//===- iterator.h - Utilities for using and defining iterators --*- C++ -*-===//
//
// 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 UTIL_ITERATOR_H
#define UTIL_ITERATOR_H

#include "Util/iterator_range.h"
#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>

namespace SVF
{

/// CRTP base class which implements the entire standard iterator facade
/// in terms of a minimal subset of the interface.
///
/// Use this when it is reasonable to implement most of the iterator
/// functionality in terms of a core subset. If you need special behavior or
/// there are performance implications for this, you may want to override the
/// relevant members instead.
///
/// Note, one abstraction that this does *not* provide is implementing
/// subtraction in terms of addition by negating the difference. Negation isn't
/// always information preserving, and I can see very reasonable iterator
/// designs where this doesn't work well. It doesn't really force much added
/// boilerplate anyways.
///
/// Another abstraction that this doesn't provide is implementing increment in
/// terms of addition of one. These aren't equivalent for all iterator
/// categories, and respecting that adds a lot of complexity for little gain.
///
/// Classes wishing to use `iter_facade_base` should implement the following
/// methods:
///
/// Forward Iterators:
///   (All of the following methods)
///   - DerivedT &operator=(const DerivedT &R);
///   - bool operator==(const DerivedT &R) const;
///   - const T &operator*() const;
///   - T &operator*();
///   - DerivedT &operator++();
///
/// Bidirectional Iterators:
///   (All methods of forward iterators, plus the following)
///   - DerivedT &operator--();
///
/// Random-access Iterators:
///   (All methods of bidirectional iterators excluding the following)
///   - DerivedT &operator++();
///   - DerivedT &operator--();
///   (and plus the following)
///   - bool operator<(const DerivedT &RHS) const;
///   - DifferenceTypeT operator-(const DerivedT &R) const;
///   - DerivedT &operator+=(DifferenceTypeT N);
///   - DerivedT &operator-=(DifferenceTypeT N);
///
template <typename DerivedT, typename IteratorCategoryT, typename T,
          typename DifferenceTypeT = std::ptrdiff_t, typename PointerT = T *,
          typename ReferenceT = T &>
class iter_facade_base
{
public:
    using iterator_category = IteratorCategoryT;
    using value_type = T;
    using difference_type = DifferenceTypeT;
    using pointer = PointerT;
    using reference = ReferenceT;

protected:
    enum
    {
        IsRandomAccess = std::is_base_of<std::random_access_iterator_tag,
        IteratorCategoryT>::value,
        IsBidirectional = std::is_base_of<std::bidirectional_iterator_tag,
        IteratorCategoryT>::value,
    };

    /// A proxy object for computing a reference via indirecting a copy of an
    /// iterator. This is used in APIs which need to produce a reference via
    /// indirection but for which the iterator object might be a temporary. The
    /// proxy preserves the iterator internally and exposes the indirected
    /// reference via a conversion operator.
    class ReferenceProxy
    {
        friend iter_facade_base;

        DerivedT I;

        ReferenceProxy(DerivedT I) : I(std::move(I)) {}

    public:
        operator ReferenceT() const
        {
            return *I;
        }
    };

public:
    DerivedT operator+(DifferenceTypeT n) const
    {
        static_assert(std::is_base_of<iter_facade_base, DerivedT>::value,
                      "Must pass the derived type to this template!");
        static_assert(
            IsRandomAccess,
            "The '+' operator is only defined for random access iterators.");
        DerivedT tmp = *static_cast<const DerivedT *>(this);
        tmp += n;
        return tmp;
    }
    friend DerivedT operator+(DifferenceTypeT n, const DerivedT &i)
    {
        static_assert(
            IsRandomAccess,
            "The '+' operator is only defined for random access iterators.");
        return i + n;
    }
    DerivedT operator-(DifferenceTypeT n) const
    {
        static_assert(
            IsRandomAccess,
            "The '-' operator is only defined for random access iterators.");
        DerivedT tmp = *static_cast<const DerivedT *>(this);
        tmp -= n;
        return tmp;
    }

