#pragma once

/// A type that spans a sized region of memory
template<typename T>
struct Span {
	virtual const void* area() const =0;
	virtual void* area() = 0;
	virtual size_t size() const = 0;

	inline T* ptr() { return (T*)area(); }
	inline const T* ptr() const { return (const T*)area(); }

	inline size_t size_bytes() const { return size() * sizeof(T); }

	inline unsigned char* as_bytes() { return (unsigned char*)area(); }
	inline const unsigned char* as_bytes() const { return (const unsigned char*)area(); }

	inline T& operator[](size_t index) {
		if(index >= size()) throw "index out of range";
		return ptr()[index];
	}
	inline const T& operator[](size_t index) const {
		if(index >= size()) throw "index out of range";
		return ptr()[index];
	}

	inline T* operator&() { return &(*this)[0]; }
	inline const T* operator&() const {return &(*this)[0]; }

	inline T* operator->() { return &(*this)[0]; }
	inline const T* operator->() const {return &(*this)[0]; }

	inline T& operator*() { return (*this)[0]; }
	inline const T& operator*() const { return (*this)[0]; }


	template<typename U>
	inline U* area_as() requires(sizeof(T) % sizeof(U) == 0) { return (U*)area(); }
	template<typename U>
	inline const U* area_as() const requires(sizeof(T) % sizeof(U) == 0) { return (U*)area(); }

	template<typename U>
	size_t size_as() const requires(sizeof(T) % sizeof(U) == 0) { return size_bytes() / sizeof(U); }

	struct Slice;

	inline bool bounds_ok(size_t start) const
	{
		return start < size();
	}
	inline bool bounds_ok(size_t start, size_t len) const
	{
		return (start + len) <= size() && bounds_ok(start);
	}

	inline ssize_t wrap_len(ssize_t len) const
	{
		if(size() ==0 ) return 0;
		return len < 0 ? wrap_len(size() + len) : ((size_t)len) % size();
	}

	/// Slice (absolute). Specify start and end.
	inline const Slice slice_abs(size_t start, size_t end) const { auto len = end -start; if(bounds_ok(start,len)) return Slice(const_cast<T*>(ptr()+start), len); else throw "Out of bounds slice"; }
	inline Slice slice_abs(size_t start, size_t end) { auto len = end -start; if(bounds_ok(start,len)) return Slice(ptr()+start, len); else throw "Out of bounds slice"; }

	/// Slice (relative). Specify start and length.
	inline const Slice slice(size_t start, size_t len) const { if(bounds_ok(start,len)) return Slice(const_cast<T*>(ptr()+start), len); else throw "Out of bounds slice"; }
	inline Slice slice(size_t start, size_t len) { if(bounds_ok(start,len)) return Slice(ptr()+start, len); else throw "Out of bounds slice"; }
	

	/// Slice from 0. Specify length.
	inline Slice slice(size_t len) { return slice(0, len); }
	inline const Slice slice(size_t len) const { return slice(0, len); }//slice(start, size()-start); }

	/// Slice total.
	inline Slice slice() { return slice(0, size()); }
	inline const Slice slice() const { return slice(0, size()); }

	/// Slice wrapping. Specify start and end that may wrap over and/or under the span's size.
	inline Slice slice_wrap(ssize_t start, ssize_t end) { return slice_abs((size_t)wrap_len(start), (size_t)wrap_len(end)); }
	inline const Slice slice_wrap(ssize_t start, ssize_t end) const { return slice_abs((size_t)wrap_len(start), (size_t)wrap_len(end)); }
	inline Slice slice_wrap(ssize_t len) { return slice_abs((size_t)wrap_len(len)); }
	inline const Slice slice_wrap(ssize_t len) const { return slice_abs((size_t)wrap_len(len)); }

	template<typename U>
	inline Span<U>::Slice reinterpret() { return typename Span<U>::Slice((U*)area(), size_bytes() / sizeof(U)); }	
	template<typename U>
	inline Span<const U>::Slice reinterpret() const { return typename Span<const U>::Slice((const U*)area(), size_bytes() / sizeof(U)); }
};

/// A slice of memory with a backing pointer and size.
template<typename T>
struct Span<T>::Slice : public Span<T> {
	inline Slice(T* ptr, size_t sz) : _area((void*)ptr), _size(sz){}
	inline Slice(const Span<T>& slice) : _area(const_cast<void*>(slice.area())), _size(slice.size()){}
	inline Slice(const Slice& copy) = default;
	inline Slice(Slice&& copy) : _area(copy._area), _size(copy._size){ *const_cast<size_t*>(&copy._size) = 0; }
	Slice() = delete;

	inline const void* area() const override { return _area; }
	inline void* area() override { return _area; }
	inline size_t size() const override { return _size; }

	
	private:
	void* const _area;
	const size_t _size;
};


template<typename T>
using Slice = Span<T>::Slice;
