SnugLog/LibSnugLog/public_include/sl/strategies.h

#pragma once


#ifdef __cplusplus

#include <vector>
#include <chrono>

#endif

/**
 * @brief Describes what should happen if the allocated buffer is full and no logs can be written
 */
enum SL_ON_SINK_FULL {
	SL_OVERFLOW = 1, /**< When the sink is full, we want to drop the oldest data even if it is not written yet */
	SL_WAIT = 2 /**< When the sink is full, we want to wait for the next write. Do that if log keeping is critical */
};

/**
 * @brief Describes what type of IO should be used to log your data
 */
enum SL_SINK_IO_TYPE {
	SL_DIRECT_IO = 1, /**< Use IO that ensure data is written on disk as soon as possible. Useful for debugging. */
	SL_MMAPED_IO = 2, /**< Use IO that ensures that logging data will survive a software crash by using a memory mapped file as buffer. You can later expunge that buffer to get the useful information out. */
	SL_FASTEST_IO = 3, /**< Write with the highest throughput. */
	SL_EXTERNAL_IO = 4 /**< Do not handle any IO. Writes to a memory mapped file and let another process handle the IO. */
};

/**
 * @brief What type of buffer should we use?
 */
enum SL_BUFFER_TYPE {
	SL_EXTERNAL = 1, /**< Use a provided memory mapped non-temporary file */
	SL_SHARED = 2, /**< Use an automatically generated temporary file */
	SL_INTERNAL = 3 /**< Use internal memory. Compatible only with the SL_SINK_IO_TYPE: SL_DIRECT_IO and SL_FASTEST_IO. */
};

/**
 * @brief On what basis do we generate new files for logs?
 */
enum SL_ROLL_LOGS {
	SL_BY_TIME = 1, /**< Will create a new log every n-hours */
	SL_BY_SIZE = 2, /**< Will create a new log every n-KB */
	SL_NEVER = 0 /**< Will never split the log. Use when doing external logging. */
};

#ifndef __cplusplus
typedef enum SL_ON_SINK_FULL SL_ON_SINK_FULL;
typedef enum SL_SINK_IO_TYPE SL_SINK_IO_TYPE;
typedef enum SL_BUFFER_TYPE SL_BUFFER_TYPE;
typedef enum SL_ROLL_LOGS SL_ROLL_LOGS;
#endif

#ifdef __cpp_concepts
/**
 * @brief Represents the behaviour if the buffer would be overflowing.
 */
enum class overflow_response_t {
	must_wait = 0, /**< Represents that on overflow, the writer should wait using the strategy provided wait function. */
	must_overflow = 1, /**< Represents that on overflow, the writer should push the fence and keep on writing immediately, even if the log would get corrupt. */
	must_drop = must_wait /**< UNUSED, may be used in the future to mean that the current write should be dropped. */
};


/**
 * @brief This concept maps an overflow strategy.
 */
template<typename T>
concept OverflowStrategy = requires (T strategy) {
	{T::on_overflow} -> std::same_as<const overflow_response_t&>;
	{strategy.wait()};
};

/**
 * @brief This concept represents something that should be writable and mapped to valid memory within the software.
 *
 * @details This is used for mapping allocated buffers made from buffer strategies.
 */
template<typename T>
concept BufferLike = requires (T buffer) {
	{buffer.data()} -> std::same_as<char*>;
	{buffer.size()} -> std::same_as<size_t>;
};

/**
 * @brief This concept maps a buffer strategy.
 */
template<typename T>
concept BufferStrategy = requires (T strategy, std::string_view filename, size_t size) {
	{strategy.build_buffer(filename, size)} -> BufferLike;
	{strategy.build_buffer(filename, size)} -> std::same_as<typename T::buffer_type>;
};

/**
 * @brief This concept maps a sink strategy.
 */
template<typename T>
concept SinkStrategy = requires (T strategy, int fd, std::string_view data) {
	{strategy.write(fd, data)};
};

/**
 * @brief This concept maps an output strategy.
 */
template<typename T>
concept OutputStrategy = requires (T strategy, std::string_view source, int fd) {
	{strategy.chunk(source)} -> std::same_as<std::pair<std::string_view, std::string_view>>;
	{strategy.on_write_completed_event(source, fd)} -> std::same_as<int>;
};
#endif