    DerivedT &operator++()
    {
        static_assert(std::is_base_of<iter_facade_base, DerivedT>::value,
                      "Must pass the derived type to this template!");
        return static_cast<DerivedT *>(this)->operator+=(1);
    }
    DerivedT operator++(int)
    {
        DerivedT tmp = *static_cast<DerivedT *>(this);
        ++*static_cast<DerivedT *>(this);
        return tmp;
    }
    DerivedT &operator--()
    {
        static_assert(
            IsBidirectional,
            "The decrement operator is only defined for bidirectional iterators.");
        return static_cast<DerivedT *>(this)->operator-=(1);
    }
    DerivedT operator--(int)
    {
        static_assert(
            IsBidirectional,
            "The decrement operator is only defined for bidirectional iterators.");
        DerivedT tmp = *static_cast<DerivedT *>(this);
        --*static_cast<DerivedT *>(this);
        return tmp;
    }

#ifndef __cpp_impl_three_way_comparison
    bool operator!=(const DerivedT &RHS) const
    {
        return !(static_cast<const DerivedT &>(*this) == RHS);
    }
#endif

    bool operator>(const DerivedT &RHS) const
    {
        static_assert(
            IsRandomAccess,
            "Relational operators are only defined for random access iterators.");
        return !(static_cast<const DerivedT &>(*this) < RHS) &&
               !(static_cast<const DerivedT &>(*this) == RHS);
    }
    bool operator<=(const DerivedT &RHS) const
    {
        static_assert(
            IsRandomAccess,
            "Relational operators are only defined for random access iterators.");
        return !(static_cast<const DerivedT &>(*this) > RHS);
    }
    bool operator>=(const DerivedT &RHS) const
    {
        static_assert(
            IsRandomAccess,
            "Relational operators are only defined for random access iterators.");
        return !(static_cast<const DerivedT &>(*this) < RHS);
    }

    PointerT operator->()
    {
        return &static_cast<DerivedT *>(this)->operator*();
    }
    PointerT operator->() const
    {
        return &static_cast<const DerivedT *>(this)->operator*();
    }
    ReferenceProxy operator[](DifferenceTypeT n)
    {
        static_assert(IsRandomAccess,
                      "Subscripting is only defined for random access iterators.");
        return ReferenceProxy(static_cast<DerivedT *>(this)->operator+(n));
    }
    ReferenceProxy operator[](DifferenceTypeT n) const
    {
        static_assert(IsRandomAccess,
                      "Subscripting is only defined for random access iterators.");
        return ReferenceProxy(static_cast<const DerivedT *>(this)->operator+(n));
    }
};

/// CRTP base class for adapting an iterator to a different type.
///
/// This class can be used through CRTP to adapt one iterator into another.
/// Typically this is done through providing in the derived class a custom \c
/// operator* implementation. Other methods can be overridden as well.
template <
    typename DerivedT, typename WrappedIteratorT,
    typename IteratorCategoryT =
    typename std::iterator_traits<WrappedIteratorT>::iterator_category,
    typename T = typename std::iterator_traits<WrappedIteratorT>::value_type,
    typename DifferenceTypeT =
    typename std::iterator_traits<WrappedIteratorT>::difference_type,
    typename PointerT = std::conditional_t<
        std::is_same<T, typename std::iterator_traits<
                         WrappedIteratorT>::value_type>::value,
        typename std::iterator_traits<WrappedIteratorT>::pointer, T *>,
    typename ReferenceT = std::conditional_t<
        std::is_same<T, typename std::iterator_traits<
                         WrappedIteratorT>::value_type>::value,
        typename std::iterator_traits<WrappedIteratorT>::reference, T &>>
class iter_adaptor_base
    : public iter_facade_base<DerivedT, IteratorCategoryT, T,
      DifferenceTypeT, PointerT, ReferenceT>
{
    using BaseT = typename iter_adaptor_base::iter_facade_base;

protected:
    WrappedIteratorT I;

    iter_adaptor_base() = default;

    explicit iter_adaptor_base(WrappedIteratorT u) : I(std::move(u))
    {
        static_assert(std::is_base_of<iter_adaptor_base, DerivedT>::value,
                      "Must pass the derived type to this template!");
    }

    const WrappedIteratorT &wrapped() const
    {
        return I;
    }

public:
    using difference_type = DifferenceTypeT;

    DerivedT &operator+=(difference_type n)
    {
        static_assert(
            BaseT::IsRandomAccess,
            "The '+=' operator is only defined for random access iterators.");
        I += n;
        return *static_cast<DerivedT *>(this);
    }
    DerivedT &operator-=(difference_type n)
    {
        static_assert(
            BaseT::IsRandomAccess,
            "The '-=' operator is only defined for random access iterators.");
        I -= n;
        return *static_cast<DerivedT *>(this);
    }
    using BaseT::operator-;
    difference_type operator-(const DerivedT &RHS) const
    {
        static_assert(
            BaseT::IsRandomAccess,
            "The '-' operator is only defined for random access iterators.");
        return I - RHS.I;
    }

