/*
	————————————————————————————————————————————————————————————————————————————
	MG Benchmark Tools.swift
	————————————————————————————————————————————————————————————————————————————
	Created by Marcel Kröker on 03.04.15.
	Copyright (c) 2016 Blubyte. All rights reserved.
*/
import Foundation
#if os(Linux)
    import Glibc
    import CBSD

    private func mach_absolute_time() -> UInt64 {
    	var tv = timeval();
        guard gettimeofday(&tv, nil) != -1 else { return 0 }

	let t = UInt64(tv.tv_usec) + UInt64(tv.tv_sec) * 1000000
        return t;
    }

    private struct mach_timebase_info_data_t {
	var numer: Int = 1000
	var denom: Int = 1
    }

    private func mach_timebase_info(_: inout mach_timebase_info_data_t) {}
#endif

private func durationNS(_ call: () -> ()) -> Int
{
	var start = UInt64()
	var end = UInt64()

	start = mach_absolute_time()
	call()
	end = mach_absolute_time()

	let elapsed = end - start

	var timeBaseInfo = mach_timebase_info_data_t()
	mach_timebase_info(&timeBaseInfo)

	let elapsedNano = Int(elapsed) * Int(timeBaseInfo.numer) / Int(timeBaseInfo.denom)

	return elapsedNano
}

private func adjustPrecision(_ ns: Int, toPrecision: String) -> Int
{
	switch toPrecision
	{
	case "ns": // nanoseconds
		return ns
	case "us": // microseconds
		return ns / 1_000
	case "ms": // milliseconds
		return ns / 1_000_000
	default: // seconds
		return ns / 1_000_000_000
	}
}

/**
	Measure execution time of trailing closure.

	- Parameter precision: Precision of measurement. Possible
	values:
		- "ns": nanoseconds
		- "us": microseconds
		- "ms" or omitted parameter: milliseconds
		- "s" or invalid input: seconds
*/
public func benchmark(_ precision: String = "ms", _ call: () -> ()) -> Int
{
	// empty call duration to subtract
	let emptyCallNano = durationNS({})
	let elapsedNano = durationNS(call)

	let elapsedCorrected = elapsedNano >= emptyCallNano
		? elapsedNano - emptyCallNano
		: 0

	return adjustPrecision(elapsedCorrected, toPrecision: precision)
}

/**
	Measure execution time of trailing closure, and print result
	with description into the console.

	- Parameter precision: Precision of measurement. Possible
	values:
		- "ns": nanoseconds
		- "us": microseconds
		- "ms" or omitted parameter: milliseconds
		- "s" or invalid input: seconds

	- Parameter title: Description of benchmark.
*/
public func benchmarkPrint(_ precision: String = "ms", title: String, _ call: () -> ())
{
	print(title + ": \(benchmark(precision, call))" + precision)
}


/**
	Measure the average execution time of trailing closure.

	- Parameter precision: Precision of measurement. Possible
	values:
		- "ns": nanoseconds
		- "us": microseconds
		- "ms" or omitted parameter: milliseconds
		- "s" or invalid input: seconds

	- Parameter title: Description of benchmark.

	- Parameter times: Amount of executions.
	Default when parameter is omitted: 100.

	- Returns: Minimum, Average and Maximum execution time of
	benchmarks as 3-tuple.
*/
public func benchmarkAvg(
	_ precision: String = "ms",
	title: String = "",
	times: Int = 10,
	_ call: () -> ())
	-> (min: Int, avg: Int, max: Int)
{
	let emptyCallsNano = durationNS(
	{
		for _ in 0..<times {}
	})

	var min = Int.max
	var max = 0

	var elapsedNanoCombined = 0

	for _ in 0..<times
	{
		let duration = durationNS(call)

		if duration < min { min = duration }
		if duration > max { max = duration }

		elapsedNanoCombined += duration
	}

	let elapsedCorrected = elapsedNanoCombined >= emptyCallsNano
		? elapsedNanoCombined - emptyCallsNano
		: 0

	return (adjustPrecision(min, toPrecision: precision),
		    adjustPrecision(elapsedCorrected / times, toPrecision: precision),
			adjustPrecision(max, toPrecision: precision)
	)
}