package util

import (
	"fmt"
	"math"
)

const bytesPerUnit = 1024

var byteUnits = []string{"KiB", "MiB", "GiB", "TiB", "PiB", "EiB"}

// HumanBytes writes a byte count the way a person would read it, using powers
// of 1024: "0 B", "1023 B", "1.0 KiB", "1.5 MiB", "16.0 EiB". Counts below 1024
// are given as whole bytes, and anything larger gets one digit after the
// decimal point.
func HumanBytes(bytes uint64) string {
	if bytes < bytesPerUnit {
		return fmt.Sprintf("%d B", bytes)
	}

	value := float64(bytes)
	unit := -1

	for value >= bytesPerUnit && unit < len(byteUnits)-1 {
		value /= bytesPerUnit
		unit++
	}

	// Rounding happens after the unit has been chosen, so a count just short
	// of the next threshold would otherwise come out as "1024.0 KiB" rather
	// than "1.0 MiB".
	if unit < len(byteUnits)-1 && math.Round(value*10)/10 >= bytesPerUnit {
		value /= bytesPerUnit
		unit++
	}

	return fmt.Sprintf("%.1f %s", value, byteUnits[unit])
}