libcruft-util/view.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2015-2018 Danny Robson <danny@nerdcruft.net>
 */


#ifndef CRUFT_UTIL_VIEW_HPP
#define CRUFT_UTIL_VIEW_HPP

#include "annotation.hpp"
#include "cast.hpp"
#include "types/traits.hpp"
#include "maths.hpp"
#include "platform.hpp"

#include <cstdlib>
#include <iosfwd>
#include <string>
#include <cstring>
#include <stdexcept>
#include <iterator>

namespace util {
    template <typename BeginT, typename EndT = BeginT>
    struct view {
    public:
        //---------------------------------------------------------------------
        using value_type = typename std::iterator_traits<
            remove_restrict_t<BeginT>
        >::value_type;

        using size_type = size_t;

        //---------------------------------------------------------------------
        constexpr
        view (const BeginT &first, const EndT &last) noexcept:
            m_begin (first),
            m_end   (last)
        { ; }

        template <
            typename ContainerT,
            typename = std::enable_if_t<is_container_v<std::decay_t<ContainerT>>,void>
        >
        view (ContainerT &rhs):
            view (rhs.begin (), rhs.end ())
        { ; }


        template <
            typename ContainerT,
            typename = std::enable_if_t<is_container_v<std::decay_t<ContainerT>>,void>
        >
        view (const ContainerT &rhs):
            view (rhs.begin (), rhs.end ())
        { ; }


        //---------------------------------------------------------------------
        // cosntruction from pointer/size represenations for ease of use with
        // legacy C code.
        template <
            typename CountT,
            typename = std::enable_if_t<std::is_integral_v<CountT>,void>
        >
        view (
            const BeginT &_begin,
            CountT _size
        ):
            view (_begin, _begin + _size)
        { ; }


        //---------------------------------------------------------------------
        // implicit conversion from const pointer const views to const pointer views
        template <
            typename ValueT,
            typename = std::enable_if_t<
                std::is_same_v<BeginT, const ValueT**> &&
                std::is_same_v<EndT,   const ValueT**>
            >
        >
        view (const view<const ValueT*const*,const ValueT*const*> &rhs):
            m_begin (const_cast<const ValueT**> (rhs.begin ())),
            m_end   (const_cast<const ValueT**> (rhs.end   ()))
        { ; }

        //---------------------------------------------------------------------
        // implicit conversion from pointer views to const pointer views
        template <
            typename ValueT,
            typename = std::enable_if_t<
                std::is_same_v<BeginT, const ValueT*> &&
                std::is_same_v<EndT,   const ValueT*>
            >
        >
        view (const view<ValueT*,ValueT*> &rhs):
            m_begin (rhs.begin ()),
            m_end   (rhs.end   ())
        { ; }


        //---------------------------------------------------------------------
        // explicitly cater for the char array case so that we don't
        // accidentally include the trailing null in the data.
        template <std::size_t N>
        view (const char (&value)[N]):
            view {std::begin (value), std::begin (value) + N - 1}
        {
            static_assert (N > 0);
        }


        //---------------------------------------------------------------------
        view (const char *str):
            view { str, str + strlen (str) }
        { ; }


        //---------------------------------------------------------------------
        view (char *str):
            view (str, str + strlen (str))
        { ; }


        //---------------------------------------------------------------------
        template <std::size_t N>
        view (char (&value)[N]):
            view {std::begin (value), std::begin (value) + N - 1}
        {
            static_assert (N > 0);
        }


        //---------------------------------------------------------------------
        template <std::size_t N, typename ValueT>
        view (const ValueT(&value)[N]):
            view {std::begin (value), std::end (value)}
        { ; }


        //---------------------------------------------------------------------
        template <std::size_t N, typename ValueT>
        view (ValueT(&value)[N]):
            view {std::begin (value), std::end (value)}
        { ; }


        //---------------------------------------------------------------------
        constexpr view (const view &) noexcept = default;
        constexpr view (view &&) noexcept = default;

        view& operator= (const view &rhs) noexcept = default;
        view& operator= (view &&rhs) noexcept = default;


        //---------------------------------------------------------------------
        // allow null construction of views where IteratorT is constructible
        // from nullptr_t
        //
        // ideally we would avoid exposing this as it promotes use of nulls but
        // it simplifies construction of views that are data members of classes
        // when we may not immediately know the values we should contain.
        constexpr view (std::nullptr_t) noexcept:
            view {nullptr,nullptr}
        { ; }


