//===----------------------------------------------------------------------===//
//
// 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_PIECEWISE_CONSTANT_DISTRIBUTION_H
#define _LIBCPP___RANDOM_PIECEWISE_CONSTANT_DISTRIBUTION_H

#include <__algorithm/upper_bound.h>
#include <__config>
#include <__random/is_valid.h>
#include <__random/uniform_real_distribution.h>
#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 _RealType = double>
class _LIBCPP_TEMPLATE_VIS piecewise_constant_distribution
{
public:
    // types
    typedef _RealType result_type;

    class _LIBCPP_TEMPLATE_VIS param_type
    {
        vector<result_type> __b_;
        vector<result_type> __densities_;
        vector<result_type> __areas_;
    public:
        typedef piecewise_constant_distribution distribution_type;

        param_type();
        template<class _InputIteratorB, class _InputIteratorW>
            param_type(_InputIteratorB __f_b, _InputIteratorB __l_b,
                       _InputIteratorW __f_w);
#ifndef _LIBCPP_CXX03_LANG
        template<class _UnaryOperation>
            param_type(initializer_list<result_type> __bl, _UnaryOperation __fw);
#endif // _LIBCPP_CXX03_LANG
        template<class _UnaryOperation>
            param_type(size_t __nw, result_type __xmin, result_type __xmax,
                       _UnaryOperation __fw);
        param_type(param_type const&) = default;
        param_type & operator=(const param_type& __rhs);

        _LIBCPP_INLINE_VISIBILITY
        vector<result_type> intervals() const {return __b_;}
        _LIBCPP_INLINE_VISIBILITY
        vector<result_type> densities() const {return __densities_;}

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

    private:
        void __init();

        friend class piecewise_constant_distribution;

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

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

private:
    param_type __p_;

public:
    // constructor and reset functions
    _LIBCPP_INLINE_VISIBILITY
    piecewise_constant_distribution() {}
    template<class _InputIteratorB, class _InputIteratorW>
        _LIBCPP_INLINE_VISIBILITY
        piecewise_constant_distribution(_InputIteratorB __f_b,
                                        _InputIteratorB __l_b,
                                        _InputIteratorW __f_w)
        : __p_(__f_b, __l_b, __f_w) {}

#ifndef _LIBCPP_CXX03_LANG
    template<class _UnaryOperation>
        _LIBCPP_INLINE_VISIBILITY
        piecewise_constant_distribution(initializer_list<result_type> __bl,
                                        _UnaryOperation __fw)
        : __p_(__bl, __fw) {}
#endif // _LIBCPP_CXX03_LANG

    template<class _UnaryOperation>
        _LIBCPP_INLINE_VISIBILITY
        piecewise_constant_distribution(size_t __nw, result_type __xmin,
                                        result_type __xmax, _UnaryOperation __fw)
        : __p_(__nw, __xmin, __xmax, __fw) {}

    _LIBCPP_INLINE_VISIBILITY
    explicit piecewise_constant_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<result_type> intervals() const {return __p_.intervals();}
    _LIBCPP_INLINE_VISIBILITY
    vector<result_type> densities() const {return __p_.densities();}

    _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 __p_.__b_.front();}
    _LIBCPP_INLINE_VISIBILITY
    result_type max() const {return __p_.__b_.back();}

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

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

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

template<class _RealType>
typename piecewise_constant_distribution<_RealType>::param_type &
piecewise_constant_distribution<_RealType>::param_type::operator=
                                                       (const param_type& __rhs)
{
//  These can throw
    __b_.reserve        (__rhs.__b_.size ());
    __densities_.reserve(__rhs.__densities_.size());
    __areas_.reserve    (__rhs.__areas_.size());

//  These can not throw
    __b_         = __rhs.__b_;
    __densities_ = __rhs.__densities_;
    __areas_     =  __rhs.__areas_;
    return *this;
}

template<class _RealType>
void
piecewise_constant_distribution<_RealType>::param_type::__init()
{
    // __densities_ contains non-normalized areas
    result_type __total_area = _VSTD::accumulate(__densities_.begin(),
                                                __densities_.end(),
                                                result_type());
    for (size_t __i = 0; __i < __densities_.size(); ++__i)
        __densities_[__i] /= __total_area;
    // __densities_ contains normalized areas
    __areas_.assign(__densities_.size(), result_type());
    _VSTD::partial_sum(__densities_.begin(), __densities_.end() - 1,
                                                          __areas_.begin() + 1);
    // __areas_ contains partial sums of normalized areas: [0, __densities_ - 1]
    __densities_.back() = 1 - __areas_.back();  // correct round off error
    for (size_t __i = 0; __i < __densities_.size(); ++__i)
        __densities_[__i] /= (__b_[__i+1] - __b_[__i]);
    // __densities_ now contains __densities_
}

