.end(), 0.0);
            for (vector<double>::iterator __i = __p_.begin(), __e = __p_.end(); __i < __e; ++__i)
                *__i /= __s;
            vector<double> __t(__p_.size() - 1);
            _VSTD::partial_sum(__p_.begin(), __p_.end() - 1, __t.begin());
            swap(__p_, __t);
        }
        else
        {
            __p_.clear();
            __p_.shrink_to_fit();
        }
    }
}

template<class _IntType>
vector<double>
discrete_distribution<_IntType>::param_type::probabilities() const
{
    size_t __n = __p_.size();
    vector<double> __p(__n+1);
    _VSTD::adjacent_difference(__p_.begin(), __p_.end(), __p.begin());
    if (__n > 0)
        __p[__n] = 1 - __p_[__n-1];
    else
        __p[0] = 1;
    return __p;
}

template<class _IntType>
template<class _URNG>
_IntType
discrete_distribution<_IntType>::operator()(_URNG& __g, const param_type& __p)
{
    static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
    uniform_real_distribution<double> __gen;
    return static_cast<_IntType>(
           _VSTD::upper_bound(__p.__p_.begin(), __p.__p_.end(), __gen(__g)) -
                                                              __p.__p_.begin());
}

template <class _CharT, class _Traits, class _IT>
_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os,
           const discrete_distribution<_IT>& __x)
{
    __save_flags<_CharT, _Traits> __lx(__os);
    typedef basic_ostream<_CharT, _Traits> _OStream;
    __os.flags(_OStream::dec | _OStream::left | _OStream::fixed |
               _OStream::scientific);
    _CharT __sp = __os.widen(' ');
    __os.fill(__sp);
    size_t __n = __x.__p_.__p_.size();
    __os << __n;
    for (size_t __i = 0; __i < __n; ++__i)
        __os << __sp << __x.__p_.__p_[__i];
    return __os;
}

template <class _CharT, class _Traits, class _IT>
_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is,
           discrete_distribution<_IT>& __x)
{
    __save_flags<_CharT, _Traits> __lx(__is);
    typedef basic_istream<_CharT, _Traits> _Istream;
    __is.flags(_Istream::dec | _Istream::skipws);
    size_t __n;
    __is >> __n;
    vector<double> __p(__n);
    for (size_t __i = 0; __i < __n; ++__i)
        __is >> __p[__i];
    if (!__is.fail())
        swap(__x.__p_.__p_, __p);
    return __is;
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___RANDOM_DISCRETE_DISTRIBUTION_H