        //---------------------------------------------------------------------
        template <typename CharT, typename Traits, typename Allocator>
        view (std::basic_string<CharT,Traits,Allocator> &val):
            view (std::data (val), std::data (val) + std::size (val))
        { ; }


        //---------------------------------------------------------------------
        template <typename CharT, typename Traits, typename Allocator>
        view (const std::basic_string<CharT,Traits,Allocator> &val):
            view (std::data (val), std::data (val) + std::size (val))
        { ; }


        //---------------------------------------------------------------------
        template <typename ValueT, typename AllocatorT>
        view (const std::vector<ValueT,AllocatorT> &rhs):
            view (std::data (rhs), std::data (rhs) + std::size (rhs))
        { ; }


        //---------------------------------------------------------------------
        template <typename ValueT, typename AllocatorT>
        view (std::vector<ValueT,AllocatorT> &rhs):
            view (std::data (rhs), std::data (rhs) + std::size (rhs))
        { ; }


        //---------------------------------------------------------------------
        template <typename ValueT, std::size_t N>
        view (std::array<ValueT,N> &rhs):
            view (std::data (rhs), std::data (rhs) + std::size (rhs))
        { ; }


        //---------------------------------------------------------------------
        template <typename ValueT, std::size_t N>
        view (const std::array<ValueT,N> &rhs):
            view (std::data (rhs), std::data (rhs) + std::size (rhs))
        { ; }


        ///////////////////////////////////////////////////////////////////////
        constexpr BeginT begin (void)       noexcept { return m_begin; }
        constexpr EndT   end   (void)       noexcept { return m_end;   }
        constexpr BeginT begin (void) const noexcept { return m_begin; }
        constexpr EndT   end   (void) const noexcept { return m_end; }

        //---------------------------------------------------------------------
        constexpr BeginT cbegin (void) const noexcept { return m_begin; }
        constexpr EndT   cend   (void) const noexcept { return m_end;   }

        //---------------------------------------------------------------------
        auto data (void)       noexcept { return begin (); }
        auto data (void) const noexcept { return begin (); }


        ///////////////////////////////////////////////////////////////////////
        constexpr bool
        empty (void) const noexcept
        {
            return m_begin == m_end;
        }

        //---------------------------------------------------------------------
        // the return type of size _should_ be whatever std::distance returns,
        // or something else that makes sense for the iterators we've been
        // handed.
        //
        // but it's a pain in the arse to use sizes that aren't unsigned given
        // that other libraries need to compare sizes pretty often and
        // everything else in the world tends to be unsigned.
        constexpr auto
        size (void) const noexcept
        {
            return static_cast<size_type> (std::distance (m_begin, m_end));
        }

        //---------------------------------------------------------------------
        [[nodiscard]] constexpr auto
        redim (size_type count) const
        {
            assert (count > 0);
            if (count > size ())
                throw std::invalid_argument ("redim to higher size not allowed");
            return view { m_begin, m_begin + count };
        };


        //---------------------------------------------------------------------
        [[nodiscard]] constexpr std::tuple<
            util::view<BeginT,BeginT>,
            util::view<BeginT,EndT>
        >
        split (BeginT pos) const
        {
            return {
                { m_begin, pos },
                { pos, m_end }
            };
        }


        //---------------------------------------------------------------------
        template <typename IndexT>
        [[nodiscard]] constexpr auto
        split (IndexT idx) const
        {
            auto last = m_begin;
            std::advance (last, idx);
            return split (last);
        }


        //---------------------------------------------------------------------
        // slices a view using python indexing semantics. ie,
        // "abc".slice(0,  3) == "abc"
        // "abc".slice(0, -1) == "abc"
        // "abc".slice(0, -2) == "ab"
        template <typename IndexA, typename IndexB>
        [[nodiscard]]constexpr auto
        slice (IndexA a, IndexB b) const
        {
            auto first = m_begin;
            auto last  = m_begin;

            std::advance (first, a < 0 ? size () + a + 1 : a);
            std::advance (last,  b < 0 ? size () + b + 1 : b);

            return util::view { first, last };
        }


        //---------------------------------------------------------------------
        template <typename IndexT>
        constexpr auto
        head (IndexT idx)
        {
            return std::get<0> (split (idx));
        }


        //---------------------------------------------------------------------
        template <typename IndexT>
        constexpr auto
        tail (IndexT idx)
        {
            return std::get<1> (split (idx));
        }


        //---------------------------------------------------------------------
        template <typename IndexT>
        [[nodiscard]] constexpr auto
        consume (IndexT count) const
        {
            auto [a,b] = split (count);
            (void)a;
            return b;
        }


