package tunnel

import (
	"encoding/json"
	"errors"
	"fmt"
)

// Frame types carried inside the NIP-44 payload. The outer event kind only
// says which direction a frame travels; the type inside the ciphertext is
// authoritative, and is checked against the direction.
const (
	frameHello    = "hello"
	frameHelloAck = "hello_ack"
	frameData     = "data"
	frameAck      = "ack"
	frameNack     = "nack"
	framePing     = "ping"
	framePong     = "pong"
	frameClose    = "close"
	frameReset    = "reset"
)

// envelope is the plaintext of one tunnel event.
type envelope struct {
	V      int      `json:"v"`
	S      string   `json:"s"`
	T      string   `json:"t"`
	Seq    uint32   `json:"q,omitempty"`
	Ack    uint32   `json:"a,omitempty"`
	Data   []byte   `json:"d,omitempty"`
	Nack   []uint32 `json:"x,omitempty"`
	MTU    int      `json:"m,omitempty"`
	Win    int      `json:"w,omitempty"`
	PV     int      `json:"pv,omitempty"`
	Chain  string   `json:"c,omitempty"`
	Nonce  uint64   `json:"n,omitempty"`
	Reason string   `json:"r,omitempty"`
}

func (e *envelope) marshal() ([]byte, error) {
	b, err := json.Marshal(e)
	if err != nil {
		return nil, fmt.Errorf("tunnel: encode envelope: %w", err)
	}
	return b, nil
}

func parseEnvelope(raw []byte) (*envelope, error) {
	var e envelope
	if err := json.Unmarshal(raw, &e); err != nil {
		return nil, fmt.Errorf("tunnel: decode envelope: %w", err)
	}
	if e.V != protocolVersion {
		return nil, fmt.Errorf("tunnel: unsupported envelope version %d", e.V)
	}
	if e.S == "" {
		return nil, errors.New("tunnel: envelope has no session")
	}
	return &e, nil
}