package loadaverage

import (
	"math"
	"time"
)

// Constants for calculating EMA

const SAMPLE_DELAY time.Duration = time.Second * 5

var (
	ONE_MIN_ALPHA     float64 = math.Exp(-SAMPLE_DELAY.Seconds() / 60.0)  // e^(-dt/W), where dt is the sample time and W
	FIVE_MIN_ALPHA    float64 = math.Exp(-SAMPLE_DELAY.Seconds() / 300.0) // is the target timeframe. eg.: 60 for one min
	FIFTEEN_MIN_ALPHA float64 = math.Exp(-SAMPLE_DELAY.Seconds() / 900.0)
)

type LoadAverageInformation struct {
	/*
	 * Load average in the past minute
	 */
	Load1 float64
	/*
	 * Load average in the past 5 minutes
	 */
	Load5 float64
	/*
	 * Load average in the past 15 minutes
	 */
	Load15 float64

	initialized bool // track whether this is the first measurement or not
}

func (loadAvg *LoadAverageInformation) Update(currentSample float64) {
	if !loadAvg.initialized {
		// Seed the initial averages with the first sample to avoid a slow ramp-up from zero
		loadAvg.Load1 = currentSample
		loadAvg.Load5 = currentSample
		loadAvg.Load15 = currentSample
		loadAvg.initialized = true
		return
	}

	loadAvg.Load1 = loadAvg.Load1*ONE_MIN_ALPHA + currentSample*(1.0-ONE_MIN_ALPHA)
	loadAvg.Load5 = loadAvg.Load5*FIVE_MIN_ALPHA + currentSample*(1.0-FIVE_MIN_ALPHA)
	loadAvg.Load15 = loadAvg.Load15*FIFTEEN_MIN_ALPHA + currentSample*(1.0-FIFTEEN_MIN_ALPHA)
}