Log/Log.h

#pragma once

#include <atomic>
#include <functional>  // std::function
#include <sstream>  // std::stringstream (buffer for log entries)
#include <string>
#include <vector>

#ifndef LOG_USEMUTEX
#define LOG_USEMUTEX 0
#endif

#ifndef LOG_ENABLEQT
#define LOG_ENABLEQT 0
#endif

#if LOG_ENABLEQT == 1
#include <QMessageLogContext>
#include <QDebug>
#endif

#if LOG_ENABLEQT == 1
template<typename T>
QDebug operator<<(QDebug dbg, const T& str) {
	std::ostringstream stream;
	stream << str;
	QString conv = QString::fromStdString(stream.str());
	QDebugStateSaver saver(dbg);
	dbg << conv;
	return dbg;
}

/*
// string specialisation, not allowed, because multiple definitions of the same operator are not allowed
template<>
QDebug operator<<(QDebug dbg, const std::string& str) {
	QDebugStateSaver saver(dbg);
	QString conv = QString::fromStdString(str);
	dbg << conv;
	return dbg;
}
*/
#endif

namespace Log {
enum class Level { off = 0, fatal, error, warn, note, info, debug, trace };

#if LOG_ENABLEQT == 1
void qtMessageHandler(QtMsgType type, const QMessageLogContext& context, const QString& message);
#endif

// set up the logger with a ConsoleOutput
void init();
// close all output streams
void stop();

void addLogfile(const std::string& filename, Level max, bool truncate = false);
void addLogfile(const std::string& filename, Level min, Level max, bool truncate = false);

void setConsoleLogLevel(Level lvl);
void setColoredOutput(bool enabled);

// Log entry that can be formed with various mixed data types
// by concatenation with the << operator
// Inspired from https://stackoverflow.com/a/8337882
class Entry {
private:
	std::stringstream ss;
	const Level lvl;
#if LOG_ENABLEQT == 1
	const QMessageLogContext* context = nullptr;
	Entry(Level lvl, const QMessageLogContext&);
	friend void qtMessageHandler(QtMsgType type, const QMessageLogContext& context, const QString& message);
#endif

	void addMetadataHeader();

public:
	explicit Entry(Level lvl);
	Entry(const Entry&) = delete;
	Entry& operator=(const Entry&) = delete;
	Entry(Entry&&) = default;
	Entry& operator=(Entry&&) = default;
	~Entry();

	Level getLevel() const {
		return lvl;
	}

#if LOG_ENABLEQT == 1
	constexpr const QMessageLogContext* getContext() const {
		return context;
	}
#endif

	using MetaFunction = std::function<std::ostream&(std::ostream&, const Entry&)>;

	template <typename T> Entry& operator<<(T&& msg) {
		ss << std::forward<T>(msg);
		return *this;
	}
};

// class to automatically stop the logger on destruction
class Deleter {
public:
	Deleter();
	~Deleter();
private:
	static std::atomic<uint32_t> refCount;
};

extern std::vector<Entry::MetaFunction> entryMetaFunctions;

std::ostream& defaultEntryMetaTime(std::ostream&, const Entry&);
std::ostream& defaultEntryMetaLevel(std::ostream&, const Entry&);

// custom io-manip
// FileSize is a iomanip to convert a filesize (fs) into a human readable format
class FileSize {
public:
	explicit FileSize(uint64_t fs) : fs(fs) {}
	FileSize(const FileSize&) = delete;
	FileSize& operator=(const FileSize&) = delete;
	operator std::string() const;
private:
	uint64_t fs;
	friend std::ostream& operator<<(std::ostream& str, const FileSize& fs);
};

struct PrintErrno {};

extern const PrintErrno err;

std::ostream& operator<<(std::ostream& str, const PrintErrno&);

std::ostream& operator<<(std::ostream& str, const FileSize& fs);

// copy Level values in Log namespace
constexpr Level off = Level::off;
constexpr Level fatal = Level::fatal;
constexpr Level error = Level::error;
constexpr Level warn = Level::warn;
constexpr Level note = Level::note;
constexpr Level info = Level::info;
constexpr Level debug = Level::debug;
constexpr Level trace = Level::trace;

// create Log lines (Entry objects) on using operator<< on Level values
template <typename T>
Entry operator<<(const Level lvl, T&& msg) {
	Entry e{lvl};
	e << std::forward<T>(msg);
	return e;
}

} // namespace Log