package soundbox

import (
	"context"
	"fmt"
	"net"
	"time"
)

// streamingPort is the default network port a soundbox is listening to for
// incoming audio stream data.
const streamingPort = 5316

const dialTimeoutSeconds = 3

// toLinkLocal converts a MAC address to the corresponding IPv6 link-local
// address.
func toLinkLocal(ha net.HardwareAddr) (net.IP, error) {
	switch len(ha) {
	case 6:
		ip := net.IP{0xfe, 0x80, 0, 0, 0, 0, 0, 0,
			ha[0] ^ 0b10, ha[1], ha[2], 0xff, 0xfe, ha[3], ha[4], ha[5]}
		return ip, nil
	default:
		return nil, fmt.Errorf("Only IEEE 802 MAC-48 addresses supported")
	}
}

func dialContext(ctx context.Context, ha net.HardwareAddr) (net.Conn, error) {
	ip, err := toLinkLocal(ha)
	if err != nil {
		return nil, err
	}

	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, err
	}

	c := make(chan net.Conn)
	dialContext, cancel := context.WithTimeout(ctx, dialTimeoutSeconds*time.Second)
	defer cancel()
	for _, iface := range ifaces {
		go func() {
			var d net.Dialer
			conn, err := d.DialContext(
				ctx,
				"tcp6",
				fmt.Sprintf("[%s%%%s]:%d", ip, iface.Name, streamingPort),
			)
			if err == nil {
				c <- conn
			}
		}()
	}
	select {
	case conn := <-c:
		return conn, nil
	case <-dialContext.Done():
		return nil, fmt.Errorf("Could not dial TCP connection to %v on port %d on any interface.", ha, streamingPort)
	}
}