package freedom

//go:generate errorgen

import (
	"context"
	"time"

	"github.com/miekg/dns"
	"v2ray.com/core"
	"v2ray.com/core/common"
	"v2ray.com/core/common/buf"
	"v2ray.com/core/common/dice"
	"v2ray.com/core/common/net"
	"v2ray.com/core/common/retry"
	"v2ray.com/core/common/session"
	"v2ray.com/core/common/signal"
	"v2ray.com/core/common/task"
	"v2ray.com/core/common/vio"
	"v2ray.com/core/features/policy"
	"v2ray.com/core/proxy"
	"v2ray.com/core/transport/internet"
)

// Handler handles Freedom connections.
type Handler struct {
	policyManager policy.Manager
	dns           dns.Client
	config        Config
}

// New creates a new Freedom handler.
func New(ctx context.Context, config *Config) (*Handler, error) {
	v := core.MustFromContext(ctx)
	f := &Handler{
		config:        *config,
		policyManager: v.PolicyManager(),
		dns:           v.DNSClient(),
	}

	return f, nil
}

func (h *Handler) policy() policy.Session {
	p := h.policyManager.ForLevel(h.config.UserLevel)
	if h.config.Timeout > 0 && h.config.UserLevel == 0 {
		p.Timeouts.ConnectionIdle = time.Duration(h.config.Timeout) * time.Second
	}
	return p
}

func (h *Handler) resolveIP(ctx context.Context, domain string) net.Address {
	if resolver, ok := proxy.ResolvedIPsFromContext(ctx); ok {
		ips := resolver.Resolve()
		if len(ips) == 0 {
			return nil
		}
		return ips[dice.Roll(len(ips))]
	}

	ips, err := h.dns.LookupIP(domain)
	if err != nil {
		newError("failed to get IP address for domain ", domain).Base(err).WriteToLog(session.ExportIDToError(ctx))
	}
	if len(ips) == 0 {
		return nil
	}
	return net.IPAddress(ips[dice.Roll(len(ips))])
}

func isValidAddress(addr *net.IPOrDomain) bool {
	if addr == nil {
		return false
	}

	a := addr.AsAddress()
	return a != net.AnyIP
}

// Process implements proxy.Outbound.
func (h *Handler) Process(ctx context.Context, link *vio.Link, dialer proxy.Dialer) error {
	outbound := session.OutboundFromContext(ctx)
	if outbound == nil || !outbound.Target.IsValid() {
		return newError("target not specified.")
	}
	destination := outbound.Target
	if h.config.DestinationOverride != nil {
		server := h.config.DestinationOverride.Server
		if isValidAddress(server.Address) {
			destination.Address = server.Address.AsAddress()
		}
		if server.Port != 0 {
			destination.Port = net.Port(server.Port)
		}
	}
	newError("opening connection to ", destination).WriteToLog(session.ExportIDToError(ctx))

	input := link.Reader
	output := link.Writer

	var conn internet.Connection
	err := retry.ExponentialBackoff(5, 100).On(func() error {
		dialDest := destination
		if h.config.DomainStrategy == Config_USE_IP && dialDest.Address.Family().IsDomain() {
			ip := h.resolveIP(ctx, dialDest.Address.Domain())
			if ip != nil {
				dialDest = net.Destination{
					Network: dialDest.Network,
					Address: ip,
					Port:    dialDest.Port,
				}
				newError("dialing to to ", dialDest).WriteToLog(session.ExportIDToError(ctx))
			}
		}

		rawConn, err := dialer.Dial(ctx, dialDest)
		if err != nil {
			return err
		}
		conn = rawConn
		return nil
	})
	if err != nil {
		return newError("failed to open connection to ", destination).Base(err)
	}
	defer conn.Close() // nolint: errcheck

	plcy := h.policy()
	ctx, cancel := context.WithCancel(ctx)
	timer := signal.CancelAfterInactivity(ctx, cancel, plcy.Timeouts.ConnectionIdle)

	requestDone := func() error {
		defer timer.SetTimeout(plcy.Timeouts.DownlinkOnly)

		var writer buf.Writer
		if destination.Network == net.Network_TCP {
			writer = buf.NewWriter(conn)
		} else {
			writer = &buf.SequentialWriter{Writer: conn}
		}
		if err := buf.Copy(input, writer, buf.UpdateActivity(timer)); err != nil {
			return newError("failed to process request").Base(err)
		}

		return nil
	}

	responseDone := func() error {
		defer timer.SetTimeout(plcy.Timeouts.UplinkOnly)

		if err := buf.Copy(buf.NewReader(conn), output, buf.UpdateActivity(timer)); err != nil {
			return newError("failed to process response").Base(err)
		}

		return nil
	}

	if err := task.Run(task.WithContext(ctx), task.Parallel(requestDone, task.Single(responseDone, task.OnSuccess(task.Close(output)))))(); err != nil {
		return newError("connection ends").Base(err)
	}

	return nil
}

func init() {
	common.Must(common.RegisterConfig((*Config)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
		return New(ctx, config.(*Config))
	}))
}