template<class _RealType>
piecewise_constant_distribution<_RealType>::param_type::param_type()
    : __b_(2),
      __densities_(1, 1.0),
      __areas_(1, 0.0)
{
    __b_[1] = 1;
}

template<class _RealType>
template<class _InputIteratorB, class _InputIteratorW>
piecewise_constant_distribution<_RealType>::param_type::param_type(
        _InputIteratorB __f_b, _InputIteratorB __l_b, _InputIteratorW __f_w)
    : __b_(__f_b, __l_b)
{
    if (__b_.size() < 2)
    {
        __b_.resize(2);
        __b_[0] = 0;
        __b_[1] = 1;
        __densities_.assign(1, 1.0);
        __areas_.assign(1, 0.0);
    }
    else
    {
        __densities_.reserve(__b_.size() - 1);
        for (size_t __i = 0; __i < __b_.size() - 1; ++__i, ++__f_w)
            __densities_.push_back(*__f_w);
        __init();
    }
}

#ifndef _LIBCPP_CXX03_LANG

template<class _RealType>
template<class _UnaryOperation>
piecewise_constant_distribution<_RealType>::param_type::param_type(
        initializer_list<result_type> __bl, _UnaryOperation __fw)
    : __b_(__bl.begin(), __bl.end())
{
    if (__b_.size() < 2)
    {
        __b_.resize(2);
        __b_[0] = 0;
        __b_[1] = 1;
        __densities_.assign(1, 1.0);
        __areas_.assign(1, 0.0);
    }
    else
    {
        __densities_.reserve(__b_.size() - 1);
        for (size_t __i = 0; __i < __b_.size() - 1; ++__i)
            __densities_.push_back(__fw((__b_[__i+1] + __b_[__i])*.5));
        __init();
    }
}

#endif // _LIBCPP_CXX03_LANG

template<class _RealType>
template<class _UnaryOperation>
piecewise_constant_distribution<_RealType>::param_type::param_type(
        size_t __nw, result_type __xmin, result_type __xmax, _UnaryOperation __fw)
    : __b_(__nw == 0 ? 2 : __nw + 1)
{
    size_t __n = __b_.size() - 1;
    result_type __d = (__xmax - __xmin) / __n;
    __densities_.reserve(__n);
    for (size_t __i = 0; __i < __n; ++__i)
    {
        __b_[__i] = __xmin + __i * __d;
        __densities_.push_back(__fw(__b_[__i] + __d*.5));
    }
    __b_[__n] = __xmax;
    __init();
}

template<class _RealType>
template<class _URNG>
_RealType
piecewise_constant_distribution<_RealType>::operator()(_URNG& __g, const param_type& __p)
{
    static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
    typedef uniform_real_distribution<result_type> _Gen;
    result_type __u = _Gen()(__g);
    ptrdiff_t __k = _VSTD::upper_bound(__p.__areas_.begin(), __p.__areas_.end(),
                                      __u) - __p.__areas_.begin() - 1;
    return (__u - __p.__areas_[__k]) / __p.__densities_[__k] + __p.__b_[__k];
}

template <class _CharT, class _Traits, class _RT>
_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os,
           const piecewise_constant_distribution<_RT>& __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_.__b_.size();
    __os << __n;
    for (size_t __i = 0; __i < __n; ++__i)
        __os << __sp << __x.__p_.__b_[__i];
    __n = __x.__p_.__densities_.size();
    __os << __sp << __n;
    for (size_t __i = 0; __i < __n; ++__i)
        __os << __sp << __x.__p_.__densities_[__i];
    __n = __x.__p_.__areas_.size();
    __os << __sp << __n;
    for (size_t __i = 0; __i < __n; ++__i)
        __os << __sp << __x.__p_.__areas_[__i];
    return __os;
}

template <class _CharT, class _Traits, class _RT>
_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is,
           piecewise_constant_distribution<_RT>& __x)
{
    typedef piecewise_constant_distribution<_RT> _Eng;
    typedef typename _Eng::result_type result_type;
    __save_flags<_CharT, _Traits> __lx(__is);
    typedef basic_istream<_CharT, _Traits> _Istream;
    __is.flags(_Istream::dec | _Istream::skipws);
    size_t __n;
    __is >> __n;
    vector<result_type> __b(__n);
    for (size_t __i = 0; __i < __n; ++__i)
        __is >> __b[__i];
    __is >> __n;
    vector<result_type> __densities(__n);
    for (size_t __i = 0; __i < __n; ++__i)
        __is >> __densities[__i];
    __is >> __n;
    vector<result_type> __areas(__n);
    for (size_t __i = 0; __i < __n; ++__i)
        __is >> __areas[__i];
    if (!__is.fail())
    {
        swap(__x.__p_.__b_, __b);
        swap(__x.__p_.__densities_, __densities);
        swap(__x.__p_.__areas_, __areas);
    }
    return __is;
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___RANDOM_PIECEWISE_CONSTANT_DISTRIBUTION_H