#ifdef __cplusplus
#ifndef __cpp_concepts

#define OverflowStrategy typename
#define BufferStrategy typename
#define SinkStrategy typename
#define OutputStrategy typename

#endif

/**
 * @brief Represent a mapped buffer. You should generally not touch this as it is internal representation for strategies.
 */
struct mapped_buffer {
	char* _data;
	size_t _size;
	
	/**
	 * @return the data pointer of the buffer
	 */
	[[nodiscard]] char* data() const { return _data; }
	/**
	 * @return the size of the allocated buffer
	 */
	[[nodiscard]] size_t size() const { return _size; }
};

/**
 * @brief a strategy type directing how buffers are allocated. This directs the buffer strategy to use a standard container to allocate.
 */
struct BufferStrategyInternal {
	using buffer_type = std::vector<char>;
	static_assert(BufferLike<buffer_type>);
	buffer_type build_buffer(std::string_view, size_t);
};

/**
 * @brief a strategy that employs a memory mapped buffer to manage its memory. Said buffer is expected to be read from the same process.
 */
struct BufferStrategyShared {
	using buffer_type = mapped_buffer;
	static_assert(BufferLike<buffer_type>);
	buffer_type build_buffer(std::string_view, size_t);
};

/**
 * @brief a strategy that employs a memory mapped buffer to manage its memory. Said buffer is expected to be read from a different process.
 */
struct BufferStrategyExternal {
	using buffer_type = mapped_buffer;
	static_assert(BufferLike<buffer_type>);
	buffer_type build_buffer(std::string_view, size_t);
};

/* * ... * */

/**
 * @brief a strategy that makes the sink flush at every write, making the IO to disk as soon as possible.
 */
struct SinkStrategyDirect {
	void write(int fd, std::string_view data);
};

/**
 * @brief a strategy that makes the sink write with the settings that have the highest throughput.
 */
struct SinkStrategyFastest {
	void write(int fd, std::string_view data);
};

/**
 * @brief a strategy that makes the sink write using memory mapped IO, making the IO always commit to system pages before returning.
 */
struct SinkStrategyMmaped {
	void write(int fd, std::string_view data);
};

/**
 * @brief a strategy that makes the sink do nothing, expecting another process to handle the process.
 */
struct SinkStrategyExternal {
	void write(int fd, std::string_view data);
};

/* * ... * */

/**
 * @brief a strategy that makes overflowing waiting. The waiting is handled by exponential backoff of factor 1.5
 */
struct OverflowStrategyWait {
	static constexpr overflow_response_t on_overflow = overflow_response_t::must_wait;
	void wait();
};
/**
 * @brief a strategy that makes overflowing overwrite the data, possibly corrupting the generated log, without waiting.
 */
struct OverflowStrategyContinue {
	static constexpr overflow_response_t on_overflow = overflow_response_t::must_overflow;
	void wait();
};

/* * ... * */

/**
 * @brief a strategy that controls how often new log files are generated. Logs are spaced by making them writable for only a certain amount of time.
 */
struct OutputStrategyTimed {
	std::chrono::seconds interval;
	std::string_view directory;
	std::optional<std::chrono::time_point<std::chrono::file_clock> > last_change = std::nullopt;
	
	std::pair<std::string_view, std::string_view> chunk(std::string_view);
	int on_write_completed_event(std::string_view, int);
};

/**
 * @brief a strategy that controls how often new log files are generated. Logs are spaced by making them at most one line longer that the amount of bytes specified.
 */
struct OutputStrategySized {
	uint64_t interval;
	std::string_view directory;
	uint64_t written_bytes = 0;
	
	std::pair<std::string_view, std::string_view> chunk(std::string_view);
	int on_write_completed_event(std::string_view, int);
};

/**
 * @brief a strategy that makes the logs be generated in the same file all the time.
 */
struct OutputStrategySimple {
	std::pair<std::string_view, std::string_view> chunk(std::string_view);
	int on_write_completed_event(std::string_view, int);
};
#endif