/*
 * 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 2010-2018 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include <cstddef>
#include <iterator>

namespace cruft::iterator {
    ///////////////////////////////////////////////////////////////////////////
    /// A numeric range that supplies a sequence of values.
    ///
    /// The value range is specified as [closed-open). ie, The last value will
    /// never be output by an iterator. This makes the object suitable as a
    /// means of iterating over the indices of an integrable indexed container
    /// (like std::vector)
    ///
    /// Primarily used for integrating into other utilities (like izip).
    template <typename ValueT = std::size_t>
    class iota {
    public:
        class iterator {
        public:
            using iterator_category = std::random_access_iterator_tag;
            using value_type = ValueT const;
            using difference_type = decltype (std::declval<value_type> () - std::declval<value_type> ());
            using pointer = value_type*;
            using reference = value_type&;

            explicit iterator ()
                : m_value {}
            { ; }

            explicit iterator (value_type _value)
                : m_value (_value)
            { ; }

            pointer   operator-> () const& noexcept { return &m_value; }
            reference operator*  () const& noexcept { return  m_value; }

            iterator& operator++ () noexcept { ++m_value; return *this; }
            iterator& operator-- () noexcept { --m_value; return *this; }

            constexpr difference_type
            operator- (iterator const &rhs) const noexcept
            {
                return m_value - rhs.m_value;
            }

            constexpr bool operator!= (iterator const &rhs) const noexcept { return m_value != rhs.m_value; }
            constexpr bool operator== (iterator const &rhs) const noexcept { return m_value == rhs.m_value; }
            constexpr bool operator<= (iterator const &rhs) const noexcept { return m_value <= rhs.m_value; }

        private:
            ValueT m_value;
        };

        using value_type = ValueT;
        using reference = ValueT&;
        using const_reference = ValueT const&;
        using const_iterator = iterator;
        using iterator = iterator;
        using difference_type = ssize_t;
        using size_type = size_t;

        iota ()
            : m_total {}
        { ; }

        iota (value_type _total)
          : m_total (_total)
        { ; }

        iterator   begin (void) const { return iterator {}; }
        iterator   end   (void) const { return iterator {m_total}; }

        iterator cbegin (void) const { return begin (); }
        iterator cend   (void) const { return cend (); }

        value_type size  (void) const { return m_total; }
        value_type max_size  (void) const { return std::numeric_limits<size_type>::max (); }
        bool empty  (void) const noexcept { return m_total == 0; }

        void swap (iota &other) { std::swap (m_total, other); }

        constexpr bool operator== (iota const &rhs) const noexcept { return m_total == rhs.m_total; }
        constexpr bool operator!= (iota const &rhs) const noexcept { return m_total == rhs.m_total; }

    private:
        value_type m_total;
    };


    template <typename ValueT>
    iota (ValueT) -> iota<ValueT>;
}