package sys

import (
	"fmt"
	"math"
	"strings"
	"time"
)

// unitBytes calculates the file size and generate user-friendly string.
func unitBytes(s uint64) string {
	const base = 1024
	var sizes = []string{"B", "KB", "MB", "GB", "TB", "PB", "EB"}
	if s < 10 {
		return fmt.Sprintf("%d B", s)
	}
	e := math.Floor(math.Log(float64(s)) / math.Log(base))
	suffix := sizes[int(e)]
	val := float64(s) / math.Pow(base, math.Floor(e))
	f := "%.0f"
	if val < 10 {
		f = "%.1f"
	}
	return fmt.Sprintf(f+" %s", val, suffix)
}

// timeSince calculates the time interval and generate full user-friendly string.
func timeSince(then time.Time) string {
	now := time.Now()
	diff := now.Unix() - then.Unix()

	if then.After(now) {
		return "future"
	}

	var timeStr, diffStr string
	for {
		if diff == 0 {
			break
		}
		diff, diffStr = computeTimeDiff(diff)
		timeStr += ", " + diffStr
	}
	return strings.TrimPrefix(timeStr, ", ")
}

func computeTimeDiff(diff int64) (int64, string) {
	// Seconds-based time units
	const (
		Minute = 60
		Hour   = 60 * Minute
		Day    = 24 * Hour
		Week   = 7 * Day
		Month  = 30 * Day
		Year   = 12 * Month
	)

	m := map[string]string{
		"second":  "second",
		"seconds": "seconds",
		"minute":  "minute",
		"minutes": "minutes",
		"hour":    "hour",
		"hours":   "hours",
		"day":     "day",
		"days":    "days",
		"week":    "week",
		"weeks":   "weeks",
		"month":   "month",
		"months":  "months",
		"year":    "year",
		"years":   "years",
	}

	diffStr := ""
	switch {
	case diff <= 0:
		diff = 0
		diffStr = "now"
	case diff < 2:
		diff = 0
		diffStr = "1 " + m["second"]
	case diff < 1*Minute:
		diffStr = fmt.Sprintf("%d "+m["seconds"], diff)
		diff = 0

	case diff < 2*Minute:
		diff -= 1 * Minute
		diffStr = "1 " + m["minute"]
	case diff < 1*Hour:
		diffStr = fmt.Sprintf("%d "+m["minutes"], diff/Minute)
		diff -= diff / Minute * Minute

	case diff < 2*Hour:
		diff -= 1 * Hour
		diffStr = "1 " + m["hour"]
	case diff < 1*Day:
		diffStr = fmt.Sprintf("%d "+m["hours"], diff/Hour)
		diff -= diff / Hour * Hour

	case diff < 2*Day:
		diff -= 1 * Day
		diffStr = "1 " + m["day"]
	case diff < 1*Week:
		diffStr = fmt.Sprintf("%d "+m["days"], diff/Day)
		diff -= diff / Day * Day

	case diff < 2*Week:
		diff -= 1 * Week
		diffStr = "1 " + m["week"]
	case diff < 1*Month:
		diffStr = fmt.Sprintf("%d "+m["weeks"], diff/Week)
		diff -= diff / Week * Week

	case diff < 2*Month:
		diff -= 1 * Month
		diffStr = "1 " + m["month"]
	case diff < 1*Year:
		diffStr = fmt.Sprintf("%d "+m["months"], diff/Month)
		diff -= diff / Month * Month

	case diff < 2*Year:
		diff -= 1 * Year
		diffStr = "1 " + m["year"]
	default:
		diffStr = fmt.Sprintf("%d "+m["years"], diff/Year)
		diff = 0
	}
	return diff, diffStr
}