/*
 * Stats.actor.cpp
 *
 * 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.
 */

#include "fdbrpc/Stats.h"
#include "flow/actorcompiler.h" // has to be last include

Counter::Counter(std::string const& name, CounterCollection& collection)
: name(name), interval_start(0), last_event(0), interval_sq_time(0), interval_start_value(0), interval_delta(0), roughness_interval_start(0)
{
	metric.init(collection.name + "." + (char)toupper(name.at(0)) + name.substr(1), collection.id);
	collection.counters.push_back(this);
}

void Counter::operator += (Value delta) {
	if (!delta) return;  //< Otherwise last_event will be reset
	interval_delta += delta;
	auto t = now();
	auto elapsed = t - last_event;
	interval_sq_time += elapsed * elapsed;
	last_event = t;

	metric += delta;
}

double Counter::getRate() const {
	double elapsed = now() - interval_start;
	return elapsed > 0 ? interval_delta / elapsed : 0;
}

double Counter::getRoughness() const {
	double elapsed = now() - roughness_interval_start;
	if(elapsed == 0) {
		return -1;
	}

	// If we have time interval samples t in T, and let:
	// n = size(T) = interval_delta
	// m = mean(T) = elapsed / interval_delta
	// v = sum(t^2) for t in T = interval_sq_time
	// 
	// The formula below is: (v/(m*n)) / m - 1
	// This is equivalent to (v/n - m^2) / m^2 = Variance(T)/m^2
	// Variance(T)/m^2 is equal to Variance(t/m) for t in T
	double delay = interval_sq_time / elapsed;
	return delay * interval_delta / elapsed - 1;
}

void Counter::resetInterval() {
	interval_start_value += interval_delta;
	interval_delta = 0;
	interval_sq_time = 0;
	interval_start = now();
	if(last_event == 0) {
		last_event = interval_start;
	}
	roughness_interval_start = last_event;
}

void Counter::clear() {
	resetInterval();
	interval_start_value = 0;

	metric = 0;
}

void CounterCollection::logToTraceEvent(TraceEvent &te) const {
	for (ICounter* c : counters) {
		te.detail(c->getName().c_str(), c);
		c->resetInterval();
	}
}

ACTOR Future<Void> traceCounters(std::string traceEventName, UID traceEventID, double interval, CounterCollection* counters, std::string trackLatestName) {
	wait(delay(0)); // Give an opportunity for all members used in special counters to be initialized

	for (ICounter* c : counters->counters)
		c->resetInterval();

	state double last_interval = now();

	loop{
		TraceEvent te(traceEventName.c_str(), traceEventID);
		te.detail("Elapsed", now() - last_interval);

		counters->logToTraceEvent(te);

		if (!trackLatestName.empty()) {
			te.trackLatest(trackLatestName);
		}

		last_interval = now();
		wait(delay(interval, TaskPriority::FlushTrace));
	}
}