package imapx

import (
	"context"
	"time"

	"github.com/emersion/go-imap/v2/imapclient"
)

// KeepaliveInterval is how often an otherwise-idle IMAP connection is pinged
// with NOOP so the server does not drop it.
//
// The destination connection sits completely idle for the entire duration of
// the source-side metadata scan (Pass 1 of CopyFolder), which on a large
// mailbox runs for many minutes across all folders. With no traffic, the
// server closes the idle connection; go-imap's reader then tears the client
// down, and every subsequent APPEND fails with "use of closed network
// connection" — aborting each folder and copying nothing. A periodic NOOP
// keeps the connection warm. 60s is well under the idle timeout of any common
// IMAP server.
const KeepaliveInterval = 60 * time.Second

// Keepalive pings c with a NOOP every interval until ctx is cancelled, keeping
// an idle connection from being dropped by the server. It is meant to run in
// its own goroutine.
//
// It is safe to run concurrently with other commands on c: go-imap serializes
// command submission and supports multiple in-flight commands over a single
// connection (RFC 9051 §5.5 pipelining). A NOOP issued while another command is
// in flight simply queues behind it and completes when the server responds.
//
// Keepalive returns when ctx is done or when a NOOP fails — a failed NOOP means
// the connection is already gone, so there is nothing left to keep alive.
func Keepalive(ctx context.Context, c *imapclient.Client, interval time.Duration) {
	t := time.NewTicker(interval)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-t.C:
			if err := c.Noop().Wait(); err != nil {
				return
			}
		}
	}
}