package future

import (
	"crypto/sha256"
	"io"
	"fmt"
	"time"
	"bytes"
	"math/rand"
)

func Seed() {
	rand.Seed(time.Now().UTC().UnixNano())
}

func ComputeId(content io.Reader) (string, error) {
	h := sha256.New()
	if _, err := io.Copy(h, content); err != nil {
		return "", err
	}
	return fmt.Sprintf("%x", h.Sum(nil)[:8]), nil
}

func HumanDuration(d time.Duration) string {
	if seconds := int(d.Seconds()); seconds < 1 {
		return "Less than a second"
	} else if seconds < 60 {
		return fmt.Sprintf("%d seconds", seconds)
	} else if minutes := int(d.Minutes()); minutes == 1 {
		return "About a minute"
	} else if minutes < 60 {
		return fmt.Sprintf("%d minutes", minutes)
	} else if hours := int(d.Hours()); hours  == 1{
		return "About an hour"
	} else if hours < 48 {
		return fmt.Sprintf("%d hours", hours)
	} else if hours < 24 * 7 * 2 {
		return fmt.Sprintf("%d days", hours / 24)
	} else if hours < 24 * 30 * 3 {
		return fmt.Sprintf("%d weeks", hours / 24 / 7)
	} else if hours < 24 * 365 * 2 {
		return fmt.Sprintf("%d months", hours / 24 / 30)
	}
	return fmt.Sprintf("%d years", d.Hours() / 24 / 365)
}

func randomBytes() io.Reader {
	return bytes.NewBuffer([]byte(fmt.Sprintf("%x", rand.Int())))
}

func RandomId() string {
	id, _ := ComputeId(randomBytes()) // can't fail
	return id
}

func Go(f func() error) chan error {
	ch := make(chan error)
	go func() {
		ch <- f()
	}()
	return ch
}