// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package tsdial provides a Dialer type that can dial out of tailscaled.
package tsdial

import (
	"context"
	"errors"
	"net"
	"sync"

	"inet.af/netaddr"
)

// Dialer dials out of tailscaled, while taking care of details while
// handling the dozens of edge cases depending on the server mode
// (TUN, netstack), the OS network sandboxing style (macOS/iOS
// Extension, none), user-selected route acceptance prefs, etc.
type Dialer struct {
	// UseNetstackForIP if non-nil is whether NetstackDialTCP (if
	// it's non-nil) should be used to dial the provided IP.
	UseNetstackForIP func(netaddr.IP) bool

	// NetstackDialTCP dials the provided IPPort using netstack.
	// If nil, it's not used.
	NetstackDialTCP func(context.Context, netaddr.IPPort) (net.Conn, error)

	mu  sync.Mutex
	dns DNSMap
}

func (d *Dialer) SetDNSMap(m DNSMap) {
	d.mu.Lock()
	defer d.mu.Unlock()
	d.dns = m
}

func (d *Dialer) resolve(ctx context.Context, addr string) (netaddr.IPPort, error) {
	d.mu.Lock()
	dns := d.dns
	d.mu.Unlock()
	return dns.Resolve(ctx, addr)
}

func (d *Dialer) DialContext(ctx context.Context, network, addr string) (net.Conn, error) {
	ipp, err := d.resolve(ctx, addr)
	if err != nil {
		return nil, err
	}
	if d.UseNetstackForIP != nil && d.UseNetstackForIP(ipp.IP()) {
		if d.NetstackDialTCP == nil {
			return nil, errors.New("Dialer not initialized correctly")
		}
		return d.NetstackDialTCP(ctx, ipp)
	}
	// TODO(bradfitz): netns, etc
	var stdDialer net.Dialer
	return stdDialer.DialContext(ctx, network, ipp.String())
}