gplib/include/gp/utils/iterator.hpp

#pragma once

#include <cstddef>
#include <cstdint>

// BUG: none of this is in a namespace
// TODO: Specify the concept of an iterator

namespace gp {
		
	/**
	* @brief An enumeration that may be used to determine iterator categories
	* 
	*/
	enum class iterator_type_t{
		contiguous_iterator, /**< Defines an iterator for something that is continuous and random access */
		non_contiguous_iterator, /**< Defines an iterator for a non contiguous datastructure, for example an iterator over a hashmap or a tree*/
		lazy_iterator /**< Defines an iterator for which the actual data layout and availability are still unknown*/
	};

	/**
	* @brief An abstraction of a pointer to iterate against, in both normal and reverse order
	* 
	* @tparam T The type of data pointed by the iterator
	* @tparam sign the direction in which data is scrutinized, should be either 1 or -1, behaviour for other value is left undefined
	*/
	template<typename T, int sign = 1>
	struct pointer_iterator final
	{
		T* data; /**< the only data field of the class */
		typedef T value_type; /**< The type of which a reference will be returned on dereferencing */
		typedef std::size_t difference_type; /**< The type of the substraction of two pointers */
		static constexpr iterator_type_t iterator_type = iterator_type_t::contiguous_iterator; /**< @see  iterator_type_t */

		/**
		* @brief Generates an empty iterator
		*/
		constexpr pointer_iterator()
		: data{nullptr}
		{}

		constexpr pointer_iterator(const pointer_iterator& oth)
		: data{oth.data}
		{}

		/**
		* @brief Generates an iterator from any pointer
		*/
		constexpr pointer_iterator(T* ptr)
		: data{ptr}
		{}

		/**
		* @brief Dereference unary operator
		* 
		* @return constexpr T& returns a reference to the pointed value
		*/
		constexpr T& operator*() const
		{
			return *data;
		}

		constexpr pointer_iterator& operator++()
		{
			data += sign;
			return *this;
		}

		constexpr pointer_iterator operator++(int)
		{
			auto p = *this;
			data += sign;
			return p;
		}

		constexpr pointer_iterator& operator--()
		{
			data -= sign;
			return *this;
		}

		constexpr pointer_iterator operator--(int)
		{
			auto p = *this;
			data -= sign;
			return p;
		}

		constexpr pointer_iterator operator+(const std::size_t offset) const
		{
			return pointer_iterator{data+sign*offset};
		}

		constexpr pointer_iterator operator+(const int offset) const
		{
			return pointer_iterator{data+sign*offset};
		}

		constexpr pointer_iterator operator-(const std::size_t offset) const
		{
			return pointer_iterator{data-sign*offset};
		}

		constexpr pointer_iterator operator-(const int offset) const
		{
			return pointer_iterator{data-sign*offset};
		}

		constexpr difference_type operator-(const pointer_iterator& oth) const
		{
			return ((T*)data-(T*)oth.data)*sign;
		}

		constexpr bool operator==(const pointer_iterator oth) const
		{
			return data==oth.data;
		}

		constexpr bool operator!=(pointer_iterator oth) const
		{
			return data!=oth.data;
		}

		constexpr bool before_or_equal(const pointer_iterator oth) const
		{
			return reinterpret_cast<std::intptr_t>(data) <= reinterpret_cast<std::intptr_t>(oth.data);
		}

		constexpr bool operator<=(const pointer_iterator oth) const
		{
			return before_or_equal(oth);
		}
	};

	/**
	* @brief An identical twin to the pointer_iterator, but which dereference to a const reference
	* 
	* @see pointer_iterator
	* @tparam T @see pointer_iterator
	* @tparam sign @see pointer_iterator
	*/
	template<typename T, int sign = 1>
	struct const_pointer_iterator final
	{
		const T* data; /**< @see pointer_iterator */
		typedef T value_type; /**< @see pointer_iterator */
		typedef std::size_t difference_type; /**< @see pointer_iterator */
		static constexpr iterator_type_t iterator_type = iterator_type_t::contiguous_iterator; /**< @see pointer_iterator */

		constexpr const_pointer_iterator(const const_pointer_iterator& oth)
		: data{oth.data}
		{}

		/**
		* @brief @see pointer_iterator
		*/
		constexpr const_pointer_iterator(const T* ptr)
		: data{ptr}
		{}

		/**
		* @brief Dereferencing returns a const version of what a pointer_iterator would return
		*/
		constexpr const T& operator*() const
		{
			return *data;
		}

		constexpr const_pointer_iterator& operator++()
		{
			data += sign;
			return *this;
		}

		constexpr const_pointer_iterator operator++(int)
		{
			auto p = data;
			data += sign;
			return const_pointer_iterator{p};
		}

		constexpr const_pointer_iterator& operator--()
		{
			data -= sign;
			return *this;
		}

		constexpr const_pointer_iterator operator--(int)
		{
			auto p = data;
			data -= sign;
			return const_pointer_iterator{p};
		}

		constexpr const_pointer_iterator operator+(const std::size_t offset) const 
		{
			return const_pointer_iterator{data+sign*offset};
		}

		constexpr const_pointer_iterator operator+(const int offset) const
		{
			return const_pointer_iterator{data+sign*offset};
		}

		constexpr const_pointer_iterator operator-(const std::size_t offset) const
		{
			return const_pointer_iterator{data-sign*offset};
		}

		constexpr const_pointer_iterator operator-(const int offset)
		{
			return const_pointer_iterator{data-sign*offset};
		}

		constexpr difference_type operator-(const const_pointer_iterator& oth) const
		{
			return ((T*)data-(T*)oth.data)*sign;
		}

		constexpr bool operator==(const const_pointer_iterator oth) const
		{
			return data==oth.data;
		}

		constexpr bool operator!=(const_pointer_iterator oth) const
		{
			return data!=oth.data;
		}

		constexpr bool before_or_equal(const const_pointer_iterator oth) const
		{
			return reinterpret_cast<std::intptr_t>(data) <= reinterpret_cast<std::intptr_t>(oth.data);
		}

		constexpr bool operator<=(const const_pointer_iterator oth) const
		{
			return before_or_equal(oth);
		}
	};
}