        //---------------------------------------------------------------------
        [[nodiscard]] constexpr util::view<BeginT,EndT>
        consume (util::view<BeginT,EndT> prefix) const
        {
            assert (prefix.begin () == begin ());
            assert (prefix.end () < end ());

            return { prefix.end (), end () };
        }


        [[nodiscard]] constexpr util::view<BeginT,EndT>
        consume (const BeginT pos) const
        {
            return { pos, end () };
        }


        constexpr auto
        operator+ (int count) const
        {
            return consume (count);
        }


        constexpr auto
        operator+= (int count)&
        {
            return *this = consume (count);
        }


        ///////////////////////////////////////////////////////////////////////
        template <
            typename ValueT,
            typename = std::enable_if_t<
                std::is_pointer_v<BeginT> && std::is_pointer_v<ValueT>
            >
        >
        view<ValueT>
        cast (void) const
        {
            return {
                util::cast::alignment<ValueT> (m_begin),
                util::cast::alignment<ValueT> (m_end)
            };
        }


        ///////////////////////////////////////////////////////////////////////
        constexpr auto&&
        operator[] (size_t idx) noexcept
        {
            return *std::next (begin (), idx);
        }

        //---------------------------------------------------------------------
        constexpr auto&&
        operator[] (size_t idx) const noexcept
        {
            return *std::next (begin (), idx);
        }


    private:
        ///////////////////////////////////////////////////////////////////////
        BeginT m_begin;
        EndT m_end;
    };


    //-------------------------------------------------------------------------
    template <typename ValueT, std::size_t N>
    view (ValueT(&)[N]) -> view<ValueT*,ValueT*>;


    //-------------------------------------------------------------------------
    view (const char*) -> view<const char*, const char*>;

    view (char*) -> view<char*>;


    //-------------------------------------------------------------------------
    template <
        typename IteratorT,
        typename SizeT,
        typename = std::enable_if_t<
            std::is_integral_v<SizeT>
        >
    >
    view (IteratorT, SizeT) -> view<IteratorT,IteratorT>;


    template <typename CharT, typename Traits, typename Allocator>
    view (std::basic_string<CharT,Traits,Allocator> &) -> view<typename Allocator::pointer>;


    template <typename CharT, typename Traits, typename Allocator>
    view (const std::basic_string<CharT,Traits,Allocator> &) -> view<typename Allocator::const_pointer>;

    template <typename ValueT, typename AllocatorT>
    view (std::vector<ValueT,AllocatorT>&) -> view<typename AllocatorT::pointer>;


    template <typename ValueT, typename AllocatorT>
    view (const std::vector<ValueT,AllocatorT>&) -> view<typename AllocatorT::const_pointer>;

    template <typename ValueT, std::size_t N>
    view (std::array<ValueT,N>&) -> view<ValueT*>;

    template <typename ValueT, std::size_t N>
    view (const std::array<ValueT,N>&) -> view<const ValueT*>;

    template <typename ContainerT>
    view (ContainerT&) -> view<
        typename ContainerT::iterator
    >;

    template <typename ContainerT>
    view (const ContainerT&) -> view<
        typename ContainerT::const_iterator
    >;

    // base + count constructor
    template <typename BeginT>
    view (BeginT, std::uint64_t count) -> view<BeginT,BeginT>;

    template <typename BeginT>
    view (BeginT, std::uint32_t count) -> view<BeginT,BeginT>;


    ///////////////////////////////////////////////////////////////////////////
    template <typename ValueT, size_t N>
    auto
    make_view (const ValueT (&arr)[N])
    {
        return util::view<const ValueT*> (arr + 0, arr + N);
    }

    //-------------------------------------------------------------------------
    template <typename ContainerT>
    auto
    make_view (ContainerT &t)
    {
        return util::view { std::begin (t), std::end (t) };
    }

    //-------------------------------------------------------------------------
    template <typename ContainerT>
    auto
    make_view (const ContainerT &t)
    {
        return util::view { std::cbegin (t), std::cend (t) };
    }


    //-------------------------------------------------------------------------
    // disable the possibility of creating a view to a temporary. note that
    // this only works if an lval version has already been defined otherwise
    // universal reference rules will capture both lval and rval here.
    template <typename ContainerT>
    auto
    make_view (ContainerT&&) = delete;


    ///////////////////////////////////////////////////////////////////////////
    template <typename ContainerT>
    auto
    make_cview (const ContainerT &t)
    {
        return make_view (t);
        //return util::view<decltype(std::cbegin (t))> { std::cbegin (t), std::cend (t) };
    }


