gplib/include/gp/iterator.hpp

#pragma once

#include <cstddef>
#include <cstdint>

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

/**
 * @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);
	}
};