package multinet

import (
	"context"
	"errors"
	"fmt"
	"net"
	"sync/atomic"
)

// BalancerType reperents the algorithm which is used to pick source address.
type BalancerType string

const (
	// BalancerTypeNoop picks first address for which link is up.
	BalancerTypeNoop BalancerType = ""
	// BalancerTypeNoop implements simple round-robin between up links.
	// It is not fair in case some links are down.
	BalancerTypeRoundRobin BalancerType = "roundrobin"
)

var errNoSuitableNodeFound = errors.New("no suitale node found")

type balancer interface {
	DialContext(ctx context.Context, s *Subnet, network, address string) (net.Conn, error)
}

type roundRobin struct {
	d *dialer
	i atomic.Uint32
}

func (r *roundRobin) DialContext(ctx context.Context, s *Subnet, network, address string) (net.Conn, error) {
	next := int(r.i.Add(1))
	for i := range s.SourceIPs {
		ii := s.SourceIPs[(i+next)%len(s.SourceIPs)]
		dd := r.d.dialer
		dd.LocalAddr = &net.TCPAddr{IP: net.IP(ii.AsSlice())}
		return r.d.dialContext(ctx, &dd, network, address)
	}
	return nil, fmt.Errorf("(*roundRobin).DialContext: %w", errNoSuitableNodeFound)
}

type firstEnabled struct {
	d *dialer
}

func (r *firstEnabled) DialContext(ctx context.Context, s *Subnet, network, address string) (net.Conn, error) {
	for i := range s.SourceIPs {
		ii := s.SourceIPs[i]
		dd := r.d.dialer
		dd.LocalAddr = &net.TCPAddr{IP: net.IP(ii.AsSlice())}
		return r.d.dialContext(ctx, &dd, network, address)
	}
	return nil, fmt.Errorf("(*firstEnabled).DialContext: %w", errNoSuitableNodeFound)
}