    //-------------------------------------------------------------------------
    template <typename BeginT, typename EndT>
    auto
    make_view (BeginT first, EndT last)
    {
        return view<BeginT, EndT> {first, last};
    }

    //-------------------------------------------------------------------------
    template <typename ValueT>
    auto
    make_cview (ValueT *first, ValueT *last)
    {
        return view<const ValueT*> {first, last};
    }

    ///////////////////////////////////////////////////////////////////////////
    inline
    view<const char*> make_view (const char *str)
    {
        return { str, str + strlen (str) };
    }


    //-------------------------------------------------------------------------
    inline
    view<char*> make_view (char *str)
    {
        return { str, str + strlen (str) };
    }


    //-------------------------------------------------------------------------
    template <typename CharT, typename TraitsT, typename AllocT>
    view<const CharT*>
    make_view (const std::basic_string<CharT,TraitsT,AllocT> &str)
    {
        return {
            std::data (str),
            std::data (str) + std::size (str)
        };
    }


    //-------------------------------------------------------------------------
    template <typename CharT, typename TraitsT, typename AllocT>
    view<CharT*>
    make_view (std::basic_string<CharT,TraitsT,AllocT> &str)
    {
        return {
            std::data (str),
            std::data (str) + std::size (str)
        };
    }


    //-------------------------------------------------------------------------
    template <typename CharT, typename TraitsT, typename AllocT>
    view<const CharT*>
    make_view (const std::basic_string<CharT,TraitsT,AllocT>&&) = delete;


    //-------------------------------------------------------------------------
    template <typename CharT, typename TraitsT, typename AllocT>
    view<CharT*>
    make_view (std::basic_string<CharT,TraitsT,AllocT>&&) = delete;


    ///////////////////////////////////////////////////////////////////////////
    // calculates a byte oriented view over an arbitrary type
    //
    // useful for passing in memory structures to file descriptors and the
    // like. but the consequences of endian conversion is on the user...
    //
    // we have to be careful that rval-references and other temporaries aren't
    // accepted in this signature.
    template <
        typename ByteT = std::byte,
        typename T
    >
    auto
    make_byte_view (T &t)
    {
        using cursor_type = std::conditional_t<
            std::is_const_v<T>,
            ByteT const*,
            ByteT*
        >;

        return util::view {
            reinterpret_cast<cursor_type> (&t),
            sizeof (T)
        };
    }


    ///////////////////////////////////////////////////////////////////////////
    /// returns a reference to a value of the designated type at the front of
    /// the byte-view. if there is insufficient data for the extraction an
    /// exception will be thrown.
    ///
    /// there are no validity or other checks performed on the returned data
    /// this is deliberate, so that the function is safe to call on user
    /// supplied data during parsing routines. it is up to the user to ensure
    /// the object is valid.
    ///
    /// the buffer object is advanced in place so that it no longer covers
    /// the extract value
    ///
    /// it is assumed the user has taken care of alignment concerns
    template <
        typename ValueT,
        typename ByteT,
        typename = std::enable_if_t<sizeof (ByteT) == 1>
    >
    ValueT const&
    extract (util::view<const ByteT*> &buffer)
    {
        if (unlikely (sizeof (ValueT) > buffer.size ()))
            throw std::runtime_error ("insufficient data for extraction");

        ValueT const &res = *util::cast::alignment<ValueT const*> (buffer.data ());
        buffer = buffer.consume (sizeof (ValueT));
        return res;
    }


    ///////////////////////////////////////////////////////////////////////////
    /// extracts an object of a specified type from the front of a byte-view.
    ///
    /// in contrast to 'extract' this will always copy the bytes out from the
    /// view, making the operation alignment safe.
    template <
        typename ValueT,
        typename ByteT,
        typename = std::enable_if_t<sizeof(ByteT) == 1>
    >
    ValueT
    read (util::view<ByteT*> &buffer)
    {
        // we disable the class-memaccess warning so that we can memcpy into
        // types that we know are safe but the compiler will complain about.
        // this occurs commonly with oddly packed structures, eg anything
        // that uses gnu::packed
#if defined(COMPILER_GCC)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wclass-memaccess"
#endif
        if (unlikely (sizeof (ValueT) > buffer.size ()))
            throw std::runtime_error ("insufficient data for extraction");

        ValueT res;
        memcpy (&res, buffer.data (), sizeof (ValueT));
        buffer = buffer.consume (sizeof (ValueT));
        return res;
#if defined(COMPILER_GCC)
#pragma GCC diagnostic pop
#endif
    }


