package syncx

import (
	"errors"

	"github.com/tal-tech/go-zero/core/lang"
)

// ErrLimitReturn indicates that the more than borrowed elements were returned.
var ErrLimitReturn = errors.New("discarding limited token, resource pool is full, someone returned multiple times")

// Limit controls the concurrent requests.
type Limit struct {
	pool chan lang.PlaceholderType
}

// NewLimit creates a Limit that can borrow n elements from it concurrently.
func NewLimit(n int) Limit {
	return Limit{
		pool: make(chan lang.PlaceholderType, n),
	}
}

// Borrow borrows an element from Limit in blocking mode.
func (l Limit) Borrow() {
	l.pool <- lang.Placeholder
}

// Return returns the borrowed resource, returns error only if returned more than borrowed.
func (l Limit) Return() error {
	select {
	case <-l.pool:
		return nil
	default:
		return ErrLimitReturn
	}
}

// TryBorrow tries to borrow an element from Limit, in non-blocking mode.
// If success, true returned, false for otherwise.
func (l Limit) TryBorrow() bool {
	select {
	case l.pool <- lang.Placeholder:
		return true
	default:
		return false
	}
}