package radio

import (
	"errors"
	"fmt"
	"math"
)

// Listeners stores the current and peak numbers of listeners.
type Listeners struct {
	current, peak int
}

// NewListeners returns a new Listeners struct instance.
func NewListeners() *Listeners {
	return &Listeners{}
}

// Current returns a number of current listeners.
func (l *Listeners) Current() int {
	return l.current
}

// Current returns a number of peak listeners.
func (l *Listeners) Peak() int {
	return l.peak
}

// Inc increments by 1 a current number of listeners and updates a peak number.
func (l *Listeners) Inc() int {
	if l.current == math.MaxInt {
		// We panic here because if this will ever happen, then something's going certainly wrong.
		panic(fmt.Sprint("a current number of listeners exceeded MaxInt which is", math.MaxInt))
	}
	l.current++
	if l.current > l.peak {
		l.peak = l.current
	}
	return l.current
}

// Dec decrements by 1 a current number of listeners. An error will occur if
// a resulting number is less than 0.
func (l *Listeners) Dec() (int, error) {
	if l.current == 0 {
		return l.current, errors.New("an attempt to decrement a number of current listeners down to less than 0")
	}
	l.current--
	return l.current, nil
}