// SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later

#pragma once

#include <algorithm>
#include <array>
#include <atomic>
#include <cstddef>
#include <cstring>
#include <limits>
#include <new>
#include <span>
#include <type_traits>
#include <vector>

namespace Common {
	/// SPSC ring buffer
	/// @tparam T            Element type
	/// @tparam capacity     Number of slots in ring buffer
	template <typename T, std::size_t capacity>
	class RingBuffer {
		/// A "slot" is made of a single `T`.
		static constexpr std::size_t slot_size = sizeof(T);
		// T must be safely memcpy-able and have a trivial default constructor.
		static_assert(std::is_trivial_v<T>);
		// Ensure capacity is sensible.
		static_assert(capacity < std::numeric_limits<std::size_t>::max() / 2);
		static_assert((capacity & (capacity - 1)) == 0, "capacity must be a power of two");
		// Ensure lock-free.
		static_assert(std::atomic_size_t::is_always_lock_free);

	  public:
		/// Pushes slots into the ring buffer
		/// @param new_slots   Pointer to the slots to push
		/// @param slot_count  Number of slots to push
		/// @returns The number of slots actually pushed
		std::size_t push(const void* new_slots, std::size_t slot_count) {
			const std::size_t write_index = m_write_index.load();
			const std::size_t slots_free = capacity + m_read_index.load() - write_index;
			const std::size_t push_count = std::min(slot_count, slots_free);

			const std::size_t pos = write_index % capacity;
			const std::size_t first_copy = std::min(capacity - pos, push_count);
			const std::size_t second_copy = push_count - first_copy;

			const char* in = static_cast<const char*>(new_slots);
			std::memcpy(m_data.data() + pos, in, first_copy * slot_size);
			in += first_copy * slot_size;
			std::memcpy(m_data.data(), in, second_copy * slot_size);

			m_write_index.store(write_index + push_count);

			return push_count;
		}

		std::size_t push(std::span<const T> input) { return push(input.data(), input.size()); }

		/// Pops slots from the ring buffer
		/// @param output     Where to store the popped slots
		/// @param max_slots  Maximum number of slots to pop
		/// @returns The number of slots actually popped
		std::size_t pop(void* output, std::size_t max_slots = ~std::size_t(0)) {
			const std::size_t read_index = m_read_index.load();
			const std::size_t slots_filled = m_write_index.load() - read_index;
			const std::size_t pop_count = std::min(slots_filled, max_slots);

			const std::size_t pos = read_index % capacity;
			const std::size_t first_copy = std::min(capacity - pos, pop_count);
			const std::size_t second_copy = pop_count - first_copy;

			char* out = static_cast<char*>(output);
			std::memcpy(out, m_data.data() + pos, first_copy * slot_size);
			out += first_copy * slot_size;
			std::memcpy(out, m_data.data(), second_copy * slot_size);

			m_read_index.store(read_index + pop_count);

			return pop_count;
		}

		std::vector<T> pop(std::size_t max_slots = ~std::size_t(0)) {
			std::vector<T> out(std::min(max_slots, capacity));
			const std::size_t count = Pop(out.data(), out.size());
			out.resize(count);
			return out;
		}

		/// @returns Number of slots used
		[[nodiscard]] std::size_t size() const { return m_write_index.load() - m_read_index.load(); }

		/// @returns Maximum size of ring buffer
		[[nodiscard]] constexpr std::size_t Capacity() const { return capacity; }

	  private:
		// It is important to align the below variables for performance reasons:
		// Having them on the same cache-line would result in false-sharing between them.
		// TODO: Remove this ifdef whenever clang and GCC support
		//       std::hardware_destructive_interference_size.
#if defined(__cpp_lib_hardware_interference_size) && !defined(__ANDROID__)
		alignas(std::hardware_destructive_interference_size) std::atomic_size_t m_read_index{0};
		alignas(std::hardware_destructive_interference_size) std::atomic_size_t m_write_index{0};
#else
		alignas(128) std::atomic_size_t m_read_index{0};
		alignas(128) std::atomic_size_t m_write_index{0};
#endif

		std::array<T, capacity> m_data;
	};

}  // namespace Common