    // We have to explicitly provide ++ and -- rather than letting the facade
    // forward to += because WrappedIteratorT might not support +=.
    using BaseT::operator++;
    DerivedT &operator++()
    {
        ++I;
        return *static_cast<DerivedT *>(this);
    }
    using BaseT::operator--;
    DerivedT &operator--()
    {
        static_assert(
            BaseT::IsBidirectional,
            "The decrement operator is only defined for bidirectional iterators.");
        --I;
        return *static_cast<DerivedT *>(this);
    }

    friend bool operator==(const iter_adaptor_base &LHS,
                           const iter_adaptor_base &RHS)
    {
        return LHS.I == RHS.I;
    }
    friend bool operator<(const iter_adaptor_base &LHS,
                          const iter_adaptor_base &RHS)
    {
        static_assert(
            BaseT::IsRandomAccess,
            "Relational operators are only defined for random access iterators.");
        return LHS.I < RHS.I;
    }

    ReferenceT operator*() const
    {
        return *I;
    }
};

/// An iterator type that allows iterating over the pointees via some
/// other iterator.
///
/// The typical usage of this is to expose a type that iterates over Ts, but
/// which is implemented with some iterator over T*s:
///
/// \code
///   using iterator = pointee_iter<SmallVectorImpl<T *>::iterator>;
/// \endcode
template <typename WrappedIteratorT,
          typename T = std::remove_reference_t<decltype(
                      **std::declval<WrappedIteratorT>())>>
struct pointee_iter
    : iter_adaptor_base<
      pointee_iter<WrappedIteratorT, T>, WrappedIteratorT,
      typename std::iterator_traits<WrappedIteratorT>::iterator_category,
      T>
{
    pointee_iter() = default;
    template <typename U>
    pointee_iter(U &&u)
        : pointee_iter::iter_adaptor_base(std::forward<U &&>(u)) {}

    T &operator*() const
    {
        return **this->I;
    }
};

template <typename RangeT, typename WrappedIteratorT =
          decltype(std::begin(std::declval<RangeT>()))>
iter_range<pointee_iter<WrappedIteratorT>>
                                        make_pointee_range(RangeT &&Range)
{
    using PointeeIteratorT = pointee_iter<WrappedIteratorT>;
    return make_range(PointeeIteratorT(std::begin(std::forward<RangeT>(Range))),
                      PointeeIteratorT(std::end(std::forward<RangeT>(Range))));
}

template <typename WrappedIteratorT,
          typename T = decltype(&*std::declval<WrappedIteratorT>())>
class pointer_iterator
    : public iter_adaptor_base<
      pointer_iterator<WrappedIteratorT, T>, WrappedIteratorT,
      typename std::iterator_traits<WrappedIteratorT>::iterator_category,
      T>
{
    mutable T Ptr;

public:
    pointer_iterator() = default;

    explicit pointer_iterator(WrappedIteratorT u)
        : pointer_iterator::iter_adaptor_base(std::move(u)) {}

    T &operator*()
    {
        return Ptr = &*this->I;
    }
    const T &operator*() const
    {
        return Ptr = &*this->I;
    }
};

template <typename RangeT, typename WrappedIteratorT =
          decltype(std::begin(std::declval<RangeT>()))>
iter_range<pointer_iterator<WrappedIteratorT>>
        make_pointer_range(RangeT &&Range)
{
    using PointerIteratorT = pointer_iterator<WrappedIteratorT>;
    return make_range(PointerIteratorT(std::begin(std::forward<RangeT>(Range))),
                      PointerIteratorT(std::end(std::forward<RangeT>(Range))));
}

template <typename WrappedIteratorT,
          typename T1 = std::remove_reference_t<decltype(
                      **std::declval<WrappedIteratorT>())>,
          typename T2 = std::add_pointer_t<T1>>
using raw_pointer_iterator =
    pointer_iterator<pointee_iter<WrappedIteratorT, T1>, T2>;

} // end namespace llvm

#endif // LLVM_ADT_ITERATOR_H
