/*
 * Stats.h
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef FLOW_STATS_H
#define FLOW_STATS_H
#pragma once

// Yet another performance statistics interface
/*

struct MyCounters {
CounterCollection cc;
Counter foo, bar, baz;
MyCounters() : foo("foo", cc), bar("bar", cc), baz("baz", cc) {}
};

*/

#include <cstdint>
#include <cstddef>
#include "flow/flow.h"
#include "flow/TDMetric.actor.h"

struct ICounter {
	// All counters have a name and value
	virtual std::string const& getName() const = 0;
	virtual int64_t getValue() const = 0;

	// Counters may also have rate and roughness
	virtual bool hasRate() const = 0;
	virtual double getRate() const = 0;
	virtual bool hasRoughness() const = 0;
	virtual double getRoughness() const = 0;

	virtual void resetInterval() = 0;

	virtual void remove() {}
};

template<>
struct Traceable<ICounter*> : std::true_type {
	static std::string toString(ICounter const *counter) {
		if (counter->hasRate() && counter->hasRoughness()) {
			return format("%g %g %lld", counter->getRate(), counter->getRoughness(), (long long)counter->getValue());
		}
		else {
			return format("%lld", (long long)counter->getValue());
		}
	}
};

struct CounterCollection {
	CounterCollection(std::string name, std::string id = std::string()) : name(name), id(id) {}
	std::vector<struct ICounter*> counters, counters_to_remove;
	~CounterCollection() { for (auto c : counters_to_remove) c->remove(); }
	std::string name;
	std::string id;

	void logToTraceEvent(TraceEvent& te) const;
};

struct Counter : ICounter, NonCopyable {
public:
	typedef int64_t Value;

	Counter(std::string const& name, CounterCollection& collection);

	void operator += (Value delta);
	void operator ++ () { *this += 1; }
	void clear();
	void resetInterval();

	std::string const& getName() const { return name; }

	Value getIntervalDelta() const { return interval_delta; }
	Value getValue() const { return interval_start_value + interval_delta; }

	// dValue / dt
	double getRate() const;

	// Measures the clumpiness or dispersion of the counter.
	// Computed as a normalized variance of the time between each incrementation of the value.
	// A delta of N is treated as N distinct increments, with N-1 increments having time span 0.
	// Normalization is performed by dividing each time sample by the mean time before taking variance.
	//
	// roughness = Variance(t/mean(T)) for time interval samples t in T
	//
	// A uniformly periodic counter will have roughness of 0
	// A uniformly periodic counter that increases in clumps of N will have roughness of N-1
	// A counter with exponentially distributed incrementations will have roughness of 1
	double getRoughness() const;

	bool hasRate() const { return true; }
	bool hasRoughness() const { return true; }

private:
	std::string name;
	double interval_start, last_event, interval_sq_time, roughness_interval_start;
	Value interval_delta, interval_start_value;
	Int64MetricHandle metric;
};

template<>
struct Traceable<Counter> : std::true_type {
	static std::string toString(Counter const& counter) {
		return Traceable<ICounter*>::toString((ICounter const*)&counter);
	}
};

template <class F>
struct SpecialCounter : ICounter, FastAllocated<SpecialCounter<F>>, NonCopyable {
	SpecialCounter(CounterCollection& collection, std::string const& name, F && f) : name(name), f(f) { collection.counters.push_back(this); collection.counters_to_remove.push_back(this); }
	virtual void remove() { delete this; }

	virtual std::string const& getName() const { return name; }
	virtual int64_t getValue() const { return f(); }

	virtual void resetInterval() {}

	virtual bool hasRate() const { return false; }
	virtual double getRate() const { throw internal_error(); }
	virtual bool hasRoughness() const { return false; }
	virtual double getRoughness() const { throw internal_error(); }

	std::string name;
	F f;
};
template <class F>
static void specialCounter(CounterCollection& collection, std::string const& name, F && f) { new SpecialCounter<F>(collection, name, std::move(f)); }

Future<Void> traceCounters(std::string const& traceEventName, UID const& traceEventID, double const& interval, CounterCollection* const& counters, std::string const& trackLatestName = std::string());

class LatencyBands {
public:
	LatencyBands(std::string name, UID id, double loggingInterval) : name(name), id(id), loggingInterval(loggingInterval), cc(nullptr), filteredCount(nullptr) {}

	void addThreshold(double value) {
		if(value > 0 && bands.count(value) == 0) {
			if(bands.size() == 0) {
				ASSERT(!cc && !filteredCount);
				cc = new CounterCollection(name, id.toString());
				logger = traceCounters(name, id, loggingInterval, cc, id.toString() + "/" + name);
				filteredCount = new Counter("Filtered", *cc);
				insertBand(std::numeric_limits<double>::infinity());
			}

			insertBand(value);
		}
	}

	void addMeasurement(double measurement, bool filtered=false) {
		if(filtered && filteredCount) {
			++(*filteredCount);
		}
		else if(bands.size() > 0) {
			auto itr = bands.upper_bound(measurement);
			ASSERT(itr != bands.end());
			++(*itr->second);
		}
	}

	void clearBands() {
		logger = Void();

		for(auto itr : bands) {
			delete itr.second;
		}
		
		bands.clear();

		delete filteredCount;
		delete cc;

		filteredCount = nullptr;
		cc = nullptr;
	}

	~LatencyBands() {
		clearBands();
	}

private:
	std::map<double, Counter*> bands;
	Counter *filteredCount;

	std::string name;
	UID id;
	double loggingInterval;

	CounterCollection *cc;
	Future<Void> logger;

	void insertBand(double value) {
		bands.insert(std::make_pair(value, new Counter(format("Band%f", value), *cc)));
	}
};
#endif