Abstract lazy connection with optional auto disconnect on idle timeout

lazy.go

package lazy

import (
	"sync"
	"time"
)

type Connection struct {
	sync.Mutex
	conn        interface{}
	expires     time.Time
	Connect     func() interface{}
	Disconnect  func(conn interface{})
	IdleTimeout time.Duration
}

func (c *Connection) Get() interface{} {
	c.Lock()
	defer c.Unlock()
	if c.conn != nil {
		return c.conn
	}
	c.conn = c.Connect()
	if c.conn != nil && c.IdleTimeout > 0 {
		c.KeepAlive()
		go c.idle()
	}
	return c.conn
}

func (c *Connection) Close() {
	c.Lock()
	defer c.Unlock()
	if c.conn == nil {
		return
	}
	if c.Disconnect != nil {
		c.Disconnect(c.conn)
	}
	c.conn = nil
}

func (c *Connection) KeepAlive() {
	c.expires = time.Now().Add(c.IdleTimeout)
}

func (c *Connection) idle() {
	for {
		til := time.Since(c.expires)
		if til > 0 {
			time.Sleep(til)
		}
		if time.Since(c.expires) > 0 {
			c.Close()
			break
		}
	}
}