// Package robotname gives random names to robots.
package robotname
import (
	"fmt"
	"math/rand"
	"time"
)
// Robot is a robot.
type Robot struct {
	name string
	init bool
}
const (
	// len("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
	alphabetSize = 26
	// letters * letters * 10*10*10
	possibility = alphabetSize * alphabetSize * 1000
)
// collects the already issued names
var issued = make(map[string]struct{})
// Name returns the name of the Robot. Generates a new name if Robot has no name yet.
// Returns error when no unique names left.
func (r *Robot) Name() (string, error) {
	if r.init == true {
		return r.name, nil
	}
	rand.Seed(time.Now().UnixNano())
	for len(issued) < possibility {
		r.name = fmt.Sprintf("%c%c%03d",
			rand.Intn(alphabetSize)+'A', rand.Intn(alphabetSize)+'A',
			rand.Intn(1000))
		if _, ok := issued[r.name]; ok {
			continue
		}
		issued[r.name] = struct{}{}
		r.init = true
		return r.name, nil
	}
	return "", fmt.Errorf("run out of possibilities")
}
// Reset resets the receiver.
func (r *Robot) Reset() {
	r.init = false
}