    ///////////////////////////////////////////////////////////////////////////
    template <typename IteratorT>
    constexpr bool
    intersects (util::view<IteratorT> a, IteratorT b)
    {
        return b >= a.begin () && b < a.end ();
    }


    ///////////////////////////////////////////////////////////////////////////
    template <
        typename BeginA, typename EndA,
        typename BeginB, typename EndB
    >
    constexpr bool
    equal (const view<BeginA,EndA> &a, const view<BeginB,EndB> &b)
    {
        return a.size () == b.size () &&
               std::equal (std::begin (a), std::end (a), std::begin (b));
    }


    //-------------------------------------------------------------------------
    // defer equality to the view/view operator by way of make_view
    template <
        typename IteratorA,
        typename IteratorB,
        typename ValueT,
        typename = std::enable_if_t<
            !std::is_same_v<ValueT, view<IteratorA,IteratorB>>,
            void
        >
    >
    constexpr bool
    equal (const view<IteratorA,IteratorB> &a, const ValueT &b)
    {
        return equal (a, make_view (b));
    }


    //-------------------------------------------------------------------------
    // reverse the arguments and forward to the above operator. we formumlate
    // equality this way to avoid implementing the operator twice for each
    // weird case.
    template <
        typename IteratorA,
        typename IteratorB,
        typename ValueT,
        typename = std::enable_if_t<
            !std::is_same_v<ValueT, view<IteratorA,IteratorB>>,
            void
        >
    >
    constexpr bool
    equal (const ValueT &a, const view<IteratorA,IteratorB> &b)
    {
        return equal (b, a);
    }


    ///////////////////////////////////////////////////////////////////////////
    template <typename IteratorA, typename IteratorB>
    constexpr bool
    operator== (const view<IteratorA,IteratorB> &a, const view<IteratorA,IteratorB> &b)
    {
        return a.begin () == b.begin () && a.end () == b.end ();
    }


    //-------------------------------------------------------------------------
    template <typename IteratorA, typename IteratorB>
    constexpr bool
    operator!= (const view<IteratorA,IteratorB> &a, const view<IteratorA,IteratorB> &b)
    {
        return !(a == b);
    }


    //-------------------------------------------------------------------------
    template <
        typename IteratorA,
        typename IteratorB,
        typename ValueT,
        typename = std::enable_if_t<
            !std::is_same_v<ValueT, view<IteratorA,IteratorB>>,
            void
        >
    >
    constexpr bool
    operator!= (const view<IteratorA,IteratorB> &a, const ValueT &b)
    {
        return !(a == b);
    }


    //-------------------------------------------------------------------------
    template <
        typename IteratorA,
        typename IteratorB,
        typename ValueT,
        typename = std::enable_if_t<
            !std::is_same_v<ValueT, view<IteratorA,IteratorB>>,
            void
        >
    >
    constexpr bool
    operator!= (const ValueT &a, const view<IteratorA,IteratorB> &b)
    {
        return !(a == b);
    }


    ///////////////////////////////////////////////////////////////////////////
    template <typename CharT>
    bool
    operator== (
        util::view<const CharT*> lhs,
        const std::basic_string<CharT> &rhs
    ) {
        return lhs.size () == rhs.size () && std::equal (lhs.cbegin (), lhs.cend (), rhs.cbegin ());
    }


    inline bool
    operator== (util::view<const char*> lhs, const char *rhs)
    {
        return lhs.size () == strlen (rhs) && std::equal (lhs.cbegin (), lhs.cend (), rhs);
    }


    ///////////////////////////////////////////////////////////////////////////
    template <typename BeginT, typename EndT>
    std::ostream&
    operator<< (std::ostream &os, view<BeginT, EndT> val)
    {
        std::copy (
            std::cbegin (val),
            std::cend   (val),
            std::ostream_iterator<typename decltype(val)::value_type> (os)
        );

        return os;
    }


    ///////////////////////////////////////////////////////////////////////////
    /// a basic stringlike comparison operator that behaves as
    /// std::string::compare would.
    ///
    /// provided so that the common case of stringlike views can be used in a
    /// std::map and similar without a great deal of work.
    inline bool
    operator< (util::view<const char*> a, util::view<const char*> b)
    {
        const auto la = std::size (a);
        const auto lb = std::size (b);

        const auto res = strncmp (
            std::data (a),
            std::data (b),
            util::min (la, lb)
        );

        return res < 0 || (res == 0 && la < lb);
    }


}


#endif