package counter

import "sync"

// Counter is a thread-safe integer counter.
type Counter struct {
	mu    sync.RWMutex
	value int64
}

// New creates a counter with the given initial value.
func New(initial int64) *Counter {
	return &Counter{value: initial}
}

// Add changes the counter by delta and returns the new value.
func (c *Counter) Add(delta int64) int64 {
	c.mu.Lock()
	defer c.mu.Unlock()

	c.value += delta
	return c.value
}

// Increment increases the counter by one and returns the new value.
func (c *Counter) Increment() int64 {
	return c.Add(1)
}

// Value returns the current value.
func (c *Counter) Value() int64 {
	c.mu.RLock()
	defer c.mu.RUnlock()

	return c.value
}

// Reset sets the counter to zero and returns its previous value.
func (c *Counter) Reset() int64 {
	c.mu.Lock()
	defer c.mu.Unlock()

	previous := c.value
	c.value = 0
	return previous
}