package main

import (
	"fmt"
	"math"
	"strconv"
	"strings"
)

var units []string = []string{"KB", "MB", "GB", "B"}

// ByteSize represents a number of bytes
type ByteSize struct {
	HumanRep  string
	NumberRep int64
}

// Byte size size suffixes.
const (
	B  int64 = 1
	KB int64 = 1 << (10 * iota)
	MB
	GB
)

// Used to convert user input to ByteSize
var unitMap = map[string]int64{
	"B":  B,
	"KB": KB,
	"MB": MB,
	"GB": GB,
}

func (b *ByteSize) parseFromString(s string) error {
	s = strings.TrimSpace(s)
	b.HumanRep = s
	var fragments []string
	unitFound := ""

	for _, unit := range units {
		fragments = strings.Split(s, unit)
		if len(fragments) == 2 {
			unitFound = unit
			break
		}
	}

	if len(unitFound) == 0 {
		return fmt.Errorf("unrecognized size suffix")
	}

	value, err := strconv.ParseFloat(fragments[0], 64)
	if err != nil {
		return err
	}

	unit, ok := unitMap[strings.ToUpper(unitFound)]
	if !ok {
		return fmt.Errorf("unrecognized size suffix %s", fragments[1])
	}

	b.NumberRep = int64(value * float64(unit))
	return nil
}

func (b *ByteSize) parseFromNumber(n int64) {
	b.NumberRep = n
	bf := float64(n)
	for _, unit := range []string{"", "K", "M", "G"} {
		if math.Abs(bf) < 1024.0 {
			b.HumanRep = fmt.Sprintf("%3.1f%sB", bf, unit)
			return
		}
		bf /= 1024.0
	}
	b.HumanRep = fmt.Sprintf("%.1fTB", bf)
}