package vpnruntime

import (
	"context"
	"errors"
	"sync/atomic"
	"time"

	"github.com/example/remote-access-platform/agents/rap-node-agent/internal/fabricproto"
	"github.com/example/remote-access-platform/agents/rap-node-agent/internal/mesh"
)

type FabricSessionFrameSender interface {
	Send(context.Context, fabricproto.Frame) error
}

type FabricSessionFrameReceiver interface {
	Frames() <-chan fabricproto.Frame
	Errors() <-chan error
}

type FabricSessionPacketTransport struct {
	Sender   FabricSessionFrameSender
	Receiver FabricSessionFrameReceiver
	Inbox    *FabricPacketInbox

	StreamID         uint64
	VPNConnectionID  string
	SendDirection    string
	ReceiveDirection string
	TrafficClass     string

	sequence uint64
}

func (t *FabricSessionPacketTransport) SendGatewayPacketBatch(ctx context.Context, packets [][]byte) error {
	packets = cleanPacketBatch(packets)
	if len(packets) == 0 {
		return nil
	}
	if t == nil || t.Sender == nil {
		return mesh.ErrForwardRuntimeUnavailable
	}
	if t.StreamID == 0 || t.VPNConnectionID == "" {
		return errors.New("fabric session packet transport identity is incomplete")
	}
	direction := t.SendDirection
	if direction == "" {
		direction = FabricDirectionGatewayToClient
	}
	frame, err := NewFabricVPNPacketDataFrame(FabricVPNPacketFrameInput{
		StreamID:        t.StreamID,
		Sequence:        atomic.AddUint64(&t.sequence, 1),
		VPNConnectionID: t.VPNConnectionID,
		Direction:       direction,
		TrafficClass:    t.TrafficClass,
		Packets:         packets,
	})
	if err != nil {
		return err
	}
	return t.Sender.Send(ctx, frame)
}

func (t *FabricSessionPacketTransport) ReceiveGatewayPacketBatch(ctx context.Context, timeout time.Duration) ([][]byte, error) {
	if t == nil || t.Inbox == nil {
		return nil, mesh.ErrForwardRuntimeUnavailable
	}
	direction := t.ReceiveDirection
	if direction == "" {
		direction = FabricDirectionClientToGateway
	}
	return t.Inbox.Receive(ctx, t.VPNConnectionID, direction, timeout)
}

func (t *FabricSessionPacketTransport) RunFrameIngress(ctx context.Context) error {
	if t == nil || t.Receiver == nil || t.Inbox == nil {
		return mesh.ErrForwardRuntimeUnavailable
	}
	frames := t.Receiver.Frames()
	errorsCh := t.Receiver.Errors()
	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case err, ok := <-errorsCh:
			if !ok {
				errorsCh = nil
				continue
			}
			if err != nil {
				return err
			}
		case frame, ok := <-frames:
			if !ok {
				return nil
			}
			if frame.Type != fabricproto.FrameData {
				continue
			}
			if t.StreamID != 0 && frame.StreamID != t.StreamID {
				continue
			}
			if err := t.Inbox.DeliverFabricSessionFrame(ctx, frame); err != nil {
				return err
			}
		}
	}
}